J. F. Brouwer - Philips Bound...362 J.F. BROUWER PhilipsTech. Rev. 42,No. 10/11/12 With...

Philips Tech. Rev. 42, No. 10/ II /12,361-373, Sept. 1986 361

Half a century of 'electronification' in telephony systems

J. F. Brouwer

The vast progress in electronics in countless fieldsof application has led to striking results. It is certainlyno mere chance that the thermionic valve (or electrontube) was first used for wireless telegraphy. The inven-tor of the diode (Sir J. A. Fleming) and the inventorof the triode (Lee De Forest) were closely involved inthis branch of electrical telecommunication, whichwas then in its infancy.

Later, the cross-fertilization between electronicsand telecommunication led to wireless transmission ofspeech and music in radio communication and radiobroadcasting, two related fields that gave rise to greatgrowth and expansion in the electronics industry.

This article is mainly concerned with another formof cross-fertilization: between electronics and line-dependent telephony systems. Without electronics itwould not have been possible to span the Earth withunderground and submarine cables for telephonetransmission. Modern digital telephone exchangescontrolled by special telephony computers would alsobe inconceivable without the use of the most ad-vanced electronic components and modules.An interesting aspect here is the long time it has

taken to introduce electronics into the most importanttelephony functions. Although the first electronictelephone repeaters were in use before World War I, itis only in the last fifteen years that electronics hasreally penetrated into the heart of the telephone ex-change. Because of the great complexity of the switch-ing operations and the reliability already achievedwith electromechanical systems, electronics had notpreviously had much to offer here - and there wasalso the question of price.In this article transmission systems will be con-

sidered first, then switching systems and the reviewconcludes with a look at the near future. Much spacehas intentionally been given over to developments atPhilips, although the treatment must necessarily beincomplete in range and detail.

Ir J. F. Brouwer was a Director of Philips' TelecommunicatieIndustrie B. v., Hilversum, and of the former Philips Telecommuni-cation and Defence Systems Division, before his retirement.

TELEPHONE TRANSMISSION SYSTEMS

Background

Not long after the invention of the triode by Lee DeForest in 1906, electronics entered the world of tele-phony in the form of repeaters. As long ago as25 January 1915 the first transcontinental telephonecircuit came into operation in America: a route some5000 km long with overhead copper wires fixed topoles, incorporating repeaters at three points [11.

Fig. 1. At first, telephone connections were almost always madewith overhead lines. Because there were so many wires, the resultwas not always particularly attractive. The picture shows a streetscene in one of the larger cities in the United States in the early daysof telephony (about 1880).

[IJ More than 1000 tons of copper wire were used in the link; thenumber of repeaters was later increased to eight. See M. D.Fagen (ed.), A history of engineering and science in the BellSystem; the early years (1875-1925), Bell Telephone Labora-tories 1975, p. 262.

362 J. F. BROUWER Philips Tech. Rev. 42, No. 10/11/12

With the rapid growth in telephone traffic, however;it very soon became necessary to use undergroundcables, first for the urban networks and subsequentlyfor the other circuits as well. This resulted in lessinterference from induction, fewer interruptions andless maintenance but - inevitably - also in a lowersignal strength at the end of the line. Although theintrinsically higher attenuation of telephone cablescould be significantly reduced by artificially increasingtheir self-inductance - as demonstrated by Pupinand Krarup - it could never achieve such low valuesas those attainable with the overhead systems using

0" ,..,

J ----~.B>......____

~L -«~}-

over thesame pair of wires. The only fundamentallycorrect solution to this problem was the four-wirecircuit (fig. 2). Connections of this type were desirablebecause of their low overall attenuation, but theywere also expensive, so that the telephone companieswanted to use them for more than one telephone callat a time. The most appropriate principle for this wascarrier telephony, a form of frequency-division multi-plexing (FDM); see fig. 3. Such systems were first usedin expensive submarine cable links and long overheadroutes, then later in both coaxial and multi-wire (sym-metrical) underground cables as well.

_,.B>>--------~~

~'""'..I---- rFig.2. a) In two-wire circuits both telephone signals for each telephone call are transmitted overonly one pair of wires. The signals from the two directions are only separated, amplified andrecombined at repeaters (A), if installed. Separation and recombination take place in 'hybrids'(>-). b) In a four-wire circuit hybrids are only found at the two ends; two wires are available forthe signals in both the go and return paths for the entire length of the circuit. (N.B. one continu-ous line in this diagram represents two wires.)

wires a few millimetres thick (overhead lines, fig. 1).After 1920, therefore, an ever-increasing number oflow-frequency ('voice-frequency') repeaters were usedon both international and long-distance national trunkcircuits. Typical distances between repeaters were 100to 200 km, depending on the diameters of the wiresused in the cables. For the time being, however, over-head lines continued to be used for very long circuits.It was soon found that transmission circuits incor-

porating repeaters had to be very carefully dimen-sioned. Excessive gain could lead to oscillation or'singing' (negative feedback had not yet been in-vented); too many repeaters connected in cascadecaused echo effects, and the longer the line the moreannoying these became. Excessive differences in signalstrength in neighbouring pairs of wires led to un-acceptable interference between one channel and an-other (crosstalk). Many of these problems were causedby the use of the traditional two-wire circuits in whichtelephone signals were transmitted in two directions

SSB r-, ~.~: ................~.' a'

o 4 8 12 16 2024kHz-f

Fig. 3. Carrier telephony is based on frequency-division multiplex-ing; a number of telephone signals are displaced to different posi-tions on the frequency scale by single-sideband modulation with asuppressed carrier (SSB). They are then combined (COM) into asingle multiplexed signal. An arbitrarily chosen example is shownhere for three signals (a, b and c), each with a bandwidth of 4 kHz,which produce a single multiplexed signal (a'b'c') extending from12 to 24 kHz.

Philips Tech. Rev. 42, No. 10/11/12 TELEPHONY SYSTEMS 363

The year 1936 was marked by extensive pioneeringactivities in this field: the first coaxial routes were laidfrom New York to Philadelphia and from Berlin toLeipzig. In the Netherlands, the Dutch PTT Adminis-tration brought its own 12-channel symmetrical cablesystem into use between Groningen and Leeuwarden..Extending for 60 km, this route was one of the firstobject lessons for the small Philips TransmissionGroup of those days. It was to be almost fifty yearsbefore it would receive an order for the longest digitalcoaxial link in the world (see page 366), which, in-cidentally, made use of a principle now also nearlyhalf a century old: Reeves's pulse-code modulation(PCM), dating from 1938.

Transmission activities in Philips - the start

After it was set up at the start of the thirties, theactivities of the Transmission Group at Philips wereinitially confined to voice-frequency amplifiers andPupin coils. The company offered fertile soil for this:knowledge in the field of thermionic valves was avail-able (the pentode patent and the negative-feedbackpatent), and use could also be made of researchresults in the field of magnetic materials. Even beforeWorld War 11a 17-channel carrier system was devel-oped for which the first export order was obtained in1938 (from Sydney to Maitland, in Australia).After World War 11the transmission activities were

continued at Philips Telecommunicatie Industrie inHilversum. Development and production centres inthis field also gradually grew up in Philips plants inother countries. Now let us look at what has happenedin Philips since those times, particularly as regardsanalog, digital and optical transmission systems fortelephony.

Analog transmission systems

Even during the war, Philips had been working ona 48-channel carrier system [21, which went into pro-duction in 1947. A significant reduction in size ascompared with the earlier 12- and 17-channel systemswas made possible by using Ferroxcube [31 as the corematerial for inductors and transformers, semiconduc-tor cells for modulators and an improved type ofvalve.The great increase in telephone traffic, which was

much stimulated by the progressive automation oflong-distance networks, resulted in turn in a growingdemand' for transmission equipment. In particular,improvements in line-amplifier techniques showed thatthe various transmission lines could be used for con-siderably higher frequencies than had been expected

Table I. Internationally recommended hierarchy of carrier systemsfor telephony.

Number of Basic frequencychannels position JkHz)

Group 12 60-108Supergroup 60 312-552Mastergroup 300 812-2044Supermastergroup 900 8516-12388

when they were purchased. Such an increase in band-width can be seen in the symmetrical carrier cable,in which the number of channels was extended to 120in about 1962.

Since not every type of cable had the same trans-mission capacity, and the number of channels requiredvaried very widely from connection to connection, theneed arose for carrier systems with varying channelcapacities. This led to international agreements abouta hierarchy of carrier systems: in a number of suc-cessive modulator stages twelve channels are firstcombined or 'multiplexed' (fig. 3) to form a 'group'with a fixed basic position on the frequency scale.Next, five groups are multiplexed to form one super-group, etc. (Tablel). When the highest required levelin the hierarchy has been reached, the signal is con-verted by a final modulation operation from its basicfrequency position to the frequency position ulti-mately required on the cable. Through the years,Philips have developed a virtually complete hierarchyof analog transmission systems for use on overheadlines, cables and microwave links. The modular struc-ture meant that, for example, the same channel andgroup modulation equipment was used in a 120-chan-nel system as in a system for 10 800 channels.More refined design techniques, space-saving con-

struction methods, the automation of production pro-cesses and the selection of the most suitable com-ponents led to new generations of equipment with im-proved characteristics [41. A good example of this isto be found in the 'channel unit' (fig. 4). Transistor-ization (1959) made the main contribution to reducingdissipation; a significant gain in space was mainlyachieved by a virtually continuous reduction in the sizeof the passive filter components, which account formore than 50070of the total number of components(fig.5).

". Widening the frequency band used on symmetricaland coaxial cables meant that ever-smaller intervals[2] G. H. Bast, D. Goedhart and J. F. Schouten, A 48-channel

carrier telephone system, Philips Tech. Rev. 9,161-170,1947/48and 10, 353-362, 1948/49.

[3] J. L. Snoek, Non-metallic magnetic material for high frequen-cies, Philips Tech. Rev. 8, 353-360, 1946.

[4] A. van Dedem, 8TR4OO: a new generation of channel equip-ment, Philips Telecommun. Rev. 31, 156-157, 1973.

were required between repeaters, because cable atte-nuation increases at higher frequencies (Table 11). Inthe 48-channel system with symmetrical cables valveamplifiers were used, spaced at about 25 km. They werehoused in above-ground repeater stations equippedwith reliable power supplies fed by the local electricitymains. The 120-channel system, which was used on thesame cables, required considerably shorter distances

Fig. 4. The channel unit, which is required for each separate trans-mission channel in the formation of a group in carrier systems,underwent substantial improvements between 1947 (background)and 1975 (foreground). The number of channels in each equipmentbay rose from 12 to 600; the dissipation in each channel fell from12 W to less than 0.1 W, while both technical performance andreliability were significantly increased.

Fig. S. The inductors (top) and capacitors (bottom) used in filtersfor telephone transmission equipment have diminished in sizethrough the years, mainly because of improvements in the magneticand dielectric materials and perfection of the winding technique.

Table Il. Analog transmission systems for carrier telephony. (Witha 'standard' coaxial cable the diameters of the inner and outer con-ductors are 2.6 mm and 9.5 mm, respectively. The correspondingvalues for a 'mini' coaxial cable are 1.2 mm and 4.4 mm, and for a'micro' coaxial cable - see Table III - 0.7 mm and 2.9 mm.)

0.20.5

Repeater spacing (km)

Highest Number of Symmetricalfrequency (MHz) channels carrier

Coaxialcable

Standard Mini

900120027003600

984.54.51.5

46121860

between repeaters. Here semiconductor technologycame into its own, because the power required for tran-sistor amplifiers is so low that they could be fed via thecable wires by a low-current d.c. supply. This resultedin a significant saving in costs, since the repeaters couldnow be installed in an underground housing (repeatercase).

Philips was one of the first companies to use tran-sistor amplifiers for coaxial cables as well [5J. On longcoaxial circuits it is often necessary to compensate foran attenuation of many tens of thousands of decibels,while as a result of seasonal variations in ground tem-perature the nominal cable attenuation varies by somehundreds of decibels (every 100 dB means a powervariation of a factor of 1010). The large number ofrepeaters in cascade puts a premium on reliability.A solution has been found for this by not incorpora-ting any 'regulation' in most of the repeaters. Theycan therefore be constructed with the smallest pos-sible number of components. The mean time betweenfailures, or MTBF, of these repeaters is about 1000years. In addition, in a small number of regulatedunderground repeaters a patented control systemmatches the gain to the varying cable attenuation bysending a control command from the terminal sta-tions via the coaxial conductors. The overall attenua-tion of the total link can thus be kept constant towithin about 1.5 dB [6J.

Digital transmission systems

Digital transmission systems use pulse-code modul-ation and operate on the time-division-multiplex prin-ciple. A number of low-frequency telephone signalsare sampled every 125 us: each signal amplitudefound is converted into an 8-bit code word by a non-linear analog-to-digital converter. On the transmis-sion line, one code word in succession from each

Philips Tech. Rev. 42, No. 10/ II / 12 TELEPHONY SYSTEMS 365

channel is now transmitted at high speed in each inter-val of 125 us, At a transmission rate of say 2 Mbit/s,30 channels can be processed. Digital systems requirea considerably larger bandwidth than analog systemswith the same number of channels, but they are rela-tively immune to impulse noise and interferenceoriginating from other circuits. In addition, the digi-tal signal can be restored to its original pure form (i.e.it can be regenerated) relatively simply in intermediaterepeaters. The regenerated signal will of course con-tain a bit error that cannot be immediately recognizedif a bit is excessivelymutilated as a result of poor con-ditions on the transmission path.Pulse-code-modulation systems have been widely

used in short-haul transmission links with voice-frequency cables where the use of carrier equipmentwould have been economically inappropriate becauseof the short distance. As these digital systems becamecheaper, they found their way into other types oflinks, which had previously been the domain ofanalog systems. Besides being cheaper, they were- of course - also more suitable for transmittingdigital information (telegraphy and data traffic) withpermissible rates of up to 64 kbit/ s per channel. Foreconomic reasons, a need arose for digital systemswith more channels for longer distances. The digitalsystem hierarchy, as laid down by the internationalorganizations CEPT and CCITT, comprises systemsof 2 to 565 Mbit/s with 30 to 7680 channels (Table IIl).In the future this hierarchy will certainly be extendedto the giga-bit/s range for optical digital systems.

Higher-order digital transmission systems consistof multiplexers (in which a number of lower-order bitstreams in the hierarchy are converted into a bitstream of the next higher order) and digitalline equip-ment. This is always specific to a particular type ofcable and therefore different for, say, coaxial cablesand optical-fibre cables.The first PCM system developed by Philips was

delivered in 1968; it was a 24-channel system and wasrapidly followed by a 2-Mbit/s system with 30 chan-nels complying with a new European standard intro-duced by CEPT. In both systems, standard circuits

Table Ill. Digital telephone-transmission systems.

Transmission Number ofRepeater spacing (km)

capacity channels Low- Coaxial(Mbit/s) frequency cable

cableStandard Mini Micro

2 30 2 - - -8 120 2 - - 4

34 480 - - 4 2140 1920 - 4.5 2 -565 7680 - 1.5 - -

Fig. 6. This standard repeater case intended for underground useis not only suitable as a housing for analog repeaters (18 MHzand 60 MHz) and digital repeaters (34 Mbit/s, 140 Mbit/s and565 Mbit/s), but also as a housing for optical repeaters.

(lCs) were used for the digital functions and discretecomponents for the analog functions. For economicreasons, the coder/decoder in which the analog-to-digital conversion takes place was still common to allchannels.

In younger generations of the 3D-channel systemlow-power Schottky circuits and custom-designed ICsare mainly used for the coder/decoder, constitutingan individual unit for each channel. (At present thecoder /decoder is combined with the associated filtersto form a single IC.) The regenerators also contain anumber of custom-built bipolar ICs for the analogfunctions.

Digital systems have of course benefited more thananalog systems from the reduction in volume anddissipation provided by modern IC technology. Thishas also led to a decrease in the number of individualcomponents, which has improved the reliability.

In addition to analog transmission on the channelsalready in use, the multiple coaxial cable ('multi-tubecable') permits digital transmisson on previously un-used 'tubes'. It was therefore a great advantage if the(analog) underground repeater cases were also suitablefor housing digital regenerators (jig. 6). However,this introduced two extra requirements for the designof these regenerators. They had to permit the samespacing between repeaters and they had to be nolarger than the corresponding analog repeaters. Tomeet these requirements, Philips designed 140-Mbit/sand 565-Mbit/s regenerators with special custom-de-signed ICs and hybrid circuits [71. A number of orderswere received for major projects, testifying to the

[5] J. F. Lansu, Transistorized line equipment with 4, 6 and12 Mc/s frequency bands for coaxial cables, Philips Telecom-mun. Rev. 26, 53-61, 1966.

[6] H. L. Bakker, The 60 MHz coaxial transmission system8TR341, Philips Telecommun. Rev. 30, 103-112,1971/72.

[7] A. M. Giacometti and Ph. Uythoven, The 565 Mb/s 8TR640system: equalisation design and performance analysis, PhilipsTelecommun. Rev. 41, 175-192, 1983.

great advantages that could be achieved with theseregenerators in digital long-distance systems.

The long-distance connection between Sacramentoand Chicago was the longest 140-Mbit/s link in theworld when it was commissioned in December 1982.It was constructed with Philips equipment, and is3750 km in length with underground regenerators at aspacing of about 3 km.

Optical transmission systems

Making use of its own research results in optical-fibre production and welding techniques, systems stud-ies and optical components such as lasers, avalanchephotodiodes and connectors, Philips constructed anexperimental opticalI40-Mbit/s system as long ago as1979 that was almost entirely based on componentsavailable within the company. After an experimentalsystem operating under normal conditions had beenset up between Eindhoven and Geldrop in 1980, anambitious development programme was started. Theobjective was the early completion of a series ofoptical-transmission systems for a complete digitalsystem hierarchy (jig. 7). Recently (April 1986) thefirst international optical-fibre communications linkin Europe was officially commissioned: Breda in theNetherlands and Herentals, 60 km away in Belgium,are now linked by a cable of twelve optical fibres, eachwith a transmission capacity of 1920 telephone chan-nels (140 Mbit/s).

The wavelength of 850 nm originally used per-mitted repeaters to be spaced at intervals of 10 km to20 km, representing a significant economic advantageas compared with coaxial cables. There was, however,one complication: optical fibres are non-conductingand electrical power for the regenerators cannot besupplied via these fibres. Even longer regenerator sec-

Fig.7. Receiving equipment for a 565-Mbit/s optical-transmissionsystem.

Table IV. Optical transmission systems.

Type of fibre Wavelength Attenuation Typical repeater(nm) (dB/km) spacing (km)

Graded-index I 850 2.7 15-201300 0.6 45-60

Step-index I 1300 0.5 50-70(single-mode) 1500 0.2 100-140

tions were therefore necessary if underground regen-erators in the links between surface regenerator sta-tions were eventually to be entirely eliminated. In thepast few years much study has consequently been de-voted to the use of other wavelengths (1300 nm and1500 nm) and to the employment of single-mode op-tical fibres with significantly lower optical attenua-tion. Table IV gives a general indication of the dis-tances that can be bridged with the various types ofsystem under operating conditions without inter-mediate regeneration [8] [9]. Further improvements inthe optical components and in optical-fibre tech-nology will certainly result in further increases inthese values in the future.

TELEPHONE SWITCHING SYSTEMS

Background

Two years after the invention of the first practicaltelephone by Alexander Graham Bell, the first publictelephone network came into use in New Haven in1878 [10], rapidly followed by other similar networksboth in the USA and elsewhere. All these networkswere manually operated in 'central offices' or 'ex-changes' (jig. 8), but an experimental automatic ex-change had already come into operation by 1892. Animproved version of this 'step-by-step' system, alsocalled the Strowger system (after its inventor), rapidlyspread throughout both America and Europe where itwas manufactured under licence.

Nevertheless, there was some initial hesitation aboutintroducing automation into large urban networks.There were doubts about the user-friendliness of aself-service system in which subscribers had to selectthe long local telephone numbers themselves. Thelarger exchanges, which came into operation shortlybefore and just after World War I, were thereforegenerally equipped for semi-automatic traffic, withthe operator - and not the subscriber - selecting thenumber requested verbally by the caller.

Experience with fully automatic exchanges was sogood, however, that operators began to disappearfrom local exchanges in the twenties.

By 1936 some 50070 of the total number of sub-scriber lines - estimated at 35 million worldwide -

IFig. 8. One of the oldest types of manual exchange (about 1880).

Fig. 9. An ordinary telephone exchange half a century ago (manualexchange, 1936).

were connected to automatic exchanges [111. This highpercentage, however, was mainly achieved as a resultof the automation of the large urban networks. Mostsmaller towns and virtually all rural areas still had tomake do with manual operation (fig. 9). Trunk calls,particularly over longer distances, were also usuallyhandled by the operator, so that long waiting timeswere frequently inevitable.

As to future developments, half a century ago moreextensive automation of the national telephone net-work was the top priority: in some smaller countries(Switzerland and the Netherlands) plans alreadyexisted for the complete automation of all local net-works [121. Apart from this, there was little indicationof other major changes. Although there were manyreasons for seeking systems that required less main-tenance, took up less space and were cheaper to pro-duce, a further evolution of the electromechanicalmodules looked more promising than using electronicswitching devices such as valves.

Nevertheless, attempts were already under way toachieve more practical electronic components. Thetelephone selector, with its dozens of outputs, inspiredmany designs of complex valves with similar facilities.Even before World War 11 there were studies of theusefulness of semiconductor elements - and theseultimately led to the invention of the transistor. Therewere also innovations in system concepts half a cen-tury ago: the first pulse-code modulation patent(1938) not only opened up new paths for digital trans-mission systems but also offered prospects for digitalswitching systems based on time-division multiplex.

Many years were to pass, however, before newtechnologies and system concepts could be adaptedfor practical application in commercial telephone ex-changes. Meanwhile the electromechanical exchangehad the field to itself.

Some basic concepts

In a telephone exchange a distinction can be made between theswitching network and the control system. In a switching network aconnecting path is set up by the exchange for every telephone callbetween a particular input and the output required for the call. It isgenerally composed of a number of successive switching stages inthe form of telephone selectors (fig. 10), each with one input andseveral outputs or - more generally - in the form of switchingmatrices (fig. 11), in which each of the M inputs can be connectedto each of the N outputs by means of crosspoints. The crosspointmay be a mechanical contact (selector or crossbar switch) or anelectronic switching element (diode or transistor).

The control system's task is to set up the required connection inthe switching network on the basis of information received fromthe subscriber, monitor it and terminate it again at the end of thecall. In a manual system, these tasks are performed by a telephoneoperator. Automatic exchanges contain control units that receivethe information dialled by the subscriber making the call and pro-cess this into control instructions for the stages in the switching net-work. In addition, the control system handles the exchange of in-formation with the subscriber (engaged or busy tone, ringing tone,dialling tone, etc.) and with other exchanges involved in setting upthe connection.

Telephone exchanges can be divided into two groups: local (orsubscriber) exchanges and trunk (or transit) exchanges. Local ex-changes have both subscriber lines and trunk lines connected tothem, while trunk exchanges only have trunk lines connected tothem (fig. 12).

[B] N. A. Buijs and A. J. M. Dingjan, Optical fibre systems: to-wards long distances, Philips Telecommun. Rev. 41, 165-173,1983.

[9] J. Drupsteen, A high-capacity 565 Mb/s optical system bridgeslong distances, Philips Telecommun. Rev. 43, 31-42, 1985.

[10] A relatively high number, in view ofthe fact that after 1000cir-culars had been distributed only one subscriber replied; see [1],p.477.

[11] R. J. Chapuis, 100 years of telephone switching: Part I, North-Holland, Amsterdam 1982.

[12] This was completed in 1959 (Switzerland) and 1962 (theNetherlands). See for example: 1. H. Schuilenga, J. D. Tours,J. G. Visser and J. Bruggeman (eds), Honderd jaar telefoon,Dutch Post Office, The Hague 1981.

-- -....--------0I

-- +---"1----0I I N: I--.... :I I___ L .....I I

20----......

; II II II II I

I :___ J I

I_______ ...J

Fig. 10. Switching stage consisting of M individual telephone selec-tors with N outputs. Each selector represents an electromechanic-ally operated N-position switch. The corresponding outputs of theselectors are interconnected.

r-----------------lIIIIIII

Fig. 11. a) Analog switching matrix with 4 inputs and 4 outputs. Aconducting cross point is indicated by a black square and a non-con-ducting crosspoint by a grey square. b) More detailed representa-tion of a crosspoint in a switching matrix. When the switch is closeda connection is made between the horizontal and vertical conduc-tors x and y.

-,-,-,

o local exchange ._........ international {inkmain trunk line

cross route~ trunk exchange

Fig. 12. Hypothetical example of a hierarchically structured tele-phone network with local and trunk exchanges.

Automatic telephony in Philips - the beginningPhilips, who are mainly known as a lighting and

electronics company, were not active in automatictelephony until the end of World War 11. This situa-tion was changed by its participation in the recon-struction work in the Netherlands of repairing themany telephone exchanges that had been destroyed ordamaged during hostilities. The next step was to startproduction of a pre-war 'two-motion selector' systemthat was widely used in the Dutch network and which,at that time, could not be supplied in sufficient quan-tities from abroad. After this, the company rapidlydeveloped their own system (the 'UR system') on thebasis of the latest electromechanical modules [131.This new activity in switching techniques fitted in

well with existing Philips activities in radio communi-cations and carrier transmission. Together, the threefields constituted the new scene of operations forits subsidiary Nederlandsche Seintoestellen Fabriek,which became Philips' Telecommunicatie Industrie in1947.

The electronification of the switching network

In most exchanges designed for switching analogtelephone signals, the path set up for every call in theswitching network and maintained for the duration ofthe call is an individualone, which is physically dif-ferent from all the other paths in existence at the sametime (fig. 13). These are analog space-division ex-changes, and differ in many respects from their mostmodern counterparts: digital time-division exchanges.In analog exchanges the switches or crosspoints in

the switching network must meet the following requi-rements:• they must be switchable from a very-low-resistancestate to a very-high-resistance state and vice versa;• they must not be affected by the relatively high volt-ages and currents that occur on conventional sub-scriber lines, e.g. when ringing the subscriber or as a

A,----------------lI

A' B'Fig.13. Switching matrix (4 x 4) with three simultaneous and physic-ally separate speech paths A-A r B-B' and C-C'.

",',, "

result of induction from external electromagneticfields (electric traction, lightning, high-voltage lines):• the switching rate must be high enough;• the resistance in both states must be reasonablystable and must not be affected by factors such asclimatic conditions or mechanical vibration, whichcan lead to contact noise.

Electromagnetic switches

The electromechanical contacts of the old 'step-by-step' systems satisfied all the above requirementsreasonably well except the last one: the step-by-steplifting and rotation of the moving part of the selectormechanism caused vibration that led to contact noisein selectors already in position. Nor could dirty andworn contacts ever be completely avoided, and cor-recting these faults required frequent maintenance.

One of the methods adopted to avoid the sharpjerky movements in the more modern one-dimensionalselector systems was to connect the rotating part ofthe selector to a central continuously driven shaft anddisconnect it only after the selector had reached therequired position. With a careful choice of contactmaterials a significant reduction in maintenance couldbe achieved for selectors of this type.The first Philips (two-wire) telephone exchange

(type UR 49 of 1955)was of this kind. It was suitablefor use both as a local and as a trunk exchange andremained in production - with appropriate modifi-cations - until 1980. In that year, 1.3 million sub-scribers were connected to these exchanges in theNetherlands alone.

Good contact quality was also achieved with cross-bar switches. These have a switching matrix consistingof contacts and a set of horizontal and vertical barsfor activating the contacts. By rotating one of thehorizontal bars and one of the vertical bars through asmall angle, the contact located at the imaginarycrosspoint of the two bars is activated. It remains inthis state for as long as one of the bars retains itsangular displacement; the other bar is released topermit the selection of the next crosspoint.

Electronic crosspoints

In the fifties and sixties the crossbar matrix servedas a model for all kinds of switching matrices withelectronic crosspoints. For example, at a fairly earlydate the cold-cathode tube was used in a number ofexperimental exchanges (by Philips [14] and others).Because of a number of disadvantages, however, thisturned out to be not very practicable: the high ignitionvoltage was a disadvantage and the relatively highresistance in the conducting state gave excessivelyhigh attenuation for speech signals.

In the later evaluation of semiconductor matricesattention was mainly concentrated on the pnpn tran-sistor, which can be switched not only as a diode butalso as a transistor. Using electronic crosspoints ofthis type Philips installed complete experimental ex-changes for 1000 subscribers in 1967 in Utrecht (theNetherlands) and Aarhus (Denmark).

Although pnpn crosspoints permitted a very highswitching rate, this was little help in analog exchanges.The resistance in the conducting state reached lowervalues than with cold-cathode tubes, but it was never-theless between 10 and 20 times higher than the resis-tance of electromechanical contacts. Since in additionthe permissible currents and voltages were limited,one of the other requirements mentioned above wasnot satisfied either, so that fairly expensive protectivecircuits were necessary for each subscriber line. Whenmodern analog exchanges with electronic control weredeveloped in the seventies, the electronic crosspointwas still not very attractive for technical and eco-nomic reasons. In this generation of exchanges elec-tromechanical switches were therefore still predomi-nant (mini-reed relays and mini-crossbar switcheswere often used); hence the name 'semi-electronic ex-changes'.

Reed relays

The modern version of the reed contact - the prin-ciple had already been known in 1936 - consists oftwo strips or 'reeds' of a material that conducts elec-trically and can be magnetized. This assembly is sealedinto a gas-filled glass tube and the reeds are positionedso that a small contact aperture is created betweenthem, giving a compact contact system that is com-pletely protected from unwanted external influences(fig. 14). The contact is energized by an external mag-netic field.

From 1973 onwards, Philips has marketed the verysuccessful PRX system, which is based on mini-reedrelays [16]. It soon became widely used in public net-works, at first in the Netherlands. Large numbers oflocal and trunk exchanges were produced (and stillare), sometimes in the form of ready-made, mobile'container' exchanges (fig. 15). These were used insystems like the ones supplied for the 'telecommuni-cations order of the century', for the modernizationof the telephone network in Saudi Arabia, whichrepresented a total value of some billions of dollars.

[181 J. M. Unk, A high-speed uniselector for automatic telephoneexchanges, Philips Tech. Rev. 18, 349-357, 1956/57.

[141 J. Domburg and W. Six, A cold cathode gas-discharge tube asa switching element in automatic telephony, Philips Tech. Rev.15, 265-280, 1953/54.

[151 T. M. Schuringa, Reed switches for telephony switching,Philips Telecommun. Rev. 27, 105-123, 1967/68.

370 J. F. BROUWER Philips Tech. Rev. 42, No.lO/ll/12

Switching matrices for digital exchanges

Switching networks for digital telephone exchangeshave to meet completely different requirements fromthose in analog exchanges. In the first place, theyhandle digital signals, which are regenerated at theinput and output of the exchange. If analog sub-scriber lines are connected to the exchange, analog-to-digital conversion takes place at the periphery of theexchange. All the problems relating to the provisionof power for subscriber calls, ringing voltage andsurge proteetion must therefore be solved there andnot in the switching network.

In the second place, the digital signal for each callis not switched separately, but a large number of callsare switched in time-division multiplex: this meansthat the switching network establishes the required

Fig. 14. Mini-reed contact from a Philips reed relay. The magnetic'reeds' can clearly be seen in the hermetically sealed glass encap-sulation. To operate the contact, a coil is required, to produce amagnetic field; one coil is often used to operate more than one con-tact simultaneously.

Fig. IS. Because automatic telephone exchanges have become muchsmaller, it is possible to use ready-made mobile 'container' ex-changes for certain applications. This container is being shippedfrom the Netherlands to Saudi Arabia.

connection from input to output very briefly for eachcall in succession and that this cycle is repeatedperiodically.

Since the internationally agreed sampling rate inpulse-code modulation for telephony is 8 kHz, theswitching network must connect each call very briefly8000 times a second (jig. 16). In modern digital ex-changes, where some 256 calls are presented to eachinput of the switching matrix in time-division multi-plex, the crosspoints therefore have to be activatedover two million times a second. High switching ratessuch as this can of course only be achieved by usingelectronic devices.

Tbe electronification of the control system

Relay control

In the simplest type of control the exchange reactsas soon as each digit dialled by the subscriber is re-ceived. Each switching stage is therefore providedwith relay circuits that immediately convert the in-coming signalling pulses into control pulses. Thesedirect systems (like type UR 49 when used as a localexchange) are very suitable for use in straightforwardnetwork configurations.Indirect systems make use of common control de-

vices, often called registers, which are only neededwhile a connection is being made. The register receivesthe information dialled by the subscriber and analysesthe digits selected so as to determine the connectionthat must be set up by the switching network. Theswitching stages are then activated. Because of theirgreater 'intelligence', indirect systems can handlemore complex routing rules than direct systems. In1967 Philips put an indirect system of this type on themarket for use as a trunk exchange. In this 'UV sys-tem' both two-wire and four-wire through-connec-tions were possible. The selector stages and the relayswere basically still the same as those of the older URsystem, but now electronic circuits were introducedfor a number of functions in the control system. Thisrelated not only to the main functions of the registers,but also to an auxiliary device (the 'number analyser')that was consulted by the register, e.g. to analyse thedialled information for the purpose of routing andbilling. Here electronics offered the advantage ofspeed, so that expensive common equipment capacitywas utilized for shorter periods at a time. However,the combined use of relays and electronic circuits alsorequired special attention, to prevent the electronicsfrom reacting to very brief interruptions of a controlsignal caused by 'bouncing' contacts, or from adverseeffects such as radio-frequency interference from therelay circuits.

Electronic control

In about 1960 Philips were already developing ex-perimental exchanges with full electronic control. Dis-crete semiconductor components were used in thelogic modules, while ferrite cores were used as mem-ory elements. The logical functions, however, werestill incorporated in the wiring and not - or onlypartly - in memories [161.

Although it had been demonstrated that exchangessuch as this operated effectively under normal condi-tions they offered few specific advantages over existingelectromechanical exchanges. They were, however, anexcellent training school for the designers of a newgeneration of computer-controlled systems using 'pro-cessor control' or 'stored-program control (SPC)'.

than two hours in forty years (the average life of anexchange).The first program-controlled exchanges appeared

on the market shortly before 1970. They generally in-cluded computers or processors specially designed foroptimum performance of the telephony process. Theinstruction sets were adapted to the specific needs oftelephony and an extensive range of communicationfacilities was provided. Because of the very strictrequirements for reliability, extra measures had to betaken to increase the reliability of both software andhardware.

For example, the Philips program-controlled PRXsystem [171 mentioned above is provided with dualprocessors. Such a pair of processors operates in the

T + 125 f-lsb -t

Fig. 16. a) Space-division matrix (4 X 4) for four time-division-multiplexed digital signals (J toIV). b) Time frame for digital signals 1 to IV. Each signal consists of a time multiplex of 256 tele-phone signals. The switching matrix operates as follows: at time T the cross points make theconnections required for signals 1-1 to IV-I; at time T + 0.5 IlS they do the same for signals 1-2 toIV-2, etc. From time T + 125 IlS onwards the entire cycle is repeated.

Processor control

The idea of using one or more computers to controla telephone exchange was a fairly obvious one. Theuse of computers, consisting of relays, was thereforeinvestigated even before 1950. Fast electronic com-puters became available in the sixties and were soonused in all kinds of fields (particularly in numericalrecord-keeping and other routine calculations), wherethey were mainly used for batch processing. Tele-phone exchanges, in which between 100 and 10000calls have to be handled simultaneously in real time,called for a different solution, however.

There were also considerable differences in the re-quirements relating to reliability. In batch processing,the supply of services can be interrupted in a relativelyflexible way for maintenance to be carried out, andcertain tasks can be repeated or postponed. Telephoneexchanges often have to meet the requirement that thetotal duration of complete failure should not be more

'hot standby' mode, in which the standby processorreceives all the information about the running of theprocess to keep it fully informed so that it can takeover immediately in the event of a switchover. Inaddition, the circuits in this system are mainly TTL-type integrated circuits, in which the probability offailure is substantially reduced by the consistent useof hermetically sealed encapsulations, aluminiumbonding wires and derating (i.e. remaining well withinthe specifications) by avoiding high equipment tem-peratures. In addition, the decline to be expected inparticular characteristics because of ageing is takeninto account in the design of the electronic circuits.An important feature of program-controlled ex-

changes is their great flexibility. The software can be

[16] W. Smit, Electronic telephone exchanges in field trials, PhilipsTelecommun. Rev. 27, 55-72, 1967/68.

[17] Special issue 'PRX', Philips Telecommun. Rev. 31, 45-112,1973.

372 1. F. BROUWER Philips Tech. Rev. 42, No. 10/11/12

altered relatively easily. One of the things this offersthe network management is the possibility of remotecontrol via data links from a central maintenance orcontrol centre. In principle, the exchanges themselvescan be unattended: any changes in the number of sub-scribers and the routing and billing data can be madefrom the control centre.The flexibility of program-controlled exchanges

also makes it easy to introduce new forms of ameni-ties for subscribers, such as temporary transfer of in-coming calls to another subscriber's number, tempo-rarily disabling a connection for incoming traffic oroutgoing traffic (to particular destinations), abbre-

Fig.17. Two suites of racks from the extremely modern digital pro-cessor-controlled 5ESS·PRX telephone-switching system. Here'electronification' is complete: both the switching network and thecontrol system consist of electronic rather than electromechanicalcomponents. (5ESS is a trademark of AT&T Technologies Inc.)

Fig. 18. Schematic representation of the architecture of the 5ESS-PRX digital switching system. The most important components arethe switching modules SM, which are relatively autonomous, thecommunication module CM and the administrative module AM.The administrative module performs a large number of centralizedfunctions. The communication module connects the switchingmodules both with each other and with the administrative module.The subscriber lines SL are connected to the switching modules, asare any trunk lines to other exchanges TL.

Fig. 19. In the 5ESS-PRX switching system 32-Mbit/s optical-fibrelinks are used for carrying information between the most importantmodules. A total of 256 telephony signals, with all the related infor-mation for functions such as control and error protection, can betransmitted (apparently) simultaneously over each optical fibre.

viated dialling, and so on. It is the network manage-ment, of course, who decide whether such amenitiesshould be introduced, and when.

Controlof digital exchanges

The first digital telephone exchanges appeared inabout 1975. Because of the high cost of processors andmemories they had centralized control, just like thesemi-electronic analog exchanges mentioned earlier.As a result of the vigorous developments in semicon-ductor technology and the related reduction in costs,however, a second generation of digital exchangessoon emerged. These were arranged to have 'distri-buted control', in which processors at more than onelocation cooperate closely with one another. This canbe illustrated with the aid of the 5ESS-PRX system [181

(jig. 17) from AT&T and Philips Telecommunications,a company formed in 1984. This system is based onthe distribution of 'intelligence' over a large numberof relatively autonomous switching modules (jig. 18).Each switching module has its own 32-bit micropro-cessor and can set up connections independently be-tween all the digital or analog subscriber lines andtrunk lines connected to it. Traffic with other switch-ing modules and the exchange of messages with theadministrative module are effected via the communi-cation module using a double 32-Mbit/s optical-fibrelink (jig. 19). In the communication module, a space-division switching network establishes the requiredconnection between two switching modules for eachindividual call in time-division.The administrative module not only performs all

the centralized switching functions, such as setting upthe connection in the communication module, butalso stores data for routing, billing, costing and trafficmetering. In addition, the administrative module has

monitoring devices, diagnostic programs and facilitiesfor communication with operating and maintenancestaff. On the other hand, some 950/0 of the call-processing operations are handled by the switchingmodules. The 32-Mbitfs optical-fibre links enable theswitching modules to be installed at distances of up to50 km from the communication module. Even greaterdistances can be bridged by using internationally stan-dardized digital transmission systems. Traffichandlingwithin any switching module continues normally evenif an interruption occurs in the link with the commu-nication module. In view of the reliability required allcommon equipment is duplicated.

THE FUTURE: INTEGRATION OF SERVICES

The oldest kind of electrical communication - tele-graphy - is in fact based on a form of digital trans-mission. The era of analog communication onlystarted with the introduetion of the telephone. Untilnow both types of communication have existed sideby side: telegraphy and telex alongside telephony.

The emergence of communication with computersand between computers (data communication) hasresulted in a sharp increase in the need for facilitiesfor transmission of digital information. By using spe-cial equipment (data modems) information of this typecan be transferred via the analog telephone network.However, there are some restrictions. The bandwidthof analog telephony channels clearly limits the capa-city for transmitting digital information. In addition,data transmission and to some extent text transmis-sion set their own special requirements for making theconnection and for the transmission quality. Conse-quently, side by side with the analog telephone net-work and the digital telex network, special data net-works have emerged - frequently based on packet-switched transmission - with their own digital ex-changes and subscriber connections.

Now that increasing use is being made of digitaltransmission and switching devices in the telephonenetwork as well, it is obvious that for both economicaland practical reasons the aim should be to achieve asingle universal digital communications network. Inaddition to telephony, this Integrated Services DigitalNetwork (ISDN) will also permit the communicationof text, data, graphics and images in many forms.This will have to take place in a gradual process ofdevelopment, extending over a period of perhapstwenty or thirty years. First of all an Integrated DigitalNetwork (!DN) will be set up which will still mainly be

used for telephony, followed by a narrow-band ISDNfor digital communication services with rates of up to64 kbit/s. At a later stage it will be possible to add ser-vices with transmission rates of up to 2Mbit/s (e.g. forvideo conferences) and this development will finallyculminate in a wideband ISDN, with the possibility ofhigh-quality video communication.Modern digital telephone exchanges already con-

tain a number of functions that permit the flexibleintroduetion of new services [191. Here the existingresources are used as far as possible; for example, thenarrow-band ISDN will be using the existing analogsubscriber lines. International standardization pro-vides for a category of digital subscriber connectionswith an effective transmission capacity of 144 kbit/s,Advanced signal processing methods will permit mostanalog subscriber lines to be adapted for this pur-pose [201.In the information society of tomorrow the ISDN

will undoubtedly be just as indispensable as the tele-phone network is today. Electronic and opto-elec-tronie modules will play an increasingly importantpart in the creation of the necessary equipment. If thestage is ever reached where integrated optics or bio-chip technology supplants electronics from transmis-sion and switching systems, it will mark the end of aparticularly fascinating era in telecommunications- and possibly herald the start of an even morefascinating age.

[18) Special issue '5ESS-PRX', Philips Telecommun. Rev. 42,109-184, 1984;5ESS is a trademark of AT&T Technologies Inc.

[19) W. Lemstra and H. van der Veer, ISDN capabilities of the5ESS-PRX, Trends Telecommun. I, 41-54, 1985.

[20) K. J. Wouda, An implementation of a 144 kbit/s transmissionsystem for two-wire loops, Trends Telecommun. I, 55-66,1985.

Summary. When the telephone was invented more than hundredyears ago, nothing of what we now knowas 'electronics' was inexistence. It was only much later, mainly in the last half-century,that the gradual development took place that can be described asthe 'electronification' of telephony systems. Present-day analogtransmission systems would not have been possible without revolu-tionary new system concepts and this is also true for digital and op-tical transmission systems - but all of them would have been quiteimpossible without electronics. Until recently, electromechanicalcomponents have been able to hold their own in the switching net-work; it is only in the digital exchange that the advantages of elec-tronie crosspoints have become so significant. In particular, theadvent of processor control with special telephony computers hasled to complete electronification in the control sections of theswitching systems. In the twenty or thirty years ahead electronictechnology will enable the telephone network and other existing net-works (e.g. for telex and data) to merge into one universal digitalcommunications network with common transmission and switchingfacilities. This Integrated Services Digital Network (ISDN) willoffer subscribers a multitude of services, both existing and new.

374 Philips Tech. Rev. 42, No. 10/11/12,374-376, Sept. 1986

Scientific publicationsThese publications are contributed by staff of laboratories and plants that form part of orcooperate with enterprises of the Philips group of companies, particularly by staff of the re-search laboratories mentioned below. The publications are listed alphabetically by journal title.

Philips GmbH Forschungslaboratorium Aachen,WeiBhausstraJ3e, 5100 Aachen, Germany

Philips Research Laboratory, Brussels, B2 avenue Van Becelaere, 1170 Brussels, Belgium

Philips Natuurkundig Laboratorium, EPostbus 80000, 5600 JA Eindhoven, The Netherlands

Philips GmbH Forschungslaboratorium Hamburg, HVogt-Kölln-StraJ3e 30, 2000 Hamburg 54, Germany

Laboratoires d'Electronique et de Physique Appliquée, L3 avenue Descartes, 94450 Limeil-Brévannes, France

Philips Laboratories, N.A.P.C., N345.Scarborough Road, Briarcliff Manor, N.Y. 10510, U.S.A.

Philips Research Laboratories, RCross Oak Lane, RedhilI, Surrey RHI 5HA, England

Philips Research Laboratories, Sunnyvale SP.O. Box 9052, Sunnyvale, CA 94086, U.S.A.

C. A. M. Mulder & J. G. van LieropE

D. C. 1.Vangheluwe (Philips Centrefor Manuf. Technoi., Eindhoven)

B. Aldefeld & H. Richter

P. A. Devijver

C. M. G. Joehem & J. W. C. van derLigt E

A. Valster, L. J. Meuleman, P. I.Kuindersma & T. van Dongen E

P. Haaker, E. Klotz, R. Koppe, R.Linde & D. G. Mathey (Univ. Hospi-tal Eppendorf, Hamburg) H

A. R. Calderbank (AT&T Bell Labs,Murray Hili, NJ) & J. M. Goethals B

J. N. Sandoe, J. R. Hughes & J. A. G.Slatter R

S. Moridi & H. Sari

M. Hartmann, K. Witter&P. WillichH

M. H. Kuhn, W. Menhardt & I. C.Carlsen H

M. 1.Verheijke, J. Hanssen, H. Jas-pers, 1.Steuten & P. Wijnen E

J. F. Verwey & D. R. Wolters

Preparation, densification and characterization ofautoclave dried Si02 gels

Exact calculation of the spring constant in the buck-ling of optical fibers

H Semiautomatic three-dimensional interpretation ofline drawings

B Cluster analysis by mixture identification

Method for cooling and bubble-free coating of op-tical fibres at high drawing rates

Improved high-frequency response of InGaAsPdouble-channel buried-heterostructure lasers

First clinical results with digital flashing tornosyn-thesis in coronary angiography

On a pair of dual subschemes of the Hammingscheme Hn(q)

Characterisation and modelling of SIPOS on siliconhigh-voltage devices

L Analysis of four decision-feedback carrier recoveryloops in the presence of intersymbol interference

Temperature dependence of anisotropy constant andsaturation magnetization of amorphous GdFeM(M = Ge, Si, Sn, Bi, Au) alloys

Real-time interactive NMR image synthesis

Neutron activation analysis for the modern elec-tronies industry

E Breakdown fields in thin oxide layers

Aerogels, J. Fricke 68-75 1985(ed.), Springer, Berlin

Appl. Opt. 23 2045-2046 1984

Comput. & Graphics 8 371-380 1984

Data analysis in astro- 29-44 1985norny, V. Di Gesu etal. (eds), Plenum, NewYorkElectron. Lett. 21 786-787 1985

Electron. Lett. 22 16-18 1986

Eur. Heart J. 6 913-920 1985

Eur. J. Comb. 6 133-147 1985

lEE Proc. I 132 281-284 1985

IEEE Trans. COM-33 543-550 1985

IEEE Trans. MAG·21 2044-2046 1985

IEEE Trans. MI-4 160-164 1985

Instrumentelle multi- 603-606 1985elementanalyse, B.Sansoni (ed.), VCHVerlag, Weinheim

Insulating films on 125-132 1986semiconductors, J. J.Simonne & J. Buxo(eds), Elsevier Science,Amsterdam

Philips Tech. Rev. 42, No. 10/11/12 SCIENTIFIC PUBLICATIONS

D. R. Wolters & J. J. van der Schoot Breakdown by charge injectionE

..H. L. Peek & J. F. Verwey

J. N. Sandoe & J. R. Hughes

P. Hansen & K. Witter

E The influence of arsenic S-D implantations on thinoxides

R Properties of the SIPOS-silicon interface

H Growth-induced uniaxial anisotropy of bismuth-substituted iron-garnet films

C. Colinet*, A. Pasturel" (. Lab. Molar enthalpies of formation of LnAh compoundsThermodyn. & Physico-ChimieMetallurgiques, St. Martin d'Hères)& K. H. J. Buschow E

B. Pichaud", N. Burle-Durbec", F.Minari" (* Univ. Aix-Marseille Ill,Marseille) & M. Duseaux L

J. van de Ven (Univ. Nijmegen),J. E. A. M. van den Meerakker &J. J. Kelly E

J. J. Kelly, J. van de Ven (Univ. Nij-megen) & J. E. A. M. van den Meer-akker E

J. Appl. Phys. 58 454-459 1985

J. Chem. Thermodyn. 1133-1139 198517

Study of dislocations in highly In doped GaAs crys- J. Cryst. Growth 71tals grown by liquid encapsulation Czorchralskitechnique

The mechanism of GaAs etching in CrOs-HF solu-tions. 1. Experimental results

The mechanism of GaAs etching in CrOs-HF solu-tions. Il. Model and discussion

A. van Eenbergen & E. Bruninx E On the intrinsic resolution of the LHS-I0 electronspectrometer

H. M. van Noort, D. B. de Mooij &K. H. J. Buschow E

M. Brouha, A. J. C. van der Borst,G. W.Turk & C. H. M. Witmer E

E. Bruninx, A. F. P. M. van Eenber-gen, P. van der Werf & J. Haisma E

J. Robertson (Central Electr. Res.Labs, Leatherhead) & M. J. Powell R

C. van Berkel & M. J. Powell

J. F. Goldenberg & T. S. McKechnieN

H. Heitmann, M. Hartmann, M.Rosenkranz & H. J. Tolle H

R. Grössinger*, X. H. Sun*, R. Eib-Ier", K. H. J. Buschow & H. R.Kirchmayr* (. Tech. Univ. Vienna) E

C. A. M. Mulder, Th. P. M. Meeuw-sen & G. E. Thomas E

57FeMössbauer investigation of ternary compoundsof the R2Fe14Btype

High frequency magnetic properties of sputteredthin films

X-ray photoelectron spectroscopy of hafnium nitride

Defect model of charge transfer doping at a-SiNx:H/a-Si:H interfaces

R The photosensitivity of amorphous silicon thin filmtransistors

Diffraction analysis of bulk diffusers for projection-screen applications

Amorphous rare earth-transition metal films formagneto-optical storage

The temperature dependence of the anisotropy fieldin R2Fe14B compounds (R = Y, La, Ce, Pr, Nd,Gd, Ho, Lu)

Analysis of the reduction of hydrogen-induced infra-red loss increases in fluorine-doped PCVD silicafibre preforms

S. M. Marcus (Inst. Perception Res., Word recognitionEindhoven) & U. H. Frauenfelder' theoretical note(Max Planck Inst., Nijmegen)

648-654 1985

J. Electrochem. Soc. 3020-3026 1985132

J. Electrochem. Soc. 3026-3033 1985132

J. Electron Spectrosc. 265-268 1985& Relat. Phenom. 37

J. Less-Common Met. 155-165 1986115

J. Magn. & Magn. 1665-1666 1986Mater. 54-57

J. Mater. Sci. 21 541-546 1986

J. Non-Cryst, Solids 1007-1010 198577 & 78

J. Non-Cryst. Solids 1393-1396 198577 & 78

J. Opt. Soc. Am. A 2 2337-2348 1985

J. Physique 46 C6/9- 1985(Colloque C6) C6/18

uniqueness or deviation? A Lang. & Cognitive 163-169 1985Process.l

E. H. L. Aarts, F. M. J. de Bont, A parallel statistical cooling algorithmJ. H. A. Habers & P. J. M. van Laar-hoven E

Lect. Notes Comput.Sci., Vol. 210, B.Monien & G. Vidal-Naquet (eds), Sprin-ger, Berlin

87-97 1986

376 SCIENTIFIC PUBLICATIONS

K. M. Lüdeke, P. Röschmann & R. Susceptibility artefacts in NMR irnagingTischler H

G. M. Loiacono & J. C. Jacco

Philips Tech. Rev. 42, No. 10/11/12

Magn. Resonance 329-343 1985Imaging 3

N Thermal characterization of KClOs, KBrOs, and Mater. Lett. 4KlOs

K. H. Nicholas, R. A. Ford & R. W.Wilks R

F. A. Vollenbroek, W. P. M. Nijssen,H. J. J. Kroon & B. Yilmaz E

R. L. Bronnes & R. C. Sweet

P. A. Devijver

A. J. E. M. Janssen

J. A. Geurst

P. Houdy, E. Ziegier (MST ArgonneNat. Lab., Argonne, IL) & L. Névot(I.O.T.A.,Orsay) L

G. Harding, J. Kosanetzky& U. Neit-zei (CHF Müller Röntgen werk, Ham-burg) H

M. R. Simpson, P. A. Gough, F. I.Hshieh & V. Rumennik N

P. M. L. O. Scholte" , M. Tegze", F.van der Woudes (. Univ. Groningen),K. H. J. Buschow & I.Vincze" (+ Cen-tral Res. Inst. Phys., Budapest) E

J. J. P. Bruines, R. P. M. van Hal,H. M. J. Boots & J. Wolter E

T. S. te Velde & A. T. A. Zegers-vanDuynhoven E

M. J. Powell

N. M. Marinovic & G. Eichmann(City Univ. New York) N

M. Erman & N. Vodjdani L

M. G. Collet E

·H. J. Cornelissen E

G. J. van Gurp & F. J. du ChatenierE

F. H. M. Sanders & J. Dieleman E

Proximity corrections for electron image projection

High resolution opticallithography by formation ofa built on mask (B.O.M.)

N Metallography of a novel Stirling engine heat recep-tor

B Probabilistic labeling in a hidden second order Mar-kov mesh

B Baum's forward-backward algorithm revisited

E On the eigenvalues of an infinite Jacobi matrix

E Two-fluid hydrodynamics of bubbly liquid/vapourmixture including phase change

Application of sputtering to the realization of amor-phous ultra-thin layers (10 Á) stacks: advantages ofin situ ellipsometry control system

Elastic scatter computed tomography

Analysis of the lateral insulate gate transistor

The influence of the conduction electrons on theEFG in amorphous intermetallic alloys

Pulsed-laser melting of amorphous silicon on glass:time-resolved reflectivity measurements

The electroscopic fluid display

R Amorphous-silicon thin-film transistors: perfor-mance and material properties

Microelectron. Eng. 3 77-84 1985

Microelectron. Eng. 3 245-252 1985

Microstruct. ScL, Vol. 571-576 198512, D. Northwood etal. (eds), Am. Soc.Met., Metals Park, OH

Pattern recognition in 113-123 1986practice U, E. S. Gel-sema & L. N. Kanal(eds), Elsevier Science,Amsterdam

Pattern Recognition 369-373 1985Lett.3

Philips J. Res. 40 323-351 1985

Philips J. Res. 40 352-374 1985

Philips J. Res. 40 375-398 1985

Phys, Med. & BioI. 30 183-186 1985

Proc.IEDM-85, 740-743 1985Washington, DC, 1985

Proc. Int. Conf. on 4 pp. 1985the Applications ofthe Mössbauer effect,Leuven 1985

Proc. MRS Conf., 525-529 1985Strasbourg 1985

Proc. sm 26 167-170 1985

Proc. sm 26 191-196 1985

Feature extraction and pattern classification in space-spatial frequency domain

Optique intégré sur substrat semiconducteur: quel-ques résultats obtenus au LEP

Solid state image sensors

Laser spectroscopy in low-pressure sodium-neon dis-charges

Measurement of thermomigration in thin metal films

Plasma etching damage: theory and practice

Proc. SPIE 579 19-26 1985

Rev. de l'ISEP, No.spécial: les perspecti-ves d'avenir de l'opto-électronique

9-10 1985

Solid state devices1985, P. Balk & O. G.Folberth (eds), Else-vier Sciende, Amster-dam

> I183-200 1986

Thesis, Eindhoven 89 pp. 1986

Thin Solid Films 131 155-162 1985

Vide/Couches Minces40 (Suppl. to No. 229)

45-61 1985

Volume 42, No.10/11/12 Published 17th September 1986pages 293-376

July 1986

'~-----------------------------------------------I'I."Supplement to Philips Technical ReviewBijlage van Philips Technisch TijdschriftNo.32

Recent United States PatentsAbstracts from patents that describe inventions from the following research laboratories,which form part of or cooperate with the Philips group of companies:

Philips GmbH Forschungslaboratorium Aachen, WeiBhausstraBe,5100 Aachen, Germany A

Philips Research Laboratory Brussels, 2 avenue Van Becelaere, 1170 Brussels,Belgium B

Philips Natuurkundig Laboratorium, Postbus 80000, 5600 JA Eindhoven,The Netherlands E

Philips GmbH Forschungslaboratorium Hamburg, Vogt-Kölln-Straûe 30,2000 Hamburg 54, Germany H

Laboratoires d'Electronique et de Physique Appliquée, 3 avenue Descartes,94450 Limeil-Brévannes, France L

Philips Laboratories, N.A.P.C., 345 Scarborough Road, Briarcliff Manor,N.Y. 10510, U.S.A. N

Philips Research Laboratories, Cross Oak Lane, Redhill, Surrey RH1 5HA,England R

Philips Research Laboratories Sunnyvale, P.O. Box 9052, Sunnyvale,-C-K94ö86, U.S.A. S

4517525Balancing compensation in differential amplifiers witha single-ended driveE. C. Dijkmans ER. J. van de PlasscheA differential amplifier with single-ended drive includes a balancingcapacitor coupled between the base of a transistor connected to thesignal input and the common point of the two emitters of transis-tors, which form a differential pair. The capacitance value of thecapacitor is substantially equal to the capacitance value of the straycapacitance of the collector-substrate junction of a transistor whichforms a current source. This provides a symmetry of the capaci-tances between the input and the common point and between thecommon point and ground via the transistor, which forms the cur-rent source. This results in an improved balance in the output sig-nals at the output terminals and a flat frequency response of the dif-ferential amplifier for higher frequencies.

4537506Atomizer for atomic absorption spectroscopyB. Lersmacher A, RM. P. Wassa//P. J. ConnorThe atomizer of the present invention serves for generating freeatoms and an atomic cloud by heating a sample for analysis. Thedevice includes a preferably tubular cuvette for receiving the sam-ple, and the cuvette consists either of a basic body of-carbon, whichis enveloped by a pyrolytic graphite layer, or only of pyrolyticgraphite layers. An electric supply unit for Joule heating the cuvetteis in contact with the cuvette by contact members. In order toachieve a radial temperature distribution in the cuvette such thatthe inner wall of the cuvette is at an essentially higher temperaturethan the outer wall of the cuvette, the contact surfaces of thècuvette and the contact surfaces of the contact members contacteach other in such a manner that the electric current applied duringoperation of the atomizer preferably flows through the inner wall ofthe cuvette.

4547801Tunable Fabry-Perot interferometer and X-ray dis-play device having such an interferometerJ. Haisma EC. L.AdemaJ. M. M. PasmansJ. H. WaitersIn a tunable Fabry-Perot interferometer, the supports for twoparallel mirrors consist of bundles of opticalfibers with the mirrorsbeing provided on the ends of the fibers. This structure may be usedadvantageously in an X-ray display device wherein the structure islocated between the display screen on which the visible X-ray imageis displayed and a television camera tube. By using the Fabry-Perotinterferometer as a light attenuator in such a device, problemswhere the camera tube is overridden when making an X-ray recordcan be prevented by causing the reflection coefficient of the mirrorsin the visible range of the spectrum to be 99OJo or more. Also, thehalf width of the transmission wavelength pass-band of the Fabry-Perot interferometer can be made less than 50 nm.

4547902Radio receiver comprising a frequency-locked loopwith audio frequency feedback, and a muting circuitW.G. Kasperkovitz ERadio-receiver having a frequency-locked loop which' comprisesa tunable voltage-controlled oscillator, a mixer stage, a filteringelement, as well as a frequency-voltage converter which is con-nected to the tunable voltage-controlled oscillator. Several stabletunings are possible for each transmitter. An unambiguous selec-tion is made from these stable timings of a tuning to a desired sta-tion by muting the radio receiver in the other stable tuning fre-quency ranges. To this end the radio receiver according to the in-vention comprises a muting circuit as well as a control circuit for themuting circuit. A further frequency-voltage converter comprisingan all-pass frequency-dependent 1800 phase shifting network, aphase detector and a limiter detects a tuning error. By adjusting themuting circuit of the radio receiver to the quiescent condition only,in the desired tuning range and by activating it outside this range, asuppression of interstation noise is obtained.

PHILIPS

4548129Coffee makerW. L. N. van der SluysJ. PastoorJ. C. M. RoelofsThe invention relates to a coffee maker comprising a water reser-voir, a filter device and a flow heater for heating water from thewater reservoir for delivery to the filter device. A problem asso-ciated with coffee makers is the deposit of scale in the flow heater. Itis proposed to provide a coffee maker with means for adding asmall amount of colfeeextract to the water before it enters the flowheater. Coffee extract naturally contains phosphoric-acld-like com-pounds which inhibit the crystal growth of metal salts in the water.Preferably, coffee extract is fed continuously from the filter deviceto the water reservoir.

4'549145Switching amplifierR. J. van de PlasscheA switching amplifier is described which is intended in particularfor sample-and-hold circuits. The switching amplifier has an outputstage of the npn-npn-type comprising two output transistors inseries. The output is connected to the emitter of a first one of thetwo output transistors and to the collector of the second outputtransistor, a diode being arranged between the output and this col-lector. The output can be switched off by switching the voltage onthe base of the first transistor and the voltage on the point betweenthe diode and the collector of the second transistor relative to theoutput voltage, a third transistor ensuring that in this situation thecollector current of the second transistor can be drained when saiddiode is turned off, so that initially said second transistor canremain conductive.

4549288Apparatus for enhancing the playback signal in anoptical data recording systemA. Y. Chan NOptical data recording apparatus which enhances a playback signalby comparing the lengths of the lands on a recording medium withthe lengths of the pits on it and changes the playback signal torepresent equality between such lengths.

4551269Non-linear resistor and method of manufacturing thesameD. HenningsA. SchnellH. SchreinemacherA non-linear resistor having an operational field strength which op-tionally is formed as a VDR or as an NTC-resistor having a ceramicsintered body on the basis of a polycrystalline alkaline earth metaltitanate doped with a small quantity of a metal oxide so as to pro-duce an n-type conductivity, in which the sintered body comprisesat its grain boundaries insulating layers formed by re-oxidation ofthe sintered body and consists of an alkaline earth metal titanatehaving a Perowskite structure of the general formula

(Al_xL11x)TiOs. yTi02 or A(Th_xMex)Os . yTi02,wherein: A = alkaline earth metal; Ln = rare earth metal; Me =metal having a valency of 5 or more; 0.0005 <x < solubility limitin the Perowskite phase; y = 0.001 to 0.02. The sintered body be-comes adjustable in its non-linear resistance variation by selectionof the re-oxidation temperature and of the re-oxidation duration insuch manner that an initially present NTC-characteristic graduallyis observable only at ever increasing temperatures and changes intoa VDR-characteristic in the range of the operating temperature ofthe resistor.

4552020Apparatus for the scanning of objects by means ofultrasound echographyM. J. Auphan LAn apparatus for the scanning of objects by means of ultrasoundechography, comprising a mosaic of ultrasound transducers whichis connected to a transmitter stage and a receiver stage for the recep-tion and processing of the ultrasound echos corresponding to theobstacles encountered by the transmitted signals in their directionof propagation, and also comprising a display stage. The trans-ducers of the mosaic are grouped in 2" subwindows in which a non-corrected echogram of an area of the objects scanned is formed.The receiver stage comprises a device for determining correctiondelays to be applied to delay devices, said device comprising 2" - 1intercorrelation circuits which operate on the basis of n successivedivide-by-two operations of the aperture of the mosaic.

E4552301Method of bonding ceramic components together orto metallic componentsM.R.Liehr HW.NoltingR. U.D.KobsR. U. OrlowskiThe invention relates to a method for the force-coupled andvacuum-tight bonding of components of ceramic material togetheror to metallic components by means of thermocompression whileusing a soldering material in the form of an A1MgZn alloy providedbetween the components to be bonded prior to the thermocompres-sion process. The soldering material used consists preferably of analuminium-zinc-magnesium alloy having 95% by weight of AI, 40/0by weight of Zn and 1% by weight of Mg.

4553234Method and system of transmitting digital informa-tion in a transmission ringJ. R. Brandsma EA. A. M. L. BruekersJ. L. W. Kessels

The invention relates to a broad-band, time-division multiplex,token-passing, ring local area network, with which both circuit-switched and packet-switched traffic, namely data, text, picture andspeech traffic can be supported. The invention has for its object toprovide a method of transmitting digital information in a ringhaving a comparatively high transmission capacity with which rapidaccess to the common ring transmission means can be obtained,without however high requirements being imposed on the process-ing speed of the stations. According to the invention this is in prin-ciple achieved by means of a method which guarantees that pertime-division multiplex frame only one time slot, which is known tothe station, needs to be accessed.

4553250Signal transmission systemS. F. Bryant RA signal transmission system comprises a transmitter, a receiverand a transmission link in which the signal to be transmitted is pulsecode modulated. The transmission link comprises a plurality ofchannels (0-7), one for each bit of the pulse code modulated sig-nal. The quality of each channel is monitored and the bits of thepulse code modulated signal are applied to the channels such thatthe most significant bits of the pulse code modulated signal areallocated to the channels having the lowest level of interferingsignal.

4553266RF circuit arrangementR.N. BatesP. M. BallardAn RF circuit with at least one RF transmission line including astrip conductor and a ground plane on an insulating substrate andhaving two diodes respectively de-connected to two portions of theground plane. The two portions are mutually de-isolated by a slotto enable the diodes to be biased. The substrate is mounted in ahousing of conductive material, and the two portions of the groundplane are mutually RF-coupled via the conductive material. One ofthe portions is electrically-connected to an adjacent housing mem-ber and the other portion is separated therefrom by a thin insulatinglayer. The slot inhibits coupling of RF energy out of the circuit intothe slot, suitably being very narrow, e.g. 20 urn, so as to form afurther transmission line with a very low characteristic impedanceand also to have a high attenuation along its length for operation atmm-wavelengths.

4554030Method of manufacturing a semiconductor device bymeans of a molecular beam techniqueJ. HaismaP. K. LarsenT. de JongJ. F. van der VeenW.A. S. DoumaF. W. SarisA monocrystalline layer of one semiconductor material is grownonto a surface of a monocrystalline semiconductor body by meansof molecular beam epitaxy. During such growth, the semiconductorbody is kept at such a low temperature that a non-monocrystallinelayer is obtained. The non-monocrystalline layer is then convertedby a heat treatment into a monocrystalline form. Accordingly, anabrupt junction between the two semiconductor materials is ob-tained.

4554471Electric motor having a U-shaped stator ironL. BertramH. SchemmannJ. de BoerThe invention relates to an electric motor having a U-shaped statoriron such as a series-, split-pole- or single-phase synchronousmotor. Between the free shank ends of the stator, pole shoes areformed and on the shanks, induction coils are provided. Theshanks of the stator iron in the area between the pole shoes and thecoils are bent with respect to the central plane of the stator iron insuch manner that the shaft of the rotor with the central plane of thestator iron encloses an angle differing from the perpendicular to thecentral plane.

4554503Current stabilizing circuit arrangementW. G. KasperkovitzA current stabilizing arrangement includes a first circuit having aseries arrangement of a first resistor, a second resistor, and the col-lector-emitter path of a first transistor having its base connected toa point between the first and second resistors. A second circuit in-cludes the collector-emitter path of a second transistor whose baseis coupled to the collector ofthe first transistor. Byproviding a thirdresistor in the first circuit, in serieswith the first and second resistorsand connected between the base of the second transistor and thecollector of the first transistor, improved current stabilization withvariations in supply voltage is obtained.

4554564Semiconductor device and method of manufacturingsame, as well as a pick-up device and a display devicehaving such a semiconductor deviceG. G. P. van Gorkom EA.M. E. HoeberechtsThe invention relates to a method for displaying a pattern on aresist using electron lithography. In particular, a cathode devicehaving a matrix of semiconductor cathodes generates an electronbeam which exposes a resist layer. The electron beam is generatedby applying control signals to selected ones of the matrix of cath-odes to cause electron emission therefrom.

4555374Method of manufacturing a disc resonatorP. Roschmann HA method is described for adjusting the temperature coefficient ofthe ferrimagnetic resonant frequency in gallium or aluminium sub-stituted YIG disc resonators. At the compensation temperature, To,the temperature coefficient of the resonant frequency, fr, in a givenfrequency range is approximately zero. Where this range lies, de-pends, inter alia, on the substitution value. By annealing the discs,To can be moved into the desired temperature range. When themanufactured disc has a compensation temperature above the de-sired temperature range, annealing must be carried out at approxi-mately 850 to 1400°C. When the manufactured disc has a compen-sation temperature below the desired temperature range, annealingis performed at approximately 400 to 850°C.

4555460Mask for the formation of patterns in lacquer layersby means of X-ray lithography and method of manu-facturing sameM.Harms HA. BrunsH. LüthjeB. MatthiessenIn a mask for X-ray lithography, in which a pattern of a layer cor-responding to the structure to be manufactured and consisting of amaterial opaque to visible light is applied to a thin diaphragm of amaterial transparent to X-ray radiation, an adjustment with visible

H radiation, such as laser light, is made possible using a diaphragmconsisting of a material opaque to visible light and using adjust-ment windows of a material transparent to the visible light of thespectrum through the diaphragm.

4555631Apparatus for transmitting signals between two rela-tively rotatable partsG.Martens HAn optical transmission system arrangement for transmitting databetween two relatively rotatable parts. A hollow cylinder with amirror-coated inner surface onto which the light is incident at thesmallest possible grazing angle and is frequently reflected. The lightis coupled in and out through a coupling section in the hollow cylin-der, at which the light is incident onto the inner surface. The systemachieves a comparatively low damping because the reflecting powerat small angles of incidence is comparatively high.

E4555673Differential amplifier with rail-to-rail input capabilityand controlled transconductanceJ. H. Huijsing ER. J. van de PlasscheA differentlal. amplifier operable between a pair of supply voltagesthat define a rail-to-rail supply range contains a pair of differentialportions that together provide representative signal amplification

across the supply range, although neither differential portion indi-vidually does so. A current control regulates operating currents forthe differential portions in such a way that the amplifier transcon-ductance can be controlled in a desired manner as the common-mode part of the amplifier input signal varies across the supplyrange. The transconductance is typically controlled to be largelyconstant. A summing circuit selectively combines internal currentsfrom the differential portions to generate at least one output signalrepresentative of the input signal.

4555676Dual-section amplifier arrangement having a protec-tion circuitR. J. van de Plassche EE. C. DijkmansAn amplifier arrangement includes a first section and a second sec-tion. The second section has an output transistor which is protectedby a proteetion circuit. The proteetion circuit acts on the input ofthe second section in order to obtain a higher gain in the proteetionloop. In order to preclude instabilities, the proteetion circuit has afalling frequency response with a flat portion in view of the fre-quency compensation of the second section.

4555729System for transmitting television picture informationusing an error-protection codeL. M. H. E. Driessen EAn error proteetion code which acts on subpictures together con-stituting a television picture for the transmission of data for recon-structing the television picture at the receiving end. First each sub-picture is transformed by Hadamard functions. Of the coefficientsthus formed, a number of most significant coefficient bits which areassociated with low frequency transformation functions are pro-tected against a bit error. Moreover, a comparatively small numberof coefficient bits within said number are protected against an addi-tional bit error.

4555797Hybrid loudspeaker system for converting digital sig-nals to acoustic signalsJ. A. M. Nieuwendijk EW.D. A. M. van GijselG. B. J. SandersJ. M. van NieuwlandIn a loudspeaker system for converting an n-bit digitized electricsignal into an acoustic signal a plurality of p sections of a digitalloudspeaker are driven directly by the p most significant bits of then-bit digitized electric signal. The loudspeaker comprises at leastone additional sectionp + 1. This (p + l)th section receives a signalfrom a digital-to-analog converter, the input signalof the digital-to-analog converter comprising at least the n - p least significantbits. In a different embodiment the digital-to-analog converterreceives all the n bits of the digitized electric signal as the input sig-nal. At least the p sections which correspond to the p most signi-ficant bits are provided with means for producing a signal which is ameasure of the sum of their instantaneous drive signals and forapplying the said signal to a signal combination unit arranged in theline from the output of the digital-to-analog converter to the(p + llh section. By means of this correction circuit the distortionin the loudspeaker system can be reduced substantially.

4555810Distribution system for a local area networka~n~ EJ. H. C. van HeuvenA distribution system for a local area network has a distributionunit which is coupled to a plurality of subscribers' premises via op-tical transmission links. Each subscriber is provided with a terminal

unit having an input coupled to an optical transmission link. Theterminal unit has a plurality of outputs which are connected to op-tical wall sockets. Opto-electrical converters are provided at eachsocket. Each terminal unit has a power splitter and a distributionbox. The distribution box has a plurality of inputs, a larger numberof optical outputs, and a plurality of links between the inputs andoutputs.

4556796Infrared radiation detectorM. Renals

An infrared radiation detector comprises two differentially con-nected pyroelectric detector elements in parallel-opposition. Thedetector elements are formed in a single body of pyroelectric mate-rial having two adjacent pairs of overlapping electrodes on oppositemajor surfaces ofthe body. The two detector elements are poled inthe same direction. To electrically connect the top electrodes ofeach pair to the bottom electrodes of the other pair, each electrodeis provided with an L-shaped extension. Each extension is arrangedsuch that at an edge of the body the extension of the top electrodeof one pair overlaps the extension of the bottom electrode of theother pair. The overlapping extensions can be electrically connectedtogether by conductive epoxy or by conductive clips on the edge ofthe body.

4556967Record carrier having an optically readable informa-tion structure comprised of information areas of twodifferent phase depthsJ.~A1.Braat EA record carrier is described which has an optically readable infor-mation structure in which information areas of adjacent informa-tion track portions have different phase depths, and an apparatusfor reading said record carrier. By a suitable choice of the phasedepths and ,by an electronic phase shift of the signals supplied bythe read detectors, cross-talk between adjacent tracks can substan-tially be eliminated.

4557564Movable scanning unit for an optical recording orplayback apparatusG. E. van Rosmalen EAn electro-optical device for reading an information disc comprisesan optical system which is movable relative to the disc by at leastone electro-magnetic actuator. The optical system is supported byelongated members whose length is great relative to their thicknessand which are pretensioned in the longitudinal direction by magnetswhich cooperate with each other via an air gap, enabling the use ofvery flexible supporting elements, for example guys which have alow resistance to bending and a very low mass.

4558448Semiconductor laser with end zones for reducing non-radiating recombinationJ. A. de Poorter EP. J. de WaardR. P. TijburgG. Li DinghsA semiconductor laser having mirror faces serving as resonators,in which the active laser region includes end zones adjoining themirror faces which have implanted ions, preferably protons, withassociated crystal damage. The end zones have a length which is atleast equal to the diffusion length of the recombining charge car-riers in the end zones. As a result of the high recombination rate inthe end zones substantially no non-radiating recombination occursat the mirror faces, so that mirror erosion is avoided.

4559280Metallized rare earth garnet and metal seal to sameR. L. Bronnes NJ. K. MeKinlayR. C. SweetW. K. ZwickerA reliable garnet to metal hermetic seal is obtained by metallizingthe garnet with successive sputtered layers of tantalum or titanium,molybdenum or tungsten and nickel, followed by soldering or braz-ing the metallized garnet to a metal member.

4559467Ion-generator for producing an air flowF. K. BeckmannH.DötschD. GosselAn ion-generator for producing an air flow includes a plurality ofrectangularly shaped plate electrodes spaced from one another andrespectively lying in planes parallel to the direction of the air flow,such plate electrodes extending perpendicularly to the direction ofthe air flow, the edge of each plate electrode facing upstream beingrounded. There is a plurality of rows of needle electrodes disposedupstream of the plate electrodes and extending perpendicularly tothe direction of the air flow, such rows of needle electrodes beingrespectively associated with and oriented towards the gaps betweenthe plate electrodes, the tips of all the needle electrodes being dis-posed in a plane perpendicular to the direction of the air flow. Thereis an electrically conductive rod-shaped support for each row ofneedle electrodes, such rod-shaped supports being arranged parallelto the rounded edges of the plate electrodes. An electrically insul-ating material covers each rod-shaped support and its associatedrow of needle electrodes except for the tip of each needle electrode.The plates electrodes are connected to one terminal of a high-voltage de source; and the rod-shaped supports are connected to theother terminal of such de source.

4559469Green emitting phosphor and cathode-ray tube pro-vided with such a phosphorT. Welker AK. CarlW. CzarnojanA green emitting phosphor for heavily loaded cathode-ray tubescomprises a mixture of a deep-green and a yellowish-green emittingphosphor. Mixtures of Zn2Si04:Mn and at least one phosphorfrom the group comprising Y2Si05:Tb; X202S:Tb; ES:Ce andXOZ:Tb, where X =Y, La, Gd, Lu; E = Ca, Sr, Ba; and Z = Cl,Br, I, F; satisfy the EBU specification.

4559612Sorting device for data wordsH. VrielinkAn integrated sorting device for data words comprises a bidirec-tional bus to which are connected the address input of a memory, acommand register for memory clear, sorting criterion and pointerreset signals, a multiplexer and an address counter. In a write modeof operation, data words arriving on the bus address the memoryand representations thereof, e.g. binary Is, are stored therein.Briefly before each such storage operation, the same memory loca-tion is read and any representation already stored therein is used totrigger a flip-flop to indicate that an overflow condition exists.During a read operation.: the address counter addresses the suc-cessive memory addresses under the control of an oscillator. Whena filled memory location is reached, a further flip-flop causes thecounter to stop and a 'ready' signal is outputted. The counterresumes counting when the relevant memory location has been readcompletely. The multiplexer feeds the overflow signal and a readtermination signal derived from the address counter to the bus.

4559635Auto-adaptive amplitude-equalizing arrangement fordigital radio linksH. Sari LAn auto-adaptive amplitude-equalizing arrangement for digitalradio links having an intermediate-frequency signal input, a trans-versal filter and a circuit for the control of the filter. The transversalfilter comprises a delay circuit providing, with respect to the inter-mediate-frequency signal input, a delay T equal to (2k - I)/4Fe,

where k is a positive integer and Fe the center frequency of the inter-mediate-frequency signal, a first and a second multiplication circuitwhose inputs are respectively connected to the output of the delaycircuit and to the interrnediate-frequency signal input, and an adderconnected to the outputs of the multiplication circuits. The firstmultiplication circuit may be an analog amplifier whose gain is con-trolled by the control circuit, or may comprise a fixed-gain amplifierand a digitally controlled attenuator, the control inputs of theattenuator being connected to the count outputs of an up/down-counter, which is controlled by a zero comparator connected to theoutput of the control circuit.

4559703Process for silver plating rotary contact assembliesD.F. Oagas NA process for silver plating a rotary switch contact assembly where-in a brass metal plate and a plastic rotor retainer are first formed,force-fitted together and then silver-plated as an assembly.

4560836Four-wire communication line circuit and conferencenetwork comprising such circuitsA. W.M. van den Enden EJ. F. P. van MilA four-wire communication line circuit for two or more two-wiresubscriber lines, comprising a pair of amplifiers respectively con-nected in the line pairs of the four-wire line for each direction oftransmission and a transmission direction detection circuit con-nected to each line pair. The detection circuit generates a controlsignal from the voltage signals transmitted on the line pairs, andwhich is dependent on the direction in which the net energy of suchvoltage signals is transmitted over the two-wire subscriber lines.The control signal is applied to control circuitry which switches thegain factors of the line amplifiers between a high and a low value, asdetermined by the direction of net energy transmission. When usedin a conference network, the four-wire communication line circuitincludes circuitry for establishing a higher threshold level at whichthe amplifier gain factors will be switched to a high level for trans-mission than the threshold level at which they are switched to a highvalue for reception.

4560898Colour picture display tubeA.O.KnappJ. R. ManselI

E A deflection colour selection system for a single beam channel platedisplay tube includes, within an envelope, a laminated dynode chan-nel plate electron multiplier having channels whose exit aperturesare aligned in columns. An apertured extractor electrode is mountedon and electrically insulated from an output face of an electronmultiplier, the apertures in the extractor electrode being alignedwith respective channels. A luminescent screen spaced from the ex-tractor electrode includes patterns of phosphor elements (R, G, B)adapted to luminesce in different colours. A current multiplied elec-tron beam exiting from an aperture in the extractor electrode is de-flected onto an associated pattern of phosphor elements by pairs offirst and second deflector electrodes insulated electrically from eachother and from the extractor electrodes, the first and second deflec-tor electrodes being disposed as pairs between each column of aper-tures in the extractor electrode. All of the first electrodes are inter-connected as are all of the second electrodes. This electrode ar-rangement enables good resolution and electrical correction of mis-alignment errors between the electron multiplier and the screen.

4560908High-frequency oscillator-inverter ballast circuit fordischarge lampsE.H. Stupp NM. W. FellowsW. G. Sten eekA current fed high frequency oscillator-inverter ballast circuit in-cludes a parallel resonant tank circuit for driving a pair of seriesconnected discharge lamps via a series ballast capacitor. A regener-ative power supply switches on when a fluctuating main de supplyvoltage drops below a given level thereby providing a constant levelauxiliary dc supply voltage to the oscillator inverter to maintainoscillation and lamp operation. When the main de supply voltageexceeds said given level, the regenerative power supply switchesout. The oscillation frequency is 12 during operation of the mainsupply and automatically switches to a frequency Ir when theregenerative power supply takes over. The frequency shift is auto-matic during each half cycle of a 60 Hz ac supply and is in a direc-tion so as to maintain lamp current relatively constant. A novelhigh frequency leakage transformer may be provided to couple thehigh frequency inverter to the discharge lamp load to provide botha current limiting (ballast) action and automatic control of the lampheater current to maintain high efficiencyoperation.

4560963Analog RC active filterR. SharpeAn RC active filter device which is implemented with integrated cir-cuit technology. Each RC filter element of the device has a distri-buted series resistance and a distributed shunt capacitance. Theseries resistance is formed by a strip of resistive material whichoverlies a resistive plate (or substrate) with an intervening insulatinglayer to form the shunt capacitance. The filter device can be de-signed to have a pass-band ripple response which is not affected byvariation in nominal absolute resistance and capacitance valuesresulting from process spreads. These variations only stretch orcompress the filter response along the frequency axis. The filter de-vice comprises three RC filter elements and an operational amplifierdetermine a low pass band, while the input filter element preventshigh frequency components outside the low pass band being leakeddirectly to the filter device output.

4561005Solid-state infrared radiation imaging devices havinga radiation-sensitive portion with a superlattice struc-ture~M.Shannon RAn infrared radiation imaging device comprises a semiconductorbody, for example of silicon, having a radiation-sensitive portion inwhich charge-carriers are generated on absorption of infrared radia-tion. The semiconductor body also includes a signal-processing por-tion in which the charge-carriers are collected in a charge-transfershift register, for example a surface-channel or buried-channelCCD. An electrical signal representative of the detected radiation isproduced at an output of the shift register. At least the radiation-sensitive portion is depleted of free charge-carriers in the absence ofthe radiation. The semiconductor materialof the signal-processingportion has an energy band gap (EB) which is greater than the quan-tum energy of the detected infrared radiation. The radiation-sensi-tive portion is of the same semiconductor material as the signal-processing portion but comprises a plurality of alternating n-typeand p-type layers. These layers form an energy band bending super-lattice structure locally in the body with a reduced effective bandgap (Es'). The ri-type and p-type layes have a doping concentrationand thickness such that the superlattice structure can be depletedthrough its thickness without producing breakdown. The charge-carriers are generated in the superlattice structure by transitionsacross the effective band gap (Es') between the conduction andvalence bands ofthe semiconductor materialof the radiation-sensi-tive portion.

4561081Opto-electronic apparatus for inscribing and! or read-ing recording tracks by means of a radiation beamP. J. M. Janssen EG. E. van RosmalenAn opto-electronic apparatus for inscribing and/or reading record-ing tracks on a record carrier by means of a radiation beam com-prises an objective mounted in an objective holder. The objectiveholder is supported in a frame by bearing arrangement for move-ment in accordance with a number of desired degrees of freedomand the appratus includes electromagnetic actuator means fordriving the objective holder in accordance with the desired direc-tions of movement. The bearing arrangement of the objective holderon the frame comprises electromagnetic bearing means for counter-acting movements in accordance with at least one undesired degreeof freedom. An objective-position measuring device supplies a posi-tional error signal which represents the deviation of the objectiveholder in accordance with the undesired degree of freedom relativeto the frame and which is utilized by a levitation control circuitwhich counteracts movement of the objective holder relative to theframe in accordance with the undesired degree of freedom by meansof electromagnetic levitation forces.

4561173Method of manufacturing a wiring systemT. S. te Velde EA self-registering method of manufacturing an air(vacuum)-in-sulated crossing multilayer wiring system of large density is dis-closed. Between the lowermost and uppermost wiring layers anintermediate layer is provided in which recesses are formed betweenthe intermediate layer and the lowermost wiring layer. By means ofsaid recesses the intermediate layer can be removed entirely at thearea of the crossings during the etching process, while elsewhereportions of the intermediate layer remain as supporting parts or asconnecting members.

4561259Method of operating a bimodal heat pump and heatpump for use of this methodW. L. N. van der Sluys EA method of operating a bimodal heat pump is provided, such heatpump operating in a first mode as an absorption heat pump and in asecond mode as a device for indirectly heating a heat-transportmedium. This procedure comprises in the first mode heating by heatexchange a generator containing a solution of a working medium ina solvent to separate a part of the dissolved working medium in thegaseous state from the solvent, passing the separated gaseous work-ing medium to a condenser for liquefaction by the giving up ofthermal energy to the heat-transport medium, thereafter expandingand evaporating the liquefied working medium in an evaporator bythe taking up of thermal energy from the environment, passing theevaporated working medium to an absorber for solution in the sol-vent while giving up thermal energy to the heat-transport medium,and passing another part of the working medium-solvent solutionfrom the absorber to the generator. The procedure also comprisesin the second mode indirectly heating by heat exchange all the heat-transport medium in a heat boiler separate from the generator. Theprocedure further comprises, in switching over from the first modeto the second mode, discontinuing the heating of the generator,discontinuing the pumping of the working medium-solvent solutionbetween the absorber and the generator, and diverting all the heat-transport medium to and through the heat boiler for indirect heat-ing by heat exchange therein. In addition, the procedure comprises,in switching back from the second mode to the first mode, restart-ing the heating of the generator and the pumping of the workingmedium-solvent solution, and discontinuing passing the heat-trans-port medium through the heat boiler.

\ 4 562 567Apparatus for controlling the write beam in an opticaldata recording systemE. J. Frankfort NG. C.KenneyR. McFarlaneApparatus for recording data by means of a beam of radiation on arecording medium which upon exposure to the beam undergoes op-tically detectable changes in the form of pits, which apparatusincludes means for reducing the beam intensity as a result of pitinitiation thereby forming more accurate pits.

4562587X-ray tube having a rotary anodeJ. GerkemaA. K. NiessenJ. B. PelzerAn X-ray tube having a rotary anode which is accommodated in avacuum-tight housing so as to be rotatable by means of at least onespirally grooved bearing. The mutually cooperating surfaces of thebearing consist essentially of Mo or of an alloy of Mo and Wandare effectively wetted by a Ga-alloy serving as a bearing lubricant.In order to extend the life of the X-ray tube, 1 to 40/0 by weight ofAg and/or Cu are added to the Ga-alloy, as a result of which theformation of crystalline compounds is inhibited.

4562591Digital dynamic range converterE. F. StikvoortA digital dynamic range converter of the forward control type forvarying the dynamic range of a digital audio signal constituted by asequence of audio signal samples. Each audio signal sample is mul-tiplied by a control signal sample which is delivered by a digital con-trol signal generator. This control signal generator has applied to itunipolar signal samples which are derived via a transmission chan-nel from the audio signal samples. In order to cause this dynamicrange converter to respond rapidly to abrupt variations in the audiosignal and to render it moreover universally usable, the control sig-nal generator is provided with a digital peak-value detector whichconverts the sequence of unipolar signal samples into a sequence ofpeak-value samples. The latter are applied to a digital non-linearamplitude transformation circuit which has an adjustable ampli-tude transmission characteristic curve determined by adjustmentquantities. It delivers the transformation samples which are prefer-ably converted in a digital low-pass filter into the control signalsamples which are applied to the multiplier device.

4562955Air-conditionerH. HörsterK. KlinkenbergAn air-conditioner comprises an air-to-air heat exchanger; a freshair supply duct, a fresh air by-pass duct, a used air exhaust duct,and a used air by-pass duct, the fresh air supply duct and the usedair exhaust duct being respectively connected to the air-to-air heatexchanger, the fresh air supply duct having a part in common withthe used air by-pass duct, and the used air exhaust duct having apart in common with the fresh air by-pass duct. Included are a con-denser provided in the common part of the fresh air supply duct,and an evaporator provided in the common part of the used air ex-haust duct, the condenser and the evaporator being parts of a heatpump. A blower is provided in the common part of the fresh airsupply duct and is connected to the used air by-pass duct, and aseparate blower is provided in the common part of the used air ex-haust duct and is connected to the fresh air by-pass duct. A firstthree-way valve is arranged in the used air exhaust duct in front ofthe air-to-air heat exchanger, and a second three-way valve is ar-ranged in the fresh air supply duct behind the air-to-air heat ex-changer viewed in the direction of fresh air supply for switching theair conditioner into first, second and third modes wherein the airconditioner functions as a heat pump, a heat pump and a fresh airsupplier, and a fresh air supplier, respectively.

4563752Series/parallel/series shift register memory comprisingredundant parallel-connected storage registers, anddisplay apparatus comprising a picture memory thusorganizedM. J. M. Pelgrom EA. SlobH.A. HarwigJ. W. SlotboomA series/parallel/series shift register memory comprises a substrateon which there are provided storage positions for multivalent dataelements. There is provided a redundancy generator for generatingone or more redundant code elements on the basis of a group ofdata elements, said redundant code elements being applied to theseries input of the shift register memory later than the associateddata elements. The code elements are conducted through parallel-connected storage registers which are shorter than those used forthe associated data elements, so that a redundancy reducer receivesthe redundant code elements from a series output before the as-sociated data elements appear on this series output. The reductionof the storage registers, expressed in periods of the shift drive, canbe performed in different ways from a technological point of view.

4564866Optical printerA. Comberg A

The invention relates to an optical printer in which light signalsemitted by an information-controlled light source are applied to aphotosensitive record carrier via a mirror system and a circular-to-linear converter which consists of optical fibers. In order to im-prove the optical coupling between the light source and the recordcarrier and hence the printing quality, the mirror system comprisesa conical mirror which opens in the direction of the circular-to-linear converter and which enables the light beam to be axiallycoupled into the circularly arranged ends of the optical fibers at theentrance of the circular-to-linear converter.

4566020Hot-electron and hot-hole transistors having silicidecontactsJ. M. Shannon RA unipolar hot-electron or hot-hole transistor has its base regionand/or collection region electrically contacted and extended to thesemiconductor body surface by a metal-silicide region which ex-tends through a silicon surface region belonging to either the tran-sistor emitter or the emitter-base barrier. The metal-silicide regionforms an isolating Schottky barrier with an adjacent semiconductorportion. Preferably, the surface region is divided into separate firstand second portions by the base-contacting met al-silicide region,with the emitter-base barrier and base-collector barrier terminatingat one or more sides in this met al-silicide region. The isolatingSchottky barriers are good quality unipolar diodes, thus avoidingminority charge carrier storage effects in these unipolar transistors,while the metal-silicide region can form good ohmic contacts tohighly-conductive base and collector regions which typically com-prise a high-doped semiconductor layer or a metal-silicide layer.

4566076Method of attenuating a digital signal and device forcarrying out said methodA. C. A. M. van der Steen EIn the method of attenuating or amplifying digital signal values asdescribed herein the desired modification is realized in two steps. Acoarse attenuation or amplification in steps of 6 dB is effected byshifting the digital word to be modified into a shift register, afterwhich fine amplification is realized by adding the word, which isattenuated by shifting it a number of times, to the word thus shifted.Furthermore, a device for carrying out said method is described, inwhich the signal processing section only comprises one shift registerand an adding circuit, the additional shift being achieved by means

of the wiring between the said shift register and the adder circuit, sothat no further signal-processing registers are required for carryingout the said cumulative addition.

4566112Tomosynthesis apparatusR. LindeE. KlotzA tomosynthesis apparatus for the formation of layer images of abody. The apparatus has a large number of radiation source posi-tions which are situated in one radiation source plane. The radia-tion from the sources is stopped by a diaphragm device so that theradiation beams passing through the diaphragm apertures irradiatea common superposition zone and are incident on a detector surfacewhich is arranged behind the superposition zone. The diaphragmapertures are shaped so that in the detector plane the edge of theradiation beam of each radiation source is at least locally tangent tothe edge of a cylinder which is centrally projected onto the detectorsurface by the radiation source and which is situated within thesuperposition zone. The axis of the cylinder extends at least approxi-mately perpendicular to the radiation source plane.

4566120Loudspeaker system and loudspeaker for use in a loud-speaker system for converting an n-bit digitized elec-tric signal into an acoustic signalJ. A. M. Nieuwendijk EF. J. op de BeekG. B. J. SandersW. D. A. M. van GijsetJ. M. van NieuwlandA loudspeaker system for converting an n-bit digitized electric sig-nal into an acoustic signal comprises an electrodynamic loudspeakerwith n voice-coil sections which cooperate with a magnet system.The loudspeaker system further comprises means for short-cir-cuiting a voice-coil section if the value of the bit corresponding tothe voice-coil section is such that the relevant voice-coil section isnot driven.

4566177Formation of electromigration resistant aluminiumalloy conductorsE. P. O. T. van de Ven SJ.M. TownerElectromigration resistance of aluminium alloy conductors in semi-conductor devices is found to significantly increase by rapidlyannealing the conductors by employing an annealing cycle with apeak temperature of 520-580 DCand a cycle time of about 5 to 30seconds such as is developed by high intensity CW lamps.

4566756Projection screenW.A. L. HeijnemansA projection screen comprises a single plate of a transparent mate-rial. The diffusion in the horizontal direction is provided by filamen-tary particles which are oriented substantially in one direction in theplate material. Both surfaces of the plate are then capable of per-forming different functions, yielding a projection screen with anoptimally uniform brightness distribution, minimal colour faultsand maximum contrast.

4566936Method of trimming precision resistorsS. L. BowlinA method for trimming precision resistors which includes forminga helical groove in a conductive film coating on a cylindrical core.Final trimming includes forming discrete circular depressions in thefilm coating by using a pulsed laser. This method enables the manu-facture of precision resistors having a tolerance of 0.25OJo or better.

4567.386Integrated logic circuit incorporating fast sample con-trolN. F. Benschop EA MOS integrated logic circuit is described which comprises a plur-ality of groups of combinatory logic elements. These groups form acascade in that a data output of a preceding group is directly coupledto a data input of a next group within the cascade. During successiveclock pulse phases the groups of combinatory logic elements aresampled in the sequence in which they are arranged in the cascade.Charging means provide the charge to be sampled, either by meansof a precharge clock phase, or by virtue of being pull-up means.

4567399Cathode ray tube with spherical aberration correctionmeansA. A. van Gorkum EA curved, electrically-conductive foil or gauze member is providedin a second cylindrical accelerating electrode of an electron gun for acathode ray tube. The curvature of the foil or gauze member initiallydecreases with distance from the longitudinal axis of the electrode,thereby modifying the shape of the field produced by the electrodeand minimizing spherical aberration. The curvature preferablyvaries according to a zero order Bessel function. Spherical aberra-tion can be made negative by adjusting the relative positions of themember and nearby ends of the second and an adjacent first cylin-drical accelerating electrode.

4567426Current stabilizer with starting circuitR. J. van de PlasscheP. J. M. SijbersTwo current circuits are between two common terminals (+ VB and- VB)' The ratio between the currents in the two current circuits isdefined by a first current-dividing circuit, and the absolute values ofthese currents are defined by means of a second current-dividing cir-cuit, in particular a resistor in this second current-dividing circuit. Inorder to ensure that the current-stabilizing assumes the proper stateupon activation, a first current-supply circuit is coupled to the inputof the second current-dividing circuit, which current-supply circuitcomprises the series arrangement of a resistor and a transistor ar-ranged as a diode, and a second current-supply circuit is coupled tothe output of the current-dividing circuit, which second current-supply circuit includes a transistor whose base is connected in com-mon with that of the transistor of the first current-supply circuit.

4567484Doppler radar measuring apparatusW. SchilzB. Schiek

Range-dependent sensitivity of an RF doppier radar apparatus isreduced to prevent false alarms when smallobjects move in closeproximity to the apparatus' antenna. The sensitivity is reduced byperiodically FM-modulating the transmitted RF signal at a fre-quency corresponding to a wavelength which is at least four timesthe operating range of the apparatus. The reflection of the trans-mitted signal is mixed with the transmitted signal to produce a dif-ference frequency signal which is sampled at instants of maximumamplitude.

4567508Two-channel compatible television transmission sys-tem for wide picture formatsM. O. Hulyer RA television transmission system for the simultaneous transmissionof television signals, depicting the same scene, for standard andwide picture formats of, respectively, a standard aspect ratio and awider standard aspect ratio. The television signal for the scenehaving 1249 lines per field is divided to produce a first television sig-nal of 625 lines per field representing the wide picture format where

adjacent lines of a field are derived from alternate lines of the scene.television signal and a second television signal also of 625 lines perfield representing the standard picture format where adjacent linesof a field are derived from the intervening lines of the scene tele-vision signal. The first and second television signals may be receivedtogether for the provision of a wide screen television display andthe invention has the advantage that the second television signalmay be received alone by currently manufactured television re-ceivers for reproduetion of a display of standard aspect ratio.

4567518System for decoding and displaying encoded televisionpicturesL. M. H. E. Driessen EAn error proteetion code which acts on subpictures for the transmis-sion of television picture information. First the picture is subpicture-wise transformed by means of transformation functions, for exam-ple, Hadamard functions. Of the coefficientsthus formed, a numberof most significant coefficient bits which are associated with low fre-quency transformation functions are protected against a bit error.Moreover, a comparatively small number of coefficient bits withinsaid number are protected against an additional bit error.

4567520Television circuit arrangement for determining in avideo signal frame periods comprising two fieldperiodsL. J. van de Polder EA television circuit arrangement for determining in a video signal,frame periods comprising two field periods when a picture signalrepeated in cycles of two successive field periods and with a possiblechange of picture content therebetween is present. Signal sources,such as, for example, cine-film television converters and 'field skip'signal storage- and display devices, supply such a signal. It may berequired for signal processing operations improving the picturequality during display, to use the cycles as frame periods. For thispurpose, the circuit arrangement is provided with a switching cir-cuit, a first and a second signal integration circuit which can be resetand are alternately operative every other field period, and a suc-ceeding signal comparison circuit for supplying a voltage deter-mining the frame period.

4567522Line synchronizing circuit for a picture display deviceM. V.C. Stroomer EF. M. BoekhorstA line synchronizing circuit for a picture display device comprising avoltage-controlled oscillator for generating a signal whose frequencyis higher than the line frequency, a frequency dividing circuit for div-iding the frequency of the oscillator signals and a phase comparisonstage for generating a control voltage in dependence on the phasedeviation between the signals applied thereto, more specifically areceived line synchronizing signal and a locally generated referencesignal. The elements of the line phase control loop, are part of anintegrated circuit which functions as a frequency synthesizing cir-cuit. The reference-frequency dividing circuit incorporated in theintegrated circuit is programmed to operate with a constant divisor.

4567605X-ray analysis apparatus comprising a four-crystalmonochromatorW. J. Bartels EIn order to achieve high resolution in X-ray analysis, a monochrom-ator comprising four crystals which are pair-wise positioned inparallel orientation is used with the two pairs being positioned in anoffset anti-parallel orientation. An X-radiation source may be ar-ranged in the immediate vicinity of the first crystal pair in order toachieve a high beam intensity. Each of the crystal pairs is preferablycut so as to form a U-shape from a single block of a monocrystal-line material which is relatively free from dislocations. Germaniumis a monocrystalline materialof preferred use.

4567644Methods of making triple diffused ISL structureaRA~M SAn ISL structure is fabricated by a process in which impurities areintroduced into a semiconductor substrate of first type conductivity(p) to form major and minor portions of a first region of oppositesecond type conductivity (n), The minor portion has a lower net im-purity concentration than the major portion and extends to a con-siderably lesser depth. An impurity is introduced into the major andminor portions to form a second region of first type conductivity.An impurity is introduced into the second region to form a thirdregion of second type conductivity spaced laterallyapart from theminor portion. Metallization is then performed to create at leastone Schottky rectifying contact with the major portion and ohmiccontacts with the substrate and second and third regions.

4567736Absorption heat pumpW.L. N. van der SluysJ. PastoorJ. C. M. RoelofsAn absorption heat pump comprising a heat-mass-exchanger whichis arranged in an absorber and has a metal pipe to which a metal finis secured. The metal fin consists of a number of interconnectedlamellae which are helically wound around the pipe, while adjacentlamellae of successive turns overlap each other in part, viewed inthe circumferential direction of the pipe. The finned pipe yields acomparatively strong heat-mass transfer in the absorber.

4568140Optical element compnsmg a transparent substrateand an antireflection coating for the near-infraredregion of wavelengthsP. van der Werf EJ. HaismaAn optical element comprises a transparent substrate. An antireflec-. tion coating is provided on the substrate for reducing reflections ofwavelengths from approximately 700 nm to approximately 1700nm.The coating comprises a plurality of stacked, uniform layers withrefractive indices which decrease toward the top of the stack. Abase coating is arranged between the layer stack and the substrate.The effective refractive index at the top of the base coating is atleast 2.5, and the base coating is a graded index layer. .

4568853Electron multiplier structureJ.-P. Boutot LAn electron multiplier structure comprising an electron multipliersection with one or more microchannel plates and a dynode stagehaving secondary electron emission. This structure makes it pos-sible to obtain an amplification which is higher than the amplifica-tion obtainable with only the electron multiplier section while main-taining the instantaneously obtained characteristics and specialresolving power associated therewith.

4568890Microwave oscillator injection locked at its funda-mental frequency for producing a harmonic frequencyoutputR. N. Bates RA microwave oscillator suitable for millimeter wavelengths com-prises a Gunn diode coupled to a waveguide by a resonant-cap struc-ture. The diode generates microwave energy both at a fundamentalfrequency fo which is below the cut-off frequency of the waveguideand at a second harmonic frequency 2fo above cut-off. To controlthe generation of microwave energy at 2fo, energy atfo is coupledinto the waveguide from an adjacent further waveguide above itscut-off, by means of an electric probe extending close to the cap.

The probe may couple in a locking signal at or close to the free-running value of fa from another oscillator having better noise per-formance and electronic tuning, thereby locking 2fo to twice thefrequency of the locking signal, or alternatively may couple to avaractor-tuned cavity resonant at fa.

4568906Sensor having a magnetic field-sensitive element withaccurately defined weight and thickness dimensions inthe nanometer rangeJ. de Wilde EW. G. M. van den HoekA sensor suitable for measuring magnetic field gradients spanningvery small regions has a magnetic field-sensitive element with a veryaccurately defined height and thickness (even into the nanometerrange) which is perpendicular to the surface of a substrate so thatthe substrate surface may be used in aligning the element.

4568993Magnetic headD. StoppelsP. F. BongersJ. P. M. DamenE. G. VisserMagnetic head for a magnetic recording and playback appara-tus includes a core of a Mn-Zn-ferrous ferrite having a very highsaturation magnetization. The Mn-Zn-ferrous ferrite has a com-position (not counting optional substitutions) according to theformula MnaZnbFeclIFecIl104 with 0 < a ~ 0.55, 0.06 ~ b ~ 0.4,0.25 ~ c ~ 0.9, (a + b + c = 1). The result is that the magnetichead may be used in combination with magnetic tapes having a veryhigh coercive force up to 104 kAlm (1300 Oersted) and may be usedfor transducing signals having a frequency of a few MHz.

4569072Clock-controlled filtering arrangementA. H. M. van RoermundA clock-controlled filtering arrangement for suppressing a numberof interference frequencies related to a clock frequency, whichcomprises a time-discrete comb filter included in a negative feed-back loop for a selective negative feedback of the said interferencefrequencies, which time-discrete comb filter is connected to an out-put of a clock generator for controlling the frequency location ofthe pass ranges of the comb filter. In order to avoid on the one handthe introduetion of quantizing noise and the use of additional cir-cuits, such as A/D and D/A converters, and on the other hand theoccurrence of error cumulation while maintaining an adequateinterference suppression, the time-discrete comb filter is of theswitched capacitor N-path filter type.

4569121Method of fabricating a programmable read-onlymemory cell incorporating an antifuse utilizing de-position of amorphous semiconductor layerS.C.P.Lim SD. F. RidleyS..A.RazaG. W.ConnerIn fabricating a PROM cell, an electrical isolation mechanism isformed In a semiconductive body to separate islands of an upperzone of first type conductivity (n) in the body. A semiconductorimpurity is introduced into one of the islands to produce a region ofopposite type conductivity (p) that forms a pn junction laterallybounded by the island's side boundaries. A highly resistive amor-phous semiconductive layer which is~irreversiblyswitchable to a lowresistive state is deposited above the region in such a manner as tobe electrically coupled to the region. A path of first type conduc-tivity extending from the pn junction through another of the islandsto its upper surface is created in the body to complete the basic cell.

4596806Method and device for manufacturing an informationcarrier of a synthetic material having a laminatedstructureP. L. Holster E

A method and a device for manufacturing an information carrier ofsynthetic material having a laminated structure, in which a trans-parent carrier is provided away from the mould with a resin layerand is then brought to a position opposite a mould with its resinlayer facing the mould, after which the carrier is pressed against themould progressively from a boundary surface of the carrier bymeans of one or more rollers and at least the part of the carrierlocated directly behind the roller or rollers is exposed for curing theresin layer, the carrier with the cured resin layer being subsequentlyremoved from the mould and further transported.

4570036Digital duplex communication systemN. S. Virdee R

EA digital duplex communication system for data signals having apower-versus-frequency spectrum having two side bands locatedone each side of a symbol frequency, the system comprising a trans-mitter/receiver which includes an echo canceller. The received sig-nal is sampled at a multiple of the bit rate and has in each symbolperiod a first time during which data is valid (true eye) and a secondtime during which data is invalid (false eye). The receiver includescircuitry to decode the data from the sample signal during the trueeye. The echo canceller is designed to be operative only during thesampling instant in the true eye and at one of the zero crossing in-stants in each bit period. This enables the storage capacity of alook-up table type echo canceller to be reduced and the processingspeed of a transversal filter type echo canceller to be reduced.

4570063Device for the optical scanning of a documentJ.H.deBie EA. J. J. FrankenThe device comprises a transducer with photoelectric elements anda coupling member which comprises an entrance face which is to beaimed at the document and an exit face which is optically coupledto the transducer. The coupling member comprises a number oflight conductors having first ends which are arranged in at least onestraight line in the entrance face and second ends which are situatedin arbitrary positions in the exit face. The relation between the posi-tions of the first ends in the entrance face and the positions of thesecond ends in the exit face is stored in a memory. The photosen-sitive surface of the transducer may have an arbitrary length/widthratio and the light conductors may extend rather arbitrarily throughthe coupling member so that the cost of the device may be com-paratively low.

4570125FSK demodulator with concurrent carrier and clocksynchronizationR. W. Gibson RA data demodulator for digital signals in which the times of thezero crossings in hard limited signals in the orthogonal outputs of adirect demodulation receiver are used to recover the carrier andclock signals.

4571276Method for strengthening terminations on reductionfired multilayer capacitorsJ. R. Akse NThe strength of end terminations on multilayer capacitors employ-ing base metal electrodes is increased by heating the terminations,subsequent to firing in a reducing atmosphere, in an atmosphere inwhich the oxygen partial pressure is at least equal to that of air for aperiod of at least 15 minutes at a temperature in the range of from375 to 600 °C.

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4571526Low-pressure discharge lamp with cooled internalballastG. A. WesselinkA compact screw-base discharge lamp having an electrical stabiliza-tion ballast which occupies a central position in the lamp. The dis-charge vessel surrounds the ballast. To dissipate the heat generatedby the ballast during operation to the environment of the lamp, athin-walled heat sink of a heat-conductive material is provided be-tween the ballast and the discharge vessel, and bears on the ballast.This body has a collar which extends to the exterior of the lamp.

4571604Method of and device for the electrophotographicprinting of informationU. Schiebel AA method of electrophotographic printing of electrically storedinformation by means of a cathode ray tube. The tube is controlledso that each time only one picture line of the information on the dis-play screen is activated several times in succession. Thus, the trans-port movement of the record carrier is continuous. The optical sys-tem provided between the cathode ray tube and the record carriermay be constructed to be rigid, so that on the record carrier there isformed an image whose individual pixels represent a small linewhich consists of several overlapping dots. The necessary bright-ness is achieved by using a cathode ray tube having a wide displayscreen on which the pictue lines to be transferred to the recordcarrier are displayed with al: 1 ratio. Furthermore, the displayscreen is provided with a coarse-grained phosphor of the zinc sul-fide type which has a high light yield. Moreover, the line frequencyof the cathode beam is increased beyond the customary value inorder to counteract phosphor saturation.

4571616Device for displaying three-dimensional imagesJ. Haisma EG. BouwhuisIn a device for displaying three-dimensional pictures, N (withN = 2,3,4 ... ) recorded images corresponding to differentialspatial observation positions are displayed on one or more inter-mediate display screens. The device comprises a viewing screenhaving lens elements via which corresponding picture segments ofthe recorded images are displayed. An optical coupling having aplurality of light conductors exists beteen the viewing screen andthe intermediate display screen(s). The light conductors unambi-guously associate groups of N corresponding picture segments withlens elements of the viewing screen. By means of the device, three-dimensional pictures can be observed without further auxiliarymeans for the viwer.

4571625Television camera with a solid-state pick-up deviceA. J. J. Boudewijns EA television camera has a solid-state pick-up device having pick-upelements arranged in rows and columns, wherein a charge transfercan be effected in the columns by means of control electrodes andan associated control circuit. To have the pick-up device generate asingle or multiple interlace picture signal without specific measuresbeing required due to the structure of the pick-up elements, the con-trol circuit supplies during at least one field scanning period out of anumber of field periods forming a picture period, a charge transfersignal for effecting a single charge transfer between all the consecu-tive pick-up elements in each column of pick-up elements.

4571637Device for optically scanning a documentM. L. G. ThooneOptical scanning device having linear opto-electronic transducerswhich are substantially aligned with spaces between adjacent trans-ducers. With each transducer is associated an individual imaging

system for imaging a narrow strip of the document on the trans-ducer. Each transducer is displaceable with the aid of adjustmentmeans with respect to the associated imaging system. As a result thetransducers can be adjusted so that the narrow strips adjoin eachother and are aligned. Together they cover a narrow elongate partof the document. In this manner, a comparatively large documentcan be scanned with a high resolving power by means of compara-tively simple and hence inexpensive transducers and imaging sys-tems.

4571664Solid electrolyte capacitor for surface mountingW.J. Hyland NA solid electrolyte chip capacitor having a conductive cathodecoating, a coated and plated conformal cathode termination and ananode termination clip providing a thin-walled conform al construc-tion with opposed termination connections on a base for surfacemounting.

4573005Current source arrangement having a precision cur-rent-mirror circuitR. J. van de Plassche SIn a digital-to-analog converter a plurality of binary weighted cur-rents are generated, which currents must be in an accurate currentratio relative to each other. By means of a coupling network whichis controlled by a control circuit, a plurality of currents from saiddigital-to-analog converter can be coupled to a precision current-mirror circuit in accordance with a cyclic pattern, this allowing de-viations in the ratios of the currents from the digital-to-analog con-verter to be detected by detection means which control correctionmeans by means of which the currents from the digital-to-analogconverter are corrected so as to reduce the detected deviations.

4573034Method of encoding n-bit information words intom-bit code words, apparatus for carrying out saidmethod, method of decoding m-bit code words inton-bit information words, and apparatus for carryingout said methodK. A. Schouhamer Immink EA method of encoding n-bit information words into m-bit codewords and the other way round is described, which code words havea specific disparity d and a digital sum value which is limited tovalues pand q. In order to enable encoding and decoding withoutthe use of an extensive look-up table, use is made of a series ofnumbers which is a modified version of numbers in conformity withthe Newton binomial. By means of this modified series, the n-bitinformation words, which are arranged in conformity with theirbinary weights, are mapped lexicographically and unambiguouslyonto code words with said limitations, and the other way round.

4573047Binary selector stage and a selector and selector sys-tem comprising such selector stagesC. J. Koomen E

Conternporary communication networks, telephony exchanges inparticular, are frequently provided with a central control. A con-sequence thereof is that they are very complex. The invention pro-vides a communication network having a high degree of distributedcontrol and processing by providing a binary selector stage fromwhich selectors and selector systems may be assembled to form theentire network. The selector stage comprises an identification cir-cuit for identifying destination addresses applied by its input andwhich are associated with the service area of the selector stage. Anindicator circuit determines from a list-of-free-outputs circuits towhich free output the destination address, which is identified byand transferred to a first output, must be conveyed. Non-identifieddestination addresses are transferred to a second output, to whichoutput a further selector stage can be connected.

4573066Breakdown voltage increasing device with multiplefloating annular guard rings of decreasing lateralwidthK. R. Whight RIn order to increase the breakdown voltage of a reverse-biased p-njunction of a semiconductor device, at least three annular regionswhich extend around the active device region are located within thespread of a depletion layer from the junction. At least one inner an-nular region is wider than outer annular regions, and this increasedwidth of the inner region or regions reduces peak electrostatic fieldsfound to occur at the bottom outer corners of the active deviceregion and inner annular regions. The spacing of the annular regionsincreases with remoteness from the active device region, althoughat least two inner annular regions may have the same spacing asthat of the innermost annular region from the active device region.A group of annular regions may have the same width as each otherin the group.

4573169Communication system for bi-phase transmission ofdata and having sinusoidal low pass frequency res-ponseP. J. van Gerwen EW.A. M. SnijdersA data communication system for transmission of bi-phase signalsmodulated by data symbols and in which the signals are filtered inaccordance with a frequency response which approximates zero ato Hz and at exceeding frequency 3/(2T) Hz and which has anapproximately sinusoidal variation between those frequencies, Tbeing the symbol interval. This filter characteristic minimizes inter-symbol interference and improves the signal-to-noise ratio. Therequisite filtering may be provided in the receiver or in part inthe receiver and in part in the transmitter of the communicationsystem.

4573330Absorption heat pump comprising an integrated gen-erator and rectifierW.L. N. van der Sluys EJ. PastoorJ. C. M. RoeloisAn absorption heat pump comprising a generator which is providedwith a condensation pipe comprising a lower generating section andan adjoining upper rectifying section. The upper section is filledwith a thermally insulating gas which separates the generating sec-tion from the rectifying section. Thus, a simple construction is ob-tained, in which the rectifier is integrated in the generator.

4573769Projection lens systemJ.A. ClarkeA lens system is provided which is suitable for back-projecting anenlarged image of a TV cathode-ray tube (CRT). To achieve a com-pact cabinet design for such a projection television set, a short pro-jection throw and a wider projection angle are required, togetherwith a wide aperture for a bright projected picture and with adefini-tion sufficient to resolve 625 line television pictures. The lens systemcomprises a concave CRT face plate and only two lens elements,each of positive power and each having one aspheric surface, thepowers of the elements being chosen so that OAK <Kl <0.60Kand 0.75K <K2 < 1.05K, where K, is the power of the elementremote from the object surface, K2 is the power of the elementadjacent the object surface and K is the total power of the projec-tion lens system.

4574216Cathode-ray tube and semiconductor device for use insuch a cathode-ray tubeA. M. E. Hoeberechts EG. G. P. van GorkomA semiconductor cathode is provided with deflection electrodes,with which a dipole field can be generated. As a result of this, elec-trons released at the surface of the semiconductor cathode leave thesurface at a certain angle. For use inter alia in camera tubes, displaytubes, such an inclined beam can be aligned without any problems.Positive ions which are released inter alia from residual gases andare accelerated in the direction of the cathode impinge on thecathode at an acute angle. As a result of this, the active part of thecathode is substantially not attacked by said positive ions, so thatdegradation is prevented.

4574257Crystal resonator oscillator having circuitry for sup-pressing undesired crystals harmonicsW. G. Kasperkovitz EH. W. van RumptOscillator circuit comprising an amplifier arrangement being con-nected to a reference level an output and an input thereof beingcoupled via a single signal-carrying terminal to a resonant networkwhich is connected to 'the same reference level as the amplifierarrangement, the resonant network comprising a crystal resonator.A stable oscillation at a higher order crystal resonant frequency isprovided by means of an LC network which selects said higher ordercrystal resonant frequency and a resistor connected in parallel acrossthe crystal resonator, which prevents parasitic oscillations at theresonant frequency determined by the components of the LC net-work and the case or holder capacitance of the crystal resonator.

4574270Analog-to-digital current converterR. J. van de Plassche SAn analog-to-digital current converter comprises n series-connectedstages which each provide one bit of the Gray code. For this pur-pose each stage m derives a difference current from the input cur-rent (if/m), which is the output current (iO/m-l) of the precedingstage, and a reference current (!/2m-l) from a source. This differ-ence current flows to the output of the stage m (io/m) either via adiode or via a current mirror circuit depending on its direction.Conduction of the diode or of the current-mirror circuit is used forthe bit indication. This results in a very fast analog-to-digital con-verter with few components and a high accuracy and resolution.

4574300High-definition colour television transmission systemM. G. Hulyer RA high definition television transmission system in which a wideband interlaced television signal having 1249 lines per field isdivided to provide first and second interlaced television signals eachhaving 625 lines per field and consequently reduced bandwidth.Adjacent lines of the first television signal have their low frequencyinformation (0-3 MHz) derived from alternate lines in the wideband signal while the corresponding information for adjacent linesin the second television signal is derived from the intervening linesin the wide band signal. The high frequency information (3-5.5 or6 MHz) for the lines of both the first and second television signals is'derived fromthe average of the corresponding information in adja-cent lines of the wide band signal. The first television signal alsocontains a colour subcarrier which is modulated by the average ofthe colour information in adjacent lines of the wide band signal.The two television signals may be jointly received for the provisionof a high definition display but the invention has the distinct ad-vantage, that the first television signal may be received alone by cur-rently manufactured television receivers for reproduetion of a dis-play of a quality which is currently acceptable.

J. F. Brouwer - Philips Bound...362 J.F. BROUWER PhilipsTech. Rev. 42,No. 10/11/12 With...

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