nal espite their advantages, digital oscilloscopes are still suspect to a good many engineers, who worry

about aliasing, undetected glitches, and other unpleasant effects of using too low a sampling rate. At the same time, the user-interfaces are unfamiliar (some would say unfriendly) and the response of the front-panel controls is sluggish.

In an effort to win over these hold- outs-and beat the ever-present cost issue as well-Hewlett-Packard has built an instrument that is modest in price but not in talent, thanks to a three-processor

architecture and a 1 -ns peak-detect cir- cuit. The 54615B is a two-channel in- strument with a bandwidth of 500 MHz, a sampling rate of 1 GHz, and 5 kilosam- ples of memory behind each channel.

The architecture takes the brakes off the instrument's response by dedicating one microprocessor just to accepting and processing control inputs. Of the other two, one accepts waveform samples from the instrument's analog-to-digital convert- ers and time-correlates the samples with the trigger point, and the last takes the time-correlated points and displays them.

A Hewlett-Packard's 54615B real-time digital scope is shown here operating in its peak-detect mode, in which the inputs are sampled at 1 GHz regardless of the sweep speed. The two-chan- ne1 unit has a bandwidth of 500 MHz.

instrumenta

nce upon a time, a low-end oscilio- scope was one with modest perfor-

mance, few features, and an attractive price Now Tektronix, with the latest ad- ditions to its TDS 300 Series, has simpli- fied the definition a low-end scope is one that doesn't cost very much

The revised definition is needed because the manufacturer refers to its three new instruments as "lower end," even though such advanced features as fast Founer trans- form capability are standard All three scopes offer wdeo and edge tnggenng capa- bilities, the ability to capture transients down to 1 ns, and a 1000-point record length, as well as four acquisition modes- sample, average, envelope, and peak detect

From the bottom to top of the line, the oscilloscopes line up as follows The TDS

60

340 has a 100-MHz bandwidth, a 500- MHz sampling rate, sweep speeds up to 5 ns/div, and a price of $2495 The TDS 360 doubles all those specifi- cations and adds a built-in floppy-disk drive, for less than double the price- $3495 The TDS 380 again doubles the first two specs, to 400 MHz and 2 GHz, keeps the same 2 5-ns/div sweep speed, and sells for $4595 It also has a disk drive, which like the one in the TDS 360, may be used to store instrument setups and data. Waveforms may be stored in a variety of formats, including MathCAD, spreadsheet (Lotus 123 and Excel), Post-Script, and TIFF. Contact: Tektronix Measurement

When activated, the peak-detect cir- cuit runs the scope's a-d converters at their full sampling rate, regardless of the sweep rate setting A smart decimator cir- cuit built onto the a-d converter chip then delivers only the largest and the smallest (most positive and most negative) samples from each frame to the acquisition memo ry For example, if the sweep rate were set to 100 ps per division, the scope would fill Its 5000-sample memory in one sweep of 1000 ps if it acquired a sample pair every 200 ns In its normal mode, then, it runs the a d converter at 5 MHz With peak-detect turned on, though, the con- verter runs at 1 CHz, but memory is sent only one data pair from each 200-11s frame

Other features of the 546 15B include automatic measurements of frequency, voltage, pulse width, and rise time, wave form storage, storage of up to 16 scope setups, and a roll mode for low sweep speeds The instrument has a built-in facility for powermg active probes, and it supplies its own calibration signals

Among the accessories available is the HP 54657A measurement storage module, whicht adds over 20 measure ments, including fast Fourier transforms, to the scope's repertoire-and US $765 to the scope's $6995 price Contact Hewle t t -Packurd CO , Direct Marketing Organization, Box 5x059, MSsiL-SJ Santa Clara, CA 9 5 0 5 1 - 8 0 5 9 800-452-4844, ext 1017, or circle 104.

Business, Literature Distribution Center, Box 1520, Pittsfield, MA 01202; 800-479-4490, action code 300; or circle 106.

A Although priced as low as $2495, all three additions to the TDS 300 Series from Tektronix include fast Fourier trans- form capability as a standard feature. The top-end TDS 380 [foreground] has a bandwidth of 400 MHz and a sampling rate of 2 GHz.

IEEE SPECTRUM DECEMBER 1995

DSP chips compared i th digital signal-processing

w ( D S P ) chips being designed into all sorts of electronic systems today, choosing the right one for a job matters more than ever. Possibly the best unbi- ased source of the data needed to make a decision is the second edition of the Buyer's Guide to DSP Processors.

Issued by Berkeley Design Technology, the 850-pager includes a performance comparison of 19 mainstream DSPs in terms of 11 benchmark tests. Among the new signal processors in this section are the Analog Devices ADSP-2106x SHARC; the DSP Group's Oak DSP core; the IBM MDSP2780 Mmwave; the SGS-Thomson D950 core; and the Texas Instruments T M S ~ ~ O C ~ X X , -C54x, and -C80 "MVF!"

Perhaps more generally useful, the report devotes over 300 pages to an in- depth analysis of 30 families of DSPs from which users can gain insight into the relative strengths and weaknesses of each of the DSP families.

The Buyer's Guide's three remaining sec- tions provide studies of typical applica- tions, a review of relevant technology, and a detailed comparison of processor fea- tures. This last includes tables of memory organization, hardware looping features, on-chip peripherals, packaging, and prices.

Finally, a summary of the state of the art in DSP ICs adds observations on and pre- dictions of industry trends. The DSP glos- sary is extensive.

A single copy of the Buyerk Guide to DSP Processors is priced at US $2450 in the United States, $100 higher outside. Volume discounts are sizeable. A detailed brochure about the study is available from Berkeley. Contact: Berkeley Design Technology Inc., 39355 California St., Suite 206, Fremont, CA 9453 8; 5 10-79 1-9 100; fax,-g 127; e-mail, dsp- chips0 bdti.com; or circle 105.

Signal-processing pack adds to Mathematica

olfram Research, the company be- w h . ind the well-known Mathematica symbolic computing software, has announced a set of tools for signal pro- cessing. Called the Mathematica Signals and Systems Pack, the new member of the company's Applications Library vaunts a good many capabilities that are not to be found in older signal-processing packages.

For one thing, the software allows users to express and modify signals of infinite extent. For another, enables them to perform operations on nonsep- arable multidimensional signals.

The pack requires Mathematica 2.2

and runs on PCs, Macintoshes, and some half-dozen Unix-type workstations. It lists for $295. Contact: Wolfidm Research Inc., 100 Trade Center Dr., Champaign, IL 6 1 8 2 0 - 7 2 3 7 ; 8 0 0 - 4 4 1 - M A r H ; in Europe, (44.9) 9 9 3 8 8 3 400; or circle 107.

A go-between for Windows PCs and Unix sewers

n a network linking Windows PC 0 client machines and Unix servers, the user accessing a Unix application should ideally remain oblivious to the greater overhead and abnormal behavior imposed by X-based applications. XVision 6 provides just such total transparency, according to its developer. Part of the package is an X Window subsystem that lets X programs be launched in exactly the same way as Windows programs- with no additional steps.

Another lure is XVision 6's automatic installation. The facility not only checks out the network and optimizes the instal- lation for each PC separately-it also completes all necessary X server and net- work checks before system launch.

T h e software includes Microsoft TCP/IP VxD libraries and is updated to support the latest X Image Extension. It also includes the Network Audio Server, further supporting multimedia Unix ap- plications on the Windows desktop.

XVision 6 lists for $495 for a single user. Volume discounts are offered. Contact: The Santa Cruz Operation, Client-Integration Dioision, Box 1900, Santa Cruz, CA 95061- 1900; 408-427-7700;faX, 408-427-5407; e-mail, info@ixi.com; in tbe United Kingdom, me Santa Cruz Operation, Client-Integration Division, Vision Park, Cambridge CB4 4ZR; (44+1+122) 351 8000;fUX, (44+1+122) 351 8001; e-mail, info@x.co.uk; or circle 108.

The SPOX real-time operating sys- tem from Spectron Microsystems, Santa Barbara, Calif., is now available for Motorola's DSP56300 family of digital signal processors. Optimized for DSP applications, SPOX includes such fea- tures as priority-based pre-emptive mul- titasking and interprocess communica- tions facilities, as well as a high-speed asynchronous streaming I/O facility. Contact: Bruce nompson at 805-968-5100; or circle 109.

To attenuate the transients generated when highly inductive or capacitive loads are switched, a line of optically isolated solid-state relays includes circuitry to extend the relays' transition times. Units in the Soft-On/Off family, from Aromat Corp., New Providence, NJ . , have rise and fall times of about 2800 ps and 1000 ps, versus the 500 ps and 100 ps of con-

ventional photo-MOS relays. In practical experiments, those lengthened transition times have reduced the rate of current rise from 250 A / s down to 60 A/s when a resistive circuit was turned on. Similarly, they have attenuated a voltage spike from 240 V to 1 10 V when an inductive circuit was turned off. Contact: Douglas J. Lionetti at 908-464-3550; or circle 110.

Harris Semiconductor, Melbourne, Fla., has announced a sigma-delta analog-to- digital converter with exceptionally low noise and high resolution. At unity gain and a sampling rate of 10 Hz, the HI71 90 has a peak-to-peak noise voltage of 2.9 pV, which translates into a resolution of 23.5 bits. According to Harris, the H17190's closest competitors generate two to four times the noise under the same conditions, so that their resolution is limited to 2 1.5-22 bits. The HI71 90 can acquire data at up to 2000 samples per second, con- sumes 15 mW or so, and has eight pro- grammable gains of 1 to 128. It sells for $1 1.19 in 1OOo-piece quantities. Contact: ~ O O - ~ - N S , ext. 7332; or circle 1 1 1.

Available with values from 5 d to 33 kQ, surface-mountable precision chip resistors in the SMRCI family from Vishay Resistors, Malvern, Pa., maintain their precision despite thermal cycling and mechanical stress. The units have a long term drift of at most +0.02 percent, a ther- mal emf of at most 0.1 pVK, and a tem- perature coefficient of resistance of +4 p p d C from 0" to 60 "C. They can dissi- pate 0.25 W at 70 "C and are available with tolerances as tight as 0.01 percent. SMRCI resistors with 0.1 percent toler- ance are priced at $2.09 each in 1000- piece quantities. Contact: Visbay Applications Engineering at 610-644-1300; or circle 1 12.

From Amphenol Fiber Optic Products, Lisle, Ill., comes a collection of right- angle boots for increasing the reliability of optical-fiber cables. The boots ensure that the minimum bend radius of the cable is not violated. The devices are av- ailable for FC, SC, and ST connectors. Contact: 800-944-6446; or circle 11 3.

Well suited for liquid-crystal display projection systems, the HI.Lux metal- halide arc lamp produces 60 lumens per watt-up to three times as much light as a halogen lamp running on the same amount of power, according to its maker, Welch Allyn Lighting Products Division, Skaneateles Falls, N.Y. Offered in 18-, 21-, and 24-W versions, the lamp oper- ates at a color temperature of 5500 K. Its parabolic reflector collimates the output light into a narrow beam. Circle 1 14.

MICHAELJ. RIEZENMAN, Editor

Consultant: Paul A.T. Wolfgang, Boeing Defense & Space Group

IEEE SPECTRUM DECEMBER 1995 61