HP-AN1075_Testing and Measuring EMC Performance of the HFBR-510X_520X

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Tes ting a nd Meas uring

Electromagn etic Comp atibi li tyPerformanc e o f the

HF BR-510X/520X Fibe r-Opt ic

Transceivers

Applica t ion Note 1075

Contents1.0 Int roduction ........................... 1

2.0 Elements of ElectromagneticCompat ibility......................... 2

2.1a What is RadiatedEm ission? ............................... 2

2.1b How System Design AffectsRadiated Emissions................3

2.2a What is Su sceptibility(Imm un ity)? ........................... 5

2.2b How System Design AffectsSusceptibility (Immu nity)......6

2.3a Wha t is ES D? ......................... 82.3b How System Design Affects

ES D......................................... 82.4a What is Conducted Noise?.........92.4b How System Design Affects

Condu cted Noise..................... 9

3.0 Summar y of HFBR- 510X/520XComponent Le velEMC Performa nce ..................10

4.0 HF BR-510X/520X ComponentLeve l E MC T est ing .............11

4.1a Radiated Emissions TestingProcedure................................11

4.1b Radiated Emissions TestingResults....................................13

4.2a Susceptibility (Immunity)

Test ing Pr ocedur e..................154.2b Susceptibility (Immu nity)

Testing Results.......................174.3a ESD Testing Procedure ..... .. .184.3b ESD Testing Results ... .. .. .. .. .194.4a Condu cted Noise Testing

Procedure................................194.4b Condu cted Noise Testing

Resu lts ................................... 20

5.0 Conclusions ........................... 21

AbstractThis a pplicat ion note explains

th e main component s of

electromagnetic compatibility

(EMC): radiated emission,

immun ity, electr ostatic

discha rge, an d condu cted noise;

an d describes how the design of

th e commun ication net work

system affects EMC

performa nce. It describes how

Hewlett-Packar d’s new H FBR-

510X/520X 1×9 SC conn ectored,

fiber-optic transceivers for datarat es up to 155 MBaud are

designed for excellent

electromagnetic compatibility

while ma inta ining low cost. The

application note also describes

the pr ocedures under which t he

HF BR-510X/520X component s

ar e tested for EMC, and r eport s

th e results of th ese tests.

The applicat ion note summ a-

rizes the HFBR-510X/520X

componen ts’ EMC per form an cean d stresses th eir reliability

un der var ious conditions and

applications.

1.0 Introd uc tionHewlett-Packard has designed

its n ew H FBR-510X/520X, 1×9

pinout , SC connector, fiber-optic

transceivers for excellent

electromagnetic compatibility(EMC) while still mainta ining

low cost. The HFBR-510X/520X

modules are int ended for h igh

data rat e applications su ch a s

ATM (155 MBau d) or F DDI (125

MBaud). At th ese high data

ra tes, achieving a ccepta ble EMC

performa nce in commu nications

network p roducts while still

maintaining low product cost

can be quite a design challenge.

The excellent EMC p erform an ce

of the HF BR-510X/520X module,plus its low cost, should make

the EMC design challenge for

th e commu nication n etwork

product easier to overcome.

EMC refers to the capability of

electr onic equipment or systems

to be opera ted in th e intended

opera tiona l electromagetic

environment at their designed

levels of efficiency. Specifically,

EMC describes how the pr oduct

behaves in term s of rad iatedemissions, commonly known as

electromagnetic interference

(EMI), and a lso how th e

produ ct’s per form an ce is affected

by immunity (susceptibility) to

ra diated ener gy, electr ostatic

discharge (ESD), and conducted

power sup ply noise. This

application n ote describes th ese

h H



2

EMC component s, how commu ni-

cation network design can affect

the E MC performan ce, and how

the excellent EMC per forman ceof the HFBR-510X/520X trans-

ceivers m akes it easier to design

fiber-optic comm un icat ion

network pr oducts with accept-

able EMC performa nce. Since

the interconnection and the

packaging of the components

used in a commun icat ion system

affect the EMC performance of

the system, HP performed

various tests on our pr oducts to

determ ine how our components

affect a fina l system -level EMCperforma nce. Th is ap plicat ion

note presents th e component -

level EMC testing procedures

and results, and explains how

the component-level performance

affects the performance of the

complet e fiber-optic da ta

commu nication network.

EMC problems worsen as th e

dat a ra te increases. This applica-

tion note details some of the

practices tha t the equipmentdesigners can observe to help

avoid being affected by EMC

when u sing HP’s new high dat a

rate HFBR-510X/520X products.

2.0 Elemen ts of

Electromagnet ic

Compa tibil ity (EMC)

2.1a What is Radiated

Emiss ion?

The first EMC area is radiatedemissions, sometimes called

electromagnetic interference or

EMI. A ra dio or TV broadcas t is

an example of intent iona lly

rad iated electroma gnetic energy.

A computing device also radiates

electromagnetic emissions,

alth ough it is not intended t o.

(The ra diation is an inh erent

by-produ ct of th e switching

currents flowing in its conduc-

tors). Electr omagnetic rad iation

occur s when a changing cur rent

flows in a conductor. At the ar eanear th e conductor (ant enna ), we

usu ally see eith er t he electr ic or

th e magnet ic field domina te th e

total radiated field. This area

near t he ant enna is called the

near field. The anten na formed

by takin g one long wire a nd

breakin g it at th e center t o form

two separat e wires, is known as

an electr ic dipole an tenn a. The

dipole anten na is usua lly driven

by a varying voltage source, with

th e positive sour ce node con-nected to one wire and t he

negative source node connected

to the oth er wire. The dipole

antenna near-field radiation is

predominately an electric field.

If a var ying cur rent flows in a

loop of wire, it crea tes pred omi-

na tely magnet ic field ra diation.

This antenna is known as a

(magnetic) loop an tenn a. At a

point far a way from this an -

tenn a, neither t he electric nor

th e ma gnetic fields dominat e.These areas are known as the

far-field region. In th is region,

th e radiat ion (or equivalently the

electr omagn etic wave) becomes

what is known as a tra nsverse

electr omagn etic wave (TEM). A

TEM wave behaves the same as

all the other rad io/TV waves th at

travel through the air. The

chara cteristics of th e air deter -

mine the electric-to-magnetic

field stren gths or, equivalently,

th e chara cteristic impedance of

th e ra diation. An actua l commu -

nication syst em cont ains various

an tenn as formed by th e circuit

interconn ections a nd by th e

other m etal bodies in t he cir-

cuitry. These antenn as ar e then

driven by var ious energy sources

within the system circuitry. One

exam ple is th e loop form by Vcc

to Data output to Ground,

through the Vcc decoupling

capa citor, then back to Vcc.

Additiona l examples are th e LEDcurr ent loop in a fiber-optic

tran smitter, and ground wires

(PCB traces) driven by voltage

noise sour ces th at act as dipole

antenn as, and so forth.

Government agencies around the

world regulate th e amount of

rad iated electroma gnetic energy

emitted by var ious sour ces.

Their inten t is to allow an y

purposely transmitted radiated

energy to be received withoutbeing interfered with by some

other radiation source at around

the same frequency. Equipment

tha t ra diates emissions could

interfere with r adios in the sam e

building or even with other

electr onic equipment th at is

sensitive to that radiation.

Electromagn etic int erference

(EMI) describes th e effect of

unwan ted ra diation interfering

with an other (inten tional or

un int ent iona l receiver) circuit’soperation.

The governmen t a gencies usua lly

set their radiated emissions

regulations to distinguish be-

tween two types of applications.

The first is a factory or office

(Class A) wher e a h igher level of

rad iation can be tolerated; the

second is the home (Class B)

where there a re more TVs an d

rad ios a nd th erefore less electr o-

magn etic rad iation can be

tolerat ed. Most man ufacturer s

want th eir systems to meet all of

the h ome environment radiated

emissions sp ecifications u sed

around th e world so tha t th ey

can be sold in the U S, in Eur ope

or in J apa n, with no restrictions.

In Eu rope, compu ter systems





4

when h igh-frequen cy cur rent s

flow th rough th em. Since cables

are often th e largest an tenna

around, they are usua lly thedominant source of radiat ion.

Chassis a nd cable shields can

also radiat e if ground noise

current or voltage drives them.

Fiber -optic cables do not, h ow-

ever, radiate energy as wire

cables do. Ther efore, fiber-optic

cables can help reduce radiat ed

emissions if using wir e cables is

a problem. At FDDI and ATM

dat a r at es, the encoding/ decod-

ing schemes, an d th e consequent

additional circuitry, needed t oreduce the bandwidth and t he

emissions on a t wisted pair wire

cable, are n ot needed if a

fiber-optic cable is used .

If an an tenn a is completely

enclosed in a s ufficient ly th ick

meta l box, then no radiat ion will

escape. If th e box ha s an aper-

tur e, then some radiation will

escape th rough it. The bigger

the opening and th e higher th e

frequen cy, the m ore r adiat ionthat escapes. If the antenn a is

sufficiently far enough away

from th e opening, then t he

theoretical far-field a tt enua tion

by a rectangular opening (slot) in

a sh ield is:

875 MHz. At 875 MHz, a slot

big enough for a du plex SC

conn ector fiber-optic module

(3.05 cm / 1.2 inches) wouldprovide 15.0 dB of shielding. At

875 MHz, a slot big enough for

a sim plex ST conn ector

fiber-optic module (1.27 cm / 0.5

inches) would pr ovide 22.6 dB of

shielding. Thus th e 1x9 module

dup lex SC hole provides 2.5 dB

more shielding than the MIC

FDDI conn ector hole does. If

th e radiat ion were at 437.5

MHz instea d of 875 MHz, then

each slot would pr ovide an

extr a 6 dB of shielding. (Thewavelength a t 437.5 MHz is

twice th at at 875 MHz. This

doubling of λ gives a 6 dB

increa se in shielding (Eq 1). If

th ere are mu ltiple identical

openings in a sh ield, then t he

total ra diation is increased by:

This formu la assumes the

openings are close together

(within 1/2 wavelength ). Thus

two ST conn ector openin gs

would a llow 3 dB m ore radia-

tion to escape t ha n one opening

would. This is the reason why a

duplex SC connector opening

ha s 22.6-15-3=4.6 dB less

shielding t ha n two ST conn ector

openings do (if th e ST openings

ar e not t oo close to each oth er).

These shielding formu las ar e

invalid if th e sour ce is too closeto the opening, if the openings

ar e so close together t ha t th ey

appear as one big hole, or if

th ere is an y conductor st icking

th rough th e opening (in which

case it rea lly should n ot be

called an opening). The shield-

ing is determined by t he longest

linear dimension of th e opening.

Thus, even a very thin, but long

hole could leak qu ite a lot of

rad iation. This often happen s at

box joint s an d seams, a nd care

must be taken to prevent radia-

tion in these area s. EMI gasket sare often u sed in seams an d

joints to make su re tha t t he

electr ical cont act a cross t he seam

an d joint is continuous. In th is

man ner, long radiation holes,

which oth erwise might form

between the screw/bolt locations

tha t h old the seam or joint

together , if no gasket were

present , ar e prevented. Good

cond uction is n ecessar y for good

shielding. Metal works th e best.

Some condu ctive spra y paint s ormeta l coatings can h elp and may

be able to approach a meta l wall

in the best case. Very-low-

frequen cy magn etic fields often

need exotic high-permittivity

materials such a s mu-metal to

attenuate these magnetic fields.

A conductive wire s ticking

thr ough an opening can pick up

radiation inside the box, conduct

the noise to th e outside of the

box, th en rera diate th e energy,

completely defeating the shield-ing provided by the opening,

were it empty. A fiber-optic

module with a m etal nose can

often condu ct ra diation outside a

chassis if it has a section of the

meta l housing th at sticks out of

the chassis and if that metal

housing is not tied to th e chassis.

The HFBR-510X/520X fiber-optic

tra nsceivers ha ve plast ic hous-

ings and do not condu ct r adiat ion

outside of the chassis in t his

manner .

Extern al shields can be added to

provide add itional shielding. An

exam ple of this would be an

external conductive vanity cover

over t he fiber-optic ports to allow

all the fibers to escape in a

bundle thr ough a relatively small

exit access hole. This hole

provides add itional shielding. If

the h ole is a tube with th e length

A slot big enough for an FDDI

MIC connector fiber-optic module

(4.06 cm / 1.6 inches) would

provide 12.5 dB of shielding a t

where λ is the wavelength a nd l

is the lar gest linear slot

dimension.

For example, at 875 MHz th e

wavelength is:

20log10

λ

2lEq. 1

(3*1010)

875*106= 34.3 cm/13.5 inches

20log10

where n is the√n dB

nu mber of openings.



5

longer tha n t he diameter, a

waveguide effect occurs and the

rad iation is drast ically reduced

as it tra vels thr ough this tu be.See Referen ce (3) for det ails.

The waveguide phenomenon, for

exam ple, can be quit e effective,

but it is sometimes difficult to

implement such a structure in

pra ctice. (Such stru ctures can ,

while reducing the radiat ed

emissions, ma ke it so mu ch m ore

difficult to rem ove t he fiber-optic

cable connections in t he field as

to mak e th eir overall product

cont ribution questiona ble. For

example, a door m ay ha ve to beopened up , the fiber conn ector

disconnected, and t hen slid

thr ough a waveguide tube in

order t o disconnect t he fiber from

the commu nication system. This

is much more difficult than

merely un plugging a fiber from a

module port th at is accessible

directly thr ough a hole in t he

chassis back pan el. The

HFBR-510X/520X fiber-optic

tr an sceivers’ low-radia ted

emissions m ake t he n eed forelaborate structures, such as

waveguides, to reduce emissions

much less necessar y.)

If noise is induced in the shield,

it can ra diate. This problem is

usually avoided by the “skin

effect” which k eeps m ost sh ield

noise cur rent s on th e inside of

th e box, close to their sources,

while no noise curr ent flows on

th e out side of th e box. If th e

shield is directly conn ected to

some noise source, ther e will be

problems. Also resona nces can

occur inside a box; and depend-

ing on th e dimen sions of th e box,

a sta nding wave can form .

Radiation a t th is standing wave

frequency can be amplified inside

the enclosure. The dominant

frequency of the radiation from a

chassis can often be at its resonan t

frequency.

Since there ar e so many factors

th at a ffect radiat ion an d since

ma ny of these factors int eract

with each other, radiatedemissions can be the m ost t ricky

EMC problem a nd sh ould be

considered as early in th e design

as possible. It is often d ifficult to

fix a ra diated emissions problem

once the system design h as been

completed an d is near

produ ction. Usin g good

shielding, good high frequ ency

PC boar d layout s, good cabling,

an d good low-emission circuit

components, such as t he

HFBR-510X/520X fiber-optictra nsceivers, will help ensur e the

radiated emissions compliance of

th e fina l produ ct. Additiona lly,

if th e EMC per forman ce is

considered ear ly in th e product

design a nd if low ra diated

emission components ar e used,

then t he designer may find that

less stringent sh ielding can be

used in the final product. Less

str ingent s hielding is often

easier t o manufacture and is

lower in cost. Thu s, lessstr ingent shielding can lower th e

overa ll produ ct cost. For

exam ple, a cond uctively coated

plastic cha ssis that needs no

extensive EMI gasketing can be

cheaper to make than a m etal

chassis with many EMI gaskets.

Thus, low radiat ed emission

components, such as t he


tra nsceivers, can allow th e

product designer t o make a

lower-cost product th at still has

good radiated emissions

performance.

2.2a What is Suscep tibi l i ty

(Immunity)?

Electromagnetic susceptibility of

a product (or imm un ity) is

defined as the effect of external

electromagnetic fields on the

perform an ce of th at product.

The performa nce is measu red in

the pr esence of an externa l

electromagnetic field relative to

the performance with the

electromagnetic field absent.The measurements must be

ma de over a var iety of electr o-

magn etic field stren gths an d

frequencies. Then the same

product performa nce is mea-

sur ed with t he electromagn etic

field t ur ned off.

Immunity and susceptibility

refer to the sam e cha ra cteristics

(immun ity is the inverse of

susceptibility). From a measur e-

men t point of view, however,what is measur ed is the perfor-

man ce penalty du e to the elec-

tromagn etic fields an d th is

penalty is th e su sceptibility.

The goal is to have zero perfor-

man ce penalty or zero suscepti-

bility, i.e. totally immune.

At th e system level, only a few

written specificat ions addr ess

sus ceptibility (imm un ity). The

au th ors of th e IEC 801-3 specifi-

cation (see Referen ce (7)) ha vestated th at the computer system

product under t est should be

immun e to 1 to 10 V/m extern al

fields. They define thr ee class es

of devices. Clas s 1 is a 1 V/m

sus ceptibility t est for devices

tha t a re expected to be used in

low level electromagnetic field

environmen ts. Class 2 is a 3 V/

m susceptibility test for moder-

ate environmen ts. Class 3 is a

10 V/m s uscept ibility t est for

environmen ts with severe

electr omagnetic r adiat ion

present. What is meant by

immun e (i.e. how much penalty

is allowed) however, is left

un clear a nd is sa id to be nego-

tiable between vendor an d

customer . Based on some of

Hewlett-Packard ’s customer

inputs, HP h as stan dardized on

a 10 V/m field str ength to test

fiber-optic tr an sceivers. Thu s



6

HP modules are tested to the

Class 3 IEC 801-3 severe envi-

ronment t est level. This is a

large field str ength a nd would bedifficult to generate inside a

computer system unless the

source is within inches (or

centimet ers) of th e circuit in

quest ion. Or it could be gener -

ated by a very lar ge ESD or by a

very-high-power r adio tra nsm it-

ter (walkie-ta lkie) tha t is h eld

very close to the system.

As an example of how large a 10

V/m field is, consider that the

FCC B r adiat ed emissions limitis 46 dB µV/m a t 500 MHz at a

test dista nce 3 meter s from the

sour ce. This is a 1 µV/m *10(46/20)

= 199 µV/m field strength . The far

field str ength varies as a function of

1/r, where r is the dista nce from

the sour ce. Thus, at a distan ce

of 1 cm (0.39 inches) from t he

source, th e field stren gth would

be 300*199 µV/m = 0.06 V/m .

This is still 20log10 (10/0.06) =

44 dB less field stren gth th an a

10 V/m field. Ther efore, togenerat e a 10 V/m field at t he

fiber-optic receiver would r equir e

a sour ce, which on its own would

fail FCC B by 44 dB, t o be placed

with in 0.4 inches (1 cm) of the

receiver. Clear ly not too ma ny

such sources can be present in a

compu ter system wh ich mu st

pass FCC B limits. So, pra cti-

cally, a 10 V/m field can be

generat ed only by a large

high-frequency current pulse,

such as a n ES D pulse, or by a

high power nea rby ra dio/TV

tran smitter. The example in the

IEC 801-3 specification ind icat es

tha t a 10-watt walkie-ta lkie held

at 1 m eter from the HP module

(with no shielding pr ovided by

the system chassis) would

gener at e a 5 V/m field. This is

the lar gest field str ength indi-

cated on the IE C 801-3 Figure

A.3 curve, (so one would a ssu me

th at in rea lity a 5 V/m field

might be the most tha t would be

seen from a walkie-talkie).

Usually an an tenna in the circuit

will pick up the external field

an d th en couple it int o a critical

circuit node where it appear s as

a noise signa l. The susceptibility

will depend on the frequency of

the field because the receiving

ant enna gain varies with fre-

quency and becau se th e circuit

noise rejection varies with

frequen cy. The noise can be

picked up d irectly at t he sensi-

tive node itself or can be con-ducted from an oth er n ode (such

as Vcc) tha t has a larger gain

an tenn a conn ected to it.

Performance degradations due to

incident electromagnetic fields can

occur as lines appearing on CRT

displays, noise/other channels

appearing on a radio broadcast

reception, larger than normal bit

error ra tes in digital networks, or

state machines getting mixed up

and the whole system becominglocked or just beha ving strangely.

Susceptibility problems a re bother -

some to the end users because it is

often difficult for t hem to fix the

problem (or even t o get it t o occur

often enough in order to try to fix it).

Many systems have built in error

correction and error trapping

routines so that if some strange

error does occur at least the only

th ing the user might experience is

the extra delay caused by the time

it took the system to catch and

recover from the error (and possibly

retransmit the data).

Obviously, the less often these

susceptibility problems occur, the

better. When component s with

low-radiated emissions are used

inside the system, such th at t he

system can pa ss the radiated

emissions requirement s easily, then

there ar e fewer possible large

sources of radiation th at could

conceivably cause susceptibility

problems. And, of cour se, compo-

nent s with h igh immunity (or lowsusceptibility) should be used

whenever possible.

Generally speaking, a 10 V/m field

strength will not occur very often

but is a reference level to use for

susceptibility testing. Components

that can with stand a 10 V/m fields

and m aintain t heir designed

performance should not creat e any

susceptibility problems wh en u sed

in a communicat ion system. The

system designer can be confidentthat the other components in his/her

system, most externa l radiat ed field

sources, and most ESD strikes (that

do not conduct current directly

through th e component itself), are

not likely to affect the performance

of these 10 V/m immune compo-

nents in any significant mann er.

The HF BR-510X/520X fiber-optic

tra nsceivers ar e a good example of

such a 10 V/m immune component .

2.2b How System DesignAffects Susce ptibi l i ty

(Immunity) .

For this discussion we will

concent ra te only on th e effects of

the extern al electromagnetic

field on t he fiber-optic module

circuitry alth ough other circuitry

can also be affected by an exter-

na l field. The effects will var y

from circuit to circuit. But t his

sus ceptibility d iscussion, concen-

tr at ing on fiber-optic receivers,

will hold tr ue, in gen era l, for

other circuits as well.

The usu al effect of an extern al

field on a fiber-optic receiver is to

degrade t he r eceived bit err or

ra te. The fiber-optic receiver

(Rx) is usually the most sensitive

an alog circuit in th e entire

commun icat ion network pr oduct.

An externa l field can induce a

signal on th e ant enna s formed by



7

the int erconn ections in the

fiber-optic Rx circuitr y. Anten -

nas are bi-directional devices.

The same phenomenon th atcauses an an tenna t o radiate an

electromagnetic field when a

voltage/current signal is applied

to its inpu ts, will genera te th e

same volta ge/current signal at

those input s, (now really the

output s), if the sa me an tenna is

placed within an identical, but

externa lly genera ted, electr o-

magnetic field. The antenna,

formed by th e Rx circuit int er-

conn ections, picks u p t he exter -

na l field an d generat es a signal.If the genera ted n oise signal is

cond ucted t o a sensit ive circuit

node, the node th en experiences

a lower signa l-to-noise r at io,

which increases th e bit error

ra te. (In a perfect fiber-optic Rx,

the signal-to-noise ratio and t he

bit error rat e are directly re-

lat ed). So th e extern al electr o-

ma gnet ic field can inject n oise

into th e fiber-optic Rx and t hu s

degrade th e bit-error ra te (BER).

Obviously, the larger the field

strength is, the bigger (higher gain)

the ant enna is, the better the

coupling to the sensitive node is,

and the more sensitive that node is

to noise, the worse the overall

susceptibility of the Rx will be. The


receivers ha ve been designed with

these concepts in mind t o ensur e

tha t the Rx can operate under a

large electromagnetic field st rength

with only a negligible effect on t he

BER. But, at the equipment level

containing m any components, h ow

can the system design affect the

overall system performance (BER

etc.) for a certain end-use environ-

ment known to contain electromag-

net ic fields of certa in frequencies

and field strengths?

The first t hing t o consider is

where th is externa l field comes

from. The field could be cau sed

by an ESD. The ESD current s

flowing in the a nt enna s formed

by the chassis a nd/or othercircuitry generate th e field. The

external fields could be gener-

at ed by other equipment outs ide

th e cha ssis, but n earby, such as

ra dio or TV tra nsm itters. The

exter na l fields could a lso be

caused by other circuitry inside

th e system cha ssis, if th at

circuitry is located near by the

fiber-optic Rx.

Fields which must pass from

outside the chassis to the inside areattenuated by the chassis shielding.

The sh ielding by the chassis, to a

field external t o the chassis, is the

same as the shielding provided by

the chassis to exiting radiation as

was discussed in section 2.1b. So if

the field has to pass through only

one 1.2 inch (3.05 cm) hole in th e

chassis to get inside, then it will be

att enuated by 26.4 dB at 237 MHz

relative to the outside field strength .

So, in this example, a 10 V/m

outside field strength would beequivalent t o a 0.5 V/m field

strength inside the chassis. Many

chassis, however, do not provide

that much shielding. Also, if the

circuit is very close to the hole, the

shielding will be less tha n t he 26.4

dB at 237 MHz value tha t is

calculated, based on t he assu mption

that the receiver is far away (in the

far field) from the hole (that is, the

source). In addition, the far ther the

component is from th e hole in t he

shield, the lower the externa l field

will be at the component because

the field strength rolls off (at 1/r) as

the distance, r, from the source

increases.

As we have said earlier, ESD can

generat e fields. The shorter the

path (from the strike contact point

in the system to earth ground) that

the ESD current flows through, the

lower th e strength of the field that

the ESD strike will generat e. The

lower th e peak ESD cur rent is (if it

can be limited somehow), the lower

the field strength t ha t will begenerat ed. Also, if the frequency

characteristics of the ESD st rike can

be lowered in frequency (by limiting

the ESD current pulse rise and

falling edges), then the strength and

the frequency of the ESD genera ted

field can be lowered. If, in addition,

the ESD current does not flow

inside the chassis, it will genera te a

larger field on the outside of the

chassis than on the inside of the

chassis. Thus , in the case where the

ESD curr ent flows only on t heoutside of the chassis, the chassis

shielding will help shield the circuit

inside from the ESD-genera ted

field. Most designs try to prevent

ESD current flow through the

printed circuit board grounds inside

the system in order to reduce both

the ESD generat ed fields inside the

chassis, and the chance of compo-

nent dam age due to ESD current

flow.

Any noisy component s nea r t hesens itive Rx could cau se pr ob-

lems. The fiber-optic Tx is

shielded, but it is still the closest

high-cur rent circuit to th e Rx.

When the tran smitter in a

tra nsceiver operates, it is pos-

sible th at it could a ffect t he BE R

of the receiver that is located

next to it inside the t ran sceiver.

The Tx could condu ctively couple

or radiatively couple noise into

th e Rx. The Tx-to-Rx crosstalk is

defined as th e change in receiver

sens itivity (in d B of optical inp ut

power) with constan t BE R, when

the tra nsmitter is operating

versus when th e tran smitter is

off (dat a inpu ts h eld at const an t

dc levels). Hewlett-Packar d has

tested the HFBR-510X/520X

fiber-optic tra nsceiver Tx to Rx

crosstalk an d foun d tha t it is

negligible (it is typically 0.0 dB

an d easily less tha n 0.1 dB worst



8

case). This result makes sense

because the Rx susceptibility is

pra ctically zero, th e Tx r adia-

tion level is very small, andth erefore, th e ra diated coupling

between th e Tx an d Rx is

extr emely low. H ewlett-

Packard h as a lso designed the

Tx and Rx to prevent crosstalk

due t o condu cted (Vcc and

ground) paths.

If there is a sensitive circuit in

the system, precautionary steps

can be taken to make it less

sensitive to electromagn etic

fields. One step is to add anadditional shield over th e

sens itive circuit. Since th e

fiber-optic Rx in t he

HFBR-510X/520X already has a

very good sh ield built in, th is

will not be necessar y. Another

step is to make sure tha t the

Vcc and ground and I/O lines

ar e short t o prevent noise from

coupling in. HP tests th e

sus ceptibility of th e

HF BR-510X/520X Rx in a test

breadboard t hat has t he typicaldat a s heet (Reference (1) and

(2)) Vcc power supply filtering

circuit an d also has typical

input /outp ut line lengths. So,

an y possible effect on t he Rx

due to th e coup ling of th e field

int o the I/O lines or t he Vcc or

ground lines in a r eal applica-

tion circuit is a ccount ed for in

th e susceptibility test.

Anoth er way to make a syst em

more immu ne t o extern al fields

is to mak e the system respond

elegan tly to any noise that is

picked up. Approaches such as

error detection and correction

ha rdwar e and /or software, or

merely a request for retrans-

mission, in case the received

errors ar e not corr ecta ble, are

possible ways to be more

immu ne t o the effects of noise.

The other th ing to consider is

tha t systems can ha ve additional

guar dban ds for n oise by using

large amplitude signals. Most

logic-level signals (like ECLoutput s) are lar ge enough in

amplitude that the n oise gener-

at ed by th e externa l field will

ha ve negligible effect on th e

circuit opera tion. Any fiber-optic

Rx, if opera ted a t optical inpu t

power levels a few dB above its

sensitivity limit, can withsta nd

more noise without degra ding

th e BER a bove its specified limit,

th an it can if th e optical inpu t

power is a t t he sen sitivity limit.

2.3a What is ESD?

Certa in n on-conductive ma teri-

als can eith er donate charge

(electrons) or acquire charge

when in cont act with other

materials. A mat erial with a net

char ge can then tran sfer i t to a

condu ctive ma terial either by

direct contact or by indu cing th e

opposite charge in the conductor.

If this charged conductor con-

tacts an ear th ground (or an y

condu ctive body with a verylarge am ount of stored char ged

ava ilable), a curr ent will flow

un til tha t condu ctor’s net charge

becomes zero. For examp le, if

your skin is char ged from walk-

ing across the car pet on a cold

dry day and you t hen t ouch a

groun ded or lar ge conductor, you

may see a spark as your skin

discha rges, an d feel a tingle in

your finger, as t he curr ent flows.

The char acteristics of th e ESD

current depend on t he am ount of

charge stored and on the imped-

an ce of the circuit th at dis-

charges it (to ground).

Pr oducts ar e usu ally specified in

term s of how mu ch electr ostatic

discharge they can withstand

without damage. Usually two

types of dischar ging cond uctors

ar e modelled. Ea ch condu ctor is

modelled as a capacitor (C) at a

certain voltage, which implies a

certa in am ount of stored charge,

in series with a r esistor (R) an d

an inductor in order to model theconductor dc and ac discha rging

impedance. The huma n body is

modelled relat ively well by a

small C an d a large R. The

machine or metal body model is

under m ore debate within th e

industry but usu ally has a large

C and low R (and t hus h as a

higher dischar ge curr ent t han

the human body).

2.3b How System Design

Affects ES D.As mentioned above, ESD can

affect a pr oduct du ring its

manufacturing or during its

operat ing lifetim e. U sua lly,

during man ufacturing, the

various component s in th e

equipment a re less protected

from ESD than when they are

insta lled in a fully assembled

system. The use of ESD reduc-

tion t echn iques can help mini-

mize ESD dam age to th e exposed

component s. Worker s reduce thecha nce and am ount of ESD by

wearing grounding stra ps on

wrists, by wearing conductive

smocks, by using conductive

mat s on surfaces, by using

an ti-sta tic packaging to keep

ESD off sens itive component s,

an d by using a nt i-sta tic devices

or equipment tha t reduce the

stat ic in th e air or on surfaces.

Since a system usu ally consists

of various components and

subassemblies, each with differ-

ent E SD toleran ce, the ESD

capacity of each item in ea ch

stage of the manufacturing

process mu st be k nown in order

to guar ant ee that each item can

be han dled safely dur ing the

man ufacturing process. If all th e

ESD events a re cont rolled dur ing

manu facturing so that they lie

safely within t he limits of the



9

most ESD-sensitive components,

then the system can be man ufac-

tured without ESD dama ge.

In a finished system, ESD can still

cause permanent product damage.

Often, however, a more important

problem is ESD distur bances to the

system performance. An ESD

performance disturbance could

include things such as lines on a

CRT display, logic getting stuck in a

locked state, or a lar ger number of

bit errors than usual. These ESD

disturbances can be accounted for in

the system design in order to ensure

that the product’s end user does notnotice any drastic performance

differences when an ESD event does

occur.


tra nsceivers are shipped in a

low-cost anti-static shipping tube

to prevent E SD during shipping

an d ha ndling. The tubes protect

the tr ansceivers until they are

removed and assembled onto the

PC boar ds. The end-use applica-

tion PC boards often provideadditional protection t o the

module from ESD after th e

module is soldered onto the P C

board. This add itional protection

comes about from the ter minat -

ing impedances found on most of

the tr ansceiver input and output

lines on the PC board . These

terminating impedances divert

some of th e ESD curr ent t ha t

would other wise flow int o an

unprotected module pin. Fur-

ther more, PCB can be designed

with guar d rings around t he

edge of the board. The guard

rings a re conn ected t o cha ssis

ground when th e boar d is in-

sta lled in th e system. The gua rd

rings divert currents to the

chassis-ground in t he event of an

ESD, thu s reducing the chance of

damage.

If the components are enclosed

inside a cond uctive or

static-dissipating chassis box in

the end product, then ESD is

more likely to go to th e cond uc-tive box tha n t o some other

non-condu ctive componen t. For

exam ple, if a pla stic-nose,

fiber-optic module is protruding

from t he chassis box, then ESD

is more likely to be cond ucted t o

th e section of th e chassis box

tha t is near t he module nose

th an it is to be conducted to the

insulat ing tra nsceiver’s

plast ic-nose itself. If th e chass is

grounding is such th at t he ESD

current s to ground flow on th echassis and do not flow inside

th e PCB component grounds,

then E SD damage or ESD

problems du e to ra diated fields

caused by the ESD pu lse will be

reduced. One such scheme to

keep ESD curren ts only on the

chassis is referred to as a

single-point grounding scheme

because th e chassis and the

circuit grounds connect at only

one point.

2.4a What is Condu cted

Noise?

The four th EMC ar ea is con-

ducted noise. Idea lly a conduc-

tor will carry only the desired

signa l. P ra ctically, however,

th ere is always some component

of th e actual signal on th e

condu ctor th at is un desirable.

This component is defined as

noise. Conducted noise ema -

nates from one section of the

produ ct’s circuitry, a nd is con-

ducted to th e section of the

circuitr y being observed. A good

example is the switching noise in

the power supply line (Vcc) of a

digital (logic gat es) circuit being

conducted over to a sensitive

analog (amplifier) power supply

line a nd adversely affecting t he

an alog-circuit’s performa nce.

There ar e thr ee main compo-

nen ts of cond ucted noise. Fir st is

the conducted noise genera tor.

Second is the pa th that the n oise

tak es to conduct from th e genera-tor circuit to th e receiving circuit.

Third is th e sensitivity of th e

receiving circuit t o this n oise.

So, conducted noise problems

could be eliminated by eliminat-

ing the noise source, removing

the conductive pat h, or by using

circuitry tha t is insensitive to the

effects of conductive noise.

Since an actual fiber-optic

commun icat ion n etwork has

many different types of circuitry,all operat ing at once, it is impor-

tant that potential conducted

noise problems be minimized to

allow all the circuitry to operate

without any section of it being

adver sely affected. In addition,

most compu ting products ha ve

limits on how much conducted

noise they ar e allowed to gener-

ate on the 120 Vac power lines to

prevent them from disturbing

other devices connected to the

same a c power line. Since th is acpower-line-condu cted noise

problem is determ ined more by

th e overall pr oduct’s power

supply circuitry an d filtering an d

is not very much affected by the

fiber-optic tra nsceiver th at might

be opera ting in the product, th e

ac power line condu cted noise

will not be discussed in this

applicat ion note. Hewlett-

Packard has tak en steps in the

design t o minimize the n oise tha t

is generated by the H FBR-510X/

520X modules. Ther efore the

probability of any possible

distur bance from th ese modules

on the a c power line has a lso

been m inimized.

2.4b How System Design

Affects Conducte d Noise.

Condu cted noise can be gener -

ated by switching power sup-

plies, digital logic gates, light -



10

ning tran sients, an d other n oise

on the ac power lines. Usua lly

th e low-frequen cy noise is

handled by filters and transientabsorbers in th e power supp ly.

Switching power su pplies can be

designed t o have as low a noise

output a s is possible. Digital

logic gat e noise can be r educed

by ha ving good decoupling

capacitors with sh ort lead

lengths between Vcc and ground

nea r th e logic gat es. Vcc an d

ground planes in a mu ltilayer

print ed circuit boar d reduce the

Vcc an d gr ound effective lead

lengths an d thus r educe theamount of Vcc and ground noise.

Sensitive circuits can h ave

additional power su pply filtering

circuits tha t redu ce th e noise

before it gets to th e sensitive

circuit. Depend ing on th e noise

frequen cies, different values of

filter capacita nce can be tr ied to

elimina te t he n oise frequency

over a wide ban dwidth. Usua lly,

for a group of ICs on a P C board,

some 0.1 µF and 10 µF Vccfilterin g capacitors will help

redu ce Vcc noise over a rea son-

ably wide bandwidth . For low

frequencies, some resistance in

the power su pply line, plus a

large capacitance, low frequency

bypass capacitor can act a s an

effective low-pass power s upp ly

filter. Indu ctors and ferrites can

also be used in power supply

filters to add additional filtering

if needed .

Some digital logic families

generate more noise than others.

Within a given logic gat e family,

usu ally the faster the logic gate,

the more noise it will genera te.

Logic fam ilies with totem pole

output s, such as TTL and CMOS,

can dr aw la rge spikes of Vcc

current during switching, thus

creat ing Vcc noise. Ther e ar e

newer families of CMOS avail-

able that ha ve been designed to

be quieter. ECL is designed with

different ial cur rent sources th at

tend t o ma inta in a more con-stant power supply curr ent

dur ing switching. The


tra nsceiver uses extensively

different ial cur rent switches an d

ECL output stages, similar to

th ose used in t he E CL fam ily.

Thus th e H FBR-510X/520X

fiber-optic t ran sceiver generat es

low am ount s of Vcc noise due to

its a lmost “dc” power su pply

current.

Besides filtering an d r educing

th e n oise sources, sometimes

problems can occur from sha red

Vccs or grounds. If a sensitive

circuit is upstr eam from a digital

logic gate generating Vcc noise,

its power su pply voltage will

bounce when the digital logic

gate switches and dra ws current .

If the sensitive circuit has its

own separat e Vcc or groun d line

or plan e it won’t det ect this n oise

due to the other digital logicgate. But, if two circuits n eed to

ta lk to each other, often their

Vccs and grounds sh ould be

common so that there a re no

noise differen ces in Vcc or

ground between t he t wo circuits

th at can a ct as equivalent n oise

sources.

An additiona l approach is to try

circuits th at are n ot too sensitive

to Vcc or groun d noise. Digital

logic gat es a re a good exam ple of

th is becau se th ey have a good

deal of noise ma rgin. Ther efore,

th ey can t olerate a fair amoun t

of noise before it causes t hem to

misr ead a logic sta te. Differen -

tial output s also help because

the follow-on logic switches when

th e two dat a outp uts cross. This

crossing point is first -order

independent of Vcc and ground

noise. Different ial outpu ts reject

noise better t ha n single-ended

output s do becau se the Vcc and

groun d n oise is effectively

reduced. The Vcc and groundnoise is comm on to both of the

different ial digital outpu ts.

Therefore, when the two outputs are

subtr acted from each other, to find

the different ial output voltage tha t

determines the output logic state,

the common-mode noise on each

output, to first order, is canceled

out. Hence, the common-mode Vcc

and ground noise does not appear in

the fina l different ial output signal.

Analog circuits can be designed to

reject n oise by adding filters an d bytrying to use different ial signal

techniques wh ere possible.

3.0 Sum mary of

HFBR-510X/520X

Component Leve l EMC

Performance

The results show that the EMC

performance of the HFBR-510X/

520X is excellent a nd s hould

ther efore ma ke t he customer’sEMC design easier.

A. The module typically pas ses

worldwide emissions limit s for

class B by more tha n 10 dB.

Therefore, one un it in a com-

put er system will not cau se the

system t o fail radia ted emissions

to the worldwide B test limits no

mat ter h ow poor t he sh ielding is.

B. The suscept ibility is basically

zero for 10 V/m fields. Becau seof th e module’s high imm un ity,

the customers n eed not worry

about the effects of nearby

circuits on th e receiver (Rx).

Fields externa l to th e system are

also not an issue. Only very

large ESDs could generat e a 10

V/m field, so the concern about

ESDs causing bit-error ra te

problems is minimized.

C. The module is a Class 1 ESD



11

component and so should be

ha ndled in a Class 1 ESD envi-

ronment . It withst ood 1800 volts

an d ther efore missed the Class 2class ificat ion limit by only 200

volts. Using the machine model

EIAJ test it withst ood 100 volts.

When th e tra nsceiver is insta lled

in the application circuit, it can

withsta nd a 25 kV zap to an y-

where on th e module with out

permanent damage.

D. In a r eal applicat ion circuit,

50 m Vp-p of Vcc noise should

cause no more tha n a 0.3-dB

sensitivity penalty, no matt erwhat the Vcc noise frequen cy is.

Most Vcc noise frequen cies will

cause zero penalty.

E. The tran smitter (Tx) to

receiver (Rx) crosstalk is also

basically zero. Thu s the Tx in

th e tra nsceiver can operat e with

any data pat tern and not dis turb

th e BER of its neighboring

receiver un der an y conditions.

4.0 HFBR-510X/520XComponent-Level EMCTest ing

The electr onics indu stry E MC

sta nda rds ar e often n ot defined

an d ar e sometimes non-existent

at th e componen t level. Most

EMC sp ecifications a pply to

system -level products only.

Therefore, Hewlett-Packard ha s

tr ied to genera te its own

componen t-level EMC specifica-

tions. A good component level

EMC sp ecification mu st a ccom-

plish two goals. First , th e

specification must be relatively

easy to measure, and t he mea-

surement m ust be repeatable

and accurate. Second, the

component performa nce mea-

sured must have a clear relation-

ship to th e performa nce of the

component, a nd its consequen t

effect on th e overall

finished-product performance,

when that component is used as

intended in t he finished product.

Since the a ctual end-usage EMCperform an ce is determin ed by

ma ny factors in th e overall

system, the usual approach is to

use some conceivable worst-case

condition to determine t he

component-level EMC test

conditions. Then either guaran-

tee th at t he component will

never experience such a

worst-case condition in the end

environment or use t hat worst

case plus known facts about h ow

the a ctual end environmentdiffers from the worst case to

predict t he actu al system perfor-

mance.

4.1a Radiated Emissions

Test ing Procedure


modules under t est were placed

in a n electrical-loopback t est

breadboard a nd were tested to

find t heir ra diated emission

spectru m u sing the F CC certified

semi-an echoic test chamber atHewlett-Packar d’s Cuper tino

site (CA). This test cham ber is

used by various H ewlett -Pa ckard

divisions t o test th eir products to

FCC an d other emissions limits.

The tests ar e mostly automated

an d a re condu cted by qualified

personnel.

For the FCC Class-B tests, th e

test ant enna was placed at a

3-meter t est distan ce from th e

module. For the FCC Class-A,

CISPR 22, VCCI, or EN 55022

tests, the test antenn a was

placed at a 10-meter t est dis-

ta nce from the module. The

worst -case peak field st rength

ra diated emissions wer e foun d

by moving the ant enna u p and

down from 0.1 to 4 meter s in

height, by chan ging from vertical

to horizont al ant enna polar iza-

tions, and by rotating, in 45-de-

gree increments, the turntable on

which t he m odule was placed.

The entire ra diated emissions

frequen cy ran ge, as deter minedby the particular test a ntenna in

use, was observed during th ese

tests so that th e worst -case peak

at each frequency could be found.

The antenna and test system

calibration factors were t hen

used to derive the peak r adiat ed

electrical field strength being

emitted, at each frequency, from

that module at tha t test distance.

Ea ch radiat ion frequency was

then quasi-peaked for t hose

frequen cies below 1 GHz.

These fina l worst-case field

strengths were th en compared t o

the relevant specification limit.

The worst-case ma rgin to the

specification limit is the smallest

difference between a worst-case

final ra diation level and t he

specificat ion limit, over th e

entire specified frequency range.

Note that because both the

rad iation levels an d th e limits

vary with frequen cy, the h ighestrad iation level will not n ecessar-

ily give th e worst-case mar gin. A

log periodic antenna is used from

200 to 1000 MHz. A biconical

an tenn a is used from 30 to 250

MHz. Above 1 GHz a horn

antenn a is used. Note tha t the

FCC and other regulatory

agencies do not r egulate ra diated

emissions below 30 MHz.

A stan dar d H FBR-510X/520X

tra nsceiver module outs ide the

test cham ber provided a 125

Mbaud or 155 Mbaud 1010

pat tern optical signal. This

optical signal wa s u sed to drive

th e Rx of th e HF BR-510X/520X

tra nsceiver module in th e

loopback test breadboard inside

the test chamber. The loopback

test board uses th e power supply

decoupling circuit recommended

in the data sh eet . The Rx drives



th e Tx using a 2.7 inch (6.86 cm)

long connection between the Tx

and Rx data and data * pins.

(The actu al Rx t o Tx lines go 1inch (2.54 cm) up an d back, an d

go 0.7 inch (1.78 cm) across.)

This connection length was believed

to reflect t he approximate length of

a connection, from th e Rx to a PHY

circuit, and then back from the PHY

circuit to the Tx, in a real applica-

tion printed circuit board. The 50

ohm to Vcc-2 Volt equivalent (split

load) terminat ions were placed at

the Tx inputs. The board ha s a 2.5

by 2.9 inch (6.35x7.37 cm) ground

plane with through-hole compo-nents and ha nd wiring. Coaxial

cable with ferrites (plus a coiled

section) brings in dc power. The

shield of this dc power supply cable

keeps any radiation from adding to

the test result. Thus, any radiation

seen in t his test is due exclusively to

the fiber-optic transceiver module

and to any interaction it might have

with the test board.

The final margin to the FCC a nd

other regulatory agencies specifi-cation below 1 GHz was obtained

by quasi-peaking each emission

peak at each frequency according

to the FCC requirements.

Quasi-peaking allows devices

such as print ers, which put out

rad iation only in short bur sts

(when a print head turn s on), a

break by averaging the ra diation

ener gy over a specified period of

time. For a fiber-optic module

with a 1010 pattern t hat put s

out cont inuous ra diated energy,

quasi-peaking drops the peak

radiation level by a small fixed

amoun t. Since quasi-peak

testing ta kes more time, only the

worst radiation peaks are

qua si-peaked. Some of th e

lower-level radiation data is

appr oximated to an equivalent

final qua si-peak r esult from the

peak result by taking the actual

peak emission result and sub-

tra cting a fixed 1.5 dB value t o

get an app roxima te final

quasi-peak result. Above 1 GHz,

no quasi peak detectors exist.Therefore, th e FCC B t est a bove

1 GHz uses the peak ra diation

value directly and a djusts its

specificat ion limit accordin gly.

The r adiat ion frequencies seen

for this test consist of harmonics

of th e fundam enta l frequen cy of

the 1010 data pattern . The

fundam enta l frequen cy of a 1010

pat tern is equa l to one-ha lf the

data rat e. Thus the 125 Mbaud

radiation t est ha s ra diation

frequencies th at occur in in tegermu ltiples of 62.5 MHz.

The worst-case qua si-peak

ra diated field stren gths for ea ch

frequency ar e compa red with t he

FCC and other r egulatory

agen cies specified limits. These

test limits var y with frequency.

The margin (positive if pass,

nega tive if fail) by which t he

final worst-case, quasi-peaked if

necessary, field str ength passes

th e test specification is th e testma rgin of th e component to the

FCC and other r egulatory

agencies limit a t t ha t frequency.

The fina l overall FCC an d other

regulatory agencies test m ar gin

for t ha t component is the

worst -case (smallest) ma rgin,

over t he en tir e specified fre-

quency ran ge. It is this final test

margin tha t is used by the FCC

an d other regulat ory agencies to

determine whether the product

passes the specification or not.

So the final FCC an d other

regulatory agencies test m ar gin

is the worst-case (quasi-peaked

below 1 GHz) mar gin of th e

detected field str ength t o the

limit for an y ra diation frequency

in t he specified range, any module

orientation, any ant enna h eight and

any ant enna orientation.

Use of a calibrated semi-anechoic

cham ber ensures results that can

be used directly to determ ine

FCC qualification. Problems due

to resonances in TE M cells areelimina ted. (A resona nce can

give large radiat ion t est err ors by

amplifying the radiation at the

resonant frequency.) Since th e

test facility is au tomat ed, we can

test modules and conduct experi-

men ts relatively quickly. We

ha ve also tested m odules inside a

simulated m etal chassis box and

ha ve verified that our plastic

nose modu les do indeed get close

to the theoretical shielding limit

predicted from the size of thehole in t he sh ield.

Hewlett-Packard radiated

emissions test s are designed to

be as close to rea l life as is

possible, so that the r esults can

be correlated to final customer

results. An attempt was made to

design a test board th at realisti-

cally mimics a typical best-case

cust omer layout. HP would like

the results of the radiated

emission test s to be such th ateven if a customer provides no

shielding, one of th e HP

HF BR-510X/520X tr an sceiver

modules will not cause t he

customer to have typically less

tha n 6 dB mar gin to any of the

worldwide B limits. Most cus-

tomers want t heir system to pass

worldwide B by 6 dB. HP ’s goal

was th erefore to pass F CC B by

10 dB. Since CISPR 22B, EN

55022, an d VCCI Class 2 E ur ope

and J apan B limits are roughly 3

dB tough er for our fiber-optic

modules to meet th an FCC B is,

meeting FCC B by 10 dB ensur es

7 dB t o worldwide B.

In an actual system, the chassis

shielding will often greatly

redu ce emission. So, in a

well-shielded system, m an y

modules could be used (in a

FDDI concentr ator or ATM

12



switch, for example). If we get

21 dB of shielding a t 437.5 MHz

from a 1.2 in ch (3.05 cm) du plex

SC hole in a chassis, th en weha ve 21 dB more ma rgin to work

with. In a concentra tor, if all the

modules’ energy were in pha se

an d th erefore directly added

together, 21 dB would be enough

for n modules, where n is found

from:

Or perha ps th e energy is not

office equipmen t (Class B) an d

th erefore th e previous a na lysis

ma y be too conser vat ive. No

matt er what t he real l imit on th enu mber of un its in concentra tors

is, we feel that we have done our

best to ensure tha t our r adiation

is as low as possible to ensu re

tha t th e largest number of

modules can be used in concen-

tra tor or switch applicat ions.

Very large concentrators can, if

necessary, add a dditiona l shield-

ing, by th e use of vanit y covers

etc. to lower th eir radiat ion. A

1010 patter n is the worst-case

data pattern for ra diated emis-sions. A psu do-ra nd om bit

sequence (PRBS) or varying

pulse-width da ta pattern tends

to spread out the energy and

lower th e rad iated emissions.

We use a 1010 pattern to be

conservat ive an d becau se a 1010

is an F DDI IDLE pa ttern which

could be sent ra ther frequen tly

in a r eal FDDI system.

4.1b Radiated Emissions

Testing ResultsThe following r esults sh ow tha t

th e typical 820 nm an d 1300 nm

HFBR-510X/520X transceivers

pass all th e worldwide B limits

by better th an 10 dB mar gin

below 1 GH z. Above 1 GH z, a

test board ground plan e reso-

nan ce causes th e unit t o pass

FCC B by 7 dB a bove 1 GHz.

Thus, one un it will not cau se a

comput er system t o have less

tha n 6 dB m argin to any world-

wide B-ra diated em issions test

limit, even if no shielding is

provided by th e customer chas-

sis. (Remember that t he FCC

radiated emissions specification

is curr ently the only one th at

requires t esting above 1 GHz.)

The fina l emissions data is quasi

peaked below 1 GHz a nd is just

the peak data above 1 GHz.

Table 1 shows a sum ma ry of th e

radiated emissions results. NA

means that a ctua l test data was

not availa ble. Based on other

data, however, the NA results have

been approximated and thoseestimates are listed in par enthesis

with an approximate sign.

Figure 1 sh ows the fina l emis-

sions da ta for the HF BR-5103/

5105/5204/5205 1300 nm tr an s-

ceiver relative to FCC B limits at

125 Mbaud. Figure 2 shows th e

final emissions da ta for t he

HF BR-5103/5105/5204/5205 1300

nm t ra nsceiver relative to FCC B

limits at 155 Mbaud. Figure 3

shows the final emissions da tafor t he H FBR-5103/5105/5204/

5205 1300 nm tra nsceiver

relative to th e rest of world B

(CISPR 22B, EN 55022, VCCI

Class 2) limits at 125 Mbaud.

Figure 4 sh ows the fina l emis-

sions da ta for the HF BR-5103/

5105/5204/5205 1300 nm tr an s-

ceiver relative to the rest of

world B (CISPR 22B, EN55022,

VCCI Class 2) limits at 155

Mbaud. Figure 5 shows th e fina l

emissions da ta for theHF BR-5104/5203 820 nm t ra ns-


125 Mbaud. Figure 6 shows th e

final emissions da ta for t he

HF BR-5104/5203 820 nm t ra ns-


155 Mbaud. The bars on the

plots in th ese figur es show the

tested final (quasi peak below 1

GHz) ra diated field strength .

The squiggly lines on the plots

show the test system noise floor.

The test limit is sh own a s a solid

line labeled with t he t est limit

name.

The ra diation is usu ally a little

worse at 155 Mbaud t han 125

Mbaud. This is becau se there is

more high-frequency energy

existing in (the four ier spectrum

of) th e higher dat a ra te signal.

Also, sometimes, a 155 Mbaud

harm onic will be closer to a

13

corr elated ; in wh ich case, even

more modules could be used.

We have never t ested a concen-

trator or switch so we do not

know exactly how th e ra diationfrom all the modules in a concen-

tra tor would add up. If an y of

our customers ha ve insight in

this area tha t t hey would like to

sha re with u s, our a pplications

depart ment would be most

interest ed. We ha ve seen FDDI

concentra tors with man y MIC

conn ector modules. These

concentra tors h ave sup posedly

pas sed F CC classification for

10

21 = 20log

= 30log10 n

This formu la is derived from t he

shielding formula for multiple

holes in a chassis plus th e

increase in ra diation for m ultiple

modules adding in phase. An

equivalent wa y of expressing

this formu la is:

n = 10(21/30) = 5

√n + 20log10 n

1021 = 20log √n + 20log10 √n

= 20log10 n

n = 10 (21/20) = 11

If the m odules’ ph ase is

un correlat ed due to each concen-

tra tor h aving its own clock

source, then perhaps th emodules’ ra diat ion would r.m .s

add. In th is case we would have:



Optical Data Worst Worst Worst Wors t Fre que ncy

Wave - Rate case case case case in MHz

le ngth Mbau d m argin m argin margin m argin w h e re

to FCC B to FCC A to World B to FCC B w orst

(be low 1 GHz) (be low 1 GHz) (CISP R 22 B, (above 1 GHz) case

dB dB VCCI 2, dB margin to

EN55022B be low 1 GHz

be low 1 GHz) FCC B

dB lim it

occurred

1300 nm 125 16.7 27.2 13.7 7.8 187.5

1300 nm 155 14.4 23.1 13.6 7.3 232.5

820 nm 125 14.9 NA (~25.4) NA (~11.9) NA (~7.8) 187.5

820 nm 155 13.1 NA (~21.8) NA (~12.3) NA (~7.3) 232.5

Table 1: HFBR-510X/520X Radia ted Em ission s Test Resu lt Summ ary

resonan t frequency than a 125

Mbaud harm onic will be and th is

can cause the r adiat ion to increase.

The 155 Mbaud radiation peak at

232.5 MHz is just past the fre-

quency where the FCC B and other

limits suddenly increase. (FCC B

increases 2.5 dB at 216 MHz and

CISPR 22B, EN55022, and VCCI

Class 2 go up 7 dB a t 230 MHz.)

Below 1 GHz, the 820 nm unit is

slightly worse than t he 1300 nm

unit by 1.3 to 1.8 dB. This increase

in the 820 nm module radiation is

due to a kn own design d ifference

in the 820 nm m odules versus

th e 1300 nm modules. This

difference is still small enough to

allow a ny wa velength

HF BR-510X/520X transceiver

module to still meet th e data sheet

claim of typically passing worldwide

B limits by 10 dB mar gin.

Above 1 GHz, the radiation

dra stically increases. This is due

to a ground plane resonan ce

effect on th e HP test board. The

boar d ha s a 2.5 by 2.9 inch

(6.35x7.37 cm) groun d plan e

with t hr ough-hole wiring.

En ergy from th e module, prob-

ably conducted th rough t he Vcc

and ground connections, excites

th e groun d plane as an electric

(dipole/monopole) an ten na . Since

th e groun d plane is acting as a

resonan t antenn a, the actua l

am ount of energy exciting it ha s

only a sma ll effect on t he a mount

of th e radiation. The frequency

of th e radiat ion pea k is rightar ound 1.3 to 1.4 GHz and a

quart er wavelength at those

frequen cies is 2.3 to 2.5 inches

(5.84 to 6.35 cm). This is jus t th e

size of the test boar d ground

plane. Therefore, the groun d

plane is acting as a one-quar ter

wavelength resonan t ant enna.

We have tried experiments in

which we changed the size of the

test board ground plane, and

found t hat the r esonan t fre-

quency of the ra diation changes just as we would have expected,

based on the ground plan e size

differen ces. We ha ve also tr ied

various fiber-optic modules in the

test board an d have measured

th eir radiation above 1 GHz. The

results are almost the sam e no

matt er what module is being

test ed. So, an y fiber-optic

module seem s to be able to excite

th e ground plan e resonan ce. And

14

Figure 1. HFBR-510X/520X (1300 nm) radiate d em ission s at 125 Mbaud to

FCC B limits.

55

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5 Q U A S I P E A K R A D I A T I O

N E L E C T R I C F I E L D S T R E N G T H I N d B µ V / m

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

FREQUENCY OF RADIATION PEAKS, MHz

FCC CLASS B TEST LIMIT (3 METER)



Figure 2. HFBR-510X/520X (1300 nm) radiate d em ission s at 155 Mbaud

to FCC B limits.


to 10 mete r test limit s, (FCC A, CISPR 22B, EN55022, VCCI clas s 2).

once the ground plan e resonates,

it domina tes th e overall radia-

tion. We are planning additiona l

experiments to mak e observa-tions regarding this groun d

plane resona nce issue. Our

applications an d R&D depar t-

ment is inter ested in any cus-

tomer experiences that m ay help

us un derstand h ow this ground

plane resonan ce phenomenon

affects our cust omer’s ra diat ed

emissions.

How would it affect our customer’s

radiated emissions? We have tested

a customer’s mu ltilayer F DDI PCB.

It reduced the radiat ion above 1

GHz by 3.5 dB but it increased theradiation below 1 GHz (in the 750

MHz area) by 5 dB. Thus , for the

1300 nm module tested at 125

Mbaud, the worst-case margin to

FCC B was 12.1 dB (at 750 MHz)

below 1 GHz and 11.4 dB above 1

GHz. Even with this different t est

board, we still pass worldwide B by

9 dB. The multilayer PCB helped

the radiation above 1 GHz, but the

larger PCB size (6" vs 3") caused the

ground plane resonance to occur at

750 MHz. Our HF BR-510X/520X

modules have low enough r adiat ion

levels so that we can see this groundplane r esonance occur without

having this phenomenon masked by

some other radiat ion source. Figure

7 shows the fina l emissions data for

the HF BR-5103/5105/5204/5205

1300 nm transceiver relat ive to FCC

B limits at 125 Mbaud using th is

3x6" customer mu ltilayer F DDI

PCB. More experiments need to be

done to furt her un derstand t his

problem and how it affects our

customers.

The typical customer PC board is

inserted into a backplane in a

chassis. Therefore the ground

ant enna st ructure, formed by the

entire computer system ground

network, could by itself be effec-

tively much bigger than the board

ground plane. Therefore, any

resonances that may occur would be

at a m uch lower frequency than the

frequency calculated from th e board

size alone. If the frequency is low,

the resonance may not occur at all,may occur at frequencies that do not

radiate efficient ly, or m ay occur

below th e 30-MHz lower-frequency

limit for the ra diated emissions test.

So, most systems will be safe from a

ground plane resonance effect

(ground plane resonance could be

excited by other ECL or other

circuitry in t he system, in addition

to the excitement provided by our

module. We therefore, have decided

to hold to our standard test board

results and those results are quoted

in this r eport.

4.2a Susc eptibi l i ty (Immu -

nity) Testing Proce dure

To measure the susceptibility, an

externa l field must be genera ted

and th e link BER mu st be

measu red. A field can be gener-

ated by an an tenna in a

semi-an echoic chamber but th is

15

55

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5 Q U A S I P E A K R A D I A T I O N E L E C T R I C F I E L D S T R E N G

T H I N d B µ V / m

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000



55

45

35

25

15

5

Q U A S I P E A K R A D I A T I O N E L E C T R I C F I E L D S T R E N G T H I N d B µ V / m

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000


FCC CLASS A TEST LIMIT (10 METER)

CISPR 22B = EN55022 = VCCI CLASS 2 TEST LIMIT (10 METER)

NO TEST DATA ABOVE 1 GHz WAS AVAILABLE



Figure 5. HFBR-5104/5203 (820 nm) radiated e mission s at 125 Mbaud to

FCC B limits.

test is slow an d cumbersome.

We use a TEM cell. The TEM cell

is situated in our R&D lab, close

to all the BER mea sur ing equip-

ment. An aut omated test pro-gram measures the BER and sets

up th e correct field strength an d

frequency inside the TEM cell.

The TEM cell is a lar ge rectangu-

lar meta l cell th at can be thought

of as a n expanded coaxial

waveguide. The voltage mea-

sur ed at t he output of th e cell

corresponds to a certain electro-

magn etic field str ength inside

th e cell. A module and tes t

board can be placed inside the

cell between the center a nd th e

outer cell conductin g planes . As

long as th e module an d the test

boar d ar e not t oo large, the cell

will still generat e a TE M wavean d th e cell will still maint ain its

calibrat ed field str ength to

output voltage correlation. Our

cell is specified to 450 MHz,

which is a dequat e for our suscep-

tibility test becau se we see zero

susceptibility penalty above 350

MHz for a ny of our H FBR-510X/

520X tr an sceivers. Above 450

MHz, the TE M cell can resonate

(i.e. sta nding electromagnetic

waves can form). Thus it cann ot

be used to test for r adiat ion.

Therefore we use t he

semi-an echoic cha mber for

radiation testing.

A sine wave genera tor an d a RF

amplifier provide the TEM cell

input dr ive voltage. A spectr um

analyzer detects the output

power from which the electric

field str ength can be der ived.

Sine wave generat ors from 10

MHz to 450 MHz ar e used to see

how the susceptibility varies over

frequen cy. A pur e, un modulated

sine wave is used. Modulat ing

the field, as is sometimes u sed insome product su sceptibility test s,

does not m ake sense for our

fiber-optic receiver s. The fact

tha t th e entire susceptibility test

is aut omated a llows us to quickly

measu re t he su sceptibility of any

fiber-optic module.

The BER pattern generat or

drives a H FBR-510X/520X

tran smitter th at is located

outside the TEM cell. This

tra nsm itter optically drives (viaa fiber-optic cable) a

HF BR-510X/520X receiver in side

the TEM cell. The tra nsceiver

Rx inside th e cell drives its

neighboring Tx via the electrical

Rx to Tx dat a line loopback

connection on the test boar d.

The Tx in side th e cell drives (via

an other fiber-optic cable) a

HFBR-510X/520X receiver

outside the TEM cell whose

output s ar e conn ected to the

BER detector inpu t. Thus a link

consist ing of two tr an sceivers is

bit error-rate tested.

The TEM cell test u ses the sa me

loopback test brea dboar d tha t is

used in the radiation test . The

loopback board dc power is

brough t in via a coaxial Vcc

cable. The coaxial Vcc cable ha s

a coiled section plu s ferrit es to

prevent noise pickup on the Vcc

16

55

45

35

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15

50 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000


Q U A S I P E A K R A D I A T I O N E L E C T R I C F I E L D S T R E

N G T H I N d B µ V / m

FCC CLASS A TEST LIMIT (10 METER)

CISPR 22B = EN55022 = VCCI CLASS 2 TEST LIMIT (10 METER)


55

45

35

25

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5 Q U A S I P E A K R A D I A T I O N E L E C T R I C F I E L D S T R E N G T H I N d B µ V / m

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000





to 10 mete r test limit s, (FCC A, CISPR 22B, EN55022, VCCI clas s 2).



cable. The coaxia l Vcc cable is a

large antenn a. It is importa nt to

prevent it from picking up noise

an d injecting that noise into thetra nsceiver power supply be-

cause we want t o measure t he

susceptibility of the module and

not its Vcc noise rejection. Thu s,

the su sceptibility test measu res

only the effects of the external

field on the module in its applica-

tion test board a nd th erefore

includes a ny possible coup ling or

intera ctions between th e module

an d its application test board.

The overall sensitivity in t he

susceptibility t est, derived from the

two fiber-optic transceivers in the

link, is determined by the errors

produced by the loopback board Rx

which, using an optical attenuator,

is run near the sensitivity optical

input power level. There are no

errors produced by the regular

breadboard Rx out side the TEM cell

because it runs at h igh optical input

power levels due to the short fiber

directly connecting the inside cell

Tx to the outside Rx.

The 1*10(-6) bit error rat e (BER)

sens itivity at th e left eye edge for

a 2(7) - 1 PRBS patt ern is mea-

sur ed in exactly the sa me fashion

as is described in th e condu ctednoise tests. The sensitivity is

first m easur ed with n o field

present in the TEM cell. Then a

field is app lied an d th e sensitiv-

ity is remea sur ed. The optical

dB change in th e left eye edge

with 2(7) - 1 PRBS pattern an d

1*10(-6) BER sensitivity, from

add ing a n electr ic field of a

known field strength an d fre-

quency, is equa l to the suscepti-

bility penalty at th at field

strength and frequency. Thesusceptibility penalty is t herefore

calculated by subtra cting the

sensitivity with th e field present

from the sensitivity with no field

present . 10 V/m is the usu al

field str ength to use in su scepti-

bility tests. We also measu re the

susceptibility at 3 V/m and 20 V/m

in to see h ow the su sceptibility

varies over field stren gth.

4.2b Susceptibi l i ty

(Immu nity) Testing Re sultsFigure 8 shows th e susceptibility

results for a 1300 nm

HF BR-510X/520X tr an sceiver for

10.33 an d 20.37 V/m field

stren gths. The 10 V/m

worst-case su sceptibility is 0.05

dB, which is pr actically zero.

You can see a slightly bigger

pena lty of 0.13 dB at 20.37 V/m

which tells you th at t he test is

indeed working. The 3.27 V/m

susceptibility test shows less

penalty t ha n does th e 10.33 V/m

test. The 3 V/m test result was

not print ed becau se the plot was

too difficult to read. The dat a

was ta ken at 125 Mbaud for a

1300 nm transceiver. The

results do not cha nge at 155

Mbaud and are n ot dependent on

data rate. The 820 nm

HFBR-5104/5203 transceiver

susceptibility data was taken at

155 Mbaud. The 820 nm su scep-

17


to FCC B l imits using cu stomer 3 x 6 inch mu lt i layer FDDI PCB.

55

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5 Q U A S I P E A K R A D I A T I O N

E L E C T R I C F I E L D S T R E N G T H I N d B µ V / m

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000



NO TEST DATA BELOW 250 MHz WAS AVAILABLE

55

45

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5 Q U A S I P E A K R A D I A T I O N E L E C T R I C F I E L D S T R E

N G T H I N d B µ V / m

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000




Figure 6. HFBR-5104/5203 (820 nm) radiated e mission s at 155 Mbaud to

FCC B limits.



tibility is just a s good a s th e

1300 nm su sceptibility. The

actua l data plot is not included

in this report becau se the result

is slightly better t ha n th e 1300

nm r esult , but is, at the same

time, within the m easurement

noise of the 1300 nm result.

Both t he 820 nm and 1300 nm

module susceptibility results a re

so good th at m easur ement noise

dominates in some of the plotted

data. (Maximum measurement

noise for the susceptibility test is

rough ly 0.05 dB.)

The n egligible penalties t o the

sensitivity for a 10-V/m externalelectr omagn etic field give us

confidence that most applications

will see no performa nce degrada -

tion in the fiber-optic link due to

other nea rby circuitry or to

externa l EMI sources (such as

radio tra nsmitters) that are

located outside th e system

chassis. Only an extrem ely large

ESD h as even a chance of creat -

ing a lar ge enough field tha t

could cau se a n oticeable, but

even th en pr obably very sma ll,

distur bance in th e HFBR-510X/

520X fiber-optic link.

4.3a ESD Testing Procedure

The E SD component level tests

are t he most stan dardized of any

of th e componen t level EMC

tests. Many industry standa rd

ESD tests were developed for

integrat ed circuits (ICs) such a s

CMOS an d TTL gates. One such

sta nda rd is th e MIL-STD-883D

Meth od 3015.7 (see Referen ce

(5)). It classifies componen ts

into categories based on how

mu ch E SD voltage they can

withsta nd. A hu man body modelES D test circuit consistin g of R =

1500 ohm s an d C = 75 pF is

charged up t o a certa in voltage

an d is then directly discha rged

to various combinations of the

component pins. Five discharges

to the pins are made. Next the

module is tested for perm an ent

perform an ce degradat ion. The

largest volta ge at which no

permanent performan ce degra-

dat ion is foun d is the E SD

withstand voltage. The ESD

withstand voltage is then used to

determ ine the ES D class of th e

component per th e table in th eMIL-STD-883D Met hod 3015.7

specificat ion. In th e

HF BR-510X/520X module t he

data input an d outpu t pins are

the m ost sensitive to ESD.

These pins are th erefore inter-

nally protected by ESD protec-

tion d evices.

There is also a J apanese varia-

tion of th e MIL-STD test wh ich

models a machine body model

electr ostatic discha rge. The testis essentially similar t o the

MIL-STD specificat ion, but

applies the discharge between

each pin and ground. The ESD

test circuit resistan ce, R, is zero

ohms an d th e capa citan ce, C, is

200 pF. The low resistance

models th e low resist an ce of a

met al body. The specificat ion is

called EIAJ #1988.3.2B Version.2.

Machine Model.

Another ESD s pecificat ion isbased on th e IEC 801-2 stan dar d

(see Refer ence (6)). Th is is

actua lly a box-level ESD t est a nd

specifies that the box product

will not be “dam aged” by an ES D

that conta cts i t an ywhere on t he

exposed outside ar eas of the

product. Exactly wha t is mean t

by dama ge is left t o the ma nu fac-

turer a nd to the customer to

decide. We ha ve defined “dam -

age” as perm an ent pr oduct

performa nce degrada tion. A

temporar y increase in BER

dur ing an E SD does not count a s

dam age for this test. Our sus-

ceptibility test, however, gua ra n-

tees good BER performance as

long as t he E SD does not cause

an electrosta tic discharge cur-

rent to flow directly thr ough th e

component an d does not produce

electr omagn etic fields above 10

V/m in strength . In an y case, as

18

Figu re 8. HFBR-510X/520X (1300 nm) s us cep tibili ty for ≈10 and ≈ 20 V/m field s.

820 nm HFBR-5104/5203 sus ceptib ility plots are no t included here, but are as

good or better than the HFBR-510X/520X to within measurement noise

(max noise ≈ 0.05dB).

0.15

0.10

0.05

0

-0.05

E M I I N D U C E D

S E N S I T I V I T Y D E G R A D A T I O N

I N

d B

( 1 ×

1 0 - 6 B E R ,

2 7 - 1 P R B S P A T T E R N , L E F T E D G E O F E Y E )

20.37 V/m

10.33 V/m

0 50 100 150 200 250 300 350 400 450

FREQUENCY OF THE TEM CELL INDUCED ELECTROMAGNETIC INTERFERENCE (EMI) FIELD, MHz



soon a s th e ESD is over, th e

fiber-optic module imm ediat ely

return s to normal operation.

The module was zapped on its

exterior su rface with an electro-

sta tic discha rge simulator wand

(zap). At first we zapped only

the nose section (where t he SC

conn ectors ar e att ached, about

th e first 0.5 inch (1.27 cm) or so).

We discharged to the top, bot-

tom, left, r ight a nd front of the

module nose. Since th is did not

cause a ny perman ent perfor-

man ce degrada tion at 25 kV,

which wa s th e limit of our testequipment, we tried discha rging

to any point on the top, left, right

or front of th e module. We used

a EDS-200 Electr osta tic Dis-

charge Simulator Wand. The

wand simulates the hum an body

an d ha s a capacitance of 300 pF

an d a r esistance of 150 ohms .

The m odule was self oscillat ing

in an electrical an d optical

loopback board. The statu s

detect out put dr ove an LED

which indicated wheth er th e link was up or not. After each set of

ESD, th e module was placed on

the man ufacturing tester to

check for an y module perfor-

mance degradation.

4.3b ESD Testing Results

The HF BR-510X/520X modules

sustained no damage with 5

discha rges at 1800 Volts, using

the MIL-STD huma n body model

test circuit t o simulat e an

electr ostatic discha rge th at goes

directly to the 1x9 module pins.

Above 1800 volts some per ma -

nent module dama ge did occur .

This test was done according to

MIL-STD-883D Met hod 3015.7

using a 1.5 k ohm r esistor an d

100 pF capa citor hu man body

model. Ther efore, according to

MIL-STD-883D Met hod 3015.7,

this is a Class 1 device an d

appropriate Class 1 ESD precau-

tions during ha ndling should be

taken. During assembly ESD

wrist straps and other

industry-standa rd E SD reduc-tion techniques should be used to

ensure an E SD environment t hat

is safe for Class 1 device han -

dling. The HFBR-510X/520X

fiber-optic transceivers are

th erefore shipped in a low-cost

an ti-sta tic shipping tube to

prevent ESDs dur ing shipping

an d handling. The module did

pass a t 1800 volts however, an d

th is is only 200 volts a way from

th e Class 2 MIL-STD ESD

classification of 2000 volts.Therefore the HFBR-510X/520X

tra nsceiver may not be as

sensitive to ESD da mage as most

MIL-STD Class 1 rated compo-

nents .

The Japanese EIAJ#1988.3.2B

Version.2 Machine Model ESD

test showed that our module

could withstand a 100 Volt level.

Once the module is installed in

its a pplicat ion boar d, it can

withstand more ESD energy.

The 25 kV zap test had no

problems. There was no perma -

nent ESD dama ge to the module,

when in its a pplication circuit,

no matt er where th e zap oc-

curred on the module surface. In

th e loopback boar d test set up,

th e link m onitor light might

blink briefly during the E SD zap,

implying a m omentar y bit err or

rate burst, but t he light immedi-at ely came back on once th e

discha rge ended. Thus, the ESD

to the module could produce

some bit err ors but th e module

recovers complet ely once th e

dischar ge ends (in a few millisec-

ond). Ther efore a 25 kV dis-

charge directly to a HFBR-510X/

520X tr an sceiver module in-

sta lled in a comput er system will

cause no permanent dam age and

worst cas e could cau se only some

bit errors. Keeping in mind the

modules’ good susceptibility

results, provides confidence thatthose bit errors will be the

absolute minimum possible for a

fiber-optic module of th is type. If

good ESD design is used in t he

computer system, it is pr obable

tha t only a very large ESD would

make even a noticeable differ-

ence in t he fiber-optic link

performance.

4.4a Conducte d Noise

Testing Procedure

A known a moun t of noise iscoup led onto th e fiber-optic test

circuit Vcc. The degrada tion in

the receiver sensitivity due to

this noise is then measured.

Sinusoidal noise signals of

different frequen cies ar e used to

check how th e sensitivity degra -

dation varies over noise fre-

quen cy. 50 mV peak -to-pea k

(p-p) of sinusoidal noise is

applied via an ac coupling bias

tee to a 1-ohm resistor, which is

directly connected to the Rx testboard Vcc connection. The

peak -to-peak noise level is

measured at the 1-ohm resistor

on the side away from the

module Vcc conn ection. The

1x10(-6) bit error rat e (BER)

sens itivity at th e left eye edge for

a 2(7) - 1 PRBS patt ern * is

measured with no Vcc noise

present an d with 50 mV p-p of

Vcc noise pres ent . The differen ce

in sensitivity is th e Vcc noise

sensitivity penalty. This value is

recorded.

The n oise sensitivity pena lty is

first t ested with no externa l Vcc

filter present on the test br ead-

board . This tells us how well th e

module’s internal Vcc decoupling

network can reject n oise on its

own. Then a portion of th e

recommen ded data sheet power

sup ply filter is ad ded in. (See

19



Figure 11 of the H FBR-510X

dat a sheet or Figur e 7 of the

HF BR-520X dat a sheet). The

extern al Vcc filter t ested con-tain ed a 0.1-µF capacitor at the

module pin, a 1-µH indu ctor in

series with t he Vcc line, and a

0.1-µF capacitor on th e oth er

side of th e indu ctor. (These

component s a re labeled C1, L1

and C3 in th e data sheets). This

test filter does not cont ain t he

10-µF, low-frequen cy capa citor

recommen ded on th e data sh eet

(C4) because our a c coupling

network a nd t he pulse generator

cannot generat e enough signal todrive the Vcc node to a 50 mV

p-p level when t he 10-µF capaci-

tor is present . The effect on the

sensitivity with t he 0.1-µF, 1-µH,

0.1-µF t est filter in place is th en

mea sur ed. Fin ally, th e effects of

the filter if the ent ire recom-

mended data sheet Vcc filter,

including t he 10-µF capacitor, ar e

estimated (but not measured).

4.4b Conducte d Noise

Testing ResultsThe sensitivity degradat ion t o a

50 mV p-p noise signa l at th e Vccconn ection was measur ed. In

summa ry, the results are that

with n o Vcc filter present on th e

test board t here is less than a 1

dB pena lty below 15 MHz an d

less than a 0.2 dB penalty above

15 MHz. With the extern al Vccfilter of a 0.1-µF capacitor at the


series with t he Vcc line, and a

0.1-µF capacitor on th e other side

of inductor, large amounts of

sensitivity degradat ion ar e

confined t o a sma ll frequ ency

ran ge around 440 kHz where the

filter resonat es. Even in th is

small frequency ra nge, the

pena lty does not exceed 1.4 dB.

Est imates of th e Vcc noise

performa nce using the real data

sheet Vcc filter, including the 10

µF recommen ded capacitor, sh ow

* There ar e different sensitivity test

windows defined for each product in the

product data sh eets. These windows are

derived from the link jitter a llocations to

ensur e that the Rx does not add more

jitter t o the overall link jitter th an is

allowed by the link specification. The

sensitivity over the window is always

worse th an the center of the eye

sens itivity. For Vcc noise and suscepti-

bility measur ement sensitivity testing,

the bit error r ate detector clock isaligned with the dat a eye so tha t the

clock is at t he left edge of th e test

window in the dat a eye. Then the optical

input power is adjusted t o get a 1x10(-6)

bit error rate. This optical input power

is then the left eye edge 1x10 (-6) BE R

sensitivity level for the dat a pa tter n

under test . See the notes in the data

sheet s (Referen ce (1) an d (2)) for th e

HFBR-510X/520X products that describe

the receiver section “Input Optical Power

Minimu m a t Window Edge” specifica-

tions. (For example, note 20 for the

HF BR-5103 Rx.)

tain ed a 0.1-µF capacitor at the


series with t he Vcc line, an d a

0.1-µF capacitor on th e oth er sideof th e inductor. (These compo-

nent s ar e labeled C1, L1, C3 in

the dat a sheet). This filter does

not contain t he 10-µF

low-frequ ency filter capacitor,

C4, present in Figure 11 (or 7)!

Figure 12 shows that th e Vcc

noise problem ar eas a re confined

to the frequencies where t he

external Vcc filter resonat es, at

aroun d 440 kHz. Even this

worst-case point h as less tha n a

1.4 dB sensitivity penalty.

In a real a pplication circuit, C4

will be present. This 10-µF

capa citor will greatly att enua te

an y low-frequen cy noise con-

ducted from t he system Vccpower sup ply circuit ry. If th e

resistance from the Vcc supply to

the m odule Vcc filter is 0.2 ohm

for example, the 10-µF capacitor

will form a filter with a 79 kHz

bandwidth . At 440 kHz, the 50

mV noise, from t he system Vccpower sup ply, will be atten ua ted

less tha n a 0.3 dB penalty for a

50 mV p-p noise signal in a real

application circuit.

In a real ap plication, if it tu rn s

out t ha t very low frequency noise

is present, an d needs to be

filtered, a 10-µF capacitor in

par allel with th e 0.1-µF C1 at

th e Rx module Vcc pin would

provide th is additional

low-frequ ency filterin g. We ar e

fairly certain that this extra 10

µF will never be needed in th e

vast majority of the HFBR-510X/

520X transceiver applicat ions.

(Therefore this extra 10-µF capaci-tor is not shown in th e recom-

mended data sheet power supply

Vcc filter .) Most applications, using

the recommended data sheet Vcc

power supply filtering, should never

experience any problems in the

fiber-optic link operation due to Vccnoise.

Figur e 9 shows th e Rx Vcc noise

sensitivity penalty without th e

externa l Vcc noise filter recom-

mended in F igure 11 of theHF BR-510X or Figur e 7 of the

HFBR-520X data sheet. The

noise is conducted , via th e 1-ohm

resistor, directly into the module

Rx Vcc pin. The plot shows th at

th e tra nsceiver module Rx

internal Vcc filtering network

filters out almost all of the noise

above 15 MHz on its own.

Therefore, the Rx has less th an a

0.2 dB Vcc noise sensitivity

penalty above 15 MHz. Figure

10 shows that less tha n a 1 dB

pena lty below 15 MHz is

present, even without an y

externa l Vcc filter.

Figure 11 shows that an external

Vcc filter can really move any

noise problems th at m ight be

present down to much lower

frequencies. For this plot, the

externa l Vcc filter tested con-

20



to a 9 mV noise signa l at t he

module Vcc filter conn ection. An

educated guess indicates th at the

sensitivity penalty will probablybe less tha n 0.3 dB at 440 kHz.

So the conclusion is that unfil-

ter ed low-frequen cy noise can

affect t he r eceiver if it r eaches

the module pin. Still, even the

Figu re 10. HFBR-510X/520X Vcc noise performance with no external Vcc filter

0 to 50 MHz.

worst possible scenario has less

th an a 1.4 dB penalty for a 50

mV p-p noise signa l.

With good Vcc noise filtering on

th e Rx Vcc conn ection per the

dat a sheet r ecommendat ion of

figur e 11 (or 7), th e rea l system

should have less than a 0.3 dB

penalty t o a 50 mVp-p Vcc noise

signal. (Such a Vcc noise signa l

could be generated somewhere

else in th e customer’s system an dthen condu cted over to the

fiber-optic module Vcc via th e

Vcc power sup ply bus). Note

that it is impossible to perform

the Vcc noise immun ity test with

C4 (10 µF) present because the

low ac impedan ce makes it

difficult to apply 50 mVp-p of

noise on Vcc with conventional

sine wave genera tors and AC

coup ling. Also, at t his point , th e

test does not really determine

what would happen in an actualcust omer applicat ion du e to the

un cert aint y of what t he Vcc line

impedance would be an d how

much filtering t he 10-µF capaci-

tor would really provide. The

gener al conclusion for now is

that the HFBR-510X/520X Vcc

noise rejection, in the real

app licat ion circuit, will be good

enough so that most applicat ions

will not suffer any noticeable

degrada tions in the fiber-optic link

performance due t o Vcc noise.

5.0 ConclusionsIt is no surprise that t he


modules have excellent electro-

magnetic compatibility because it

was ta ken int o accoun t ear ly in

their design. Over th e years, we

ha ve learn ed a lot about EMC

an d made a great dea l of im-

provement s in th e design of

fiber-optic modules t o sat isfy our

cust omers' needs t o meet global

EMC requirements. The inte-

grat ed circuits used in the

modules are designed to reject

Vcc noise. The circuits are also

designed t o be as different ial as

is possible in order to help reduce

Vcc noise generat ion a nd t o help

improve the Vcc noise an d

sus ceptibility n oise r ejection.

The intern al edge ra tes inside

21

1.0

0.8

0.4

0.6

0.2

0 L E F T E Y E E D G E 1 ×

1 0 - 6 B E R S E N S I T I V I T Y P E N A L T Y I N d B F O R

V c c N O I S E C A S E v s . N O

V c c N O I S E C

A S E

0 50 100 150 200 250 300Vcc NOISE FREQUENCY, MHz

1.0

0.8

0.4

0.6

0.2

0 L E F T E Y E E D G E 1 ×

1 0 - 6 B E R S E

N S I T I V I T Y P E N A L T Y I N d B F O R

V c c N O I S E C A S E v s .

N O

V c c N O I S E C A S E

0 5 10 15 20 25 30 35 40 45 50

Vcc NOISE FREQUENCY, MHz

Figure 9. HFBR -510X/520X Vcc noise performance with no e xternal Vcc filter.



the ICs ha ve been carefully

limited t o help reduce the

rad iated emissions. Special

module packaging techniques,

including inter na l shielding, are

used t o reduce the emissions

from the transmitter a nd to

improve the susceptibility of the

receiver. The modular print ed

circuit board u ses good

high-frequency layout techniques

that reduce loop sizes to improve

emissions, susceptibility and Vcc

noise.

All th ese improvement s were

mad e while keeping the m odule

cost low. The cost of th e EMC

improvement s is a small percent-

age of the overa ll module cost

an d we think customers will find

it well wort h it when t hey

consider the m oney an d time it

saves th em in th eir final product

design an d man ufacturing cost.

The HF BR-510X/520X tra ns-

ceiver m odules will make th efinal product easier t o meet EMC

complia nce, will ma ke it less

likely for the final product to

experience strange intermittent

intern al EMC-related perfor-

man ce problems an d, if th e


module EMC per forma nce is

tak en a dvant age of, will allow

cheaper lower-cost shielding to

be used in th e final product.

The HF BR-510X/520X tra ns-ceiver module EMC performance

is sum ma rized below.

The module’s rad iated em issions

typically passes worldwide B

limits (FCC B, CISP R 22B, EN

55022, an d VCCI Class 2) by

more tha n 10 dB. One unit in a

computer system will not cause

this syst em t o fail th e worldwide

radiated emissions limits, for

either the home or office usage

environments, no matter how

poor the shielding is. The

excellent m odule emissions level

allows the best attempt at u sing

a lar ge num ber of modules in

concentr at or a pplications while

still allowing th e concentra tors t o

pass ra diated emission limits.

The susceptibility is basically

zero for 10 V/m fields. Becau se

of th e module’s high imm un ity,

22

Fi gu re 1 1. HFBR-510X/520X Vc c n o i s e p e r f o r m a n c e w i t h 0 .1 µF , 1 µH,

0.1 µF external Vcc filter (C1, L1, C3 in the data s hee t).

1.4

1.0

1.2

0.6

0.8

0.4

0.2

0

L E F T E Y E

E D G E

1 × 1

0 - 6 B E R

S E N S I T I V I T Y

P E N A L T Y

I N

d B

F O R

V c c N O I S E

C A S E

v s . N O V c c N O I S E

C A S E

0 50 100 150 200 250 300

Vcc NOISE FREQUENCY, MHz

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

L E

F T E Y E E D G E 1 ×

1 0 - 6 B E R S E N S I T I V I T Y P E N A L T Y I N

d B F O R

V c c N O I S E C A S E v s . N O

V c c N O I S E C A S E

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.54.0 5.0Vcc NOISE FREQUENCY, MHz

Figu re 12. HFBR-510X/520X Vc c noise performance w ith 0.1 µF, 1 µH, 0.1 µF

external Vc c filter 0 to 5 MHz (C1, L1, C3 in the d ata sh eet).



the customers n eed not worry

about the effects of nearby

circuits on th e receiver. Fields

generat ed externa l to th e com-put er system ar e also not a

worry. Only very lar ge ESD

events could generate a 10 V/m

field, so the concern about ESD

zaps causing bit errors is mini-

mized. This unit is suit able for

use in Class 3 severe electromag-

netic radiat ed field environment s

as described in the IEC 801-3

specification.

The crosstalk from the transmit-

ter to the receiver in t he tr ans-ceiver modu le is virt ua lly zero.

Thus the operat ion of the Tx in

the tra nsceiver will not a ffect t he

operation of its neighboring Rx

in the sa me tra nsceiver un der

an y circum sta nces.

The E SD test is conducted per

the MIL-STD-883D Method

3015.7 specificat ion. The


modules withs tan d 1800 V

hu man -body model electrosta ticdischarge to any combination of

pins with no perman ent dam age.

The m odules a re classified as

MIL-STD Class 1 E SD compo-

nent s, but a re close to the 2000

Volt Class 2 minimum limit.

These tr an sceivers also with -

sta nd a 100 Volt level to the

Japanese EIAJ#1988.3.2B

Version.2 Machine Model ESD

test.

When th e tra nsceiver is inst alled

in th e applicat ion circuit, the

module withst an ds a 25 kV ESD

zap to anywhere on th e module

with no permanent dama ge. It

should not be dama ged by an y 25

kV human body zap in any

compu ter system a pplicat ion.

This is a variat ion of the IE C

801-2 test. A ra re ESD directly

to the module tha t condu cts

current thr ough th e module can

cause some bit errors but th e

module r ecovers ver y quickly.

In t he r eal application circuit,

with the da ta sheet recom-

mended power supply filter, 50

mVp-p of Vcc noise should cau se

no more than a 0.3 dB sensitivity

penalty, no matter what the Vccnoise frequ ency is. Most Vccnoise frequ encies will cause zer o

penalty. In most applicat ions

th ere sh ould be no noticeable

effect on the fiber-optic link

perform an ce due t o Vcc noise.

References

[1] Hewlett Pa ckard Optical Communica-

tions Division. FDDI and 100 Mbps

ATM T ransceivers in L ow Cost 1x9

Package S tyle. Technical Data.

HFBR-5103 1300 nm 2000 m.

HFBR-5104 800 nm 150 m . HFBR -5105

1300 nm 500 m. 1994. H P OCD.

[2] Hewlett Pa ckard Optical Communica-

tions Division. ATM Multimode Fiber

Transceivers For S ONET OC-3/ SDH

S TM -1 in Low Cost 1x9 Package Style.

Technical Data. HFBR -5203 800 nm 150m. HFBR-5204 1300 nm 500 m.

HFBR-5205 1300 nm 2 km . 1994.

HP OCD.

[3] Henry W. Ott. Noise Reduction

Techniques in E lectronic Systems 2nd

Edition 1988. John Wiley & Sons.

[4] Various authors. Test & Design

Magazine. Argus Business.

[5] Depart ment of Defense. United

Stat es of America. Military Stand ard.

Test Methods and Procedures For

Microelectronics. MIL-STD-883D Method 3015.7 1991. Rome Laboratory

AFSC.

[6] Bureau Centra l de La Commisscion

Electrotechnique Internationale IEC

International Stan dard 801-2. E lectro-

ma gnetic Com patibility For

Industrial-Process Measurement and

Control Equipm ent. Part 2 Electrostatic

Discharge R equirements} Second

Impression 1987. Interna tional

Electrotechnical Commission.

[7] Bureau Centra l de La Commisscion

Electrotechnique Internationale IEC

International S tand ard 801-3. Electro-

ma gnetic Comp atibility For

Industrial-Process Measurement and

Control Equ ipment. Part 3: Ra diated Electroma gnetic Field R equirements}

Third Impression 1992. Interna tional

Electrotechnical Commission.

23



For more information call:

United States*

Europe*

Far Ea st/Austr alasia: (65) 290-6305

Can ada : (416) 206-4725

J apa n: (813) 3331-6111

* Call your local HP sa les office listed

in your teleph one directory. Ask for a

Components representative.

Data Su bject to Change

Copyright © 1994 Hewlett-Packard Co

h H

Documents

HP-AN1075_Testing and Measuring EMC Performance of the HFBR-510X_520X