ENGINEERING
REPORTS
Amplifier*
Operational
JE-990Discrete
DEANEJENSEN
North Hollt'v,otxl
JcnsenTrunslbrmers,
, CA 91601, USA
O INTRODUCTION
JE-990, cxccpt firr a technicaldata sheeton a 170-kHz
bandwidthnricrophoneinput transformer(JensenTransThe performanceof a number of popular audio intewith the
fomrers)dcsignedfirr optinrumnoiseperfcrrmance
grated-circuit
operationalamplifiers,such as the NE-5534,
JE-990operationalamplifier.Full-sizedetailedgraphsof
HA2625,and LM3l8, hasbeendescribedby JungI I ]. The
thoseshownin this text areavailablefrom the author.
presentpaperpresentsa discreteoperational-amplifier
circuit which exhibits lower noise voltage,distortion,gain
1 GENERAL DESCRIPTION
error,outputimpedance,and responsctinrc (delay)as well
as higherslew rate, output voltage,outputcurrent,phase
The JE-990<lperational
arnplifieris a discreteuniversal
margin(stability),and gain- bandwidthproductthanmost
gainblockin thestandardsingle-triangle
configuration
with
of theseintegrated-circuit
operationalamplifiersand also
one noninvcrtinginput, one invertinginput for feedback,
thanmostearlierdiscreteoperational
amplifiersin common andone singlc-cndcd
outpul.The principalobjectiveofthe
use for audio applications.The developmentof this amdevcloprnentwas t() synthesizea stablehigh-performance
plifier, calledthe JE-990operationalamplifier,involveda
operationalarnplifierwhich would take advantageof the
data,and
carefulmixtureof texttxloks,laboratory-collcctcd
of the National
low-noisc and matching characteristics
pairtransistort2l - t4l
computercalculations
and graphics.Its applicationmay be
[,M394 supermatch
Semiconductor
consideredwhere some of theseparametersarc to be improved.
2 NOISE CONSIDERATIONS
l) Input stagefor any applicationwherethc sourceim2.1 The Input Device
pedanceis 2500 f,) or less,
2) Line outputamplifierfor drivinga 75-O loadup to an
The LM394 is actuallya monolithic integratedcircuit
rms voltagelevel re 0.115 V of +2-5dB, which is an rms
per sectionare
with 100transistors;
25 pairs(50 transistors)
voltageof 13.8V anda peak-to-peak
voltageof 39 V,
randomlyintsrconnected
in parallelto take advantageof
3) Summingamplifier,
statisticalvariationsand random cancellationof offsets.
4) Active filtersrequiringa high degreeol'stability,
The matchingratiosinlproveproportionallyto the square
5) Laboratorypreamplifierfor extendingthc sensitivity rclotof the nunrberof transistors.
Extrinsicemitterandbase
of noiseor distortionmeasurements.
resistances
are much lower than thoseof other available
and
You canbuildthecircuityourselffrom theschematic
transislors,
eithermonolithicor discrete,giving extremely
partslist given here if you have the necessary
equipment low noise. To guaranteelong-termstabilityof matching
anddetermination,
oryou canobtaina listof known sources parameters,gain, and noise, internalclamp diodeshave
of manufactured
990 amplifiermodules.r
beenaddedacrosstheemitter- basejunctionofeach transThe circuit is "public domain" and can be usedfor any
istor. Thesepreventdegradionfrom reverse-biased
emitter
purposewithout licenseor permission.Beyond this text
current,the mostcommoncauseof fieldfailuresin matched
thereare no availableapplicationnotesspecificallyfor the
devices.The parasiticisolationjunction formed by the
diodesalsoensurescompleteisolationbetweendevicesby
'Manuscript received1979July 9; revised1979Scpt. 27.
I Sendwritten requestfbr 990 sourcesto: JcnsenTransformers,
clampingthe substrate
regionto the most negativeemitter
1 0 7 3 5B u r b a n kB l v d . , N o r t h H o l l y w o o d .C A 9 l 6 0 I .
t2,31.
V .O L U M E 2 8N
. U M B E R1 / 2
JOURNALOFTHEAUDIO
E N G I N E E R I NS
GO C I E T Yl.g s o J A N U A R Y / F E E B U A R Y
CAODISCRETEOPERATIONALAMPLIFIER
ENGINEERINGREPORTS
2.2 Optimizingthe Input-Transistor
CollectorCurrent
To determine an optimum collector current for the
LM394 input pair, we measured'thenoise performancetn
our laboratoryfrom severalsamples,using models.techniques,and computerprogramssimilar to thosegiven by
of the
Motchenbacher
and Fitchen[5]. Two measurements
noisein a2}-kHzbandwidth,one with a shortedinput and
the other with a known sourceimpedance,were taken at
eightcollectorcurrentsrangingfrom 400 pA to 4 mA. The
2O-kHz bandwidth data for each collector current were
first convertedto a valueof noise-voltage
spectraldensity
and of noise-currentspectraldensity with a noise-model
program.Then a polynomialregression
progtramwas used
t o a v e r a g eo u t a t y p i c a lv a r i a t i o n si n t h e s a m p l e sa n d
measurements.
The resultingsmoothednoise-voltagespectraldensity
versuscollectorcurrentis shown in Fig. I, and the noisecurrentspectraldensityversuscollectorcurrentis shownin
Fig. 2. From thesedata, valuesfirr five collectorcurrents
programto calculatethenoise
wereusedin the noise-nrodel
for eachof thc five collccindexversussourceac resistance
tor currents.Fig. 3 showsa plot of this calculationfor thc
casewhere the two sectionsof an LM394 are used as a
differentialpair. Fig. 4 shows the casc whcrc the two
sectionsof an LM394 are parallclcd,and two of thesc
constitutethe dill'erentialpair. Notethat usingtw()dcviccs
insteadof one resultsin a noisereductionof 0.5 dB tirr a
ec
s o u r c ea L r^e s i s t a n coef 1 2 5O a n do f I . 0 d B f i r r a s ( ) u r c a
NorsE voLract SpEcrRAL otNSrIy/[.v,/H-
resistanceof 3 I . 5 O. The valueof the ac resistancein these
at the noninverting
graphsis the sum of the ac resistance
inputandtheparallelvalueofthe seriesandshuntfeedback
resistors.
It is importantto note that the ac resistanceof many
Furthermoreonly
sourcesis greaterthanthe dc resistance.
resistivesourcesarenrodeledin thiscalculation.With some
magneticdevices(for instance,magnetictapereproducing
heads)both the reactanceand the ac resistancerise with
increasingtiequency. For such devicesa more complex
model shouldbe used,taking into accountboth the reacand
tanceof the sourceand the changeof both resistance
with fiequency.
reactance
The graphicfirrm of the dataof Figs. 3 and4 is usefulto
determincthe optimunr collectorcurrent for a range of
C)urnlr-asurenrcnls
agreewith the pubsourceresistances.
. o t et h a t
l i s h e dv a l u e s[ 2 l a t t h o s ed a t ap o i n t st h a tc o i n c i d eN
the valueof I .6 nrA is a go<xlbalancefor a low noiseindex
withoul an unnccessary
increaseat high
at low inrpedances
This "highest reastlnable"collectorcurrent
impedances.
lavorsa high slew rateol' ltt V/ps, but causesa fairly high
i n p u tb i a sc u r r e n <
t t f2 . 2 1 ; - A .
]
F i g . 3 . N o i s c i r r t l c r v c r s u s s ( ) u r c ca c r c s i s t a n c c t i r r a d t f l c r c n t i a l
p u r r o l ' l r a r r s i s t o r sw, h e r c c a c h t r a n s i s t o ri s o n c h a l f o l a n t - M 1 9 4 .
C a l c u l a t c d l r o r r a n r c u s u r en r c n t i n a 2 0 - k H z b a n d w i d t h . P a r a t n c {cr: col lccl0r currenl.
Fig. l. Noise-voltage spcctral dcnsity vcrsus collcctor currcnt
f c r r a s i n g l e h a l f - s e c t i o n o f a n l - M 1 9 4 . C a l c u l a t c d f r t t t t . ta t t t c a surementin a 20-kHz bandwidth.
N o s E . C U R R € N T5 P E C l R A LO E N S I I Y / I 9 A / / I I ' ]
o.9
o.e
o.7
o6
o.5
2r
05
q63
0.a
.o
2a
r6
t o
2.4
1.5
C O L L E C I O RC U R R N
f ', imAl
Fig. 2. Noise-current
spectral
lirr
densityvcrsuscollcctorcurrcnt
a singlehalf-sectionof an LM394. Calculatetlfionr a measurementin a 20-kHzbandwidth.
li 5
t, l
25
25O
o
hLt a
500
qL5'laNLL
lOl
lirr a dillerential
Fig. ,1. Noisc intlcx vcrsussourcci.lcrcsistance
nair ot' transistors.whcrc cach transistoris both halvesof an
in a 20-kHz
i-HAfC+in parallel. Calculatedf'roma nreasurcment
bandwidth.Pararnctcr:
collector currcnt.
V ,O L U M E 2 8N
, U M B E R1 / 2
J O U R N A L O F T H E A U D I O E N G I N E E R IS
NO
GC I E T Yl,g s 0 J A N U A B Y / F E B R U A R Y
ENGINEERING
REPORTS
JENSEN
With one LM394 at a collectorcurrentl t 0 nrA the
noisevoltagespectraldensityis 0.8 nV/VHz per transistor, or l.l3 nV/yEi for a differentiglpair; ancla noisec u r r e n ts p e c t r adl e n s i t yo f 1 . 0 p A l V H z y i e l d sa 0 . 6 - d B
noise index at the optimurn sourceresistanceof I kO.
Above 8 kO the noiseindexexceeds2 dB. andat -50kO thc
n o i s ei n d e xi s 6 d B . S o a h i g h - i n r p e d a n icned u c t i v cs ( ) u r c c
may exhibit rising high-liequencynoise.Thc noise ctrntributionof the secondstaseis lessthan 0.5 dB at unity
gain.
The equivalentinputnoisevoltagelevcl ol'thc conlplcte
JE-990 operationalarnplifieras a tunction ol sourceac
resistance
is shownin Fis. -5.
2.3 Noise Measurement Filters and Corrections
bandwidthwas linritcdwith an
The noisemeasurernent
8-pole (4tt-dB per octavc) active low-passfilter [61. Ttt
thc data, a singlc-polchighexcludehum from aft-ecting
passfilter at 800 Hz was used.This reduccsthe bandwidth
by 500 Hz l80OHz./(n/2)1,requiringa
of the measurement
+0.1 | dB corection t() rcstorethc clatato 20-kHz bandwidth. The hurn filter also rcntovesthc low-frcquencyl/l
noiseof the arnplifier.We vcrified,however,that thc l/l
noise of the JE-990 operationalanrplificrcontribulesan
insignificantpart of the noise lirr the total 2(lkHz bantlwidth.
The voltnrctcr used was a Hcwlctt-Packard4(X) Ft.,
which is an averagercspondingrcctifierwith a scalccalibratedfor the rms valueo1'a sinc wave. For the Gaussian
noisewaveforma correctionlevel of + | .0-5dB has bccn
addedto give the equivalentnns valuettf noiscvoltage.
uratetransicntrcsponse.Enritterresistorsof 30 O are recluiredfirr high-frcqucncystability,but theseincreasethe
noisevoltagelevel nrorethan 3 dB abovethe cascwithout
ernitterresistors.To preventthis noisc increase
, enritter
inductorscanbe placedin paralleI with thecmitterresislors.
of 20-pr.H
inductorsis 30 O at 240 kHz; soat
The impcdance
is 30O.
f
r
e
q
u
c
n
c
i
e
t
s
h
c
highcr
c r n i t t e rc i r c u i t i m p e d a n c e
l
o
w
e r st h e
i
n
d
u
c
t
o
r
But al l0 kHz thc 20-pH, 2-5-rn0
O
.
T
h
i
s
r
e
d
u
c
e
t
s
h
en o i s e
c n r i t t e cr i r c u i li r r r p e d a n ct oe 1 . 3
v o l t a g el ev c l i n a 2 0 - k H zb a n d w i d t h
t o w i t h i n0 . 4 d B o f t h e
c a s cu i t h o u te r t t i l l c r t s i s t o r s .
'l'he
ol'thc t,M394 a( a collectttrcurenriltcrirrrpedancc
'l'his
r e s u l t si n a f i r s t - s t a gsei n g l e r c n to f I . 6 r n A i s I 6 O .
p o l cr c s p o n su
and 10.4-o
c p t o 8 3 k H z , w h e r ct h e 2 O - t r l H
irnpcdanccre r() crcalcsa lwo-polc responseto 240 kHz..
wherc thc 20-ptl and ,lO-O inrpcdanccpolc createsa reto thatof a singlcpolc.
sp()nsczcro,rcturningthc rcsp()nse
3 STABILITY ANALYSIS
3.1 Open-Loop Response Compensation
'l-hc
s c h e r r r a t iocl ' t h e J B - 9 9 0o p e r a t i o n aal r n p l i l i e ri s
s h o w ni n f r i g . 6 . - l i r h c y c t a l . l 7 l a n d R o b c r g cI t i l d i s c u s s
'l-hc
p h a s cn r a r g i nc r i t e r i o nf i r r a
s t a b i l i t ya n a l y s i si n d c t a i l .
" u n i v c r s a lg a i n b l o c k " s u g g e s t ctdh c n r e r i t so l ' a M i l l c r c ( ) n l p c n s a t tcwd( ) - s l a uacr n p l i t i c rI.n i t i a l l yt h cp o l e sr e c l u i r i n g c o r n p c n s a t i our' ct r ck r c u t c tbl y o b s er v i n gt h eu n i t yg a i n
a d j u s t i n gR 9 . T h e l i c q u c n c i c s
t r a n s i c n tr e s p o n s c
"vhile
w c r ei n p u ta st h ec o c l f i c i c n (osl ' a l r a n s f ' cl 'ru n c t i t tgni v c ' ni n
t h c H c w l c ( t - P a c k a r d ' l ' r a n sFl curn c t i o nA n a l y s i sp r o g r a l n .
'Ihe
o u t p u ti s u s c l c c t i o nt l l .l o p o l o g i c sw i t h v a l u e s( o s y n t h e s i z et h c r c s p o n s feu n c t i o n .W i t h t h e z c r oo f R 9 a n d C l
c o i n c i d i n gw i t h t h c u n i t y g a i nf r c q u e n c y . lt,h, es y n t h e s iiss
2.4 Preventing NoaseDuetothe Emitter Resistors
c o r n p l e t eicnlt h cc r n i t t c cr i r c u i to l ' Q 6w i t h C 2 , C 3 , a n dR t i .
and analyzedin the laboraThc arnplilicrwas constructed
The noisegraphsshowntirrthe LM394do not includethe
t
h
c
r
c
s
u
l
t
i
n gu n i t y - g a i nf r e q u e n c y . l , ,
t
l
o
c
u
r
r
r
e
n
t
t
o
r
y
t
o
limit
to
noisedue to theemitterresisttlrswhich arercquired
Then an itcrative
phasc
transicnt
rcsponsc.
nrargin,
antl
stage
in
the
case
product
of
the
first
the gain-bandwidth
c
o
n
l
p
o
n
e
n
c
t
h
a
n
g e sa, n d n r e a s u r e s
e
r
i
e
s
o
f
c
a
l
c
u
l
a
t
i
o
n
s
,
zero-itnpedance
input
to
a
that someoneconnecls the
of the threczeros
to
the
ticque
ncies
was
usctl
ad-iust
ments
resistanec,
source.If this is donewithout sufficien(enritter
o b t a i no p t i m u m
p
o
l
c
o
f
c
o
r
u
p
e
n
s
a
t
i
o
c
n
i
r
c
u
i
t
t
o
t
h
e
a
n
d
t
h
e
insullicicnt
wrll
causc
other
stagcs
the time delay of the
phascrnarginand transicntrcsponse
. This rnethodensures
phasemarginof thefirststagefrrrunity-gainstabilityandac
not isolatedand identified
that any rcsponsccharactcrislics
s c l u d e di n t h e o p t i m i z a l i n g a r c n c v e r l h e l c si n
in thc nrode
T
l
4
I
I
T
Fig. 5. Equivalent input noisc voltagc lcvcl ol thc conrplcte
J E - 9 9 0 o p c r a t i o n a l a m p l i f i c r v e r s u s s ( ) u r e cu e r c s i s t a n c c . C a l c u l a t e d f r o m a m e a s u r c m e n ti n a 2 0 - k H z b a n d w i d t h . N o i s c l e v c l o l a
t h e o r e t i c a lr e s i s t o r i s s h o w n l i r r r c f c r e n c e .
tlon.
The result r!:Jcsa eapacitor and a serics RC network
acrossthe crrri' r tc:;istrlrot-Q6 ttt crcate two zeros, onc at
3 . 3 M H z i l D do 1 ' 1r'r t2 5 . 4 M H z , w i t h a p t l l e a t 5 . 8 M H z . T h e
'Ihe
H-P AC CircuitAnalzcrool ll9 a. . i is at ti. I MHz.
ysi; (C'N,,\l' l)i()gl-ilillr','asusetl to tnodel the responseand
to balance tht: ilrrpcdanceratio of the f'eedbackand entittcr
circuits of the scconclstage to give a 4-5"phase margin by
adjusting L to approrirnately | /Kf , where T is the amplifier
r e s p o n s et r n l e .
The resulting resp()nsemagnitude (Fig. 7) and phase
angle (Fig. tJ) show a unity-gain frequencyf, of l0 MHz
with about 38" phasc n.rargin,increasingto above 60" below
2MHz, including the region of the first-stageemittercircuit
83-kHz- response polc- and 240-kHz, response zero. The
gain-bandwidth product is greater than 50 MHz in the
l0-kHz to 100-kHz range and 25 MHz in the I -MHz range,
YO
, L U M E2 8 , N U M B E R1 / 2
GO C I E T Y1, 9 8 0J A N U A R Y / F E B R U A RV
J O U R N A LO F T H E A U D I OE N G I N E E R I N S
JE-990DISCRETEOPERATIONALAMPLIFIER
ENGINEERINGREPORTS
must have an input capacitanceCs6 lower than the Jedec
specificationin order to achieve the short responsetime
which favors good phase margin, stability, and transient
with an increasingrate of attenuationto the actual frequencyof unity gain, l0 MHz.
The transistorsfor Q5, type 2N4250A or PN4250A'
1 l
I
,rorr;
\.
I
aR8
3oon
f
| ";'
$.
.)
I
lr 1
cR4
- tN
t'1
C}
,'
Y.I
ol
:;,,
t
'"'"""fl
f,.
l*,"
,ru\zv
Rrs
I
l' 3 e n l
t00 j
L3
40 ltq
I ",'r,
r
I
to LoAD
]ezr.
I
I
I
Y
lcRT
I:-"
^ FEED
eac*
-[
I
',
l'*u
d
6 . S c h en r a t i c d r a w i n g o l ' t h e J E - 9 9 0 o p c r a t i o n a l a m p l i f i e r
JE-990 Operational Arnplifier: PartsList
Quantity
Circuit#
ldentification
I
Ql,2
Q3,5,6
Q4,7
Q8
LM-394H
2N42-50A,PN42-s0A
2N2484,PN24U4
M J E -l t i l ( r )
M J E - l 7 l( l )
lN9l48
30()
160f)
3
2
I
I
t2
2
I
3
I
I
I
2
I
2
Qe
cRl-12
Rl,2
R3
R 4 , 5n
,
R6
R7
R9
Rl0,lI
Rl2
R13,r4
Rl5
CI
C2
c3
C4.5
2
Ll.2
2
lL3
ThermalCouplingAids
(t)
2
(t)
2
(t)
2
I
(l)
(6)
Manufacturer
Description
l ttoo
130()
62k o (2)
l100
3 . 9o
39O (-5)
l50pF-5c{
62pF5va
9 l p F5 7 a
o.l p.F
2op.H(a)
4 0 p H( 5 )
Dualnpn translsl()r
pnptranslstor
npn transistor
npn transrstor
pnp translstor
Ditxlc
R e s i s t o r 5 T cl /,4 W
R c s i s t o r 5 %l,/,4 W
Resistor5%,,l/4 W
Resistor5olc,l/4 W
R e s i s t o r 5 %l ,/ ,4 W
Resistor57c, l/4 W
Resistor-57c,l/4 W
Rcsistor5o/r,l/4W
R e s i s t o r 5 %l,/,4 W
IW
Resistor-5%,,
Capacitor
Capacitor
Capacitor
CapacitorCY20Cl04P
Shieldbead26132251| |
lnduckrr
NationalSemiconductor
NationalSemiconductoror Fairchild
or Fairchild
NationalSemiconductor
Motorola
Motorola
Fairchild
Amperexfilm
Amperex film
Amperexfilm
Amperexfilm
Amperexfilm
Amperexfilm
Amperexfilm
Amperexfilm
Amperexfilm
Allen Bradley
3/32wirearea
2-56x l/4
2-56x3/16xl/1
4951or 4952
256D
C I a m p# C - 2 0 1
Screw# KF-461
Nut # KF-554
Thermaladhesive
Brassclip
Waldom
Waldom
Waldom
Thermalloy
Wakefield
3m0
2 kf)
Ccntralab,/USCC
Fair-RitcProd.
Notes:( I) CR9 mustbe thermallycoupledto Qtl with clampor adhesive
CR l0 mustbethermallycoupledto Q9 with clampor adhesive.
( 2 ) R l 0 , I I : 6 2 k O f o r b i p o l a r 2 4 - V s u p p l yR.l 0 , l I : 3 3 k O t b r b i p o l a rl 5 - V s u p p l v .
(3) R4,5may be trimmedfordc balance(alsoaffectsslewsymmetry).
(4) L I ,2 starterkit with sampleassemblyis availablefrom Jensen.
(5) L3 (40 tums #30 wire woundaroundR I 5) is availableassembled.
(6) Wakefieldbrassclip canbe uscdto thermallycoupletwo transistorsfirr Q3 andCR3 (seetext)
1/2
28,NUMBER
VOLUME
1980JANUARY/FEBRUARY,
SOCIETY,
ENGINEERING
OFTHEAUDIO
JOURNAL
ENGINEERING
REPORTS
JENSEN
havebeen
response.
Fairchildand NationalSemiconductor
testedand used;other types with the same part number
without analysisof the resultcannotbe safelysubstituted
ing response
tinreandphasemargin.
3.2 Closed-LoopResponseCompensation
The JE-990 operationalamplifier is unity-gainstablc.
The only overshootremainingwith a dirr-ct c()nnection
from theoutputto the invertinginputis the servortvershoot
causedby theamplifierresponse
time of about l5 ns. If the
circuit precedingthe JE-990 is equivalenttu a low-pass
filter of 4 MHz or less,thercis no ovcrshootat unity gain.
Componentvariationsmay causc sorne ringing ncar l0
M H z , w h i c hc a nb e m i n i n r i z c db y a d j u s t i n g
t h ev a l u eo f R 9
by no morethan5%'.
Feedbackzcro c()mpensation
as shown in Fig. 9 is rccommended
A
c
a
p
a
c
i
t
o
Cr 1 i s c o n n e c t eadc r o s st h c
1 8 1 1. 9 1
seriesf'eedback
resistorRr to crealea phaselead(advancc)
in the f'eedbackto avoid servo overshrxrtcausedby thc
'fhis
responsetime of the amplifier (about l-5 ns).
dclay
causesthe feedbackto arrive late, during which tinrc thc
o u t p u te x c e e d st h e e q u i l i b r i u nar m p l i t u d .e A l s o t h e t r a n s i e n tr e s p o n s a
e t l o w c k r s e d - k x rgpa i n w i l l e x h i b i to v e r translerfunction( l/p) docs
shootif the invertcdt'eedback
not cxhibit a pole at a liequencyreasonablykrwcr thanthe
'Ihc
trequencyof interccptwith the open-looprcsponsc.
J E - 9 9 0w i l l e x h i b i tn o o v e r s h o owt i t h u p t o 4 5 - d Bc l o s c d '
in
loopgain with feedbackzero(phaselead)cornpcnsation
t h e f e e d b a c ko f z r : R r C r : 1 . 3 p s . T ' h i sy i c l d s a
o f 1 2 0k H z . T h e v a l u eo l ' t h ec a r r a c i t oi sr c a l c u
bandwidth
tdFl
lated as Cr : 1.3 p.s/R, Ifarads]. At 40-dts closed-loop
gain, rr : 0.9/.r.stirr a bandwidth of l7-5 kHz.
For applications where 120-kHz bandwidth is sufficient,
Rs and C1 can be fixcd values, and (6un, can be ad-justedto
control closed-l<lopgain frorn 6 dB to 45 dB with nearly
constant bandwidth and accuratc transicnt response.
For applications whcrc lhe nraxinrumrclosed-ltxtp gain
required is less than .1-5
dI], thc bandwidth can be increased
by reducing the L.l-g.s tirllc constant. Thc requircd comp e n s a t i o ni s d c t c r n r i n e d i n i t i a l l y b y c a l c u l a t i o n t i o m t h e
ficqucncy ol interccpt and thc amount of f'cedbackchosen
lirr thc frcqucncy rangt: abovc inlcrcept l9l. Then the value
i s f i n a l i z e d b y o b s e r v i n g t h c s n t a l l - s i g n a lt r a n s i e n t r c 'l'hc
f'rcqucncyof intcrccpt is the intcrsectionof thc
sponse.
open-loop gain and thc uncontpensatedinverted f'eedback
'I'hc
l'unction(l/0).
lnr()un[ of tccdback choscn firr the
f'rctluencyrangc above intcrccpt could initially bc sct at 2
'l'he
( 6 d B ) o r I . ; 1l . t ( 3 d B ) .
p o l c f r c q u c n c yt i r r t h e i n v e r t c d
t'ecdbacklirnction is thc interccpt I'requencydivided by thc
l'ccdback voltage ratio. Convcrt lhe frequency into a timc
c()nstantby r, - t /(InJ ).'l'hcn thc compensation capacitor
is delcrnrinctl by ('r - r,./R1. ['hc value is finc-trinrrnedby
o b s c r v i n gt h c s r n a l l - s i g n atl r a n s i en t r e s p o n s t. :
I f v a r i a b l c g a i n i s r e a l i z e db y a d j u s t i n g R , w i t h R . n , , n ,
l i x c t l , t h e c l o s c d - l o o pr c s p ( ) n s cw i l l a l w a y s b e c l o s e t o t h c
r n a x i r n u r na l l o w a b l c f i r r s t a b i l i t y a n d a c c u r a t c t r a n s i c n t
r c s p ( ) n s cN
. o t e t h a t s i n c c t h c b a n d w i d t ha n d t h e g a i n d o n o t
l r a c k a c c u r a { c l yu t l o w c l o s e d l t x r p g a i n , t h c l r a n s i c n t r e sponsc rtrusl be obscrvcd al low gain to dctcrnrinc the
rrraxinrurn
a l l o w a b l c g a i n - b a n c l w i d t ht h a t t h i s n r c t h o dc a n
rcal i zc .
Adjustrnent ol Rr with R.1,,,,,fixed yiclds rnaxrnrur.r.rbandwiclthcloscd' kxrp resp()nsc.
A d j u s l n r c r r t o l ' R . 5 , , , , 1w i t h R r f i x c d y i c l d s c o n s t a n t bandw idth closed-kxrp rcsp()nsc.
4 SLEWRATE,DC BALANCE,AND
LARGE.SIGNALBANDWIDTH
'l'hc
s l c w r a t c ( ) l ' t h c . l t r - 9 9 ) o p e r a t i o n a la r n p l i f i e r i s l t l
V/ps with a 150-O krad and 16 V/ps with 75 O.'Ihe
II
I
;:i
F i g . 7 . O p c n - l o o p n r a g n i t u d er e s p ( ) n s co t - t h c J l r 9 9 O o p c r a t i o n a l
a n r p l i f i c r . C u r v c l i t t o t h c m e a s u r e dd a t a .
I
1
I1
rO
I
I1
rlo
r50
ro"
!5'
6r'
"'r"r"',li-,.,,,ti,^
ofthe JL,'990opcrationalantFig. 8. Open-loopphaseresponsc
plifier.Curvefit to the measured
data.
s y n l n r e t r yi s a l i r n c l i o n 0 l ' t h c r n a t c ho l ' R 4 a n d R 5 a n d t h e
V1,,,nralch ol'Q3 and CRl. Thesc nratchesalso affcct the dc
balancc of the dift'crcntial input stage. In the prtxluction of
t h i s c i r c u i t , l l r es c r r r a t c h e sm a y r e q u i r e s o r n e m o n i t r l r i n g .
ltl di<ilcs arc vcry consistent, or a diodeFairchild lN
connected t' r .,it)r car) be uscd lirr CR3. Thermal coupl i n g s h o u l t l ! - ' r r : o n s i d c r c dl o r a p p l i c a t i o n sr e q u i r i n g d c
'i
; r t ' . ' ho l ' l l - l a n r i R 5 c a n b c t r i n r m e dt o a d j u s t
stabil;ty
inpul otl'scr(rurren( l.cccpta.rlr tolerances must be determined according to tlic application and component variations. If separatc.lc and ac (slew) balance adjustmentsare
required, an ac-coupled shunt rcsistor across R4 or R-5will
adjust the slew synrmetry without affecting thc dc balance.
The slew rate .l is deterrnined by the total available
current / fronr thc differential input stage, and the Miller
compensation capacitor Cll: S : I/C I . I'he current of the
input stagc has becn set by the noise analysis at 1.6 mA per
t r a n s i s t o ro
, rtotal I =. 3.2nrA, and thecapacitorCl : 150
pF, a value that cannot be reduced without affecting the
GO C I E T Y1, 9 8 0J A N U A R Y / T ' E A R U A RVYO, L U M E2 8 , N U M E E R1 / 2
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symmetryof voltageoverload(clipping). Thus S : 3.2
mA/150 pF : 2l pVls. The impedanceratio of the feedback and emitter circuits of Q6 affectsf, which, for 45'
phasemargin, cannotexceedf, : l/Kf , where I is the
time. So reductionof C I will requirean
amplifierresponse
of theemittercircuitcomponents
increasein the impedance
which would affect the symmetry of voltage overload. If
to restorethe zeroto
thisis done.R9 mustalsobe increased
8.1 MHz. Actually the iterativeprocedureto optimizethe
phasemargin should be repeated.At higher slew ratesthe
currentsetby Rl2 becomesa dominantlimit to slew rate.
The "current-mirror" collector load for the first stage
loadfbr its factor-of-2
waschosenovertheconstant-current
advantagein ac gain and availablechargingcurrentfor C I .
The modifiedDarlingtonsecondstagewas chosenoverthe
straightDarlingtonfor speed.
bandwidthdefinedas B : S/228,,,,.sis
The large-signal
1 4 5k H z w i t h a b i p o l a r( - r ) 2 4 - V s u p p l ya n d2 3 0k H z w i t h a
b i p o l a r( i - ) l 5 V s u p p l y .
5 OUTPUTSTAGE
The Motorola 11-03 packageoutput translstorswcre
chosenfor thermaland secondarybrcakdownpertbrmancc
o v e rt h eT O - 5 p a c k a g et y p e s .A t t h er e l a t i v ley h i g hq u i e s centcollectorcurrentof I-5mA requiredfirr low distortion
with a 7-5-0 load, the higherspeedTO--5typestailed the
s h o r t e d - o u t p ut te s t s e v e n w i t h h e a t s i n k s a n d y i e l d e d
academicallysmall improvementsin distortion and rcsponsetime. The biasingdiodesCR9 and CRl0 must bc
thermally coupled to Q8 and Q9, respectively,for low
distortionwith low-impedanceloads. Even at quiescent
rcducesthe
of theoutputtransistors
currentthetemperaturc
voltagedrop of the diodesas part of the criticalbalanccof
m u l t i p l ep a r a m e t e rdse t e r m i n e db y R l 2 , R l 3 , a n d R l 4 .
The currentsetby Rl2 in diodesCR9 andCRl0 is 5.4 tttA;
it affectsthe slew rate and distortionwith low load inrpedances.The resultingvoltagedrop acrossRl3 and Rl4
determinesthe l5-mA quiescentcurrcnt throughQ8 and
Q9, and this current sets lower limits on the open-loop
perflormance
of the output transistors:it contrcllstheir current gain, which in tum controls the open-lottpoutput
impedance,especiallyat high liequencies;it controlsthc
frequencyof unity gainj; and it controlsthe time delay
introducedby the transistors.At lower currentsthe output
stagecould introducea pole belowfr, andthis would reduce
thephasemargin.
5.1 Current Limiting CRl1 and CRl2
the current-limit
The valueof Rl3 and Rl4 also alTects
magnitude.When the outputcurrentreachesa valuewhich
is just less than the current correspondingto two-diode
voltagedrops divided by Rl3 or Rl4, the basecurrentis
starvedto the outputnodeby a three-diodepath including
CRg. CR I 0. andeitherCR I I or CR I 2.
will
Withoutheatsinksthe MJE-l7l and I 8l transistors
reliably drive a full-level signalinto a shortedoutput indefinitely.Thermaldissipationmay be a packagingconsideration.
.IF,.OO' DISI'' I]ETE OPERATIONAL AMPLIFIER
5.2 Load lsolation R15 and L3
To isolatecapacitiveloads(in orderto preventthemfrom
reducingthe phasemargin by delayingthe feedback)without significantlossesin the operatingfrequencyrange,the
parallelnetworkof R l5 and L3 is connectedin serieswith
is still derivedfrom the output
the loadonly. The f'eedback
network.The 40-pH inducnodebeforethe load-isolation
tancewith the 39-O resistorexhibitsan impedancepole at
l5-5kHz. Thereforethc seriesimpedanceis 39 O abovel55
to about
kHz. But bclow 155kHz the impedancedecreases
0.2 o at dc. At 20 kHz the impedanceis -5 C) at 80o,
r e s u l t i n gi n o n l y 0 . I I d B l o s sw i t h a 7 5 - O l o a d .
5.3 Clamp Diode CR4
Althoughthe modifiedDtulingtonis preferredfor speed,
it does not prcvent saturationof Q6 through t'eedback
clampingas docsthc straightDarlington.The clampdiode
CR4 restorcsthal f'eatureof the straightDarlingtonto the
higher specd mrldified Darlingtonby starvingthe drive
currentto thc baseof Q5 whcn the collectorof Q6 reaches
t h c v o l t a g eo l - t h cb a s eo f Q 6 . T h i s m e a n st h a tt h ea m p l i f i e r
will exhibittastrecoveryfrom voltageoverload(clipping).
6 OTHER CONSIDERATIONS
6.1 Anti-Latch-Up Diodes CRl and CR2
The diodes CR I and CR2 prevenlsignalsfasterthanlhe
responsclime ol'the arnplifierliom causingzero bias of
is too slow to
If the t-eedback
eitherof the inputtransist<lrs.
rnaintainlirrwardbiasfirr eitherinputtransistor,one of the
d i o d e sC R I o r C R 2 w i l l p r o v i d eb i a sf r o m t h e i n p u ts i g n a l
when thc dill'erentialvoltagc reachesone-diodevoltagc
drop. Without lhesediodcs the output could latch up to
e i t h e rs u p p l ya sa r es u l to f a s t e e pi n p u tw a v ef o r m .
6.2 Separate Regulators for Q4 and 07
'I'hc
s c p a r a l rce g u l a t o rR
s l 0 , C R 5 , a n dC R 6 f o r Q 4 , a n d
coupling
R l l , C R 7 , a n d C R 8 f o r Q 7 , p r e v e n tc a p a c i t i v e
and interactionbetwecnQ7 and Q4; suchcouplingwould
all'ectthe phascmargin.
6.3 Internal Decoupling C4 and C5
Thc internal high-fiequcncydecouplingfrom the power
supply ensuresthat any serieslossesin the connectoror
conncctionto the supply lincs will not increascthe impewhich areusuallyexterdanceof thedecouplingcapacitors
n a lt o t h eb a s i c" t r i a n g l e" a m p l i f i e r .
Rc
with zerocompensation
Fig. 9. Circuitsof fcedbackconrponents
bv meansofC,.
YO
, L U M E2 8 , N U M B E R1/ 2
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REPORTS
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7 CONSTRUCTION
Table l. Typicat performance of the JE-990 operational :unplifier
7.1 LayoutConsiderations
Quantrty
Specification
The node common to the collectorsof Q2 and Q3, the
base of Q5, CR4, and R9, is a very high impedance.
Thereforethis areashould be made as small as possible.
to avoid noisefrom externalsources
Shieldingis suggested
or responseerrorscausedby capacitivecouplinginto this
node. Paralleland symmetricallayttutof the input section
will yield improvedcommon-moderejection.
The collectorsof Q8 andQ9 draw heavycurrents.They
should be connectedto the supply terminalsdirectly in
order to preventthesecurrentsfrom causingany IR drop in
the resistances
of the circuit-boardfoils which supplyvoltage to the othercomponentsin the circuit.
l25dB
Open-loopgain from dc kr 30 Hz
0 . 4d B
Gainenor at 100-dBgain
density:
Noise-voltagespectral
0 . 8n V / V H z
Foreachtransistor
l.l3nY/lHz
For thedifferentialpair
I pA/\/Hz
spcctruldcnsitl
Nrrisc-current
0 . 6d B
resistance
Noiseindexu ith a lO(X)-Os()urce
Equivalentinputnoisevoltagein a 20-kHz
l60nV
bandwidthwith shortedinout
- l 3 3 . 7d B
voltageievcl re ().775V
CorrcspontJing
1 3 t. i v
M a x i n r u nirn p u tv o l l u g ci j t u n i t ) g a i n
+25d8
voltagelevelre 0.775 V
Corresponding
> l0Mo
l n p u ti m p c t l a n c tn' .o n i n v e r l i nign p u t
+ 2 . 2 1 tA
lnputbiascunent
1 3 . 8V
MaximurnoutputvoltagcwithR' - 75 11
+25dB
voltagelcvelre 0.775V
Corresponding
260 mA
MaxinrurnpeakoutPutcurrent
anoutput
kHz,
and
harmonic
distortion
at
20
Total
Construction
lnductor
7.2 Emifter
v<rltage
of 12.3 V (voltagelevel : +24 dB):
:
0.06('/a
R
r
7 5 ( 1 .g a i n: 4 0 d B
The emitter inductorsare constructedby threadinga
0.005o/c
R r : 7 5 O . g a i n: 2 0 d B
pieceof 250-pm diameter(AWG 30) magnetwirc through
o.('tl50/(
Rr : 6(XO
) . g a i n= 4 0 d B
shieldbeadin an apparSlew ratc:
the six holesof a nickel-compound
It'tV/ps
R, - l50tl
ently noninductivepattern creatingelTcctivelyonc half
l6 V/ps
R, :75o
t u m , b u t w i t h t h ec h a r a c t e r i s t iocfs5 7 m m ( 2 . 2 5i n c h e so) f
I 4 5k H z
L a r g cs r g n abl u n t j w i d t uh i t h R , - l 5 o l !
l0 MHz
bandwidthat unitygain(1,)
Snrall-signal
wire surroundedwith a magneticmaterial of high perlnearange
product,
in
the
ficqucncy
bandwidth
Ciain
b i l i t y ( 2 5 0 0 ) .T h i s c o n s t r u c t i oins l o w i n s h u n tc a p a c i t a n c c
>50 MHz
l 0 k H zt o l ( X )k H z
which could alterthc tlpen-loop
andrelatedself-resonance,
Phascrnargin:
>3tt'
AI I0 MHZ
responseand affectstabilityand transicntresponse.Allcr>60.
<
2
M
H
z
a
t
would requirean analysisol'theeflects
nativeconstructions
<20 ns
tintcat unitygain
Responsc
upon open-loopresponse,phasernargin,and transientrc2 5m A
Supplycurrcntwith no load
+24V
Supplyvoltagc(bipolar)
sponse.
8 PERFORMANCE OFTHE JE.99O
OPERATIONALAMPLIFIER
of theJE-990
Table I givesthe valuesof thepertirmrance
operationalamplifierwhich havebecnverifiedby multiple
prototypemeasurements
and calculations.The JE-990 is
unity-gainstableand exhibits no overshttotup to 45 dB
closed-loopgain, with | .3-ptsphaseleadcompensalionin
thefeedbackcircuit(bandwidth120kHz).
Also, Jung has kindly suppliedus with his measurementsof the total harmonicdistortionunder scvcraltcst
conditions,the equivalentinput noise,and the l.requency
r e s p o n sa
e t 6 0 - d B g a i n . J u n g ' ss t a n d a r dt e s t s e t u pI l I i s
shownin Fig. 10, and the testconditionsand thc purposcs
of the testsare summarizedin Table 2. The resultsare
shownin Fig. I I for a 30-V ( + l-5-V)powersupplyand an
rms output voltageof 7 V, and in Fig. 12 firr a 4u-V (i
24-V) powersupplyandan rmsoutputvoltageof I 4 V . The
detailedsignificanceof theselestsand comparalivetrlcaoperationalamplifiers
for the integrated-circuit
surements
p . A 7 4 t ,N 8 5 5 3 4 ,H A 2 6 2 5 ,L M 3 l 8 , R C 4 l 3 6 , L F 3 5 l , a n d
LF356, aredescribedin [], sec.2.41.Note that the output
linearitytests(G) areperformedwith a 2200-Oloadfor all
operationalamplifiers,whereasthe
the integrated-circuit
JE-990 is testedwith a 150-O load. Also note that the
operationalamplifiersarc limited to a
integrated-circuit
power-supplyvoltageof t l5 V, whereasthe JE-990will
operate up to a -r 24-V supply. Therctbre the JE-990
suppliesabout twice the maximum output voltageof the
operationalarnplifiers.
integrated-circuit
preamplificrin Fig. l3 showsa typical
The nricrophone
applicationof the JE-990 with offset compensationand
gain.Thc dioderegulatorandfiltercircuitsupply
adjustablc
for the
a currentinto the invertinginputwhich compensates
oftiet causetlby the unequaldc sourceresistancesat the
noninvertingand thc invertinginputs.The offsetvoltageat
each input is first firund by multiplying the input bias
at that input.
resistance
currcnt(2.2.p.A) by the dc s<turce
Frlr the noninvcrtinginput the dc-sourceresistanceis the
transfilrrncrsecondaryresistanceparalleledby the load
resistor.For the invertinginput, the f'eedbackresistor(10
path.Sincethe closedk0) is theonly dc-sourceresistance
unity,
the dc offset at the
krop dc gain of the anrplifieris
voltagesat the
of
the
offset
ou(putis ctlualto the ditlcrcnce
'fhc
into the
rcquired
current
compe'nsution
two inputs.
by the
voltage
divided
is
t,;tput-ol1.set
invcrtinginput the
(
kO).
resistance
l0
l'eetlback
dc
will significantlyreducethe
This dc-offsetcompcnsation
fbr
those
applicationswithout an
the
output
offset
at
dc
outputcouplingcapacitor.
hasa gainrangeof I2 dB to
The microphonepreamplifier
4 5 d B w i t h a b a n d w i d t ho f I l 5 k H z .
9 REFERENCES
tll W. G. Jung, Audio IC Op-AmpApplicutittns,no.
2 1 5 5 8 ,H o w a r dS a m s ,I n d i a n a p o l i s1, 9 7 8 '
I2l Linear (lntegruted Circuits) Duta Book (National
YO
, L U M E2 8 , N U M B E R1 / 2
GO C I E T Y1,9 8 0J A N U A R Y / F E B R U A RV
J O U R N A LO F T H EA U D I OE N G I N E E R I N S
Itr.9CO
D I S C R € T EO P E R A T I O N AALM P L I F I E R
ENGINEERINGREPORTS
r ok n
(2700 rL)
a
r ok n
(2200n)
(3V)
ol
S T A N O A R OT E S T A
#
K=l
=
srllolao
rest r
I uur)----I----------------
f-'-------v''
I
O
r
vour
Vrr
Y
Res,slor odded for
h,gh oulpul vo loqe
omo 'l er lesl
I- f f i
=
S T A N D A R DT E S T B
rItr
{
S T A N D A R OT E S T S C , O , E , A N D G
t yapriec a lo l v a l u c s
Fig. 10. TestsetuplilrnrcasurcrncntsaccordingtoTablc2.Valucsshowninparcnthcscsli)rtcstA
used in all tests firr thc high-output-voltagc ( l'1-V) amplificr.
rizationI I I.
characte
Tablc2: Tcsl serieslirr operational-arnplifier
Test
A
B
C
Test Objecl
THD vsl:
Slewrate
(general)
THD vsl:
Slew rate
(conrmon
mode)
Small-signal
bandwidth
D
Noise
E
THD vsl:
'lran
sfer
Ii nearity
THD vs/:
Input
nonlinearity
THD vsl:
Output
nonlinearity.
F
c
GeneralConditions
Load
Open
, ithunity-gain
U n i t yg a i n . *i n v e r t i n gw
Full ratedoutputvoltage.t
compensation.
U n i t yg a i n , *n o n i n v c r t i n gw, i t h
Full ratcd
unity-gaincompensation.
outputvoltage.f
()pen
Opcn
60-dB noisegain;inverling,unity
as approsignalgain,*compensation
p r i a t e l.V r m s o u t p u t .
Opcn
as
60-dB noisegain;compensation
R. : l0 0 No signalapplied.
appropriate.
6 0 - d Bn o i s eg a i n ;i n v c r t i n gu. r r r t r
as approsignalgain,*compensation
priate.Full ratedoutputvoltagc.t
6 0 - d Bn o i s cg a i n ;n o n i n v c n i n gu. n i t l
as approsignalgain,*compensation
priate.Full ratedoutputvoltage.t
6 0 - d Bn o i s eg a i n ;i n v e r t i n gu. n i t y
as approsignalgain,*compensation
priate.Full ratedoutputvoltage.t
RatedR,.
Rcntarks
Frcquency
l(X)Hz to
I00 kHz
(or to./,,)
l ( X )H z t o
lfi) kHz
(or tol,,)
of
Checksslew ratcindependent
common-modeandoutput
nonlinearities.
slew
Checksinpul comnron-modc
ratcif dilierentthanin tcst A.
l0 Hzto
-3 dB point
Chccksamplifiergain- bandwidth
productto determincopen-loop
frequencyresponse.
M e u s u r ccsq u i v u l e ni tn p u tn o i s c
tirr low R.; usedto calculatcspectral
noisevoltagedensity.
linearityof
Checksbasictransf'er
of testA or B
amplilier,indcpendent
Anrplifier's
bandwidth.
pcr test('
Open
l0 Hz.t<'tt/t
ol'-l dB
trequcncy
Open
l0 Hzto
V zo f - 3 d B
frequency
IC's:
l0 Hzto
lzof-3dB
2 k0;
JE-990: frequency
Checksinputstagenonlinearity,
of testsA, B and E.
independent
C h e c k s( ) u t p ust t a g en o n l i n e a r i t y ,
independent
of testsA, B, E, and F.
I 50c)
I For use with a + 24 V power supply only: Since thc test oscillatorused would not deliver an input voltageof 14 V, which
is necessary
for the full output voltagetest at unity gain, the gain was increasedto 13.4 dB by changingthe input.resistorfrom
l0 kO to 'ZOOt>; thus an input voltageof 3 V would give an output voltageof l4 V for tes( A. For test B, a non-invertinggain
o f 1 3 . 4d B w a su s e d .
*24-V supply
t For integratedcircuits and JE-990 with +15-V supply voltage, rms output voltage : 7 V; for JE:990 with
rrnsoutput voltage : 14 V
1/2
VOLUME
28,NUMBER
1980JANUARY/FEBRUARY,
SOCIETY,
JOURNAL
OFTHEAUDIOENGINEERING
JENSEN
ENGINEERING
REPORTS
S e m i c o n d u c t oM
r ,o u n t a i nV i e w , C A , 1 9 7 8 ) .
GA N/{V/VI
lr€slcl
roooo
s a t c h e dT r a n s i s t oPr a i r s , "
[ 3 ] B . C o l e ," l C S i m u l a t e M
Electronics,p. l 4l , ( 1976 Oct. 28).
[ 4 ] C . T . N e l s o n , " S u p e r - M a t c h e dT r a n s i s t o rP a i r
Application Note 222, National Semiconductor
C o r p . ,S a n t aC l a r a ,C A , 1 9 7 9 .
and F. C. Fitchen,Low-Noise
t5l C. D. Motchenbacher
ElectronicDesign(Wiley, New York , I 973).
[6] D. Jensen,"A 20 kHz Low PassFilter fbr Audio
Noise Measurements,"Record.Eng./Pntd., vol. 8, no.
6 , p p . 3 0 - 3 5 ( 1 9 7 ' lD e c e m b e r ) .
t 7 l G . E . T o b e y ,J . R . G r a e m e ,a n d L . P . H u e l s r n a n ,
Operational AmpliJicrs, Design und Applicutiotts
( M c G r a w - H i l lN, e w Y o r k , l 9 7 l ) .
; R E o l r F N i / l Nz 1
[8] J. K. Roberge,OperatittnalAmpltfiers,T'heoryund
Fig. 12, Rcsultsof thc nreasurenrents
accordingto Tablc 2 lirr
P r a c t i c e( W i l e y , N e w Y o r k , 1 9 7 5 ) c, h a p .8 , " O p e r a t i o n a l the JE-990opcrationalanrplifieroperatingtiom a +24-V supply,
deliveringan rnrs output voltageof l4 V into an opcn circuit,
A m p l i f i e rD e s i g nT e c h n i q u e s , a" n d c h a p .4 , - 5 ,a n d l 3 o n
cxccDtfi)r tcstG wherea 150-Oload is used.
stabilityandcompensation.
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R E O U I R E OO N L Y W I T H
f)
ro
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c o uo " - . . . f *
F i g . l l . R c s u l t so l t h c r n c a s u r e n r e natcsc o r d i n gt o T a b l e2 l i r r
thc JE-990operational
anrplilicropcrating
frorn a 1 |5-V supply,
deliveringan rms()utputvoltagcof 7 V intoan open circuit,cxccpt
lirr tcstG whcrca l-50-Oloadis uscd.
34
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t conrpcnsation
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Fig. 13. Microphoncprcarnplilicrwith ofl.se
adjustahlcgain.
VOLUME28, NUMBER1/2
JOURNALOF THE AUDIO ENGINEERINGSOCIETY,1980 JANUARY/FEBRUARY,