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 J O U R N A LO F T H EA U O I OE N G I N E E R I NS ENGINEERING HEPORTS 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 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 31 REPORTS ENGINEERING JENSEN 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. " S t a b i l i z i n g A m p l i f i e r s , " D . J e n s e n , O p e r a t i o n a l [9] R e c o r dE . n g . / P n i l . , v o l 9 , n o . 3 , p p . 4 2 + ( l 9 T UJ u n e ) . r t-il I-iF R E O U I R E OO N L Y W I T H f) ro zT\'Lr/F 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 .T rcrr<v ??o/F - il-2 7 k \,r I ?7rir f t conrpcnsation and Fig. 13. Microphoncprcarnplilicrwith ofl.se adjustahlcgain. VOLUME28, NUMBER1/2 JOURNALOF THE AUDIO ENGINEERINGSOCIETY,1980 JANUARY/FEBRUARY,