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ANALOG DEVICES FAX-ON-DEMAND HOTLINE - Page 16 ~ ANALOG W DEVICES I

FEATURES

.MultipleOutputOptions(AbsoluteValue,RMS, Log RMS, Log AbsoluteValue,Average AbsoluteValue) .Wide Dynamic Range :..100dB .PreblasOptionforFastResponse atlow Signalleyels .On-Chip Log Output Amplifier .OptionalInternallog Output Temperature Compensation .Low DriftInternalYoltageReference .Low Cost

APPLICATIONS

.Audio Dynamic Range Processors .Audio MeteringSystems .DigitalMultlmeters .Noise Testers .Panel Meters .Power Meters .Process ControlSystems FUNCTIONAL DIAGRAM f I LOG OUT ABSOLUTE VALUE LOG RECOVERY AMPLIFIER ~11w.1-LOGIN - 10 -t.OGIN_11 LOG SCALE - I.- IHPUT - 17 VRII' J V- LOG ~ TrueRMS-to-DC Converter SSM-211O I GENERAL DESCRIPTION The SSM-211 0 isa trueRMS-to-DC converterdesignedtopro- vide multiplelinearand logarithmicoutputoptions.The linear outputs,trueRMS and absolutevalue,can be obtainedsimulta- neouslywiththeabsolutevalueoutputconfigurabletogivea peak function.The logarithmicoutputscan providelogRMS, logab- solutevalue or log average absolutevalue.Fullon-chiptem. peraturecompensation isavailableforeach outputoption. Continued PIN CONNECTIONS ABSOLUTE VALUE m. 1S-PIN PLASTIC DIP I (P.Sufflx) . 1!JN.C. EIv- rnc-

2 LOG SCALE

10 _LOG IN C- V. RItIS 13 16 5 II LOG n 17 RECOVERY tl BASE TRANSISTOR I EMITTER ~I- 4 GNOO. RMS COMPUTING LOOP SSM-211 0 PRESIAS LOG- The SSM-21 10 h.. been granted meak work protection under the semiconductor Chip Protaction Act of 11183. OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE SSM-2110 - Page 17

ORDERING INFORMATION

SupplyVoltage ,.f18V StorageTemperatureRange -65°C to+150°C Lead TemperatureRange (Soldering,60 see) " +300°C Operating Temperature Range -25°C to+75°C PACKAGE TYPE elA(Notet) 9JC uNITS lB.PinPlasticDIP (P) 75 33 °crw NOTE: GENERAL DESCRIPTION Continued The SSM-2110hasadynamic rangeof1OOdS. Auniqueon-chip prebias circuitenables the users totradedynamic range atlow signallevelsfora fasterresponse time.As a precisionlevel detector,theSSM-211 0 has applicationsindigitalmultimeters. panel meters,process controland audio systems. -2S.C to+75.C UNITS dB dB nA nA kHz mV/dB dB ppm/"C V ELECTRICAL CHARACTERISTICS at V s '":t15V. T A" +25cC and RSCALE = 4.7kn, unless otherwise noted, SSM-2110 PARAMETER SYMBOL CONDITIONS MlN TYP MAX Dynamic Range DR 30nAp.pS IINP-PS 3mAp.p 100 ttO Unadjusted Gain 'IN-:!:1mA 0.95 1.0 1.05 Error(Mean or RMSI - - :to.S Output OffsetCurrent 1005 I,N-:l:1mA - 5 15 105Shin 41005' RpAESIAS 3MG - 50 120 For 0.1dB AdditionalErrol - 2.5 CrestFactor@ 1mAAMS CF For0.5d8AdditionalError - 5 For 1.OeIe Additional Error - 8 RMS FilterTime Constant tcON lAMS> 10l-lAAMS 11kQxC'NT Frequency Response (SineWave) ',N>1mAA!.IS - 400 Fo10.1dSAdditionalError 'IN> 10j.lA"MS - 10 IIN > 11-1AAMS - 2 "N > 1mAA!.Is - 1000 For O.5dB AdditionalError BW IIN> 10J.IA"IAS - 50 'IN> 1J1AAIAS - 7.5 IIN> 1mA"lAs - 1500 -3dB Bandwidth 'IN> 1Oj1A"MS - 300 I'N> tJlA""s - 50 Log Amp Output OffsetCurrent loos--l.OG :1:3.3 :1:13(Pin9) Max Log Amp Output (pin91 IOUT--I.OO :1:250 :1:265 :1:288 Log ScaleFactor +6(Pin20r Pin6) Log Mode ZaroCrossing RMS InTo Get ZeroOut (See Figure7) 10(Mean orRMS, Pin9) Log Amp Unearity(Pin9) -240m V < VPIN'0-VpIN11< +240mV - 0.1 0.25 Log OutputTempco Tc O.C < TA< +70.C - :1:75 V"'EF(Pin310 V-) 6.7 7.5 78 OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE - Page 18 SSM-2110 ELECTRICAL CHARACTERISTICS at V s ",:t15V, TA'"+25°C and RSCALE '"4.7kil,unless otherwise noted.Continued SSM-2110 Specificationssubjectto change; consultlatestdata sheet. IOpf .I$V ~VI1f;' 41GND ~ ~ ABSOLUTE VALUE PREBIAS - - - - - - - 2 11 _'IN ILOGA8SVAl INPUT v.p!12 ~ O.I"F "'" C... .f--o V,N .15V C- ~'A_.... -15V ~O.'"F 'OP11OHAL PREBIAS COtoINECTlON, SEE TEXT VA"S'V_.~ R", TYPICAL VALUES, "1N-IOIen RAIlS' 10111} CIM' O""F C_slpF FIGURE 1: RMS OutputCircuit THE RMS COMPUTING LOOP The RMS sectionof the SSM-211 0 consistsof an implicitRMS computing loop whose outputfollowstheequation: 10 '" IIN2 where 10 istheaverage of 10 The time constant foraveraging isdetermined by the value of theaveragingcapCRMS (onpin13)and an internalresistorwhose effectivevalue is1O.8ka. A very low leakage capacitormust be used forCAMS to prevent limitingthe dynamic range. Increasingthevalue ofCAMS willresultinlowerlevelsofrippleon theRMS Output attheexpense ofan increaseinsettlingtimefor a stepchange intheinputsignalamplitude.Thisisa proportional relationshipwhere increasingthevalueofCAMS tenfoldresultsin a tenfoldincreaseinthe settlingtime. I Forthe circuitinFigure 1,thepeak-to-peakrippleapproximately followsthe equation: V 212 x VRMS RRMS RIPPlE(p-p) = x - 47tf R1NTCRMS RIN where RINT '" 10.8kil The settlingtimeoftheSSM-2110 alsodepends on thefrequency ofthesignalbeing processed. Ittakes approximately1OOms for a 30°I-lAp-p,50Hz signaltosettlewithin0.1% when CAMS '"1~F, and ittakes 10ms fora 500Hz signalto settlewithinthe same value.The generalruleisa tenfoldincreaseinfrequencycauses a tenfoldreductionin settlingtime. The settlingtime also varies withthe amplitude of the signal.The largerthe signa!levelthe fasterthe settlingtime. PARAMETER SYMBOL CONDITIONS PositiveSupplyCurrent Is+ "N-ONegativeSupplyCurrent Is- SupplyVoltageRange Vs MIN TYP MAX UNITS 480 - 920 uA 2.1 - 3.3 mA :1:12 - :tIS V -=- r 14v- a Loa- CfIIIS13

1 IIAtE LOG SCALE 12

. EMITTER -LOG IN 11 -=- II LOG OUT 10.LOG IN OBSOLETE

ANALOG DEVICES FAX-ON-DEMAND HOTLINE - Page 19 SSM~2110 INPUT TheINPUT (pin17)isan AC virtualgroundwithapproximately +1.3V DC offsetvoltage.The usefuldynamicrangeofinput currentthe device can process is1COde (3mAp.p to30nAp.p). The inputRC network isusuallychosen to allow close to 20dB of headroom inordertoprocesshighcrestfactorsignalsand pro- vide a DC blockbelow a given frequency band. Since inevery case the ratioof ROUT (RAV and RRMS) to RIN determines the overallgain ofthe circuit,ROUT must alsobe consideredwhen selectingthe low frequency breakpoint.The maximum recom. mended valuesforROUT varyfrom 4kflto1akflforthecircuitsin Figures 1,3,4, and 5. Referringtothe circuitinFigure3,and assuming a gain of 1 is desired,RINshould be setto4kfl(RRMS and RAv'"4kfl).Based on thisvalueofR'N'GINshould be 2~F toplacethesubsonicfilter poleat20Hz. Ifyou wishtolimitthelowerfrequencytosome- thingotherthan20 Hz thenGINshouldbe changed accordingly. The low frequency pote 'sgovernedby thesimpleequation fMIN'" 1/27tRINC'N. GIN shouldbe a verylow leakagecapacitortoavoidimpairing the dynamic range atlow signallevels(many electrolytictypes willnot work). The choiceofR'N;; 1akfl inFigure1 isgood forprocessingOdBV referencesignals.Given a nominal signallevelofOdBV (2.828Vp. p ".1 V RMS)'thisvoltageacross the 10kflinputresistorgivesa nominal inputcurrentof 28311Ap-p,which allows20dB ofhead- room. The threeothercommon choicesforR'Nare4kfl,5kfland 8kn.whichprovide12dB,14dB,and 18dB respectively. The values ofGIN'RIN and ROUT can be changed accordinglyto vary output levelstosystem requirements. .,--'O..A -40<1- ,000A -2Ode 'OOI>A ...-'_A --'"A INPUT CURRENT FIGURE 2: Normalized Time Constant Relativeto 1mAAM$ The PREBIAS pin(pin18),can be used toincreasethespeed of the RMS computing loopatlow signallevelsatsome expense to thedynamic range. Below a 10l!ARMS inputlevel,thetime con- stantot the RMS loop willincrease from itsnominal value by a factorof 10 forevery 20dB drop inlevel. By use ofthe PRE BIAS pin,one can ensure thaIthe loop time constantwillnotincreaseabove a chosen maximum as the sig- nallevelcontinuestodecrease. The equationrelatingthe maxi. mum timeconstantincreasetothevalue of RpREBIAS connected between pin18 and V- isgiven by: 'MAX ".10~ x RPAEaAS 'NOM 6.8V (See Figure2) VAY (orV"va) AB5<X.UTE VALUE PREBIAS ,e' 2 LOG'..VAL INPUT \\7

3 VA'" V+ 16

4 OND \\5

RIN ~ V.. 2"F - .,5V 41<U ~ !..tIUE .IEMmeR II'LOGOUT c J!! LOG SCALE 112 -15V -LOG IN J!.!. +LOG IN "D 'OPTIONAL PREBIAS COHNECTIOH "CAva CAN BE ADDeD TO AVERAGE THE AIISOI.UTE VALUE VAllIS.-V R-R'N FIGURE 3: Simple RMS/Absolute Value/Average Absolute Value Configuration 'GOO '110 j 10 ,y...-' ; .,R,.e.,OMO" !! i=R...31010 OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE - Page 20 SSM-2110[ CAI/O 10pF AAY .IIV VAV A..v VAVaIV-A; TYPICAL VALUES: "",.IKn AAV"BIen c...1~F FIGURE 4: Absolute Valueand AverageAbsoluteValueOutput V_. ":' FIGURE 5: Peak VoltageOutput c.. A," .r-o v.. :;J;O.I~f * o.l~f .IIV -15V AI< c.. r-o v.. ~ O.I~F *O.I~F .IIV -'IV I ABSOLUTE VALUE PREBIAII 18 Z LOGAN VAl. INPUT 17 3 V..., V. II GNO 15

5 MIS V- 14

""" 5 LOO- c- 13

7 BASE LOG SCALE 12

8 EMlTTEA 4.OG IN 11 t LOG OUT .LOG IN 10 I AISOLUTE VALUE PRiBIAII 18 3 V- V. 18 "QND 15 51'tU8 V- 14 = 'L 13 1 8&SE LOG SCALE 12 . EIIITrIR 4.OG IN 11 t LOG OUT .lOG IN 10 TYPICAl VALUES: R...51<1) AOUT .51<>1 c",.I-'\\sF.1F OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE - Page 22 SSM-2110 10pF .l~A~ J;v- AAY .,5V VUIO(AVI -=- A_, "'-" 'C.;.yoCAN 8. ADOED TO OBTAIN THE AVEIU4Ii 01' THE A88OI.UTI VALUti FIGURE 7: Log ofAbsolute Value/Average Absolute Value 10pF A.... .IIV VUIO(I Roo ~ v.. ~O"I'" ~O.,"" Aec.au ~V- 4IONI) v.J1! ~ ~ I 2 LOG_yAI. INPUT 17 1 .... ,,-, "'- 'OI'TIDICAL- CONNEC'TJ()III,lEE TEXT AGURE 8: Log ofRMS ~~.~ .,5V 0.'" VyAAV log (~) J VLOO\\AVI -R'CALI I"", x I"..., TYI'ICAL VALUES: Roo.IGkn c,.,.o""'" AAV,'I,1IcO ~...nn A"",.,. 1.51kl ",-.~ VLOO\\AY,;;log!. .ftuoL\\ l00mvl Rw ~ v.. o11V ~O.,"" ,*°,'"" -\\IV WHIM! I.1V I"",.A"." TYPICAL VoU.UU: Roo' IGkn c,.,.0""'" "- . II1.111Q ~ .4.1IIQ "-'.1.51kl "-- .43OIon~.1"" VLOOIAMIII;;log~V,~~i) 1 A880LUTI VoU.UIiI'A8I1A8II Z LOG""VAL INPUT 17 3 V.., V. 11

4 CHI) 11

7 IA8E LOG ICAU! 12 I EMInI'A . LOG OUT - v_ - . Loa- 1J 7- LOGSCALI '2 I DUrEA . LOG OUT OBSOLETE

~~M-lllU ANALOG DEVICES fAX-ON-DEMAND HOTLINE -Page 23 range ofthedevice willbe roughlysymmetrical about the inter- nalnegativevoltagereference.Also.the outputimpedance will be low enough to drivethe logamplifier'sinput(s)withoutintro- ducing significanterrors.The biascurrentintothepinsofthelog amplifieristypicallylessthan 1J.lAbutcan be as highas 21lA.For thisreason the currentthrough the log recoverytransistorA" should always be sethigherthan 51-1A.The current'REFIshould not be settoo high (above SellA) because the base currentof 0'0 induceserrorsintheRMS computing loop.Ifhigherreference currents are required then they should be taken care of by changing thecurrentthroughOlj'Thiscan be done by changing RREF2'The Log Recovery AmplifierSectionexplainsthisinmore detail. The output sensitivityat EMITTER (pin8) isabout +60mV for every 1Ode ofsignallevelincreaseat25°C. Thissensitivityhas a temperature coefficientof +3300ppm/oC. The fog of absolute value output can be converted to a log of mean value by connectinga capacitorbetween LOGABS VAL(pin 2)and V- (see Figure7).Since thisisan emitterfolloweroutput. the response to a large-signallevelincreasewillbe fastwhile thetime constantoftheoutputfollowinga large-signallevelde- crease willbe determined by the productofcapacitorC AVG and resistorRREFI' One might thinkthatconnecting a capacitor to the logoutput would produce the average of the log of the absolute value. However, since the capacitor enforces an AC ground at the emitterof theoutputtransistor,the capacitorchargingcurrents areproportionaltotheantilogofthe signalatthebase. Since the base voltage isthe log of the absolutevalue,the log and the antilogterms cancel,and the capacitorischarged as a linear integratorwitha currentdirectlyproportionaltotheabsolutevalue of the inputcurrent.This effectivelyinvertsthe order ofthe av- eragingand loggingoperations.The signalatthe output.there- fore,isthe logofthe average of the absolutevalue ofthe input signal. LOG RECOVERY AMPLIFIER (PINS 9,10,11 AND 12) The log recovery amplifieris a linearizedvoltage-to-current transconductorwhose gain can be made proportionaltoabso- lutetemperature.Itisused toreferencethelogoutput(s)toground and alsoto temperature compensate the V T (KT/q)terms inthe logoutput recoverytransistors(0/0'0 anda,,). One inputof the log recovery amplifierisusuallyconnected to EMITTER (theemitterofthelogrecoverytransistor-pin8)while the otherisconnectedto V REF (pin3). Figure 6 shows the internaland externalconnections used to obtainan outputvoltageequaltoVlOG(RMSr The transferchar- acteristicofthelogrecoverytransistorsisgivenby thefollowing equation: .1VIN ,.VT x In VIN(RMS)/RIN) 2 )IREF' x IAEF2 where, IREF' = ( 8.W )RREF' IREF2 '" 7.5V )+ 1J.lA ~EF2 The transfercharacteristicofthe logrecoveryamplifierisgiven by the followingequation: lOUT = 64mV.1 V1N RSCALE VT Combining thetwo equationsyieldstheoveralltransfercharac- teristicforthe ouput voltageVlOGIRMSj: V O.148xRRMS I (VINlR,N) 2 LOG (AMS) = x og RSCALE IREFI x IREF2 IREF' '"( 8.1V )~EFI 'REF2 '"( 7.5V )+ 1IJA RREF2 Ideallythisvoltageiscompletely independent of temperature. However, due tothe temperaturecoefficientofseveraltransis- torsinternaltothe SSM-211 0,thisisnotentirelytrue.The tem- peraturecoefficientisapproximately:t75ppm/aC. With thevalues shown inFigures7 and S,thistransferfunction corresponds to an output change of 50mV/dB, The reference currentisset to 10IJ.Ato provide the widest possibledynamic range. The followingresultscan be expectedforthe circuitin Figure8: where, An RSCAlE value of approximately 4.7kQ givesthebestoverall linearityand temperaturecompensationperformance.ThisISan improvement of about a factorof 40 over the uncompensated drift.A 2k.aresistorinserieswitha silicondiode can be connected fromLOG SCALE (pin12)tothe negativesupply todefeatthe temperaturecompensation forcertainapplicationssuch as compressorllimiterswhere the logdriftwillcancel the thermal gain driftofa VCA's dB/volt control port. The maximum outputcurrentforboth the compensated and uncompensated examples above is:!:250~A.This output current isconvertedtoavoltagewiththe circuitsinFigures7 and S. For these circuitsthiscorresponds to a maximum outputvoltageof :!:3.975V.IfRSCAlE ischanged fromthenominalvalueof4.7kn the maximum outputcurrentwillalso change by the following equation: ILOGOUT(MAX) '"'1.1SV RSCALE Ifthe logrecovery amplifierisnotused,+LOG IN (pin10)and - LOG IN (pin11) must be connected to V REF (pin3) forproper operationofthe restofthecircuit. Itispossibleto use one ofthe logconfigurationsinFigure7 or8 inconjunctionwiththe linearoutputcircuits(Figures1.3.4 and 5) but care must be taken in choosing the appropriate resistor values.This providesthe user withsubstantialflexibilityfrom a singledevice. V,N(RMSI 100)l.V tmV 10mA 100mV , 'V I ,av, i, I'NIRMS) 'OnA 100nA ')l.A 1OI'A 100)l.A 1mA i v,"" OUT -3V -2V -'V ov 1V ! 2V OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE [' .- - Page c~ SSM-211D

1 AIISOUITE VA~UE "RE81A11 II

3 VAl, Y. ,. 4 aND 15 $- V-'4 . LOG- ew. 13 7 lASE ~OG SCA~I! 12 . EIIoIIT'TER -I.OGIN 11 , LOG OUT .I.OGIN 1.0 i 1.51«) 1001d1 +-./l1lI'- OFFSI!T T-v- 131cn SCAL!! TAJM -IIIQ 10p/' VLQQ(-I 1.5MG S37~ .". 1OOI<Q REFEAEHCE TRIll FIGURE 9: ErrorTrimming ERROR TRIMMING The offset,reference and scale factortrims(Figure9) can be used toimprove the overallaccuracy ofthe device.The correct procedure fortrimmingoutthe variouserrorsisas follows.First, +LOG IN (pin10)and -LOG IN (pin11) should be connected to V REF(pin3).The offsettrimshould be adjustedtoachieve OV at theV LOG(RMS)output.This nullsout any DC errorsdue tooffsets inthe log recovery amplifier.Second, reconnect the f:LOG IN pins as shown inFigure 9. Apply an inputsignalof 1OOmV RMS (1O~ARM_!»'AdjustthereferencetrimtoobtainOV attheV LOG(RMS) output.This compensates forthe inputbias currentof the log 10loI) 0.81>' r-ov.. .15V -I$V ".841<0 recoveryamplifierand othererrors.Itsetsthereferencecurrent to 10f.1A.Third.change the inputsignalto 1V R'-AS(1OO!lARMS)' Adjustthescaletrimtoobtain1.OODV attheV LOG(RMS)output.This adjuststhe scale factorto obtain 1V/20dB (50mV/dB). Ifother referencecurrentsorscalefactorsareusedthen steps2 and 3 willhave to be changed accordingly. Thissame procedure can be used forthelogabsolutevalueand logaverage absolute value configurations.Ifthe log recovery amplifierisnotused then the circuitinFigure 10 should be used to trimthe offsets. OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE SSM-2110 - Page 25 l_n~ OfI'SET Tl't1M I ABSOLUTE VALUE 2 . LOOMS VAl. 3 V"... 4QHO I Loa,..

7 BASI

. EIIIITT1:R \\I LOG OUT PflEBlAS INPIJT 17 V. II .!! C 13 LOG SC: 12 -l.OG IN 11 .lOGIN 10 1010G O~F 1-0 V.. 10pF .15V -15V 10lln *O.I~F .1511 11- ':" FIGURE 10: OffsetTrimming AVERAGE OF CREST ABSOLUTE FACTOR VALUE Vp WAVEFORM RMS (AAV> =RMs i Vp* /"'\\' I I Vp 2.Vp i "-/ ./2=1.414 I Vi I It SINEWAVE --- Vp* ;- Vp Vp l ' i I i SQUAREWAVE j --"I , , Vp* A Vp Vp -/3'"1.732 V 7i 7i TRIANGLEWAVE --..-' 2Vp1 A /' Typicallyvariesfrom1to6de- RMS AxRMS pending onthecharacteristicof thenoise.Theoretically,the crestfactorisunlimited. GAUSSIANNOISE : FIGURE11: RMS, Average ofAbsolute Value and Crest FactorsforDifferentWaveforms A OBSOLETE

ANALOG DEVICES fAX-ON-DEHAND HOTLINE - Page 26 SSM-2110 -15V 10lIO 3.321<11 NOM- INVEImNO INPUT INVER11NG INPUT ONO .... an GAIN > 1110 LIMIT O.02~F SSM-211 0 l1r1n .15V r -15V 31.11<11 w--- 112 Op.215GP I00kI} AGC ~ 1011n fW.I!ASI FAST 22Mt1 -: OUTPUT UOVEL 10l<U -: -: I -IIV 1.sIID U, _2013 U2' Us SSIII-21:M U. _2110 U. 1I2OP-21- U. 1120p.21- 15110 NOTE: U2'US'U,,' U. POWER SUPPLY COHIIECTtONS AltO BYPASSING ARE NOT SNO- ! I -: -11V TYPICAL APPLICATIONS AUTOMATIC GAIN CONTROL (AGC) AMPLIFIER The automaticgaincontrolamplifiershown belowfeaturesse- lectablegainreductioncompressionratiosand timedomain adjustableAGC attackand release.The designemploys the SSM-2013 VCA. SSM-21 10 trueRMS-to-DC converter.two SSM-2134lownoiseopampsand anOP-215 FET inputop amp. Foradditionalinformationaboutthiscircuit.pleasesee appli- cationnoteAN-116. I tOlln GAIN TtON -15V OISTNULL -'IV 111<11 Y O.1F, -::JOpf I00kI} U, 14 MI'- In'O 110 ==1- -co.nnr-. n__; 5OpF £: 1N1td 1N1148 tl2OP-2t5GP "TrACt( O.O,I)'F IHt14 1Ok!} OBSOLETE