ANALOGDEVICES FAX-ON-DEMANDHOTLINE - Page 16

~ ANALOGW DEVICESI

FEATURES

.Multiple Output Options (Absolute Value, RMS,Log RMS,Log Absolute Value, Average Absolute Value).Wide Dynamic Range :.. 100dB.Preblas Option for Fast Response at low Signalleyels.On-Chip Log Output Amplifier.Optional Internal log Output TemperatureCompensation.Low Drift Internal Yoltage Reference.LowCost

APPLICATIONS.Audio Dynamic Range Processors.Audio Metering Systems.Digital Multlmeters.Noise Testers.Panel Meters.Power Meters.Process Control Systems

FUNCTIONAL DIAGRAM

f

I

LOG OUTABSOLUTE

VALUE

LOGRECOVERYAMPLIFIER

~11w.1-LOGIN - 10

-t.OGIN_11

12LOGSCALE -

I.-IHPUT - 17

-:

VRII'J

2

V- LOG ~

TrueRMS-to-DCConverter

SSM-211O I

GENERAL DESCRIPTION

The SSM-2110 is a true RMS-to-DCconverter designed to pro-vide multiple linear and logarithmic output options. The linearoutputs, true RMS and absolute value, can be obtained simulta-neously with the absolute value output configurable to give a peakfunction. The logarithmic outputs can provide log RMS, log ab-solute value or log average absolute value. Full on-chip tem.perature compensation is available for each output option.

Continued

PIN CONNECTIONS

ABSOLUTEVALUE m.

1S-PIN PLASTIC DIP I(P.Sufflx) .

1!J N.C.EIv-rnc-

&

2 LOG SCALE

11 -LOG IN

10 _LOG IN

C- V. RItIS

13 16 5

!II

LOG n 17RECOVERY tl BASE

TRANSISTOR0"

I EMITTER

~I-

4GNO

O.RMS

COMPUTINGLOOP

-:

SSM-2110

PRESIAS LOG-

The SSM-21 10 h.. been granted meak work protection under the semiconductor Chip Protaction Act of 11183.

OBSOLETE

ANALOGDEVICES fAX-ON-DEMAND HOTLINE

SSM-2110- Page 17

ORDERING INFORMATIONPACKAGE

PLASTICtS-PIN

SSM2t10P

OPERATINGTEMPERATURE

RANGE

ABSOLUTE MAXIMUM RATINGSSupplyVoltage ,. f18VStorage Temperature Range -65°C to +150°CLead Temperature Range(Soldering, 60 see) " +300°CJunction Temperature """"""""""""""""""""""""" + 150°COperating Temperature Range -25°C to +75°C

PACKAGETYPE elA(Note t) 9JC uNITS

lB.Pin Plastic DIP (P) 75 33 °crw

NOTE:

1. ell. is Specified for worst case mounting corlditjons. i.e., eA is specIfied for devicein socket forP.DIP. I

GENERAL DESCRIPTION Continued

The SSM-2110hasadynamic range of 1OOdS.Auniqueon-chipprebias circuit enables the users to trade dynamic range at lowsignal levels for a faster response time. As a precision leveldetector, the SSM-211 0 has applications in digital multimeters.panel meters, process control and audio systems.

-2S.C to +75.C

UNITS

dB

dB

nA

nA

kHz

~A

~A

mV/dB

~A

dB

ppm/"C

V

~

--

ELECTRICAL CHARACTERISTICS at V s '" :t 15V. 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 Offset Current 1005 I,N-:l:1mA - 5 15

105Shin 41005' RpAESIAS 3MG- 50 120

For 0.1dB Additional Errol - 2.5

Crest Factor@ 1mAAMS CF For0.5d8 AdditionalError - 5For 1.OeIe Additional Error - 8

RMS Filter Time Constant tcON lAMS>10l-lAAMS 11kQxC'NT

Frequency Response (Sine Wave)

',N> 1mAA!.IS- 400

Fo10.1dS AdditionalError 'IN> 10j.lA"MS- 10

IIN > 11-1AAMS- 2

"N > 1mAA!.Is - 1000For O.5dB Additional Error 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 Offset Currentloos--l.OG :1:3.3 :1:13(Pin 9)

-

Max Log Amp Output (pin 91 IOUT--I.OO :1:250 :1:265 :1:288

Log Scale Factor+6

(Pin 20r Pin 6)-

Log Mode Zaro CrossingRMS In To Get Zero Out (See Figure 7) 10

(Mean or RMS, Pin9)-

Log Amp Unearity (Pin 9) -240m V<VPIN'0- VpIN11<+240mV- 0.1 0.25

Log Output Tempco Tc O.C < TA< +70.C - :1:75

V"'EF(Pin 310 V-) 6.7 7.5 78

OBSOLETE

ANALOGDEVICES fAX-ON-DEMAND HOTLINE - Page 18

SSM-2110

ELECTRICAL CHARACTERISTICS at Vs ",:t 15V, TA'" +25°C and RSCALE'" 4.7kil, unless otherwise noted. Continued

SSM-2110

Specifications subject to change; consult latest data sheet.

IOpf

.I$V~VI1f;'

41GND

~ ~.

ABSOLUTE VALUE PREBIAS - - - - - - -2 11 _'IN I

LOGA8SVAl INPUT

v.p!12

~ O.I"F

A.....

v-

"'" C.... f--o V,N

.15V

C- ~'A_....-15V

~O.'"F

'OP11OHAL PREBIAS COtoINECTlON, SEE TEXT

VA"S'V_.~R",

TYPICAL VALUES,

"1N-IOIenRAIlS' 10111}CIM' O""FC_slpF

FIGURE1: RMS Output Circuit

THE RMS COMPUTING LOOP

The RMS section of the SSM-211 0 consists of an implicit RMScomputing loop whose output follows the equation:

10 '" IIN210

where 10 is the average of 10

The time constant for averaging is determined by the value ofthe averaging capCRMS (on pin 13) and an internal resistor whoseeffective value is 1O.8ka. A very low leakage capacitor must beused for CAMSto prevent limiting the dynamic range.

Increasing the value of CAMSwill result in lower levels of ripple onthe RMS Output at the expense of an increase in settling time fora step change in the input signal amplitude. This is a proportional

relationship where increasing the value of CAMStenfold results ina tenfold increase in the settling time.

I

Forthe circuit in Figure 1, the peak-to-peak ripple approximatelyfollows the equation:

V 212 x VRMS RRMSRIPPlE(p-p) = x -

47tf R1NTCRMS RIN

where RINT '" 10.8kil

The settling time ofthe SSM-2110 also depends on the frequencyof the signal being processed. It takes approximately 1OOmsfor

a 30°I-lAp-p, 50Hz signal to settle within 0.1 % when CAMS'" 1~F,and it takes 10ms for a 500Hz signal to settle within the samevalue. The general rule is a tenfold increase in frequency causesa tenfold reduction in settling time. The settling time also varieswith the amplitude of the signal. The larger the signa! level thefaster the settling time.

PARAMETER SYMBOL CONDITIONS

PositiveSupplyCurrent Is+ "N-ONegativeSupplyCurrent Is-

SupplyVoltageRange Vs

MIN TYP MAX UNITS

480 - 920 uA2.1 - 3.3 mA

:1:12 - :tIS V

-=-

r14v-

a Loa- CfIIIS13

1 IIAtE LOG SCALE 12

. EMITTER -LOG IN 11

-=-II LOGOUT

10.LOG INOBSOLETE

ANALOG DEVICES FAX-ON-DEMANDHOTLINE - Page 19

SSM~2110INPUT

TheINPUT(pin 17) is an ACvirtualground withapproximately+1.3V DC offset voltage. The usefuldynamicrangeof inputcurrent the device can process is 1COde (3mAp.p to 30nAp.p). The

input RC network is usually chosen to allow close to 20dB ofheadroom inorder to process highcrest factor signals and pro-vide a DC block below a given frequency band. Since in everycase the ratio of ROUT(RAVand RRMS)to RINdetermines theoverall gain of the circuit, ROUTmust also be considered whenselecting the low frequency breakpoint. The maximum recom.mended values for ROUTvary from 4kfl to 1akfl for the circuits inFigures 1,3,4, and 5.

Referring to the circuit in Figure 3, and assuming a gain of 1 isdesired, RINshould be set to 4kfl (RRMSand RAv'"4kfl). Basedon this value of R'N'GINshould be 2~F to place the subsonic filterpole at 20Hz. If you wish to limit the lower frequency to some-thing otherthan 20 Hzthen GINshould be changed accordingly.The low frequency pote 's governedby the simple equation

fMIN'" 1/27tRINC'N.

GIN should be a very low leakage capacitor to avoid impairingthe dynamic range at low signal levels (many electrolytic typeswill not work).

The choice of R'N;; 1akfl in Figure 1 is good for processing OdBVreference signals. Given a nominal signal level ofOdBV (2.828Vp.

p ".1 VRMS)'this voltage across the 10kfl input resistor gives anominal input current of 28311Ap-p,which allows 20dB of head-room. The three other common choices for R'Nare 4kfl, 5kfl and8kn. whichprovide 12dB, 14dB,and 18dBrespectively.

The values of GIN'RINand ROUTcan be changed accordingly tovary output levels to system requirements.

1.,--'O..A -40<1-,000A

-2Ode'OOI>A

...-'_A --'"AINPUTCURRENT

FIGURE 2: Normalized Time Constant Relative to 1mAAM$

The PREBIAS pin (pin 18), can be used to increase the speed ofthe RMS computing loop at low signal levels at some expense tothe dynamic range. Below a 10l!ARMS input level, the time con-stant ot the RMS loop will increase from its nominal value by afactor of 10 for every 20dB drop in level.

By use of the PRE BIAS pin, one can ensure thaI the loop timeconstant will not increase above a chosen maximum as the sig-nallevel continues to decrease. The equation relating the maxi.

mum time constant increase to the value of RpREBIASconnectedbetween pin 18 and V- is given by:

'MAX ".10~ x RPAEaAS'NOM 6.8V

(See Figure 2)

VAY(orV"va)

~

AB5<X.UTEVALUE PREBIAS ,e'

2 LOG'..VAL INPUT \7

3 VA'" V+ 16

4 OND \5

v- 14

RIN ~ V..

2"F - .,5V

41<U

v.....

~ !..tIUE

. I EMmeR

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

V.v.-IV...,RA.RIN

VAllIS.-V R-R'N

FIGURE 3: Simple RMS/Absolute Value/Average Absolute Value Configuration

'GOO

'110

j10

,y...- ' ;

!;

.,R,.e. ,OMO" !!

i=R... 31010

! I .....i"""'-

OBSOLETE

ANALOGDEVICESfAX-ON-DEMANDHOTLINE - Page 20

SSM-2110[

CAI/O

10pF

AAY

.IIV

VAV

.~~IW~~':"'~ ~~~E USEDTOA..v

VAVaIV-A;TYPICAL VALUES:

"",.IKnAAV"BIenc... 1~F

FIGURE 4: Absolute Value and Average Absolute ValueOutput

V_.

;~

":'

FIGURE5: 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 ABSOLUTEVALUE PREBIAII 18

Z LOGAN VAl. INPUT 17

3 V..., V. II

GNO15

5 MIS V- 14

""" 5 LOO- c- 137 BASE LOG SCALE 12

8 EMlTTEA 4.OG IN 11

t LOG OUT .LOG IN10

I AISOLUTE VALUE PRiBIAII 18

2 LOG.... VAl. INPUT 11

3 V- V. 18

"QND 15

51'tU8 V- 14

= 'L 13

1 8&SE LOGSCALE 12

. EIIITrIR 4.OG IN 11

t LOGOUT .lOG IN 10

V_.jV..""...d.....

TYPICAl VALUES:R...51<1)AOUT .51<>1

c", .I-'\sF.1F

OBSOLETE

AHALOGDEVICES fAX-OH-DEHAHD HOTLIHE - Page 21

SSM-2110

LINEAR OUTPUTS (ABSOLUTE VALUE AND RMS)The instantaneous absolute value ofthe inputsignalappears asa current absolute value pin (pin 1). The true RMS value of theinput signal similarly appears as a current into the RMS pin (pin5). With :t:15 volt supplies. the voltage compliance on theseoutputs is trom T 15 to -6 volts. For simple applications it ispossible to convert these currents to negative output voltagesby connecting a resistor in series with the pin(s) to ground (seeFigure 3). For a maximum 3mAp-p input signal, the resistor(s)value should be 4.0kQ or less. To obtain an average of the abso-lute value output, capacitor CAvacan be added in parallel withRAV'More commonly, a positive going voltage at tow impedance isdesired as an output. This can be accomplished by connecting alinear output pin to the virtual ground of an op amp configured asa current-to-voltage converter (see Figures 1 and 4). The scalelactorforthe conversion is determined by the value of R'Nand thefeedback resistor (RRMSor RAv)'For the absolute value circuit in Figure 4. a maximum feedbackresistor (RAv)of BkQ allows maximum swing of the SSM-2131output amplifier. Given a maximum output signal of 1.5mApEAKthe SSM-2131 willbe able to swing to +12V. Ifvalues larger thanBkQ are used. then signal clipping may result.

For the RMS output circuit in Figure 1. the maximum feedbackresistor (RAMS)can be 10kQ since the RMS level should neverexceed 1.2mA.

A peak output can be implemented by using the circuit in Figure5. The output scale factor is determined by Rour'R'N' The decaytime constant is equal to the product ROVTCHOLO'For this circuit,the feedback resistor (ROUT)should be kept below SkQ.A small capacitor (10pF) is usually added in parallel with thefeedback resistor for stability particularly ita high slew rate JFET

V..

V"-I (."'"

Ioouz~9~R

R"u,.V-

3-7JV

V~EI'

v-

input op amp is used. In Figure 4, this capacitor (CAVG)can bemade large to obtain an average ofthe absolute value output. Ifthe averaging circuit is implemented then R'Ncan be increasedto a maximum of 10kQ since the 1.5mA peaks will no longer bepresent.

Ifthe signal levels being processed are less than 3mAp.pthen theabove mentioned feedback resistors can be increased accord-ingly.The circuits in Figures 1 and 4 can be connected at the sametime providing the userwith multiple functions from a single SSM-2110. RIN' RAMSand RAVshould be set so that clipping does notoccur.

The linear output pins must be kept within their voltage compli-ance range for proper device operations. An unused linear out.put must always be terminated. preferably to ground.

LOG OUTPUTS (LOGRMS AND LOGABSVAL)

The log of the instantaneous absolute value and the log of trueRMS of the input signal appears as voltages on pins 2 and 6respectively. However, these outputs must be buffered. levelshifted and. in many applications, temperature compensated inorder to be made useful.

The log recovery transistor is an internal level shifting compo-nent which may be switched between the two log outputs. Thiswill reference the log output(s) to the internal voltage regulatorwhich is about 7.5V above the negative supply (see Figure 6).

Figures6.7, and 8show the recommended connection between

the log output transistor Q~or °10' and the log recovery transis-tor °11' Note that although the log recovery transistor can beswitched between the two log outputs, only one logoutput can

be recovered at a time. With the resistor values RREF1and AREF2shown, the output swing at the emitter of 0" over the dynamic

'Op/'

V.OOf-1

. A,g,.,. ""ID'I' R"... AND R..,... ARE EXTERNAL RESISTORS

V-

FIGURE6: Log Recovery Circuit

1.

OBSOLETE

ANALOGDEVICES fAX-ON-DEMAND HOTLINE - Page 22

SSM-2110

10pF

.l~A~J;v-

AAY

.,5V

VUIO(AVI

-=-

y-

A_, "'-"

'C.;.yo CAN 8. ADOED TO OBTAIN THE AVEIU4Ii 01' THE A88OI.UTI VALUti

FIGURE 7: Log of Absolute Value/Average Absolute Value

10pF

A....

.IIV

VUIO(I

V-

Roo ~ v..

~O"I'"

~~O.,""

Aec.au

~V-4IONI)

v.J1!15

~ ~I

A8IIOLUTII VALUI I'flllILU - ----- - ,2 LOG_yAI. INPUT 17 1

.... ,,-, "'-

'OI'TIDICAL- CONNEC'TJ()III,lEE TEXT

AGURE 8: Log of RMS

~~.~

........

.,5V(

"0.'" VyAAVlog (~) J

VLOO\AVI - R'CALI I"", x I"...,

-15'1_JIIIi I".~, . ..UYA".;;-

I"." . ~. . '.....IfiiUa

TYI'ICAL VALUES:

Roo.IGknc,., .o""'"AAV,'I,1IcO~...nnA"",., . 1.51kl",-.~VLOO\AY,;; log !..ftuoL\

l00mvl

Rw ~ v..o11V

~O.,""~,*°,'""

-\IV

11~"""'i'i0.14&x R- log\. A'N I

VLOOm..) - AaCALI I"... ' ""'"

WHIM! I. 1VI"", . A"."""" . JAY . 3j.AA"."

TYPICAL VoU.UU:

Roo' IGknc,.,. 0""'""- . II1.111Q~ .4.1IIQ"-' .1.51kl"-- .43OIon~.1""

VLOOIAMIII;; log ~V,~~i)

1 A880LUTIVoU.UIiI'A8I1A8 II

Z LOG""VAL INPUT 17

3 V.., V. 11

4 CHI) 11

lA118 v- 14

.... I 1.00-'3

7 IA8E LOGICAU! 12

I EMInI'A

. LOGOUT

- v_- . Loa- 1J

7- LOGSCALI '2

I DUrEA

. LOGOUT

OBSOLETE

~~M-lllU

ANALOG DEVICES fAX-ON-DEMAND HOTLINE - Page 23

range of the device will be roughly symmetrical about the inter-nal negative voltage reference. Also. the output impedance willbe low enough to drive the log amplifier's input(s) without intro-ducing significant errors. The bias current into the pins of the logamplifier is typically less than 1J.lAbut can be as high as 21lA. Forthis reason the current through the log recovery transistor A"should always be set higher than 51-1A.The current 'REFI shouldnot be set too high (above SellA) because the base current of

0'0 induces errors in the RMS computing loop. If higher referencecurrents are required then they should be taken care of by

changing the current through Olj' This can be done by changingRREF2'The Log Recovery Amplifier Section explains this in moredetail.

The output sensitivity at EMITTER (pin 8) is about +60mV forevery 1Ode of signal level increase at 25°C. This sensitivity hasa temperature coefficient of +3300ppm/oC.

The fog of absolute value output can be converted to a log ofmean value by connecting a capacitor between LOGABSVAL(pin2) and V- (see Figure 7). Since this is an emitter follower output.the response to a large-signal level increase will be fast whilethe time constant of the output following a large-signal level de-crease will be determined by the product of capacitor CAVGandresistor RREFI'

One might think that connecting a capacitor to the log outputwould produce the average of the log of the absolute value.However, since the capacitor enforces an AC ground at theemitter of the output transistor, the capacitor charging currentsare proportionalto the antilog ofthe signal atthe base. Since thebase voltage is the log of the absolute value, the log and theantilog terms cancel, and the capacitor is charged as a linearintegrator with a current directly proportional to the absolute valueof the input current. This effectively inverts the order of the av-eraging and logging operations. The signal at the output. there-fore, is the log of the average of the absolute value of the inputsignal.

LOG RECOVERY AMPLIFIER (PINS 9,10,11 AND 12)

The log recovery amplifier is a linearized voltage-to-currenttransconductor whose gain can be made proportional to abso-lute temperature. It is used to reference the log output( s) to groundand also to temperature compensate the VT (KT/q) terms in thelog output recovery transistors (0/0'0 anda,,).One input of the log recovery amplifier is usually connected toEMITTER (the emitter of the log recovery transistor-pin 8) while

the other is connected to VREF(pin 3).Figure 6 shows the internal and external connections used to

obtain an output voltage equal to VlOG(RMSr The transfer char-acteristic of the log recovery transistors is given by the followingequation:

.1VIN ,. VT x In(

VIN(RMS)/RIN) 2

)IREF' x IAEF2

where, IREF' = (8.W )RREF'

IREF2 '" (7.5V )+ 1J.lA~EF2

The transfer characteristic of the log recovery amplifier is givenby the following equation:

lOUT = 64mV.1 V1NRSCALE VT

Combining the two equations yields the overall transfer charac-

teristic for the ouput voltage VlOGIRMSj:

V O.148xRRMS I(

(VINlR,N) 2LOG (AMS) = x og

RSCALE IREFI x I REF2

IREF' '" (8.1 V

)~EFI

'REF2 '" (7.5V )+ 1IJARREF2

Ideally this voltage is completely independent of temperature.However, due to the temperature coefficientof several transis-tors internal to the SSM-211 0, this is not entirely true. The tem-perature coefficient is approximately :t75ppm/aC.

With the values shown in Figures 7 and S, this transfer functioncorresponds to an output change of 50mV/dB, The referencecurrent is set to 10IJ.Ato provide the widest possible dynamicrange. The following results can be expected for the circuit inFigure 8:

where,

An RSCAlEvalue of approximately 4.7kQ gives the best overalllinearityand temperature compensation performance. This IS animprovement of about a factor of 40 over the uncompensateddrift. A 2k.a resistor in series with a silicon diode can be connectedfrom LOG SCALE (pin 12) to the negative supply to defeat thetemperature compensation for certain applications such ascompressorllimiters where the log drift will cancel the thermalgain drift of a VCA's dB/volt control port.

The maximum output current for both the compensated anduncompensated examples above is :!:250~A. This output currentis converted to a voltage with the circuits in Figures 7 and S. Forthese circuits this corresponds to a maximum output voltage of

:!:3.975V.If RSCAlE is changed from the nominal value of 4.7knthe maximum output current will also change by the followingequation:

ILOGOUT(MAX)'"' 1.1SVRSCALE

If the log recovery amplifier is not used, +LOGIN (pin 10) and -LOG IN (pin 11) must be connected to VREF(pin 3) for properoperation of the rest of the circuit.

It is possible to use one of the log configurations in Figure 7 or 8in conjunction with the linear output circuits (Figures 1.3.4 and5) but care must be taken in choosing the appropriate resistorvalues. This provides the user with substantial flexibility from asingle device.

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

iv, "" OUT -3V -2V -'V ov 1V ! 2V

OBSOLETE

ANALOGDEVICES fAX-ON-DEMAND HOTLINE

[' .-

- Page c~

SSM-211D

1 AIISOUITE VA~UE "RE81A11 II

2 ~O<IA"V"" ~ 11

3 VAl, Y. ,.

4 aND 15

$- V-'4. LOG- ew. 137 lASE ~OGSCA~I! 12

. EIIoIIT'TER -I.OGIN 11

, LOGOUT .I.OGIN 1.0

v.

i1.51«)

1001d1 +-./l1lI'-OFFSI!TT-

v-

131cn SCAL!!TAJM -IIIQ

10p/'

VLQQ(-I

1.5MG S37~

.".1OOI<Q

REFEAEHCETRIllV-

FIGURE 9: Error Trimming

ERROR TRIMMING

The offset, reference and scale factor trims (Figure 9) can beused to improve the overall accuracy of the device. The correctprocedure for trimming outthe various errors is as follows. First,+LOG IN (pin 10) and -LOG IN(pin 11) should be connected toVREF(pin 3). The offset trim should be adjusted to achieve OV at

the VLOG(RMS)output. This nulls out any DC errors due to offsetsin the log recovery amplifier. Second, reconnect the f:LOG INpins as shown in Figure 9. Apply an input signal of 1OOmV RMS

(1O~ARM_!»'Adjust the reference trim to obtain OVat the VLOG(RMS)output. This compensates for the input bias current of the log

10loI) 0.81>'

r-ov...15V

-I$V

".841<0

recovery amplifier and other errors. It sets the reference current

to 10f.1A.Third. change the input signal to 1VR'-AS(1 OO!lARMS)'

Adjustthe scale trim toobtain 1.OODVat the VLOG(RMS)output. Thisadjusts the scale factor to obtain 1V/20dB (50mV/dB). If otherreference currents or scale factors are used then steps 2 and 3will have to be changed accordingly.

This same procedure can be used for the log absolute value andlog average absolute value configurations. If the log recoveryamplifier is not used then the circuit in Figure 10 should be usedto trim the offsets.

OBSOLETE

ANALOG DEVICES fAX-ON-DEMAND HOTLINE

SSM-2110- Page 25

V.

~

I~l_n~

OfI'SETTl't1M

v-

-

I ABSOLUTEVALUE2 .

LOOMS VAl.

3 V"...

4QHO

5-I Loa,..7 BASI

. EIIIITT1:R

\I LOG OUT

PflEBlAS

~

1'

INPIJT 17

V. II

.!!

V_

~

14

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-

':"

FIGURE10: Offset Trimming

AVERAGE OF CRESTABSOLUTE FACTORVALUE Vp

WAVEFORM RMS (AAV> = RMsi

Vp * /"'\'II

Vp 2.Vpi

"-/./2=1.414 I

ViI

It

SINE WAVE---

Vp *;

-Vp Vp l ' i

I

i

SQUARE WAVE j

--" I

, ,

Vp * A !

Vp Vp-/3 '"1.732V 7i 7i

TRIANGLE WAVE--..-'

2Vp1

A /'Typically varies from 1 to 6 de-

RMS A xRMSpending on the characteristic of

the noise. Theoretically, the

crest factor is unlimited.

GAUSSIAN NOISE :

FIGURE11: RMS, Average of Absolute Value and Crest Factors for Different Waveforms

A

OBSOLETE

ANALOGDEVICESfAX-ON-DEHANDHOTLINE - Page 26

SSM-2110

-15V

10lIO

3.321<11

NOM-INVEImNO

INPUT

INVER11NGINPUT

ONO

....

an

GAIN > 1110LIMIT

O.02~F SSM-2110

l1r1n

.15V

r

-15V

31.11<11w---112 Op.215GP

-:

I00kI}

5

AGC ~ 1011nfW.I!ASI

.-FAST

22Mt1-: OUTPUT UOVEL

..

10l<U

-: -:I0

-IIV1.sIID

U, _2013U2' Us SSIII-21:MU. _2110U. 1I2OP-21-U. 1120p.21-

R.15110 NOTE: U2'US'U,,' U.

POWERSUPPLYCOHIIECTtONSAltO BYPASSINGARENOTSNO-

! I

-: -11V

TYPICAL APPLICATIONS

AUTOMATIC GAIN CONTROL (AGC) AMPLIFIERThe automatic gain control amplifiershown below features se-lectable gain reduction compression ratios and time domainadjustable AGC attack and release. The design employs theSSM-2013 VCA. SSM-2110 true RMS-to-DCconverter. twoSSM-2134lownoiseopampsand an OP-215 FETinputop amp.Foradditionalinformation about this circuit.please see appli-cation note AN-116.

I

tOlln

GAINTtON

-15V

OISTNULL

-'IV

111<11 YO.1F,

-::JOpf

,(

I00kI}

U, 14

MI'-

.

In'O,

1 10

==1--co. nnr-. n__; 5OpF £:

1N1td

1N1148tl2 OP-2t5GP

"TrACt( O.O,I)'F

-=

IHt14

1Ok!}OBSOLETE