OT changing font in PDF

Hi all, I downloaded this AN from TI,

a471a&fileType=pdf

?Effect of heavy loads on the accuracy and linearity of opamps? (4Mb file)

And found the font to be almost unreadable. Is there anyway to change the font in a PDF document? Just making it bigger doesn?t seem to help at all.

Thanks

George H.

It's searchable, so extractable. So select the text and paste into a text file. Or wear your glasses ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

It IS text, but you put your finger on it... it was scanned then OCR'd.

Since I was able to select text, it might be possible to select, process-out the bold in a text editor, then paste back-in. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Which pdf viewer are you using ??

Looks just fine here, Firefox, Adobe Reader X, works in the browser.

hamilton

Though, I seem to recall a post that discussed a PDF-to-DOC converter?? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

I saved it, opened it in Acrobat reader X, then saved it as text:

LF356,LF411,LF412,LF442,LM10,LM1458, LM318,LM324,LM358,LM6142,LM741,LM8262, LM833,LMC6022,LMC6042,LMC6062,LMC6482, LMC6492,LMC660,LMC662,LME49720,LMP2012, LMV751,LMV771,LMV932

Application Note 1485 The Effect of Heavy Loads on the Accuracy and

Linearityof Operational Amplifier Circuits

Literature Number: SNOA471A

 The Effect AN-1485Operational

The Effect of Heavy Loads on the Accuracy and Linearity of Operational Amplifier Circuits (or, "What's All this Output Impedance Stuff, Anyhow?")

!#

Introduction

Itis well known that the ideal operational amplifier (op amp) should have very high gain, very high bandwidth, very high inputimpedance, andvery lowoutputimpedance. 1 It is possible to get conventional amplifiers with very high gain (120 dBorhigher), andvery highbandwidth(100MHz, 1000MHz, or more). However, most op amps do not have a very low open-loopoutputimpedance(Zout). Only afewareaslowas

50ohms, andcandrivea50-ohmloadwithoutany significant degradation ofgain (barely 2:1). See Figure 1.

20194945

FIGURE 1. Model of Operational Amplifier (Op-Amp) with finite output impedance Ro. If Ro is significant compared to RL, the effective Av (Vout/ VE) will be degraded vs. Avol.

Many opampsdesignedoverthelast50years haveClass B or class A-B emitter-follower output stages, which help providelowoutputimpedanceandhighefficiency. Manyofthese usematurebipolartransistortechnology, andcanoperateon ± 15 volts. See Figure 2a.

National Semiconductor Application Note 1485 Bob Pease May 7, 2008

20194946

FIGURE 2. (a) Conventional high-gain Op-Amp with emitter-follower output stage (simplified). (b) Op-amp with collector-loaded "rail-to-rail" output stage (simplified).

(c) CMOS Op-amp with drain-loaded "rail-to-rail" output stage (simplified) It is also known that the closed-loop output impedance of a typical operational amplifier can be MUCH lower than the open-loopoutputimpedance. Ifan op amphas, forexample, an open-loop gain of 10,000, and its open-loop output impedance is 50 ohms, the output impedance after the loop is closed can be as low as 50 milliohms or lower, depending ontheapplication(assumingtheamplifierisusedatagainof

5orlower). Soformany applications, atleastatlowfrequencies, it is a fair statement that the closed-loop output impedance can be very low.

However, anewclassofamplifiershasbeenintroducedover thelast30years, whichdonothaveemitter-followeroutputs. Why not? Because many of the new amplifiers are designed tooperateonlowvoltagessuchas± 5volts,or± 2.5volt,or ± 0.9voltsorsometimesevenlower. Formaximumsignal-tonoise ratio, the output must swing from (nearly) the + rail to (nearly) the -rail. 2

Obviously any emitter-followers would reduce the output swing by about 0.7 volts in either direction (and even worse atcoldtemperatures), soamplifierdesignsthatusefollowers havebecomeobsoleteforsuchlow-voltageapplications.See Figure 2b.

©2008NationalSemiconductorCorporation 201949

 AN-1485

The first "rail-to-rail" output stage was introduced in Bob Widlar'sLM10. Thiswasdesignedandreleasedin1976, and is still in production. It can operate from ± 20 volts to ± 0.6 volts(orfrom40voltsdownto1.2-voltsoftotalpowersupply) and its outputcan swing within a fewdozens millivolts ofthe power supply rails. It does not have any output emitter followers. The LM10's output consists of one big NPN output stagetopulltheoutputdown,andsink15to20mA ofcurrent, and comparable PNP transistors tosource as much as 15 to

20 mA. It has some very complicated bias circuits to make sure these two transistors take turns at driving the load, as required. Figure 2b.

Morerecently,overthelast15years,therehavebeendozens ofdifferentdesigns,mostly usingCMOS technology,andall have "Drain-loaded" outputs, with N-channel and P-channel FETs which can source and sink many milliamperes, Figure

2c. These all havehighoutputimpedances. Oneway to look atitis, thatthegaingetslowerwhenyouloadtheoutputwith aheavy load. Anotherway tolookatitis, thatthegainRISES when the load gets lighter. See Figure 3.

In concept, a Drain-loaded output stage could use negative feedback to an internal stage, so that the gain would not change much as the load gets heavy or light. Practically, it wouldtakealotofhigh-valueresistorstoaccomplishthis,and suchresistorswouldbevery expensiveinmonolithicIC technology. In practice, the disadvantage that the gain changes as the load is changed, is not serious. This is largely because thegainisveryhighwhentheloadisheavy, anditjustgets higher when the load is lightened.

20194947

FIGURE 3. Bode plot for high-gain amplifiers with various DC gains, operating at a gain of 1000.

Ionceheardsomeengineersarguethatthereisnoadvantage whenanopamp'sgaingetsvery high, andinconceptthere maybedisadvantages.Oneargumentisthatthereisnoneed forany op-amptohaveagaingreaterthan200,000, because ifthe gain gets higher, itwould have to be tested atvery low frequencies,lowerthan0.1 Hz.Suchtestingwouldtakemany seconds, and this testing would be quite expensive, and nobody would want to pay for that.

However, this turns out to be untrue, as modern amplifier testing can resolve a "dc gain"as high as 2 million or20 million, injustafewmilliseconds. No20-secondtestisrequired. Anoperationalamplifierwith1 MHzofGain-BandwidthProduct, operatingataclosed-loopgainof1000,hasaclosed-loop bandwidthof1 kHz.Thusitstimeconstantis160"seconds, and it can settle in less than 20 tau, or 4 milliseconds, per Figure 3.

Initsgaintest, theoutputisrequiredtogotoitspositiverated output, and the input error settles quickly and is then mea

sured, for perhaps 16 milliseconds. The output is then requiredtogotoitsnegativeratedoutput, theinputsettles, and then is measured again. The gain depends on the reciprocal ofthesmalldifferencebetweenthoseinputtests. Thisiseasy todoquickly, evenforhighgains. Ittakeslessthan1/10second, not"several" seconds, to testforamplifiers even with a gainof1 millionor10millionormore.See Figure 3.

FIGURE 4. Gain test where Av = 1000 x Vout / 1000 x

VE, using separate preamplifier and X-Y oscilloscope.

Another argument is that an amplifier with a gain of 2 million or 20 million, would not be useful except for signals slower than 0.1 Hz. This also turns out to be a misconception. If a modernop-ampisconnectedforagainof+ 1000.00, anda

1.0 mV dc signal is applied to the input, the outputwill settle inafewmilliseconds, perFigure 5. However, anampliferwith ameregainof200,000wouldsettleitsoutputto995millivolts. A gainof2millionwouldsettleto999.5millivolts, andanamplifierwith a gain of20 million will settle to 999.95 millivolts in milliseconds! MUCH betteraccuracy. 20194960

FIGURE 5. High-gain amplifier operating at a gain of 1000. Its precision depends on high Avol (and low Vos).

Furthermore, ifyouputin1.0000millivoltp-psinewaves, at

5 or 10 Hz or 20 Hz, the output amplitudes of those three amplifiers would be, respectively, 995 mv p-p, 999.5 mv p-p, and999.95mV,p-p.Evenat10or20Hz,aprecisionamplifier canprovideenhancedaccuracyoverlow-gainamplifiers.The claimthatahighopen-loopgainat0.1 or0.01 Hzisuseless, unlessyoursignalisat0.01 Hz,isjustincorrect.

Some other engineers say that an amplifier with high output impedanceandgoodgain(suchas1 millionat1 Hz) canhave its dcgainriseto10millionormore, iftheratedloadis taken off. TheDC gainwouldrisesohigh, they claim,thatwhenit startstorolloff, itwouldrollofftoofast, withexcessivephase shift, and be unstable. Refer to Figure 6. In actuality, all opamps thesedays havesmooth6-dBperoctaverolloff, all the way back to very lowfrequencies. Op amps thatrolled offat

2

 10or12dBperoctave, whentheratedloadistakenoff, have notbeen seen forover30 years.

20194948

FIGURE 6. High-gain amplifiers with extremely high gain.

So an operational amplifierwith very high gain actually does have some good advantages, and not really any disadvantages.

When an op-amp is asked to drive a heavy outputcurrent, it can have large errors if it does not have plenty of gor

m

transconductance. Thisistruewhetherithasoutputfollowers and low output impedance, OR if it has high output impedance.Sothegisveryimportant,andagoodamplifier

m

design must have an appropriate amount of g-plenty of

m

mhos (milliamperes per millivolt). Many precision amplifiers havemanymhosofg.Asweshallsee,precisionamplifiers

m

such as the LM627, LMC6022 , and LMP2012 have a gof

m

atleast10,000mhos.Otherpopularamplifiershave50to500 mhos. Special-purpose amplifiers may have as little as 2 to

20 mhos, which may be adequate for particular needs.

Instrumentation

Many modern op amps have such high gain that a preamp with a gain such as 1000 is needed, to let you see the gain error.Eventhen,atime-basedscopedoesnotletyouresolve the linear and nonlinear components of the gain error. So I used a Tektronix 2465 (analog) oscilloscope in X-Y(crossplot) mode. Onegoodwaytotesttheamplifieristoconnect the Device Under Test (DUT) as a unity-gain inverter as showninFigure 4 andfeedtheoutputoftheDUTtothescope horizontal display, through a 10X (10 megohm) probe. The outputwasalsofedtooneoftheverticalchannels, sowesee the cross-plot of Vout versus itself, as a straight line, with a slope of + 45 degrees. Typically, the first amplifiers I tested werehigh-voltagebipolaramplifiersswinging± 10volts, with thescopesetat5volts perdivision. Thesignalsourcewasa Wavetek 193, withadjustableamplitudeandvariableDC offset. I used the variable offset to adjust the output to swing exactly± 10volts,forthehigh-voltageamplifiers.Theoutput swingwassetat± 4voltpeaksforCMOSamplifiersrunning on ± 5 volts, and ± 2.0 volts for amplifiers running on ± 2.5 volts, in general.

The -input voltage (the gain error) is fed to a preamp with a gainof+1000. Thiswassometimesfeddirectly tothescope's verticalinput(DC coupled) atsensitivitiesvaryingfrom2000 mV to5mV perdivision,yieldingaresolutionof2mV down to5 "V perdivision. By usingthecross-plotmode, itwaspossibletoresolve1 or2 "V p-p ofgain errorin the presence of afewmicrovoltsofnoise. Foramplifierswithlargeoffsetvoltage, I fed the signal in to the scope's DC input through 11

"F, so that 0.2 Hz signals could be resolved without appreciable phase shift. ThetestcircuitIactually usedwasFigure 7, with the amplifier actingas aunity gaininverterforthesignals, andactingas a preampofgain= 1000foritsownerrorsignals. Thismakes the test set-up easier. The output voltage is plotted in each Testasastraightlineat45° slope, versusthesamesignalon thehorizontalaxis. Theoutputvoltageispositiveandtheoutput is sourcing current on the right side of each Figure, and theoutputvoltageisnegative, andsinkingcurrent, ontheleft.

20194950

FIGURE 7. Gain test where the DUT acts as its own preamp. Gain = 1001 x ( Vvert)/( Vhoriz.)

Igenerally usedatrianglewaveforalmostalltests.Thisgave betterresolution ofp-p errors forthegaintest, anditallowed metorunatmoderatefrequencies(1 to10to80Hz)andnot gettheDC gainerrorsignalconfoundedby theacgainerror. Referto Figure 31, theplotofTestA11. Eventhoughthegain at8Hz onthisamplifierwasjust2,500,000, Iwas easily able to resolve the 2.5 "V of gain error, which is completely independent from the AC gain error. The AC gain error (due to finite gain-bandwith product) causes the upper and lower traces to separate by 8 "V, yetwecanstill seethe"DC" gain errorof2.5"V (gainof8million).ThegainerroristheSLOPE of either the upper or the lower trace, as the output ramps back and forth. This gives muchbetterresolutionthan a sine wave, and is easierto instrumentata highersweep rate.

For example... measuring the dc gain of the LMP2012 with TestF01A wouldrequireoperatingatsinefrequenciesbelow

0.1 Hz;butbyusinga2Hztrianglewave,wecouldseethat the DC slope would be less than 1 "V at 0.01Hz, by "subtracting" the opening between the upper and lower traces. AN-1485

3

 AN-1485

20194907

TestD07B,LMC6022 F=2Hz. Vs = ± 5Vdc;Vout= ± 4voltspeak,Iout= ± 4mA peak. UpperTrace: Gain Error, No Load, 4"V p-p at20"V/div. Middle Trace: Gain Error, Full Load, 7"V p-p at20"V/div. (TRIANGLE) LowerTrace: Gain Error, Full Load, 7"V p-pat20"V/div. (SINE)

FIGURE 8.

Also,whenwestartseeingnonlinearity,wecaneasilyresolve whatis nonlinear, because the errorcorrelates with the locationontheX- Y plot.InFigure 8,weseethecurvestakenfrom TestD07B. Thisisanexampleofanamplifier, theLMC6022, with distortion down near 1/2 ppm (+/- 2 "V). When we use triangle waves itis easy to see this distortion, perthe middle trace. Ifwe relied on sine waves, itwould be hard to resolve this amountofdistortion, perthe lowestcurve.

20194921

TestA01,LM709,CurveofGainError, F=10Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: Gain Error, No Load, 480"V p-pat200"V/div. LowerTrace: Gain Error, Full Load, 540"V p-pat200"V/div.

FIGURE 9.

Bipolar Amplifiers -- And Funny Errors

I started by measuring the old LM709, one ofthe firstmonolithicop- amps,almost40yearsold.Thiswasagoodtest.The gainerrorat1 megohmloadwas480microvolts,sotheAv was 42,000 at10 Hz. This was safely betterthan the 25,000 publishedspecofthedevice.Ithenappliedthe1 kilohmload.

Most of these op amps were rated to drive a 2 kilohm load, but I put on a 1k load, to see what was going to happen. It madeerrorsabouttwiceasbigasthey wouldhavebeenwith a2k load, which was slightly unfair, buthelped the resolution of the errors, which were often pretty small. (On rare occasions, I could tell thata 1k load was unfair, so I wouldre-test ata 2k load, to see whatwas really going on atrated load.)

InthecaseoftheLM709, (Figure 9) a1kloadactuallycaused theoverallgainslopetodegradeby about60"V. This corresponds to an output impedance of about 120 ohms, not too bad. However, there was definitely some non-linear error about

80 "V p-p. Where did that came from? This nonlinear errorseemstobebiggerthanthelinearerrorcausedbyZout.

FIGURE 10. AN-A shows that the heat from an amplifier's output transistors can flow past its input transistors.

Thishasbeenthoroughlyanalyzedina1975technicalarticle, knownasNSC ApplicationNoteA (AN-A)byJamesSolomon. This App Noteanalyzes thecircuitandlayoutofamonolithic amplifier, where an outputstagedrives a heavy load. Oneor the otherofthe outputtransistors gets warmto the extentof

25 or 50 milliwatts, and sends thermal gradients across the IC chip. SeeFigure 12. Foracompleteoverview, refertoAN- A at . But in their simplest form, the drawings from AN-A are included here. Figure 11 and Figure 13 show that a mere 49 milliwatts can causea40milli-degreeC temperaturegradient, betweenthe inputtransistors oftheop-amp, located10milli-inches apart. If the input transistors were laid out transverse to the heat gradient, they would be heated to the same extent, and the thermal error referred to input could have been quite small. TheLM709'sinputtransistorsareQ1 andQ2,perFigure 14. They were located along the gradient, 10 milli-inches apart, (Figure 15) and did a very good job of detecting the thermal gradient. Every competitor who copied Widlar's LM709 was afraid to change anything, for fear of making something worse!EvenaftertheLM709becameobsolescent, otheramplifiers' layouts still didnotdoavery goodjobofrejectingthe thermal gradients, formany years.

4

 AN-1485

20194951

FIGURE 11. AN-A shows the shape of the input error caused by output heat flow, when cross-plotted vs. Vout on an X-Y scope.

20194954

FIGURE 12. AN-A shows the shape of the input error caused by output heat flow, when cross-plotted vs. Vout on an X-Y scope.

5

 AN-1485

20194953

FIGURE 13. AN-A shows that the shape of the error voltage (gain error) can be a summation of electrical and thermal errors. Compare to Figure 9.

20194957

FIGURE 14. Schematic Diagram of the LM709.

6

 AN-1485

20194958

FIGURE 15. Layout of LM709 Die. The spacing from Q1 to Q13 or Q14 is 56 milli-inches, and to Q2 is 10 mils.

Eventually,neweramplifierstookadvantageofsymmetryand common-centroid layouts (See at "What's All This Common- Centroid Stuff, Anyhow?")

Index.cfm?ArticleID=6121 to reject thermal gradi

3

ents. Most of the CMOS amplifiers we will study, below, do nothaveany appreciablethermalerrors, becausetheCMOS amplifiers were carefully laid out with good layouts to reject thermal gradients. These wereaccomplished mostly withthe use ofsymmetry, and notwith the use ofcomputers. Thatis because computers are not generally suitable for analyzing theheatflowamongthemillionsofpointsinsideasilicondie, nottomentionthethousandsofpointsintime,whenathermal transient occurs. Also, if an amplifier is modelled in SPICE, theSPICE modelsofmosttransistorsdonotallowthetransistors to be at different temperatures. New and improved transistor models do now (2001 to 2006) have the ability to analyzetemperaturedifferences, butthesemodels arebulky and slow and not highly successful. Symmetry generally works much better.

Other than that, the LM709's gain error was quite adequate for most applications. And if the 709 was run with a load of notsuchaheavy resistanceas1kor2k, but4kohmstotal, its linearity would be as low as 2 ppm. So even the oldest amplifierdesigns are nottoo bad.

The nextexample ofa good amplifierwith imperfectthermal layoutis thefamiliarLM301A, perFigure 16. Its no-load gain wasmeasuredat280,000. Butatfullload, itsnon-linearerror is also about 80 "V p-p. This, too, gives acceptable over-all performance. Figure 17 shows an LM301A's thermal errors at various frequencies. The errors at 2 Hz are as expected. When the frequency increases to 20 Hz, the thermal errors are decreasing rapidly. At200 Hz, they haveshrunk to a low level, sothedistortionismuchless. Thisisacharacteristicof thermalerrors,thattheydecreaserapidlyathighfrequencies.

7

 AN-1485

20194961

TestA02,LM301A,CurveofGainError, F=5Hz Vs = +/-15Vdc;Vout= +/-10voltspeak,Iout= +/-10mA peak. UpperTrace: Gain Error, No Load, +75"V p-p at100"V/div. LowerTrace: Gain Error, Full Load, 70"V p-p at100 "V/div.

FIGURE 16.

TestA02B, LM301A, Curve ofGain Error. Vs = +/-15Vdc;Vout= +/-10voltspeak,Iout= +/-10mA peak. UpperTrace: Gain Error, Full Load, 60"Vp-p at100"V/div., F = 2 Hz

Middle Trace: Gain Error, Full Load, 60"Vp-p at100"V/div.,F = 20Hz LowerTrace: Gain Error, Full Load, 25"Vp-p at100"V/div.,F = 200Hz.

FIGURE 17.

8

 Group A: High-Voltage Amplifiers

Nowwewillgothroughabiglistofoperationalamplifiersthat runon± 15volts,andaredesignedwithmostlybipolartransistors. Manyoftheseolderamplifiershaveimperfectthermal errors, butthere are some exceptions.

Test A01 is the LM709, as we have already discussed, included here just for comparison with the other amplifiers in this group.

20194921

TestA01,LM709,CurveofGainError, F=10Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: Gain Error, No Load, 480"V p-pat200"V/div. LowerTrace: Gain Error, Full Load, 540"V p-pat200"V/div.

FIGURE 18. Test A02 is the LM301, included again, forcomparison.

20194961

TestA02,LM101A, F=10Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: Gain Error, No Load, +28"V p-p at20"V/div. LowerTrace: Gain Error, Full Load, 30"V p-p at50"V/div.

FIGURE 19.

20194923

TestA02B,LM301, F=4Hz VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA Peak. UpperTrace: Gain Error, No Load, 6"V p-p at20"V/div. LowerTrace: Gain Error, Full Load, 90"V p-p at50"V/div.

FIGURE 20.

Test A03 isanLM741. It, toohassignificantthermalerrors. Note that the left-side hump is larger than the right-hand hump, indicating that the output transistor that sinks current has more thermal effectthan the one thatsources.

20194924

TestA03,LM741, F=2Hz VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA Peak. UpperTrace: Gain Error, No Load, +9"V p-p at20"V/div. LowerTrace: Gain Error, Full Load, 120"V p-pat50"V/div.

FIGURE 21.

AN-1485

9

 AN-1485

20194925

TestA03B,LM741, F=1Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 20"V p-pat50"V/div. LowerTrace: GainError, Full Load, 120"V p-pat50"V/div.

FIGURE 22.

Test A04 istheoldLM725,notbasedontheFairchild"A725. Thisamplifierhadmuchlowerthermalerrorsthantheamplifierswehaveseensofar, reflectinganimprovedlayout. This was a 3-stage amplifier with much higher dc gain, about 2 millionatnoload, and1.8millionevenatfull load. However, this designhadalargedie, was expensive, was hardtoprovidewithdampingcomponents, andwasneverpopular.But itdidhaveimprovedlinearity andlowthermal errors.

NOTE thatthe frequency response caused the p-p dynamic errorto be about5"V p-p largeratthe right-hand side, than attheleft.ThisisbecausetheLM725wasdampedlargelyby diodecapacitances, ratherthanby discretedampingcapacitors. Thecapacitancewaslargerwhentheoutputvoltagewas positive.Itisalsonoticeabletoseethelittleblipastheoutput hasabitofcross-overdistortionat0volts. Still, weareonly seeing these tiny errors (with a resolution ofabout2"V) because this amplifier's gain and noise arebetterthan mostof thepreviousamplifiers.Atmoderateloadssuchas4kohms, itwascapableofabout0.1 ppmlinearity.

20194926

TestA04,LM725*, F=75Hz. VS= ±15Vdc;Vout= ±9voltspeak,Iout= ±9mA peak. UpperTrace: GainError, NoLoad, 10"V p-pat20"V/div. LowerTrace: GainError, Full Load, 11"V p-pat20"V/div.

FIGURE 23.

Test A05 istheoldLM308.Itsthermalerrorshumpuponone side, and downontheotherside, indicatingthatthethermal errorscoupleintotheinputstagedifferentlyforoutputssourcingvs. sinkingcurrents.This,too,isdownnear1 or2ppmof error. However, the LM308 was only rated for a 2 mA load, and this unitwas run atjust5 mA, as itcould notdrive a 1k resistiveload.

20194927

TestA05,LM308, F=100Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±5mA peak.(RL= 2k) UpperTrace: GainError, NoLoad, 40"V p-pat50"V/div. LowerTrace: GainError, Full Load, 80"V p-pat50"V/div.(F = 2Hz)

FIGURE 24.

Test A05B isanolderLM308. Wedon'tknowhowold--perhaps25or30years-- butthisshowsthatthechiplayoutwas quite different, with a distinctly different thermal signature, compared to Test A05. The total thermal error is not much betterthan A05, butitsure is different! RobertWidlarmade manyexperimentsofdifferentlayouts.Mostamplifierdesignersmadeonelayout, butWidlarknewthatitwasimportantto try differentlayouts, as layoutis such an importantfactor in amplifierperformance.

20194928

TestA05B,LM308,OLD, F=4Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 160"V p-pat100"V/div. LowerTrace: GainError, Full Load, 260"V p-pat100"V/div.

FIGURE 25.

10

 AN-1485

Test A06 is theoldLM318. This is notaperfectdesign, and Test A08 istheLF411,withBiFET(TM) inputFETs.Itused notaverygoodthermallayout,butitwasveryfast,andran averycomplicatedlayout,thatdidnotworkespeciallywell, ratherrich,andhot,anditsmediocrethermalerrorsareac-intermsofgainorthermals.Nobetterthanaverage. ceptablecomparedtogeneral-purposeamplifiers.

20194929

TestA06,LM318, F=10Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 40"V p-pat50"V/div. LowerTrace:GainError,FullLoad,+ 125"V p-pat50"V/div.

FIGURE 26.

Test A07 isanNSC OP-07.Itsthermalerrorsarenotappreciably betterthannormal.

20194930

TestA07,OP-07*, F=1.2Hz. VS= ±15Vdc;Vout= ±7.5voltspeak,Iout= ±7.50mA peak. UpperTrace: GainError, NoLoad, 18"V p-pat20"V/div. LowerTrace: GainError, Full Load, 26"V p-pat20"V/div.

FIGURE 27.

20194931

TestA08,LF411, F=6Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 24"V p-pat50"V/div. LowerTrace:GainError,FullLoad,+ 140"V p-pat50"V/div.

FIGURE 28.

Test A09 was the older LF356 BiFET amplifier. It had a unique and proprietary outputstage, thatworked justso-so. Itdidprovideadequateoutputimpedanceat4MHz,soitwas alittlefasterthanmostofthegeneral-purposeamplifiers.But itsnonlinearity wasonly average.

20194932

TestA09,LF356, F=6Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 55"V p-pat50"V/div. LowerTrace:GainError,FullLoad,+ 130"V p-pat50"V/div.

FIGURE 29.

11

 AN-1485

Test A10 istheLM607. Atonetimeitwasthe~ bestopamp in the world, but it was discontinued as no customers ever found out about it. Its non-linearity is down at the 0.2 ppm level. Thedistortiondoesnotlooksogood, only becausethe gainisturneduptwiceashighas any previousamplifier. I usedtothinktheLM607 hadaperfectdesignandlayout, but it does seem to show a couple microvolts of thermal error, mostlyonthepositiveside,whensourcingcurrent.Thiscould easily leadtoanonlinearity of0.15ppm.

20194933

TestA10,LM607*, F=3Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 1"V p-pat10"V/div. LowerTrace:GainError,FullLoad,+ 5"V p-pat10"V/div.

FIGURE 30.

Test A11, theLM627,wasasimilardesigntotheLM607,but thelayoutmusthavegottenlucky,andthethermalerrorsare downbelow1 microvolt,evenattheheavyload.Imustadmit, Iamnotsurewhythegaintendstogofrom(+ 10million) at noload, to(+ 4million) atfullload. Addingaheavyloaddoes notusuallycausethegaintogomore(positive).Thisamplifier also was not well promoted, was not well known, and was discontinued.

20194970

TestA11,LM627*, F=8Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 2"V p-pat10"V/div. LowerTrace: GainError, Full Load, +5"V p-pat10"V/div.

FIGURE 31.

Test A12 is the LM10. As mentioned earlier, this is the first amplifier with a "rail-to-rail" output. This amplifier met many dc characteristics with miraculous accuracy, but the ac linearity was NOT quite as good as you would expect from Widlar. Later, Widlar's LM12showedthathecoulddoexcellentaccuracy fordynamic errors and linearity, butthe LM10 was primarily a DC amplifier. Its errors look "pretty bad", but actually its non-linearity was noworsethangeneral-purpose amplifiers --barely 1 or2 ppm. Its cross-overdistortion was NOTverygood,evenat1 Hz,andathigherfrequencies,itis notgoodatall.TheLM10was NOTagood, linearaudioamplifier.

20194935

TestA12,LM10, F=1Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 4"V p-pat20"V/div. LowerTrace: GainError, Full Load, 170"V p-pat50"V/div.

FIGURE 32.

Test A13 shows anLM10runningslightly faster, at10Hz. If you look at the lower trace, done with a sine wave, it looks very distorted and confusing , and it is hard to see what is going on. The upper trace shows the error using a triangle wave.Thislooksjustlikeaspeededupversionofthecurveat Test A12. This is one of the major reasons we prefer using triangle waves, rather than sines --so we can see and understandwhatis goingon.

20194936

TestA13,LM10, F=10Hz.

VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak.

Upper Trace: Gain Error, No Load, 230"V p-p at 100"V/div., TRIANGLE

wave. LowerTrace: GainError, Full Load, 290"V p-pat100"V/div., SINE wave.

FIGURE 33.

12

 AN-1485

Test A14 showsanLM307,aversionoftheLM301 witha30 pF compensation capacitor built in. This re-layout caused somewhat different thermal errors. The distortion is about typicalforgeneral-purposeamplifiers.

Thiscompletesthestudy ofsinglehigh-voltageamplifiers.

20194937

TestA14,LM307J, F=2Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 55"V p-pat50"V/div. LowerTrace: GainError, Full Load, 60"V p-pat50"V/div.

FIGURE 34.

13

 AN-1485

Section B, High-Voltage (±15V) DUAL Amplifiers

Test B01, the LM358, is the dual version of the LM324. No study of amplifiers would be complete without a mention of thepioneeringLM324/LM358.Thisisthefirstamplifierwhose honestgainissonon-linear.Thatisbecausetheoutputstage has a Darlington to source the output current, but only one verticalPNPtodrivethesinkingcurrent.Soitreallyisdeficient in gain, for negative currents. The DC distortion is STILL at the1.5ppmlevel. Butthethermalerrorsarenegligible.

20194938

TestB01,LM358, F=1.5Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 10"V p-pat20"V/div. LowerTrace: GainError, Full Load, 65"V p-pat20"V/div.

FIGURE 35.

LM324sreallyareusedforaudioamplifiersandpreamps.But whowoulduseanamplifierwithpoorlinearity likethatforan audio amplifier? It's easy: the output of the amplifier gets a pre-loadorpull-downresistor, suchas5kfromtheoutputto the-supply, sotheoutputvoltagecanswingupanddowna couplevolts,buttheoutputcurrentisonlysourcing.Thisprovidesvery adequatelinearity forsmallsignals. TheLM324or LM358 can only swing a couple volts at 10 kHz, but that is adequateforpreamps.

Test B02 is an LF412, a dual version ofthe LF411. Despite strenuouseffortstomakeagoodlayout,itsthermalerrorsare only alittlebetterthanaverage(about1/4ppm).

20194939

TestB02,LF412, F=4Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 5"V p-pat20"V/div. LowerTrace: GainError, Full Load, 15"V p-pat20"V/div.

FIGURE 36.

Test B03 is theLF442, alow-powerversion oftheLF412. It wasnotratedtodrivemorethan2mA,anddriving5mA did causepoorgain,hundredsofmicrovoltsofgainerror,andnot very linear. When driving light loads, less than 1 mA, the LF442wasagoodgeneral-purposeamplifier.

20194940

TestB03,LF442, F=2Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 6"V p-pat20"V/div. LowerTrace: GainError, Full Load, 380"V p-pat200"V/div.

FIGURE 37.

14

 Test B04 is the LM833, an amplifieroptimized foraudio applications. Ithasreasonably goodlinearity, underratedconditions butis notableto drive more than theover-load of-8 mA withoutsomedistortion.

20194963

TestB04,LM833, F=10Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±8mA peak. UpperTrace: GainError, NoLoad, 6"V p-pat20"V/div. LowerTrace: GainError, Full Load, 380"V p-pat200"V/div. (Rl = 2k)

FIGURE 38.

Test B05 is anothergeneral-purposeamplifier, theLM1458, basically, adualLM741. Itserrorsareonly alittleworsethan typical.

Note thatthe humps are upside down, compared to mostof theotheramplifiers. Thisjustmeanstheheat-sensinginputs are arranged to detect the thermal gradients in the reverse sense.

20194941

TestB05,LM1458, F=1.1Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace:GainError,NoLoad,+ 3"V p-pat20"V/div. LowerTrace: GainError, Full Load, 70"V p-pat50"V/div.

FIGURE 39.

Test B06 is an LM6182, and its gain errors are quite large the voltage gain is just2,500, and the gainerrordegrades 1 millivoltwiththe1k load. Its gmis only 20mhos. Whowould beinterestedinanamplifierwithsuchmediocregain? It'snot evenasgoodgainasanoldLM709!

The answeris, the LM6182 is quite fast. Its distortion atDC is notgreat, butthe distortion holds loweven up to 10 MHz (-50 dBc). So while we would not say it is a good general- purpose amplifier, it actually is a fairly popular amplifier for high-speedapplications. Thisisoneofthefirstcurrent-mode amplifiers wehaveseen.

20194942

TestB06,LM6182, F=500Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±10mA peak. UpperTrace: GainError, NoLoad, 7.8mV p-pat2mV/div. LowerTrace: GainError, Full Load, 8.8mV p-pat2mV/div.

FIGURE 40.

Test B07 is theLM6142, arail-to-rail amplifier. Wedon'texpect its gain to not change with load -and its gain DOES changewithload. Butitsvoltagegainfallsfromjust3million to1/4million. Its nonlinearity is still aboutaverage, witha1k load. Note that its cross-over distortion is MUCH improved overtheLM10(TestA12).Thisamplifier,runningonlessthan

0.7 mA perchannel, hasa17 MHzgain-bandwidthproduct, muchimprovedovertheslowLM10. 20194943

TestB07,LM6142, F=20Hz. VS= ±15Vdc;Vout= ±10voltspeak,Iout= ±5mA peak. UpperTrace:GainError,NoLoad,+ 7"V p-pat20"V/div. LowerTrace: GainError, Full Load, 80"V p-pat50"V/div. (RL= 2k)

FIGURE 41.

AN-1485

15

 AN-1485

Test B08 istheLM6152,afaster75MHzamplifier,whichalso isa"rail-to-rail"Test. Itsnonlinearity at1kload(middletrace) ismediocre,butatitsrated2kload(lowertrace) itslinearity is well below 1 ppm.

20194944

TestB08,LM6152, F=100Hz. VS= ±15Vdc;Vout = ±10voltspeak,Iout = ±5mA peak. UpperTrace: Gain Error, No Load, ?7"V p-p at20"V/div. Middle Trace: Gain Error, ±10 mA Load, 120"V p-p at50"V/div. LowerTrace:GainError,±5mA Load,76"V p-p at50"V/div.

FIGURE 42.

Test B09 istheLM8262,anotherfastamplifier.Itsgainishigh at no-load, but the gain falls to 2700 at the 1k load. The crossoverdistortionisnotverygood,either.Butitisfast.Also, itis tolerantofcapacitive loads.

20194964

TestB09,LM8262 F=200Hz. VS= ±11 Vdc;Vout = ±10voltspeak,Iout = ±10mA peak. UpperTrace: Gain Error, No Load, 1.3"V p-p at1mV/div. LowerTrace: Gain Error, Full Load, 4.8mV p-p at1mV/div.

FIGURE 43.

In Test B10, wehave"savedthebestforlast". Thisprecision amplifier,theLME49720,(alsoknownasanLM4562) notonly testsgood,butitsoundsgood.Thedistortionisnotonlydown somewherebelow0.15ppmat25Hz, butitkeeps improving at frequencies up to 1 kHz. It was designed as a precision audio amplifier, but is well suited for many other precision opampfunctions, withthebest, lowestdistortionintheindustry. Asyoucanplainlysee,thethermalsfoundinmostotherbipolar transistor op-amps have been banished by excellent layout. Distortion as low as -159 dB has been observed as an inverter, evendrivinga2kilohmload. Forastudy ofhowto test an op-amp with such low distortion at 1 kHz, refer to AN-1671.

20194965

TestB10,LM4562(alsoknownasLME49720) F=25Hz. VS= ±15Vdc;Vout = ±10voltspeak,Iout = ±10mA peak. UpperTrace: Gain Error, No Load, +1.5"V p-p at10"V/div. LowerTrace: Gain Error, Full Load, 1.5"V p-p at10"V/div.

FIGURE 44.

Group C: Single CMOS Op-Amps

Ididnotincludeortestanyofthese;Itestedthemorepopular dual amplifiers.

16

 Group D: Dual CMOS Op-Amps

Theseareallratedtorunon±7.5volts. Ioperatedthemon ±5.0volts,andIrequiredthemtodrivea1 kilohmloadto±4 volts.

Test D01 is the basic old LMC662, a dual version of the LMC660, NSC's first CMOS amplifier. Its gain error looks quitenon-linear; however, itisreally notbad. Thepeakerror is 27"V p-p, andthep-pnonlinearerrorisabout13"V p-p. If tested with a 4k load, it would have a nonlinearity of better than 1 ppm (as a unity-gain inverter, for example). The de- signer,DennisMonticelli,pointedoutthatthisamplifierdesign has 3 honestgain stages forsinking current(leftside ofthe trace) but4stagesofgainforsourcingcurrent(rightsideof the trace). Since gain forsourcing currentis usually considered more important, he let the design go as "plenty good enough". I tend to agree that a linearity of 1 ppmis "plenty goodenough"forany general-purposeamplifier.

Hereisanamplifierwheretheoutputimpedancereallyishigh. Whentheloadislightenedfrom1kto2k,4k,8k,etc.,thegain keepsgoingup. Howhighdoesitgo? It'salmostimpossible to resolve how high the gain goes, or how high the output impedanceis. Thegaingoesupby ATLEASTafactorof30, andquitepossibly60ormore.Sotheoutputimpedancegoes uptoatleast30k, andmaybe100or200k. Istheexactnumberimportant? Is itimportantifthegaingoes upto4million, or 8 million? In theory, it is fun to imagine that a gain of 4 millionisnotquiteasgoodas8million.Orthatifthegaingoes up to 8 million, then the low-frequency gain roll-off starts fallingfromtheDCgainof8millionat0.1 Hz.Butasyoucan see, theseamplifiers arewell-behaved, andtheloopis obviously stable for all conditions. If you only looked at the lefthandside( Vout= negative) wheretheoutputissinkingload current, the gain may be finite, butthis amplifieris very well behaved. Likewise on the right-hand side, it is a very high- gain amplifier--and very well behaved. Ifthe amplifierruns anywhere in the middle, or on either end --the amplifier is STILLverywell-behaved.Itjusthasasmallbitofnonlinearity. Wedon'tusuallythinkof1 ppmasasignificantamountofnonlinearity

--butthatis the only thing wrongwith this amplifier! We are discussing this at great length, primarily because it showsthatveryhighgain,whetheratnoloadoratheavyload, does not cause any problems. Also because several other CMOS amplifiers havevery similarcharacteristics.

20194901

TestD01,LMC662, F=6Hz. VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 1"V p-pat10"V/div. LowerTrace: GainError, Full Load, 27"V p-pat10"V/div.

FIGURE 45.

The traces on D01B are for the same amplifier. In the topmost trace, a 500 pF filter capacitor is added across the 1 megohmgain-setting resistor inFigure 7, to cutthe noise a little.Themiddletraceshowshownoisythisset-upwas,when I neglected to ground the operator's body while pushing the shutter button! The standard noise was on the lower trace. Notethateventhoughthesetraces seemnoisy, thenoiseis barely 3or4"Vp-p,andthegainerrorsaslargeas1 or2"V canberesolved, nicely.

20194902

TestD01B,LMC662, F=6Hz. UpperTrace: GainError, Full Load, 27"V p-pat20"V/div., C= 500pF. MiddleTrace: GainError, Full Load, 27"V p-pat20"V/div., with60Hz Am

bientNoise.. LowerTrace: GainError, Full Load, 27"V p-pat20"V/div., Normal Test.

FIGURE 46.

AN-1485

17

 AN-1485

Test D02 isaLMC6492, astandardCMOS amplifiersimilar Test D05A isamicropoweramplifier, theLMC6572, drawing totheLMC6482,withrail-to-railinputsandoutput,ratedfrom just40"A ofcurrent.Eventhoughitisrunningverylean,in-

40to+125degreesC. ternally,itcandrivea±4mAloadwithagainover1million,

and a nonlinearity better than 0.2 ppm. It is characterized downto2.7 voltsofpowersupply.

20194971

TestD02,LMC6492, F=6Hz. VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 1"V p-pat10"V/div. LowerTrace: GainError, Full Load, 22"V p-pat10"V/div.

FIGURE 47.

Test D03 isastandardCMOSamplifier,theLMC6482,similar toLMC6492,ratedfrom-40to+85degreesC.Itsgaincurves are-typical.

20194972

TestD03,LMC6482, F=6Hz. VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 1"V p-pat10"V/div. LowerTrace: GainError, Full Load, 18"V p-pat10"V/div.

FIGURE 48.

20194904

TestD05A,LMC6572, F=0.8Hz. VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 2"V p-pat10"V/div. LowerTrace: GainError, Full Load, 5"V p-pat10"V/div.

FIGURE 49.

Test D06A is an LMC6042, another micropower amplifier, runningonjust10"A.Itsgainandlinearityareaboutasgood asthepreviousexample,withagainover1 millionandgain linearitybelow0.2ppm.Itisonlyratedtorunfrom+ 15volts downto+ 5voltsoftotalpowersupply.

Test D06B isanotherLMC6042.

20194905

TestD06A,LMC6042, F=0.6Hz. VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 2"V p-pat20"V/div. LowerTrace: GainError, Full Load, 6"V p-pat20"V/div.

FIGURE 50.

18

 20194906

TestD06B,LMC6042, F=0.6Hz VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 3"V p-pat20"V/div. LowerTrace: GainError, Full Load, 6"V p-pat20"V/div.

FIGURE 51.

Test D07B isanotherlow-poweramplifier,requiringlessthan

100"A perchannel. Itsnonlinearityisdownbelow0.3ppm. As noted earlier, our testing with triangle waves help us resolvenon- linearitiesbelow1 ppm.Ifweweretestingwithsine waves,asinthelowertrace,itwouldbehardtoresolvethese small sub-ppmerrors.

Test D08 istheLMC6062, aprecisionamplifierwithVosas goodas 350"V, max. Itslinearity isdownnear0.2ppm.

20194908

TestD08,LMC6062, F=0.6Hz. VS= ±5Vdc;Vout= ±3.5, ?4.5voltspeak,Iout= 8mA p-p. UpperTrace: GainError, NoLoad, 3"V p-pat20"V/div. LowerTrace: GainError, Full Load, 6"V p-pat20"V/div.

FIGURE 53.

AN-1485

20194907

TestD07B,LMC6022, F=2Hz. VS= ±5Vdc;Vout= ±4voltspeak,Iout= ±4mA peak. UpperTrace: GainError, NoLoad, 4"V p-pat20"V/div. MiddleTrace: GainError, Full Load, 7"V p-pat20"V/div. (TRIANGLE) LowerTrace: GainError, Full Load, 7"V p-pat20"V/div. (SINE)

FIGURE 52.

19

 AN-1485

Group E: Low-Voltage Single Amplifiers ( ± 2.5-volt Supplies)

Test E01 is the LMV715, a low-voltage amplifier. Its linearity is as good as 1.5 ppm, 3"V p-p at the input compared to 4 volts p-p of output swing.Of course, at lighter loads, the linearity would improve.

20194910

TestE01,LMV715, F=26Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, No Load, 2"V p-p at20"V/div. LowerTrace: Gain Error, Full Load, 12"V p-p at20"V/div.

FIGURE 54.

Test E02 is an LMV751. This amplifier has poorer gain for positive swings (sourcing current). The no-load gain curve (lower trace) is obviously well under 1 "V p-p. The linearity with a 4k load would be slightly better than 1 ppm, even thoughthegainerrorlooksprettybad!TheLMV751 hasvery lownoise, about6.5 nV persquare-rootHertz.

Test E03 isanLMV771,withmediocregaininbothdirections! Itlooksawful -yetthenonlinearitywitha4kloadwouldbestill be betterthan 1/2 ppm.

20194912

TestE03,LMV771, F=~6Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, No Load, 1"V p-p at5"V/div. LowerTrace: Gain Error, Full Load, 3"V p-pat5"V/div.

FIGURE 56.

Test E04 is an LMV301 (bipolar, not CMOS) with very high gain and linearity betterthan 1/2 ppm.

20194913

TestE04,LMV301, F=12Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, No Load, 2"V p-p at20"V/div. LowerTrace: Gain Error, Full Load, 4"V p-pat20"V/div.

FIGURE 57.

20194911

TestE02,LMV751, F=12Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, Full Load, 11"V p-p at5"V/div. LowerTrace: Gain Error, No Load, 1"V p-p at5"V/div.

FIGURE 55.

20

 Group F: Low-Voltage Duals (± 2.5-volt Supplies)

Test F01A is the LMP2012, a chopper-stabilized amplifier withgain well over2 million. Thelinearity seems to be better than 1/4 ppm. The offsetvoltage is typically below4"V.

20194914

TestF01A,LMP2012,SideA, F=2Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, No Load, 1"V p-p at10"V/div. LowerTrace: Gain Error, Full Load, 2"V p-pat10"V/div.

FIGURE 58.

Trace F01D is an LMP2012 with the 500 pF filter capacitor added, tohelpresolvethesignalsdowninthenoise; linearity is still below1/4 ppm.

20194915

TestF01D,LMP2012,SideB, F=~2Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, No Load, 1"V p-p at10"V/div. LowerTrace: Gain Error, Full Load, 3"V p-pat10"V/div.

FIGURE 59.

Test F02 is an LMV932, with 1/4 ppm, most of which is its cross-overdistortion.

20194916

TestF02,LMV932,F= 12Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, No Load, 3"V p-p at20"V/div. LowerTrace: Gain Error, Full Load, 8"V p-pat20"V/div.

FIGURE 60.

Test F03

The low-voltage LMV358 does not have the exact same shapeofnonlinearity astheLM358(seetestB01, Figure35) but a somewhat different shape. Its gain is OK, but its nonlinearity when driving a 4 kilohmload is about6 ppm. This is noticeably inferiorto many othermodern op-amps --butyet, when do you measure an amplifier with linearity worse than

3ppm, orcomplainaboutit? AswiththeLM358, theLMV358 can provide excellent linearity if the output has a pre-load (pull-downorpull-upresistor) connected.

20194917

TestF03,LMV358, F=20Hz. VS= ±2.5Vdc;Vout = ±2voltspeak,Iout = ±2mApeak. UpperTrace: Gain Error, Full Load, 150"V p-pat50"V/div. LowerTrace: Gain Error, No Load, 5"V p-p at20"V/div.

FIGURE 61.

AN-1485

21

 AN-1485

Test X06 is a very low-voltage amplifier, running on ±0.45 volts, withgainerrorbelow7"V p-p, andlinearity near2ppm.

20194973

TestX06,LMV751 F=75Hz. VS= ±0.5Vdc;Vout = ±0.4voltspeak,Iout = ±0.4mA Peak. UpperTrace: Gain Error, No Load, 7"V p-p at10"V/div. LowerTrace: Gain Error, Full Load, 20"V p-p at10"V/div.

FIGURE 62.

Conclusions

Therearemanyinterestingthingstolearnaboutanamplifier's gain, not just one number on a datasheet. Not all amplifiers are the same -or even SIMILAR!! Amplifiers with output followers are not simple to analyze, when thermal errors can causebiggererrorsthanthegainerror.CMOSamplifierswith highoutputimpedance, wouldseemtohaveamajorsource of error at heavy loads, but in actuality, good amplifiers can drive loads with accuracy and linearity much better than 1 ppm. A high output impedance can allow the gain to go extremely highatlightloads, andthismay beusefulinprecision applications.

Design Engineers havemany things tothink about. Thegain forpositiveoutputsversusnegativeoutputsmaybeimportant forprecisionamplifiers. Thermalproblemsmay alsohaveto be studied, in areas where computers are not helpful.

Mask Designers have to be concerned with precise placementofcriticalcomponents. Theyhavetomakesuretheyare given complete instructions on placementand matching.

ApplicationsEngineershavetomeasureandcharacterizethe new amplifiers, to make sure the characteristics are as good asexpected. Thedatasheetmayneedtoberevised,toshow good orbad features ofan amplifier's gain.

The Customerdoes nothave to worry so much aboutthe internal design of the amplifier, but he/she may have to be concerned, for critical applications, about some of these features of amplifiers.

Philosophical Insights

Many engineers have opinions or preconceptions that operational amplifiers made with bipolar transistors have better, highervoltagegainthanCMOSamplifiers.Manypeoplehave a sense that bipolar op-amps are more linear than CMOS amplifiers.Wehaveshowedthatthisisnotexactlytrue.There are many amplifiers of each Type that are very good --with linearity betterthan0.3 parts permillion. Some arebarely as good as 2 parts per million --but at light loads, they can be

used with excellent accuracy and linearity. And of course,

many applications do not require linearity better than 1 ppm! Amplifiersarenotsimple.Siliconisnotsimple.Understanding circuits is not simple, but it is possible.

Appendix A: List of Amplifiers with Low and Lower Distortion

The testing of amplifiers in this Applications Note was done onamplifiersthatweremostly ratedwitha2kilohmload. Iran mostofthetestswithaheavyloadof1 kilohm,tomakesure I had enough nonlinearity to see a signal.

For this Appendix, the engineering was done for a 10k/10k unity-gaininverter,witha6.67kload,makingavirtual4kilohm total load, so the nonlinearity would be done with a moderate load(halfthecurrentoftherated2k load, notdoublethecurrent). The nonlinearity was sort of interpolated as 1/4 of the nonlinearity with a 1k load. As you will see, many ofthe amplifiers have surprisingly good linearity, even though the curveswithRL = 1klookedprettybad.Theyarelistedinorder of improving linearity. All data are approximate, and typical. Nodataareguaranteed. Availability ofoldamplifiertypesdenoted by *is notguaranteed, and are very unlikely.

Example: An LM709, perthedatashownonTestA01, has a

100"Vp-pnonlinearerroratitssummingpoint,drivinga1 k load. That is the total p-p deviation from the best-fit straight line. When it is driving 4k of total load, the error would be 25"V p-p, referredtoinput. The709'serrorwillbedecreased quite strictly by this factor of 4, because it is a thermal error, which heats the inputtransistors in a highly predictable way.

A unity gain inverter runs at a Noise Gain of 2, so its output wouldhave50"V p-p. Its outputswingis 20volts p-p. Thereforewewill callthedistortion, 2.5ppm, asitis2.5ppmofthe total output swing. All other amplifiers get the same conversion done for them. It is true that SOME amplifiers will not improveby this transformation, by theexactfactorof4, butit is still approximately correct. Thecomputations weredonein termsofp-perrors,asRMScomputationswouldprobablynot be applicable for such nonlinear signals. If you wanted an LM709 to have betterlinearity than 2.5 ppm, you could run it with a lighter load, or, choose a better amplifier. Or get a helper amplifier to put out most of the load current.

22

 Amplifiers with Bipolar Transistors Low Voltage Amplifiers with ~ Rail- and with ± 10-Volt output swing to-Rail outputs and with ± 2-Volt (supplies = ± 15 volts) output swing (supplies = ± 2.5 volts)

AN-1485

Type Test Nonlinearity Type Test Nonlinearity

LM8262 (B10B) 12 ppm LMV358 (F03) 6 ppm

LF442 (B03) 8ppm(lightload) LMV715 (E01) 1ppm

LM6182 (B06) 6 ppm LMV771 (E04) 0.6 ppm

LM709* (A01) 2.5 ppm LMV751 (E02) 0.4 ppm

LM318 (A06) 2.1 ppm LMV771 (E03) 0.4 ppm

LM741 (A03) 2 ppm LMV932 (F02) 0.3 ppm

LM301A (A02) 1.5 ppm LMP2012 (F01A) 0.2 ppm

LM10 (A12) 1.5 ppm

Very Low Voltage Amplifier with ~

LF411 (A08) 1.4 ppm

Rail-to-Rail outputs and with ±

LM308 (A05) 1.3 ppm

0.4Volt output swing (supplies = ±

LM1458 (B05) 1.3 ppm

0.5 volts) LM307J (A14) 1.3 ppm

Type Test Nonlinearity

LF356 (A09) 1.2 ppm

LMV751 (X06) 5 ppm LM358N (B01) 1.0 ppm

LM6142 (B07) 0.5 ppm Footnotes

OP-07* (A07) 0.4 ppm

1. IdealamplifiersarecharacterizedinT. Frederiksen'sbook, "Intuitive IC Opamps", NSC 1984, p. 23.

LM833N (B04) 0.4 ppm

1. Somewiseengineershavepointedoutthatevena"rail-toLF412N (B02) 0.3 ppm

rail" output stage can not literally swing all the way to the rail, LM6152 (B08) 0.3 ppm even driving as light a load as a megohm, or even

10 LM607* (A10) 0.12ppm megohms.Therearepracticalreasonswhyanamplifiercan

notdrivea1 or10 "A loadmuchcloserthan10or20mVto

LM725* (A04) 0.10 ppm

eitherpowersupplyrail: iftheytriedtorunwithsuchastarved LM627* (A11) 0.04 ppm bias, the output loops would go out of control. For loads as heavyas100"A,20to50mVisapracticaloverheador"drop

LM4562 (B10) 0.025 ppm out"limitation.For1 or2mA,thedrop-outisinthevicinityof

*Amplifiersdenotedby*areobsoleteandarenolongeravailablefromNSC. 100 to 200 mV. For typical real data, refer to the specific

amplifier's data sheet. The typical curves of"OutputCharac-

CMOS AMPLIFIERS with ~ Rail-to

teristics, CurrentSourcing"and"OutputCharacteristics, Cur- Rail outputs and with ± 4-Volt output rent Sinking" will show what you can expect to get, for this

dropout. It may not be terribly small, but at moderate loads, it

swing (supplies = ± 5 volts)

is a lot better than the 600 or 700 mv of the best amplifiers

Type Test Nonlinearity

with emitter followers. LMC662 (D01) 1.4 ppm

1. "What's All This Common-Centroid Stuff, Anyhow?"http:// LMC6482 (D03) 1.1 ppm
   formatting link
   R. A. Pease, Electronic Design, October1, 1996. LMC6492 (D02) 1.1 ppm

1. "What'sAllThisOutputImpedanceStuff, Anyhow?"R. A. LMC6022 (D07B) 0.3 ppm

Pease, Electronic Design. LMC6042 (D06A) 0.3 ppm 5. Appendix A.,ListofOperationalamplifierswithlowdistorLMC6062 (D08) 0.2ppm tionatdcandlowfrequencies LMC6572 (D05A) 0.2 ppm

23

 AN-1485 The Effect of Heavy Loads on the Accuracy and Linearity ofOperational Amplifier Circuits

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r=s

     ...Jim Thompson

OK thanks, (all) I was hoping for someway to just make it look pretty.

George H.

Looks like the embedded font used for the body text is Helvetica Rounded Black, which is a terrible choice. The character spacing on a lot of the lines is awful as well, which doesn't help.

--
Rich Webb     Norfolk, VA

Copy & paste it into a word processor, then dress it up any way you like. You can even copy & paste the graphics into a new document. :)

com:

umber=s

en.

       ...Jim Thompson u

Got it, thanks.

George H.

It can be done, using a PDF editor, but it's a line-by-line effort. I can ctrl-click to select a bunch of lines and change them all together but that still leaves individual lines to be cleaned up for letter- spacing and justification. Possibly faster just to re-type it... ;-)

--
Rich Webb     Norfolk, VA

Arial Rounded Bold. Best font ever as it emulates ALL drafting strokes perfectly, and has rounded line ends which is perfect for optical ablation methodologies, silk screen mask burns, etc..

The bold base font is even better further bolded, in some instances.

I had reasonable results converting to PostScript with pdftops, hand-editing the PS to use plain Helvetica instead of the embedded HelveticaRounded-Black, then converting back with pstopdf.

on this linux box I'm seeing vector fonts (all the curves are smooth upto the limit of easy software magnification (about 100 pixels high) if you're seeing jagged edges I suspect the problem may be (as you say) a poor choice of font - one that's not available on your computer, I've seen this with documents composed using LaTEX.

as for how to change the font. I'm not sure.

--
?? 100% natural 

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

With Acrobat v4 I was able to write it out as PostScript, Acrobat v7 refuses. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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