AN242 ,Applying a New Precision Op Ampapplications where it needs to be lower.Parameter Conditions ValueReferring back toInputOffsetVolta ..
AN2441S ,Video Camera SECAM Color Encoder ICMaintenance/DiscontinuedMaintenance/Discontinued includes following four Product lifecycle stage.pl ..
AN2458SH ,For Video稟udioElectrical Characteristics (Ta=25– 2˚C)Parameter Symbol Condition min typ max UnitSupply current I ..
AN2492FH ,Luminance and chrominance signal processing circuit for 8 mm video (NTSC)Block Diagram27NL in16GCA4 CTL28LNC out1529REC C outCCL det.30CDL in31G1 det.32ADD out33CTL13414CON ..
AN2510S ,V(cc): 5.3V; 400mW; ; video camera electronic viewfinder drive circuitFeatures 24-Lead PANAFLAT Package (SO-24D).Low operating voltage (Vcc=4.8 V)ODirect vertical deflec ..
AN2510S ,V(cc): 5.3V; 400mW; ; video camera electronic viewfinder drive circuitE‘?7T7J>’\5FEIC AN2510SAN25'I OS'ttT E CL - 7 , 4 V ' F' 5 ’f Cr'lrCallliL/Video Camera ElectronicV ..
AP358NL-U , LOW POWER DUAL OPERATIONAL AMPLIFIERS
AP3602BKTR-E1 , 100mA REGULATED CHARGE PUMP
AP3605FNTR-E1 , CHARGE PUMP CURRENT SOURCE FOR LED DRIVER WITH BRIGHTNESS CONTROL
AP3607FNTR-G1 , 4/6 CHANNEL CHARGE PUMP CURRENT SINK FOR LED DRIVER
AP3615FNTR-G1 , 5 CHANNEL CHARGE PUMP CURRENT SINK FOR LED DRIVER
AP3706 , PRIMARY SIDE CONTROL IC FOR OFF-LINE BATTERY CHARGERS
AN242
Applying a New Precision Op Amp
TL/H/7479
Applying
New
Precision
Amp
AN-242
National Semiconductor
Application Note 242
April 1980Applyinga New
Precision Op Amp
RobertJ. Widlar
Apartado Postal 541
Puerto Vallarta, Jalisco
Mexico
Bob Pease and Mineo Yamatake
National Semiconductor Corporation
Santa Clara, California
U.S.A.
Abstract:A new bipolarop amp designhas advancedthe
stateoftheartby reducing offset voltageand bias current
errors.Its characteristicsare described here, indicatingan
ultimate input resolutionof10mV and1pA underlaboratory
conditions. Practical circuitsfor making voltmeters, amme-
ters, differential instrumentation amplifiersanda varietyof
other designs thatcan benefit fromthe improved perform-
anceare coveredin detail. Methodsof couplingthe new
deviceto existingfast amplifiersto take advantageofthe
best characteristicsof both, evenin follower applications,
are explored.
introductionlow cost, mass-producedop amp with electrometer-type
input currents combined withlow offset voltageanddriftis
now available. Designatedthe LM11,thisICcan minimize
production problemsby providing accuracy without adjust-
ments, evenin high-impedance circuitry.Onthe other hand, pushedtoitsfull potential, whathas been impossiblein
the past becomes entirely practical.
Significantly,the LM11isnot restrictedto commercialand
industrial use. Devicescanbe completely specified overa
b55§Cto a125§C range. Preliminary data indicates that
reliabilityisthe sameas standardICs qualifiedfor military
and space applications.
The essential detailsofthe design along withan introduc-
tiontothe peculiaritiesof high-impedance circuits have
been presented elsewhere.* Thiswillbe expanded here.
Practical circuitry that reduces effective bias currentfor
those applications where performance cannotbe madede-
pendenton offset currentare described.In addition, circuits
combiningtheDC characteristicsofthe new part withthe performanceof existing fast amplifierswillbe shown.
Thiswillbe capped witha numberof practical designsto
provide some perspectiveinto what mightbe done. errors
Barringtheuseof chopperor reset stabilization,the best
offset voltage,driftand long-term stabilityare obtainedus-
ing bipolar transistorsfortheop amp input stage. Thishas
been done withthe LM11. On-wafer trimming furtherim-
proves performance. Typically,a 100 mV offset with mV/§C drift results.
Transistors with typical current gainsof 5000 have been
usedinthe manufactureofthe LM11.The input stage em-
ploysa Darlington connection thathas been modifiedso
that offset voltageand driftarenot degraded. The typical
input currents, plotted inFigure1, demonstratethe valueof
the approach.
TL/H/7479–1
Figure1. Below 100§C,bias current varies almost linear- with temperature. This means that simple
circuitrycanbe usedfor compensation. Offset
currentis unusually low.
The offset currentofthisop ampissolow thatit cannotbe
measuredon existing productiontest equipment. Therefore, probably cannotbe specified tighter than10pA.Forcrit-
ical applications,the user should have little difficultyinse-
lectingtoa tighter limit.
The bias currentofthe LM11 equalsthatof monolithic FET
amplifierat 25§C. Unlike FETs,it doesnot double every
10§C.In fact,thedrift overa b55§Cto a125§C temperature
rangeis aboutthe sameasthatofa FETop amp during
normal warmup.
Other characteristicsare summarizedin TableI.Itcanbe
seen thatthe common-mode rejection, supply-voltagere-
jectionand voltage gainare high enoughto takefull advan-
tageofthelow offset voltage. The unspectacular 0.3V/ms
slew rateis balancedbythe300mA current drain.
*R.J. Widlar, ‘‘WorkingwithHigh ImpedanceOp Amps’’, NationalSemiconductor AN-241.
C1995National SemiconductorCorporation RRD-B30M115/PrintedinU.S.A.
