TLH7759

May 1989

LM108ALM208ALM308A Operational Amplifiers

General Description

The LM108LM108A series are precision operational ampli-

fiers having specifications about a factor of ten better than

FET amplifiers over their operating temperature range In

addition to low input currents these devices have extremely

low offset voltage making it possible to eliminate offset ad-

justments in most cases and obtain performance ap-

proaching chopper stabilized amplifiers

g

18V and have sufficient supply rejection to use unregulat-

ed supplies Although the circuit is interchangeable with and

uses the same compensation as the LM101A an alternate

compensation scheme can be used to make it particularly

insensitive to power supply noise and to make supply by-

pass capacitors unnecessary

The low current error of the LM108A series makes possible

many designs that are not practical with conventional ampli-

fiers In fact it operates from 10 MX source resistances

introducing less error than devices like the 709 with 10 kX

sources Integrators with drifts less than 500 mVsec and

analog time delays in excess of one hour can be made us-

ing capacitors no larger than 1 mF

The LM208A is identical to the LM108A except that the

a

The LM308A devices have slightly-relaxed specifications

Features

Y

Offset voltage guaranteed less than 05 mV

Y

Maximum input bias current of 30 nA over temperature

Y

Offset current less than 400 pA over temperature

Y

Supply current of only 300 mA even in saturation

Y

Guaranteed 5 mV C drift

Compensation Circuits

Standard Compensation Circuit

TLH7759 – 1

Alternate Frequency Compensation

Improves rejection of power supply

noise by a factor of ten

TLH7759 – 2

Feedforward Compensation

TLH7759 – 3

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A