LT1126AMJ8 datasheet(6/8 Pages) LINER

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LT1126/LT1127

APPLICATI

I FOR ATIO

Matching Specifications

In many applications the performance of a system de-

pends on the matching between two op amps, rather than

the individual characteristics of the two devices. The three

op amp instrumentation amplifier configuration shown in

this data sheet is an example. Matching characteristics are

not 100% tested on the LT1126/LT1127.

Some specifications are guaranteed by definition. For

example, 70

µV maximum offset voltage implies that mis-

match cannot be more than 140

µV. 112dB (= 2.5µV/V)

CMRR means that worst case CMRR match is 106dB

µV/V). However, the following table can be used to

estimate the expected matching performance between the

two sides of the LT1126, and between amplifiers A and D,

and between amplifiers B and C of the LT1127.

High Speed Operation

When the feedback around the op amp is resistive (RF), a

pole will be created with RF, the source resistance and

capacitance (RS, CS), and the amplifier input capacitance

(CIN ≈ 2pF). In low closed loop gain configurations and

with RS and RF in the kilohm range, this pole can create

excess phase shift and even oscillation. A small capacitor

(CF) in parallel with RF eliminates this problem. With

RS (CS + CIN) = RF CF, the effect of the feedback pole is

completely removed.

FREQUENCY (Hz)

0.01

0.1

1.0

0.1

100

LT1126 • TA04

0.001

GAIN ERROR =

CLOSED LOOP GAIN

OPEN LOOP GAIN

TYPICAL

PRECISION

OP AMP

LT1126/LT1127

Gain Error vs Frequency

Closed Loop Gain = 1000

–

OUTPUT

LT1126 • TA02

CIN

LT1126AM/AC

LT1126M/C

LT1127AM/AC

LT1127M/C

PARAMETER

50% YIELD

98% YIELD

50% YIELD

98% YIELD

UNITS

VOS Match, ∆VOS

LT1126

110

130

µV

LT1127

150

180

µV

Temperature Coefficient Match

0.35

1.0

0.5

1.5

µV/°C

Average Non-Inverting IB

618

Match of Non-Inverting IB

722

CMRR Match

126

115

123

112

PSRR Match

127

118

127

114

Expected Match

APPLICATI

TYPICAL

Gain 1000 Amplifier with 0.01% Accuracy, DC to 5Hz

–

OUTPUT

LT1126 • TA03

365

Ω

INPUT

15k

340k

20k

TRIM

+15V

–15V

RN60C FILM RESISTORS

THE HIGH GAIN AND WIDE BANDWIDTH OF THE LT1126/LT1127 IS USEFUL IN LOW FREQUENCY HIGH CLOSED

LOOP GAIN AMPLIFIER APPLICATIONS. A TYPICAL PRECISION OP AMP MAY HAVE AN OPEN LOOP GAIN OF ONE

MILLION WITH 500kHz BANDWIDTH. AS THE GAIN ERROR PLOT SHOWS, THIS DEVICE IS CAPABLE OF 0.1%

AMPLIFYING ACCURACY UP TO 0.3Hz ONLY. EVEN INSTRUMENTATION RANGE SIGNALS CAN VARY AT A FASTER

RATE. THE LT1126/LT1127 “GAIN PRECISION — BANDWIDTH PRODUCT” IS 330 TIMES HIGHER, AS SHOWN.

LT1126

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