![](http://datasheet.mmic.net.cn/330000/LT1126AM_datasheet_16425901/LT1126AM_6.png)
6
LT1126/LT1127
U
S
A
O
PPLICATI
U
U
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
μ
V maximum offset voltage implies that mis-
match cannot be more than 140
μ
V. 112dB (= 2.5
μ
V/V)
CMRR means that worst case CMRR match is 106dB
(5
μ
V/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 (R
F
), a
pole will be created with R
F
, the source resistance and
capacitance (R
S
, C
S
), and the amplifier input capacitance
(C
IN
≈
2pF). In low closed loop gain configurations and
with R
S
and R
F
in the kilohm range, this pole can create
excess phase shift and even oscillation. A small capacitor
(C
F
) in parallel with R
F
eliminates this problem. With
R
S
(C
S
+ C
IN
) = R
F
C
F
, the effect of the feedback pole is
completely removed.
C
F
FREQUENCY (Hz)
G
0.01
0.1
1.0
0.1
10
100
LT1126 TA04
0.001
1
GAIN ERROR =COPEN LOOP GAIN
TYPICAL
PRECISION
OP AMP
LT1126/LT1127
Gain Error vs Frequency
Closed Loop Gain = 1000
–
+
OUTPUT
LT1126 TA02
R
S
C
S
R
F
C
IN
LT1126AM/AC
LT1127AM/AC
LT1126M/C
LT1127M/C
PARAMETER
V
OS
Match,
V
OS
LT1126
LT1127
Temperature Coefficient Match
Average Non-Inverting I
B
Match of Non-Inverting I
B
CMRR Match
PSRR Match
50% YIELD
20
30
0.35
6
7
126
127
98% YIELD
110
150
1.0
18
22
115
118
50% YIELD
30
50
0.5
7
8
123
127
98% YIELD
130
180
1.5
25
30
112
114
UNITS
μ
V
μ
V
μ
V/
°
C
nA
nA
dB
dB
Expected Match
U
S
A
O
PPLICATI
TYPICAL
Gain 1000 Amplifier with 0.01% Accuracy, DC to 5Hz
–
+
OUTPUT
365
1%
INPUT
15k
5%
340k
1%
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