LT1024_1 Datasheet, PDF (7/12 Pages) Linear Technology – Dual, Matched Picoampere, Microvolt Input, Low Noise Op Amp

LT1024
APPLICATIO S I FOR ATIO
The LT1024 may be inserted directly into OP-10, OP-207
or 0P227 sockets with or without removal of external
nulling components.
The LT1024 is specified over a wide range of power supply
voltages from ±2V to ±18V. Operation with lower supplies
is possible down to ±1.2V (two NiCad batteries).
Advantages of Matched Dual Op Amps
In many applications, the performance of a system
depends on the matching between two operational
amplifiers rather than the individual characteristics of the
two op amps. Two or three op amp instrumentation
amplifiers, tracking voltage references, and low drift active
filters are some of the circuits requiring matching between
two op amps.
The well-known triple op amp configuration illustrates
these concepts. Output offset is a function of the dif-
ference between the offsets of the two halves of the
LT1024. This error cancellation principle holds for a
considerable number of input-referred parameters in
addition to offset voltage and its drift with temperature.
Input bias current will be the average of the two
noninverting input currents (I_B+ ). The difference between
these two currents (I_OS+) is the offset current of the
instrumentation amplifier. Common mode and power
supply rejections will be dependent only on the match
between the two amplifiers (assuming perfect resistor
matching).
The concepts of common mode and power supply rejec-
tion ratio match (∆CMRR and ∆PSRR) are best demon-
strated with a numerical example:
Assume CMRR_A = +1.0µV/V or 120dB
and CMRR_B = +0.5µV/V or 126dB,
then ∆CMRR = 0.5µV/V or 126dB
if CMRR_B = – 0.5µV/V, which is still 126dB,
then ∆CMRR = 1.5µV/V or 116.5dB.
Typical performance of the instrumentation amplifier:
Input offset voltage = 25µV.
Input bias current = 30pA.
Input resistance = 10¹²â„¦.
Input offset current = 30pA.
Input noise = 0.7µV_P-P.
Power bandwidth (V_O = ±10V) = 80kHz.
Clearly, the LT1024, by specifying and guaranteeing all of
these matching parameters, can significantly improve the
performance of matching dependent circuits.
Three Op Amp Instrumentation Amplifier
–INPUT
15V
4₊
14
A
1/2 LT1024
3_–
12
–15V
R4
100Ω
13
1%
R1
10k
1%
R3
2.1k
1%
R8
200Ω
C1
100pF
+INPUT
15V
10 _– 7
B
1/2 LT1024
11 ₊
5
6
R2
10k
1%
R5
100Ω
1%
–15V
TRIM R8 FOR GAIN
TRIM R9 FOR DC COMMON MODE REJECTION
TRIM R10 FOR AC COMMON MODE REJECTION
R6
10k
1%
15V
2_– 7
R10
6
100k ₃
LT1037
+
4
–15V
GAIN = 1000
R7
9.76k
1%
R9
500Ω
OUTPUT
LT1024 • AI01
1024fa
7