LT1002_15 Datasheet, PDF (10/16 Pages) Linear Technology – Dual, Matched Precision Operational Amplifier

LT1002
APPLICATIONS INFORMATION
Advantages of Matched Dual Op Amps In many applica-
tions the performance of a system depends on the match-
ing between two operational amplifiers rather than the
individual characteristics of the two op amps. Two or three
op amp instrumentation amplifiers, tracking voltage refer-
ences 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 differ-
ence between the offsets of the two halves of the LT1002.
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 non-inverting input currents
(I_B+). The difference between these two currents (I_OS+) is
the offset current of the instrumentation amplifier. The
difference between the inverting input currents (I_OS–) will
cause errors flowing through R1, R2, and R3. Common-
mode and power supply rejections will be dependent only
on the match between the two amplifiers (assuming
perfect resistor matching).
Three Op Amp Instrumentation Amplifier
INPUT ^–
+
A
1/2 LT1002
–
INPUT ₊
–
B
1/2 LT1002
+
R1 ^R4
R6
10k ^100Ω
10k
1% ^1%
1%
R3
2.1k
1%
R8
200Ω
R2
10k
1%
R10
100k
C1
100pF
–
LT1037
+
GAIN = 1000
R5
100Ω
1%
R7
9.76k
1%
R9
200Ω
Trim R8 for gain
Trim R9 for DC common mode rejection
Trim R10 for AC common mode rejection
OUTPUT
1002 TA07
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 = + 0.75µV/V or 122.5dB,
then ∆CMRR = 0.25µV/V or 132dB;
if CMRR_B = – 0.75µV/V which is still 122.5dB,
then ∆CMRR = 1.75µV/V or 115dB.
Typical performance of the instrumentation amplifier:
Input offset voltage = 25µV
Input bias current = 0.7nA
Input resistance = 200 GΩ
Input offset current = 0.6nA
Input noise = 0.5µV p-p
Power bandwidth (V₀ = ±10V) = 80kHz
Clearly, the LT1002, by specifying and guaranteeing all of
these matching parameters, can significantly improve the
performance of matching dependent circuits.
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