Datasheet

LMC6001
SNOS694H –MARCH 1995–REVISED MARCH 2013 www.ti.com
R1 100k + 3500 ppm/°C
R2 68.1k
R3, 8 5k
R4, 9 100k
R5 36.5k
R6 619k
R7 97.6k
D1 LM4040D1Z-2.5
C1 2.2 μF
(1) Micro-ohm style 137 or similar
Figure 29. pH Probe Amplifier
ULTRA-LOW INPUT CURRENT INSTRUMENTATION AMPLIFIER
Figure 30 shows an instrumentation amplifier that features high differential and common mode input resistance
(>10
14
Ω), 0.01% gain accuracy at A
V
= 1000, excellent CMRR with 1 MΩ imbalance in source resistance. Input
current is less than 20 fA and offset drift is less than 2.5 μV/°C. R
2
provides a simple means of adjusting gain
over a wide range without degrading CMRR. R
7
is an initial trim used to maximize CMRR without using super
precision matched resistors. For good CMRR over temperature, low drift resistors should be used.
If R
1
= R
5
, R
3
= R
6
, and R
4
= R
7
; then
∴A
V
≈ 100 for circuit shown (R
2
= 9.85k).
Figure 30. Instrumentation Amplifier
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