8.0 Instrumentation Circuits

The LMC6464 has the high input impedance, large

common-mode range and high CMRR needed for designing

instrumentation circuits. Instrumentation circuits designed

with

the

LMC6464

can

reject

a

larger

range

of

common-mode signals than most in-amps. This makes in-

strumentation circuits designed with the LMC6464 an excel-

lent choice for noisy or industrial environments. Other appli-

cations that benefit from these features include analytic

medical instruments, magnetic field detectors, gas detectors,

and silicon-based transducers.

A small valued potentiometer is used in series with Rg to set

the differential gain of the three op-amp instrumentation cir-

cuit in

Figure 14. This combination is used instead of one

large valued potentiometer to increase gain trim accuracy

and reduce error due to vibration.

A two op-amp instrumentation amplifier designed for a gain

of 100 is shown in

Figure 15. Low sensitivity trimming is

made for offset voltage, CMRR and gain. Low cost and low

power consumption are the main advantages of this two

op-amp circuit.

Higher frequency and larger common-mode range applica-

tions are best facilitated by a three op-amp instrumentation

amplifier.

DS012051-20

FIGURE 14. Low Power Three Op-Amp Instrumentation Amplifier

DS012051-21

FIGURE 15. Low-Power Two-Op-Amp Instrumentation Amplifier

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