Don't fall in love with one type of instrumentation amp

摘要

The instrumentation amps I covered in my last col-umn are difference amps made with internal resistor (Reference 1). Difference amps have high CMR er rors when you use them with high-resistance sensors. Their input resistance is low-usually in the tens of kilohms-so any mismatch in sensor resistance causes a CMR error. Manufacturers set differential amps' gain because resistor-matching errors cause CMR errors.