Microchip Technology Incorporated
Dynamic correction of gain error in current-feedback instrumentation amplifiers

Abstract:

A current feed-back instrumentation amplifier (CFIA) comprises a differential pair with degeneration for amplifying small differential voltages in the presence of large common-mode voltages. The CFIA includes input and feedback transconductors and a chopping modulator circuit that continuously swaps tail current sources between the transconductors. This tail current swapping reduces the contribution to the CFIA's gain error caused by random mismatch between the tail currents of the input and feedback transconductors. The modulator circuit operates on a clock cycle to periodically swap the tail current sources. As a result, even if the tail currents are mismatched, on average the tail currents (transconductor gains) will approximately equal out, and the contribution of the tail current difference to the gain error is canceled out.