CMRR in Voltage-Op-Amp-Based Current-Mode Instrumentation Amplifiers (CMIA)

The common-mode rejection ratio (CMRR) of a power-supply current-sensing current-mode instrumentation amplifier (CMIA) has theoretically been analyzed and formulated. The theory was further investigated by doing experiments using mu A741 and TL071 as op-amps and CA3096 transistors as the current mirrors of the CMIA. Both theoretical and practical investigations proved that both the dc and ac performances of CMRR depend on the matching status of parameters such as CMRR, open-loop gain A, gain-bandwidth product GB, and the output resistance R _O of the input op-amps of the CMIA. It has also been shown that, in the CMIA, unlike the voltage-mode instrumentation amplifier, voltage gain is independent of the bandwidth.