In general, this disclosure is directed to a mixer amplifier that can be utilized within a chopper stabilized instrumentation amplifier. The chopper stabilized instrumentation amplifier may be used for physiological signal sensing, impedance sensing, telemetry or other test and measurement applications. In some examples, the mixer amplifier may include a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, an amplifier configured to amplify the input signal to produce an amplified signal, and a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.
