A chopper modulated instrumentation amplifier with first order low-pass filter and delayed modulation scheme

A low-noise chopper-modulated CMOS instrumentation amplifier intended for low-frequency thermoelectric micro-sensors is presented, that achieves sub-microvolt offset and noise. Key to its performance is a delayed chopping scheme combined with a first order low-pass filter. The achievable reduction of residual offset due to charge injection spikes of the input modulator has been analyzed and experimentally verified. Compared to a similar design with a second order bandpass-filter [1], matching requirements have been relaxed by more than one order of magnitude and the capacitor area could be substantially reduced. The chopping clock does not need to be matched to any particular circuit parameter and can be set within a certain range. The amplifier features a gain of 70, a low-frequency input noise of 8.5 nV/√Hz, sub-microvolt offset and a minimum dc CMRR of 144 dB.