A fully integrated, untrimmed CMOS instrumentation amplifier with submicrovolt offset

A low-noise CMOS instrumentation amplifier intended for low-frequency thermoelectric microsensor applications is presented that achieves submicrovolt offset and noise. Key to its performance is the chopper modulation technique combined with a bandpass filter and a matching on-chip oscillator. No external components or trimming are required. The achievable offset performance depends on the bandpass filter Q and the oscillator-to-bandpass filter matching accuracy. Constraints are derived for an optimum Q and a given matching accuracy. The improvement of common-mode rejection ratio (CMRR) in chopper amplifiers is discussed. The amplifier features a total gain of 77/spl plusmn/0.3 dB and a bandwidth of approximately 600 Hz. The measured low-frequency input noise is 8.5 nV//spl radic/Hz and the input offset is 600 nV. The measured low-frequency CMRR is better than 150 dB. The circuit has been implemented in a standard 1-/spl mu/m single-poly CMOS process.