A low-noise microsensor amplifier with automatic gain control system

A 0.35-mum CMOS instrumentation amplifier with automatic gain control (AGC) system for the sensor interfaces is presented in this paper. The circuitry employs a chopper stabilization technique to significantly reduce the low-frequency noise and DC offset. The AGC is used in the system where the amplitude of an incoming signal can vary over a wide dynamic range. The AGC circuit provides relatively constant output amplitude in spite of the sensitivity of the sensor due to the parameter variations. Furthermore, the whole system has been kept fully differential operation in order to get higher immunity to environmental noise of supply voltages, clock feedthrough, charge injection, even harmonic distortion, etc. It features a gain of 53plusmn17 dB with 25-kHz bandwidth. The equivalent input noise is about 1.13 muV_pp at 98.2-kHz chopper frequency