A 0.26 μVrms instrumentation amplifier based on discrete-time DC servo loop with successive-approximation-compensation technique and Chopper DAC Array

A low-noise instrumentation amplifier for bio-signal recording is proposed in this paper. One of the significant disturbances, electrode DC offset, is suppressed using the proposed successive-approximation-compensation (SAC) circuit based on a discrete-time DC servo loop with Chopper DAC Array. Firstly, the DC offset at the output is quantified using the SAR quantizer. Next, the digital code produced by the SAR quantizer is used to control the chopper DAC array. Finally, a suitable compensation voltage is generated and used directly to correct the electrode DC offset at the input of the chopper amplifier. By using the proposed compensation technique, the first-stage chopper amplifier’s quiescent operating state is unaffected. When a 50-mV DC offset voltage exists at the differential input, the SAC circuit can compensate the DC offset voltage close to zero in a relatively short time. At the same time, there are fewer capacitors, which significantly decrease the area consumption. The proposed instrumentation amplifier is implemented in a standard 0.18μm CMOS process. The experiment results show that over a bandwidth from 0.1 Hz to 100 Hz, an input referred noise of 0.26 μVrms at the TT corner has been attained. The total power consumption is about 13.72 μW at the supply voltage of 1.8 V. The gain of the instrumentation amplifier is about 39.15 dB and its Noise Efficiency Factor (NEF) is 2.76.