A chopper instrumentation amplifier with discrete-time compensation based on current generation unit to eliminate electrode DC offset

Abstract

A capacitively-coupled chopper instrumentation amplifier (CCIA) for bio-potential signals acquisition is proposed in this paper. A novel discrete-time compensation scheme based on the current generation unit is adopted to suppress the DC offset caused by the sampling electrode. Different with the traditional analog DC servo loop (DSL) used in previous works, the circuit based on this scheme is more straightforward and consumes less power. Moreover, it can suppress a larger electrode DC offset in a short time. This work is designed in a standard 180 nm CMOS process. The CCIA operates from a 1.8 V supply, from which it draws a total current of 0.72 $\mu$A. The simulation result shows that the signal bandwidth of the proposed CCIA is 1.2 – 500 Hz and the mid-band gain is about 31.49 dB. In the frequency band of 1 – 500 Hz, the input-referred noise of the circuit is 2.01 $\mu V_{rms}$. Inputting a single-tone sine wave with an amplitude of 14.1 mV at the frequency of 56.152 Hz, the total harmonic distortion (THD) of the CCIA’s output is −51.38 dB. This circuit can suppress a large electrode DC offset within a few milliseconds, and the maximum electrode DC offset that can be tolerated up to 130 mV.