A 60 nV/$\surd$ Hz <0.01%-THD ±200 mV-DC-Rejection Bio-Sensing Chopper Amplifier With Noise-Nonlinearity-Cancelling Loop

Abstract

In this brief, a low-noise and high-linearity capacitively coupled chopper instrument amplifier (CCIA) is presented for low-power bio-sensing applications covering 0.5~500 Hz. When applying it to amplify weak signals from differential electrode-tissue interfaces with large potential difference, we introduce a noise-nonlinearity-cancelling loop (NNCL) to alleviate CCIA's compromise among the maximum electrode dc offset (EDO) rejection, referred-to-input (RTI) noise and power consumption. A low-gain stage is inserted into the Miller-compensated output stage to drive the large capacitor of the following programmable gain amplifier. Without the extra inverting stage, only one common-mode feedback loop using switched-capacitor is needed, which achieves a large output differential swing with high linearity and wide common-mode bandwidth with low power. Implemented in a 0.18-μm CMOS process, the whole analog front end, including bandgap circuit, consumes 2 μA from a 1.2 V supply. It can reject ± 200 mV EDO and achieve RTI noise of 60 nV/√Hz. The mid-band gain is 40 dB and the total harmonic distortion for a 800 mVp output is less than 0.01%.