Why the study?
To alleviate trade-offs among maximum electrode DC offset rejection, referred-to-input noise, and power consumption when amplifying weak bio-sensing signals across differential electrode-tissue interfaces.
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The proposed bio-sensing chopper amplifier achieves low noise, high linearity, and high DC offset rejection with low power consumption, suitable for bio-sensing applications.
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%.
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Li et al. (2019) studied this question.
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