Closed-loop neuromodulation is essential for the advance of neuroscience and for administering therapy in patients suffering from drug-resistant neurological conditions. Neural stimulation generates large artifacts at the recording sites, which easily saturate traditional recording front ends. This paper presents a neural recording chopper amplifier capable of handling in-band artifacts up to 40 mVpp while preserving the accompanying small neural signals. New techniques have been proposed that solve the issues of low input impedance and electrode-offset rejection, which enable a DC input impedance of 300 MΩ and a dynamic range of 69 dB (200 Hz-5 kHz) and 78 dB (1-200 Hz). Implemented in a 40-nm CMOS process, the prototype occupies an area of 0.071 mm2/channel, and consumes 2 μW from a 1.2 V supply. The input-referred noise is 7 μV rms (200 Hz-20 kHz) and 2 μV rms (1-200 Hz). The total harmonic distortion for a 20-mV p input at 1 kHz is -74 dB. This paper improves the linearity by 14-26 dB, dynamic range by 11-28 dB, and input-impedance for chopped front ends by a factor of 11 as compared with the current state of the art, while achieving similar power and noise performance.
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Chandrakumar et al. (2017) studied this question.