An 80-mVpp Linear-Input Range, 1.6-GΩ Input Impedance, Low-Power Chopper Amplifier for Closed-Loop Neural Recording That Is Tolerant to 650-mVpp Common-Mode Interference

Abstract

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 differential and common-mode (CM) 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 80-mVpp differential artifacts and 650-mVpp CM artifacts while preserving the accompanying small neural signals. New techniques have been proposed that introduce immunity to CM interference, increase the input impedance of the chopper amplifier to 1.6 $\text{G}\Omega $ , and increase the maximum realizable resistance of duty-cycled resistors (DCR) to 90 $\text{G}\Omega $ . These techniques enable our recording front-end to achieve a dynamic range of 74 dB (200 Hz–5 kHz) and 81 dB (1–200 Hz). Implemented in a 40-nm CMOS process, the prototype occupies an area of 0.069 mm2/channel, and consumes 2.8 $\mu \text{W}$ from a 1.2-V supply. The input-referred noise is 5.3 $\mu \text{V}_{\mathrm {\mathbf {rms}}}$ (200 Hz–5 kHz) and 1.8 $\mu \text{V}_{\mathrm {\mathbf {rms}}}$ (1–200Hz). The total harmonic distortion for a 40-mV $_{\mathrm {\mathbf {p}}}$ input at 1 kHz is −76 dB. This work improves the input impedance by 5.3 $\times $ for chopped front-ends, linear-input range by 2 $\times $ , maximum resistance of DCR by 32 $\times $ , and tolerance to CM interferers by 6.5 $\times $ , while maintaining comparable power and noise performance.