85 dB dynamic range 1.2 mW 156 kS/s biopotential recording IC for high-density ECoG flexible active electrode array

We present the design, implementation, and experimental characterization of a low-noise low-power biopotential recording integrated circuit (IC) in support of a fully implantable, high-density, actively multiplexed and flexible 32×32 electrode array for electrocorticography (ECoG) neural recording. Each ECoG recording IC contains an 8-channel ADC, each serving one column and multiplexing up to 32 rows in the external ECoG array. Each column ADC converts signal coarsely by 10-bit successive approximation (SA), and performs fine conversion of the residue by 7-bit 1st order incremental delta-sigma (ΔΣ) conversion. One bit of overlap between SA and ΔΣ stages supports wide dynamic range with an instantaneous core range of 3.9 mV, sufficiently larger than typical ECoG signals, while handling electrochemical and process variations in the ECoG electrode array up to ±1 V. Tests show a measured dynamic range of 85 dB and CMRR of 87 dB at 19.5 kS/s and at 19.4 μA from 3.3 V per ADC channel. The 8-channel IC occupies 18 mm² in 0.6 μm 2P3M CMOS.