A CMOS BD-BCI: Neural Recorder With Two-Step Time-Domain Quantizer and Multipolar Stimulator With Dual-Mode Charge Balancing

This work presents a bi-directional brain-computer interface (BD-BCI) including a high-dynamic-range (HDR) two-step time-domain neural acquisition (TTNA) system and a high-voltage (HV) multipolar neural stimulation system incorporating dual-mode time-based charge balancing (DTCB) technique. The proposed TTNA includes four independent recording modules that can sense microvolt neural signals while tolerating large stimulation artifacts. In addition, it exhibits an integrated input-referred noise of 2.3 $\mu$ V _rms from 0.1- to 250-Hz and can handle a linear input-signal swing of up to 340 mV _PP . The multipolar stimulator is composed of four standalone stimulators each with a maximum current of up to 14 mA ( $\pm$ 20-V of voltage compliance) and 8-bit resolution. An inter-channel interference cancellation circuitry is introduced to preserve the accuracy and effectiveness of the DTCB method in the multipolar-stimulation configuration. Fabricated in an HV 180-nm CMOS technology, the BD-BCI chipset undergoes extensive in-vitro and in-vivo evaluations. The recording system achieves a measured SNDR, SFDR, and CMRR of 84.8 dB, 89.6 dB, and $>$ 105 dB, respectively. The measurement results verify that the stimulation system is capable of performing high-precision charge balancing with $\pm$ 2 mV and $\pm$ 7.5 mV accuracy in the interpulse-bounded time-based charge balancing (TCB) and artifactless TCB modes, respectively.