Multi-channel neural recording enables simultaneous monitoring of neuronal activities across multiple brain regions, while the in-vivo common-mode interference (CMI) significantly degrades the signal quality of implantable neural-recording chips. For a multi-channel neural-recording chip, the total common-mode rejection ratio (T-CMRR) of the analog front-end (AFE) is limited by the input imbalance between the signal electrode and the shared reference electrode, as well as the intrinsic CMRR (I-CMRR) of its circuits. The traditional common-mode replication (CM-REP) technique is only applicable to single-channel systems such as ECG monitoring devices. In addition, conventional pre-amplifier and frequency-controlled differential regulator (FCDR) techniques suffer from gain mismatch and high power consumption, respectively. To address these issues, this work presents a 32-channel neural-recording chip fabricated in a 65 nm CMOS process, which effectively suppresses the CMI in two operational modes: 1) In high-gain mode, the proposed CM-tracking-dynamic-power-rail (CM-TDPR) instrumentation amplifier (IA) achieves 50 GΩ CM input impedance, 117 dB I-CMRR, and 100 dB power supply rejection ratio (PSRR), resulting in a T-CMRR of 87 dB; 2) In low-gain mode, a CM-canceling-in-idle-phase (CM-CIP) technique is proposed to increase the I-CMRR to 102 dB and match the signal-reference input impedance, thereby achieving a 95 dB T-CMRR. In-vivo experiments were conducted on a Sprague-Dawley rat, successfully validating the CMRR performance of the proposed chip.
Shen et al. (Thu,) studied this question.