A High DR, DC-Coupled, Time-Based Neural-Recording IC With Degeneration R-DAC for Bidirectional Neural Interface

Abstract

The bidirectional neural interface is essential to realize the closed-loop neuromodulation, which is the core of next-generation neurological devices. For the bidirectional neural interface, a recording circuit with a high dynamic range (DR) is required to record the neural signal while stimulating the neuronal cells simultaneously. This article presents a voltage-controlled oscillator (VCO)-based neural-recording IC, which directly quantizes the input signal and achieves a large DR to process the small-amplitude neural signal in the presence of the large-amplitude stimulation artifact (SA). A feedback-controlled source degeneration is applied to the input transconductor circuit (<inline-formula> <tex-math notation= LaTeX >$G_{\\mathrm {m, in}}$ </tex-math></inline-formula>) by using a resistor digital-to-analog converter (R-DAC). It mitigates the circuit nonlinearity, resulting in a large signal-to-noise-and-distortion ratio (SNDR) and a high input impedance (<inline-formula> <tex-math notation= LaTeX >$Z_{\\mathrm {in}}$ </tex-math></inline-formula>). The implemented neural-recording IC achieves 81.3-dB SNDR over 200-Hz signal bandwidth and 200-mV_pp maximum allowable input range with consuming 3.9 <inline-formula> <tex-math notation= LaTeX >$\\mu \\text{W}$ </tex-math></inline-formula> per channel. The <italic>in-vitro</italic> measurement with prerecorded neural signal demonstrates that the original neural signal is well preserved in the presence of the large-amplitude artifact without any saturation or significant distortion.