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

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 ( G_{\mathrm {m, in}} ) 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 ( Z_{\mathrm {in}} ). 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 \mu \text{W} per channel. The in-vitro 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.