A 2.5-20 kS/s In-Pixel Direct Digitization ECoG Front End With Submillisecond Stimulation Artifact Recovery

Neural stimulation is used routinely to diagnose and treat neurological disorders. The stimulation artifacts are, however, problematic for closed-loop neuromodulation therapy, which dynamically adjusts the electrical stimulation parameters based on real-time feedback from the recorded neural activity because they can cause saturation or prolonged recovery times in traditional recording front ends. This article presents a per-pixel second-order \Delta \Sigma analog-to-digital converter (ADC) for direct digitization of neural signals, which addresses the stimulation artifact recovery time in voltage-controlled oscillator (VCO)-based quantizers with a fast-recovery, overrange-detecting phase quantizer. The ADC uses a pseudo-virtual ground feedforwarding (PVG FF) technique and a complementary input G _{\text{m}} - C filter with per-pixel decimation. It supports four recording modes covering 2.5-20 kS/s through a power-efficient, bandwidth-scalable continuous time \Delta \Sigma modulator. Fabricated in a 180-nm CMOS process, this 300 \times 300 \mu m ^{2} ADC achieves > 250 \times faster (0.05-0.4 ms) stimulation artifact recovery time, enabling in-stimulation recording. Recording with artifact tolerance was demonstrated through an in vivo whisker barrel rat experiment.