A 2.5-20 kSps in-pixel direct digitization ECoG front-end with sub-millisecond stimulation artifact recovery

Neural stimulation is used routinely to diagnose and treat neurological disorders. However, the stimulation artifacts are problematic for closed-loop neuromodulation therapy, which dynamically adjusts the electrical stimulation parameters based on real-time feedback from recording neural activity, because they can cause saturation or prolonged recovery times in traditional recording front-ends. This paper presents a per-pixel 2^nd-order $\text{ΔΣ}$ 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 $G_{\text{m}}\text{-}C$ filter with per-pixel decimation. It supports four recording modes covering 2.5-20 kSps through a power-efficient, bandwidth-scalable continuous time $\text{ΔΣ}$ modulator. Fabricated in a 180-nm CMOS process, this 300×300 μm² ADC achieves >250× 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.