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. 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ΔΣ</mml:mtext></mml:mrow> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msub><mml:mi>G</mml:mi> <mml:mtext>m</mml:mtext></mml:msub> <mml:mtext>-</mml:mtext> <mml:mi>C</mml:mi></mml:mrow> </mml:math> filter with per-pixel decimation. It supports four recording modes covering 2.5-20 kSps through a power-efficient, bandwidth-scalable continuous time <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ΔΣ</mml:mtext></mml:mrow> </mml:math> 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 <i>in vivo</i> whisker barrel rat experiment.