A 4-Channel 0.23$mm^{2}$ Voltage-to-Time Converter AFE with $3.7\mu V_{rms}$ Noise and $480nW$ Galvanic Impulse Uplink

We present a 4-channel 15kS/s Voltage-to-Time Converter (VTC) analog front-end (AFE) with a 0.49<i>μW</i> impulse-based galvanic uplink for a peripheral nerve interface. Multiple, low-noise, high-data-rate channels are needed to sense compound action potentials and measure their conduction velocity as they propagate down a peripheral nerve. To achieve high energy efficiency for these constraints, the AFE encodes and transmits data with time-domain charge-balanced impulses through an implantable galvanic link. Each channel consists of an integrator with charge-based sampling and amplification for rapid multiplexing. A shared VTC encodes the amplitude-domain outputs of each integrator into differential time-domain impulses. Since the timing can be synchronized with stimulation, this AFE achieves instant artifact recovery after rail-to-rail stimulation events. We designed this AFE in a 180 nm CMOS process, and the simulation results show an SNDR of 60 dB and noise of 3.7<i>μVrms</i>. Thanks to the new galvanic uplink protocol, this front-end only consumes 11.28<i>μW</i> including wireless data transmission for four channels.