An AC-Coupled Wideband Neural Recording Front-End With Sub-1 mm2×fJ/conv-step Efficiency and 0.97 NEF

Abstract

This letter presents an energy-and-area-efficient ac-coupled front-end for the multichannel recording of wideband neural signals. The proposed unit conditions local field and action potentials using an inverter-based capacitively coupled low-noise amplifier, followed by a per-channel 10-b asynchronous SAR ADC. The adaptation of unit-length capacitors minimizes the ADC area and relaxes the amplifier gain so that small coupling capacitors can be integrated. The prototype in 65-nm CMOS achieves $4\times $ smaller area and $3\times $ higher energy–area efficiency compared to the state of the art with 164 $\mu \text{m}\times 40\,\,\mu \text{m}$ footprint and 0.78 mm $^{2}\times $ fJ/conv-step energy-area figure of merit. The measured 0.65- $\mu \text{W}$ power consumption and 3.1 - $\mu \text{V}_{\mathrm{ rms}}$ input-referred noise within 1 Hz–10 kHz bandwidth correspond to a noise efficiency factor of 0.97.