A 0.13- $\mu\text{m}$ CMOS SoC for Simultaneous Multichannel Optogenetics and Neural Recording

This paper presents a 0.13- $\mu \text{m}$ CMOS system-on-chip (SoC) for simultaneous multichannel optogenetics and multichannel neural recording in freely moving laboratory animals. This fully integrated system provides 10 multimodal recording channels with analog-to-digital conversion and a four- channel LED driver circuit for optogenetic stimulation. The bio-amplifier design includes a programmable bandwidth (BW) (0.5 Hz–7 kHz) to collect either the action potentials (APs) and/or the local field potentials (LFPs) and has a noise efficiency factor (NEF) of 2.30 for an input-referred noise of 3.2 $\mu V_{\text {rms}}$ within a BW of 10–7 kHz. The low-power delta–sigma ( $\Delta \Sigma $ ) MASH 1-1-1 analog-to-digital converter (ADC) is designed to work at low oversampling ratios (OSRs) (≤50) and has an effective number of bits (ENOB) of 9.75 bits at an OSR of 25 (BW of 10 kHz). The utilization of a $\Delta \Sigma $ ADC is the key to address the flexibility needed to address different noise versus power consumption tradeoff of various experimental settings. It leverages a new technique that reduces its size by subtracting the output of each $\Delta \Sigma $ branch in the digital domain, instead of in the analog domain as done conventionally. The ADC is followed by an on-chip fourth-order cascaded integrator-comb (CIC4) decimation filter (DF). A whole recording channel, including the bio-amplifier, the $\Delta \Sigma $ MASH 1-1-1, and the DF consumes 11.2 $\mu \text{W}$ . Optical stimulation is performed with an LED driver using a regulated cascode current source with feedback that can accommodate a wide range of LED parameters and battery voltages. The SoC is validated in vivo within a wireless experimental platform in both the ventral posteromedial nucleus (VPM) and cerebral motor cortex brain regions of a virally mediated Channelrhodopsin-2 (ChR2) rat.