A 0.13-μm CMOS SoC for Simultaneous Multichannel Optogenetics and Neural Recording

This paper presents a 0.13-mu 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-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 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.