A SoC for an active implantable microsystem for closed-loop optogenetic neuromodulation

This paper presents a system-on-chip (SoC) architecture for an active implantable microsystem that combines electrical recording with optogenetic stimulation for closed-loop neuromodulation. The SoC is designed to support a 4-shank optrode (opto-electrode) fork with 8 differential recording channels (0.1-5000Hz bandwidth, 10mVpp range, 12-bit resolution) to observe neural signals on electrodes and 32 driver circuits (2mA range, 6-bit current resolution with μs timing resolution) for microLED optical stimulation. Each SoC additionally integrates diagnostic instrumentation to measure electrical resistance across any of its I/O lines. The SoC features a custom 4-wire interface that provides power and data communication across multiple chips using a shared bus allowing for multiple forks to be stacked to form two dimensional optrode arrays. Each chip has an independent controller that receives, interprets and executes commands, and can transmit neural data while simultaneously controlling LED outputs. The circuit is implemented in a 180nm CMOS process, with each chip occupying a 5mm×2.45mm silicon footprint, designed specifically to mount on the base of the silicon optrode fork.