NeuroFlare: An mm³-Scale Wireless Neural Interface Device with Simultaneous Neural Recording and Optical Stimulation

This paper presents the creation of a wireless, miniature implantable opto-electro neural interface device called NeuroFlare, capable of simultaneous neural recording and optical stimulation. NeuroFlare features a low-power, dual-modal application-specific integrated circuit (ASIC) fabricated using the 180 nm CMOS process. To support the power-intensive optical stimulation in NeuroFlare, the ASIC employs a novel linear-charging switched-capacitor stimulation (LC-SCS) structure. The LC-SCS, operating under only a 1.2 V supply voltage, can illuminate the LED with a driving voltage three times the supply voltage and large current pulses of up to 12 mA while maintaining a high charging efficiency of 86.4%. In addition, LC-SCS requires only one off-chip capacitor, greatly facilitating device miniaturization. To accurately record neural signals in the presence of stimulation artifacts, the ASIC employs a delta-sigma modulator ( $\Delta \Sigma M$ )-based recording frontend with a wide dynamic range (DR) to directly digitize the neural signals. The $\Delta \Sigma M$ features a 2^nd-order loop architecture implemented using a linearized Gm-C integrator followed by an active noise-shaping (NS) successive approximation register (SAR) quantizer. The $\Delta \Sigma M$ with power consumption of 9.8 μW provides a peak DR of 83.7 dB, corresponding to a 400 mV_PP linear input range. The $\Delta \Sigma M$ 's 173.8 dB Figure-of-Merit ( ${FoM}_{DR}$ ) indicates its superior energy efficiency. The ASIC is assembled into a prototype of NeuroFlare measuring 2.8 × 3.5 × 0.7 mm³. The recorded light-evoked local field potential (LFP) verified the functionality of NeuroFlare in vivo.