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

This article 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 front end with a wide dynamic range (DR) to directly digitize the neural signals. The $\Delta \Sigma $ M features a 2nd-order loop architecture implemented using a linearized transconductance-capacitor (Gm-C) integrator followed by an active noise-shaping (NS) successive approximation register (SAR) quantizer. The $\Delta \Sigma $ M with a power consumption of $9.8~{\mu }$ W provides a peak DR of 83.7 dB, corresponding to a 400-mVPP linear input range. The $\Delta \Sigma $ M’s 173.8-dB figure of merit (FoMDR) indicates its superior energy efficiency. The ASIC is assembled into a prototype of NeuroFlare measuring $2.8 \,\, {\times } \,\, 3.5 \,\, {\times } \,\, 0.7$ mm3. The recorded light-evoked local field potential (LFP) verified the functionality of NeuroFlare in vivo.