Fully Wireless ASIC With MagSonic Operation Using Magnetoelectric Transducer for Neural Stimulation and Recording

A wireless application-specific integrated circuit (ASIC), operating with the MagSonic modality using one magnetoelectric (ME) transducer, is presented for neural stimulation and recording. The ASIC integrates a bridge circuit that forms both power management and data transmitter with voltage doubling, rectification, regulation, and over voltage protection, a biphasic AC stimulator with high voltage tolerance and direct external control simplifying downlink complexities and on-chip processing overhead, an active charge balancing circuit adjusting the duration of second stimulation phase, and a continuous neural recording and uplink communication. The prototype MagSonic ASIC was fabricated in a 180 nm standard CMOS process (2 ${\boldsymbol\times}$ 1.75 mm² total area) and requires only one ME transducer and an external storage capacitor to operate. In measurements, a bar shaped millimeter-scale ME transducer (5.1${\boldsymbol\times}$2.29${\boldsymbol\times}$1.69 mm³) with length mode operation at 330 kHz was used to power the ASIC, achieving up to 8.1 mW of received power at 40 mm depth. The biphasic AC stimulator occupying only 0.027 mm² of active chip area provided 6.6 V (2${\boldsymbol\times}$V_DD) tolerance (using 3.3 V transistors) with residual electrode voltage of < 50 mV. The amplified signals were converted into time using an analog-to-time converter and transmitted at a data rate of 186.2 kbps (< 10^-3 BER) using the ME transducer's thickness mode frequency (1.66 MHz). Animal experiment results demonstrate the feasibility of ASIC's direct AC stimulation.