A High-Density Transcranial Electrical Stimulation System on Chip with Real-Time Bio-Impedance Sensing

This paper presents a system on chip (SoC) designed for high-density transcranial electrical stimulation (HD-TES) with real-time bio-impedance sensing. Multiple chips can work collaboratively to generate arbitrary waveforms for HD-TES including temporal interference (TI) stimulation. This design implements a combined digital calibration and analog switch mechanism for common-mode voltage holding (CMVH), ensuring long-time safety of HD-TES. The SoC can perform impedance measurement (IM) through transcranial alternating current stimulation (tACs) allowing to monitor the biological impedance variations during tACs. To ensure the safety of current stimulation, switched-capacitor overcurrent protection (OCP) circuit is integrated. Measured results show that the SoC can apply arbitrary stimulation currents within the voltage range of ±13V. The amplitude range of the current is from - 2.5mA to 2.5mA with a 10 μA minimum step. The common-mode voltage of the electrode remains stable near 0V when operating in HD-TES mode. Impedance measurement error is less than 5% within the extensive range of 0.5kΩ to 500kΩ.