A 40V Voltage-Compliance 12.75mA Maximum-Current Multipolar Neural Stimulator Using Time-Based Charge Balancing Technique Achieving 2mV Precision

Abstract

Summary form only given. Electrical brain stimulation (EBS) is a technique to stimulate neurons by current pulses. Charge accumulation due to these pulses leads to voltage build up, causing electrode corrosion and tissue damage. To ensure the safety and longevity of EBS operation, various charge balancing (CB) methods have been introduced. One existing CB technique employs charge-pack injection (CPI) to compensate for residual voltage [1,2], yet it suffers from the trade-off between fast compensation time (which requires large pack) and accuracy (which requires small pack). Dynamic current mirrors (DCMs) are utilized in [3,4,5] to monitor and balance the anodic and cathodic injected charges during stimulation. However, their CB accuracy degrades due to the absence of closed-loop monitoring of the residual voltage and incapability of capturing mismatches during transitions. Other CB techniques, such as offset regulation (OR) [2,6,7] and inter-pulse charge control (IPCC) [7], are either unable to immediately remove the residual voltage after each stimulation or not well controlled in terms of compensation current and pulse-width. This paper presents a CMOS integrated neural stimulation system incorporating a time-based charge balancing (TBCB) technique that achieves a record-breaking 2mV of residual voltage and <;1nA of remaining DC current on all multipolar stimulation channels. When the residual voltage is large, like CPI, TBCB maximizes pulse-width, ensuring fast compensation. On the other hand, for a small residual voltage, TBCB automatically modifies the pulse-width based on the residual voltage value to improve CB accuracy. Compared to previously disclosed CB techniques, TBCB breaks the trade-off between compensation time and accuracy, provides closed-loop monitoring of the residual voltage on each channel separately, and achieves immediate charge removal. Moreover, self-defined idle window (using comparator's hysteresis) and auto-zero offset removal are incorporated to avoid toggling and further improve CB accuracy.