Abstract
Spatiotemporal stimulation (STS) has emerged as a novel method for multi-channel neural electrical stimulation but suffers from severe crosstalk. The crosstalk includes electric field distribution and current distribution, which affect spatial resolution and charge balance, respectively. Compared with monopolar stimulation, bipolar stimulation exhibits less electric field distribution, making it more suitable for STS. However, an offset voltage on charge imbalance occurs in traditional bipolar stimulation under STS due to the current distribution. This article first analyzes the causes and effects of offset voltage in two traditional bipolar stimulation configurations and quantitatively compares the results under experimental measurement. To simultaneously achieve high spatial resolution stimulation and precise charge balancing (CB) for bipolar stimulation, we propose a four-channel tripolar spatiotemporal stimulator with a return-electrode-based charge-pack injection (RECPI) technique. By introducing a return electrode (RE), the residual voltages on both working and counter electrodes (CEs) can be effectively compensated. The stimulator is fabricated in a 180-nm standard CMOS process, with a core area of 1.209 mm 2 and each stimulation channel occupying 0.256 mm 2 . It achieves a voltage compliance of ±10.4 V and a maximum stimulation current of 2.8 mA. Electrical and in vitro tests demonstrate that with RECPI, residual voltage on each electrode and offset voltage of each channel are compensated within ±7.5 mV after CB. Furthermore, in vivo tests validate the functionality of the tripolar stimulator.