A pulse-width-adaptive active charge balancing circuit with pulse-insertion based residual charge compensation and quantization for electrical stimulation applications

Charge balancing is an important task for the stimulators used in chronic electrical stimulation applications. In this paper, a pulse-width-adaptive (PWA) active charge balancing (ACB) circuit with pulse-insertion based residual charge compensation and quantization is proposed to fulfil this task. The proposed circuit dynamically adapts the pulse width (Tc) of counter phase (Φc) over a stimulation pulses train to achieve charge balancing. The adaptation step ΔTc is based on the quantized residual charge (Qres) of the initial stimulation pulse. Pulse insertion technique is used to quantize Qress and perform instant charge balancing after each stimulation pulse. The PWA ACB circuit mainly consists of an auxiliary pulse generator, residual voltage (Vres) monitoring and Qres quantization block, and a digital controller. A successive approximation (SA) algorithm is implemented in the digital controller for fast Tc searching. The proposed circuit is implemented in 0.18μm CMOS process with 24V LDMOS option, occupying a core area of 700μm by 150μm. The functionality and effectiveness of the circuit are verified through bench-top and animal experiments.