An active charge balancing method based on anodic current variation monitoring

Abstract

Charge balancing is a major safety concern in neural and functional electrical stimulation. This paper presents a novel and safe active charge balancing approach in which after each cathodic and anodic stimulation pulse, the value of the remaining voltage is monitored using a window comparator. Consequently, according to the value of the remaining voltage, a current is added or subtracted from the original anodic current which is designed to compensate a mismatch up to 5%. The proposed method enables a straightforward hardware implementation, while guaranteeing that the remaining voltage be constrained within a safe window of ±100 mV. Furthermore, thanks to the simple structure of the proposed method, the control loop does not need any settling time. The proposed charge balancer is designed to operate with a retinal stimulator, however, the method can be adapted to any kind of implantable stimulator. System-level mathematical modeling shows that the charge balancer is stable throughout any stimulation parameter domain allowed for a retinal stimulator. In addition, the system stability and accuracy is verified using discrete component implementation.