A design methodology for charge-balanced stimulators based on anodic current variation monitoring

Charge balancing is a major safety concern in neural and functional electrical stimulation. This paper presents a novel and safe active charge balancing design methodology in which, after each cathodic and anodic stimulation pulse, the value of the remaining voltage is compared to different voltage levels. According to the value of the remaining voltage, a specific amount of additional current is added or subtracted from the anodic current of the next stimulation cycle. The proposed method enables a straightforward hardware implementation, while guaranteeing that the remaining voltage is constrained within a safe window, well below the water window (e.g., ± 100 mV). Furthermore, in the proposed method, the control loop does not need any settling time when the stimulation starts (stimulator start-up). Using this method, different design examples are introduced for a retinal stimulator. A comprehensive system level simulation using MATLAB is presented for the first time, in order to prove the stability of the stimulators. This type of simulation shows the performance of the stimulators throughout any allowed stimulation parameter in a single plot. In addition, discrete-component implementations of an example of the proposed method confirms the results obtained from system-level mathematical modeling.