Implantable stimulator for bipolar stimulation without charge balancing circuits

It is critically important to maintain charge balance in neural stimulation, employing biphasic current pulses. Any mismatch in biphasic current pulses will result in charge imbalance, possibly leading to tissue damage. In this paper, we propose an implantable stimulator for bipolar stimulation to minimize the mismatch of biphasic current pulses, without dc blocking capacitors or charge balancing circuits. Using 0.35 μm HV CMOS process with 20 V power supply, the maximum mismatch between cathodic and anodic current is achieved less than 0.4 μA out of full scale current of 1 mA. (equivalent to 11 bit accuracy at 1mA) Residual dc current of less than 1 nA is achieved with shorting enabled, under 0.1 ms stimulation for each cathodic and anodic phase out of 3 ms period.