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 0.35μm HV CMOS process with 20V power supply, the maximum mismatch between cathodic and anodic current is achieved less than 0.4μA out of full scale current of 1mA. (equivalent to 11 bit accuracy at 1mA) Residual dc current of less than 1nA is achieved with shorting enabled, under 0.1ms stimulation for each cathodic and anodic phase out of 3ms period.
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