Biphasic-current-pulse self-calibration techniques for monopolar current stimulation

Monopolar biphasic current stimulation is widely used for neural prosthetic devices. The major design challenge is to ensure charge-balanced stimulation. This paper describes a compact negative-feedback self-calibration scheme to minimize the current amplitude mismatch between the anodic and the cathodic pulses for achieving the charge balance without using any large-value blocking capacitors and long duration of interpulse shorting. Dummy transmission gate technique is also adopted in the calibration circuit to minimize the charge injection error. With a 0.35-¿m high-voltage CMOS process, the maximum amplitude mismatch between two current pulses in the stimulator is < 0.3 ¿A (0.03%) after calibration with a full-scale stimulation current of 1 mA. It corresponds to < 7.5 nA residual DC current error for supporting 10-¿s pulse and high stimulation rate of 2500 pulses per second (pps).