Pulse count modulation based biphasic current stimulator for retinal prosthesis and in vitro experiment using rd1 mouse

For a retinal prosthesis, retinal nerve cells are electrically stimulated by current pulses. Typically, the amplitude of the current pulses is modulated to control the amount of injected charges. However, a high spatial resolution can be difficult to achieve with this amplitude modulation method, because the neural response spreads more widely as the amplitude of the current pulses is increased. In this paper, a biphasic current stimulator integrated circuit (IC) using a new modulation method called, the pulse count modulation, is proposed. In the pulse count modulation method, the amplitude and the width of the current pulses are fixed, and the amount of injected charges is controlled by the number of applied current pulses in a base period. The proposed stimulator IC is fabricated by a 0.35 μm bipolar-CMOS-DMOS (BCDMOS) technology. The operation and performance of the stimulator IC are evaluated in an in vitro experiment environment with rd 1 mice. It is shown that a higher spatial resolution can be achieved compared with the amplitude modulation method.