CMOS DAC-sharing stimulator for neural recording and stimulation arrays

A compact biphasic neural stimulator for use in multi-channel integrated neural recording and stimulation interfaces is presented. The stimulator is a part of an envisioned closed-loop implantable microsystem for adaptive neural stimulation. The stimulator reuses the capacitive DAC inside the recording SAR ADC to provide 8-bit current amplitude resolution and reconfigures the digital SAR controller logic to provide 4-bit tunability of the duty cycle of the current pulse. A voltage-to-current converter and a current driver are the only additional circuits required. An OTA is reused to provide accurate current matching and to remove excess charge on the electrode. The stimulator is implemented in a standard 0.13μm CMOS technology. Post-layout and Monte Carlo simulation results show 8-bit functionality from 5μA to 1.2mA, a 2.5V swing and 1 percent current matching between positive and negative pulses.