8 Channel neural stimulation ASIC for epidural visual cortex stimulation with on board 90 ppm/°C current reference

This paper presents an 8 channel neural stimulator ASIC for biphasic stimulation of the visual cortex, realized in a 0.35 μm AMS HV process. Each channel is composed of an SPI interface, an 8-bit current digital-to-analog converter (DAC) and 120 V compliant HV output stage. Thus it is possible to deliver to the tissue arbitrary current waveforms with amplitudes up to ±10.24 mA with 40 μA steps. According to the simulation results the maximum differential non-linearity is equal to 0.27 LSB. The on board current reference provides the output current of 16 μA with the variation of 90 ppm/°C in the temperature range of 0-85° C. While the anodic and cathodic currents mismatch does not exceed 13 μA. The HV output interface of the ASIC was previously fabricated and measured. The measured interpulse leakage current does not exceed 60 pA.