8-Channel Neural Stimulation ASIC for Epidural Visual Cortex Stimulation

This paper presents an 8-channel neural stimulator application-specific integrated circuit (ASIC) for biphasic stimulation of the visual cortex, fabricated in a 0.35 mu m AMS HV process. Each channel is composed of a standard SPI interface, an 8-bit current digital-to-analog converter (DAC) and 120V compliant HV output stage. Thus, it is possible to deliver to the tissue arbitrary current waveforms with amplitudes up to +/- 8.192mA with 32 mu A steps. The measured maximum differential nonlinearity (DNL) of the current output does not exceed 1.1 LSB. The on-board current reference provides the output current of 16 mu A with a very low temperature variation. The maximum anodic and cathodic current mismatch after calibration is 25 mu A. The measured interpulse leakage current does not exceed 60 pA. The ASIC was also tested with the electrode-tissue model, which describes the PEDOT electrodes of 560 mu m diameter in the phosphate buffer saline (PBS). The measurement results approve the possibility to stimulate with arbitrary current amplitudes with frequencies up to 1.5 kHz.