A 32-channel modular bi-directional neural interface system with embedded DSP for closed-loop operation

A prototype bi-directional neural interface system is presented with closed-loop and embedded DSP capabilities. The system includes 32-electrode stimulation capability, eight multiplexed low-noise low-power bio-potential sensing channels with on-chip digital FFT, and a Cortex M3-based microcontroller for implementing closed-loop algorithms. The stimulation subsystem can provide a maximum stimulation current of 12mA with approximately 3% accuracy per channel. The sensing subsystem uses a fully differential chopping amplifier achieving a noise floor <;100nV/rtHz with approximately 1μA current from 2V supply. A 13bit continuous-time sigma-delta ADC is used to sample the amplifier output at the rate of 33kHz. The ADC consumes approximately 100nA while achieving an ENOB of 12b with a 250Hz date rate. A hardware implementation of a cached-FFT is included in the sensing IC to perform spectral analysis of the bio-potential signal. The resulting multiple spectral signatures can be selectively sent to the microcontroller allowing for algorithmic control of the stimulator system. The system partition was designed to minimize overall computational power while providing user flexibility. The sensing performance of the prototype has been demonstrated with 2-D cursor control in a non-human primate brain machine interface (BMI) model using 20 features simultaneously.