Adaptive resolution ADC array for neural implant

This paper describes an ADC array for an implantable prosthetic processor which digitizes neural signals sensed by a microelectrode array. The ADC array consists of 96 variable resolution ADC base cells. The base ADC has been implemented in 0.13 mum CMOS as a 100 kS/s SAR ADC whose resolution can be varied from 3 to 8-bits with corresponding power consumption of 0.23 muW to 0.90 muW achieving an ENOB of 7.8 at the 8-bit setting. The resolution of each ADC cell in the array is varied according to neural data content of the signal from the corresponding electrode. Resolution adaptation reduces power consumption by a factor of 2.3 whilst maintaining an effective 7.8-bit resolution across all channels.