Adaptive signal acquisition and wireless power transfer for an implantable prosthesis processor

This paper describes an ADC array and wireless power transfer link 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 0.13μm CMOS as a 100kS/s SAR ADC whose resolution can be varied from 3 to 8-bits with corresponding power consumption of 0.23μW to 0.90μW. The resolution of each ADC cell is adapted according to neural data content of the signal from the corresponding electrode, this reduces power consumption by a factor of 2.3 whilst maintaining an effective 7.8-bit resolution across all channels. A wireless power transfer system for implanted medical devices which uses antenna area 100 times smaller than previous designs has also been realized. Adaptive simultaneous conjugate matching and a high efficiency rectifier and regulator in 0.13μm CMOS together with a 4mm² antenna deliver 140μW at 1.2V DC from a 4cm² transmit antenna and a 0.25W 915MHz source through 15mm of tissue to power the implanted device.