A Tri-State FSK Demodulator for Asynchronous Timing of High-Rate Stimulation Pulses in Wireless Implantable Microstimulators

A tri-state FSK modulation protocol and demodulator circuit have been developed and explained in this paper for wireless data rates as high as the carrier frequency. This method is used for asynchronous timing of high-rate stimulation pulses in wireless implantable microstimulators to improve the timing resolution of the stimulation pulses from one data-frame period to only one carrier cycle period. The demodulator circuit is used in a 16-site wireless active stimulating microprobe fabricated in the University of Michigan 3-mum, 1-metal, 2-poly, N-epi, BiCMOS process, occupying 1.17 mm
²
of the probe active area. The FSK demodulator circuit is simulated up to 2.5 Mega bits per second (b/s) and tested up to 300 kb/s