A wideband frequency-shift keying wireless link for inductively powered biomedical implants," Circuits and Systems I: Regular Papers

Abstract—A high data-rate frequency-shift keying (FSK) modu-lation protocol, a wideband inductive link, and three demodulator circuits have been developed with a data-rate-to-carrier-frequency ratio of up to 67%. The primary application of this novel FSK modulation/demodulation technique is to send data to inductively powered wireless biomedical implants at data rates in excess of 1 Mbps, using comparable carrier frequencies. This method can also be used in other applications such as radio-frequency identifica-tion tags and contactless smartcards by adding a back telemetry link. The inductive link utilizes a series-parallel inductive-capac-itance tank combination on the transmitter side to provide more than 5 MHz of bandwidth. The demodulator circuits detect data bits by directly measuring the duration of each received FSK car-rier cycle, as well as derive a constant frequency clock, which is used to sample the data bits. One of the demodulator circuits, dig-ital FSK, occupies 0.29 mm2 in the AMI 1.5- m, 2M/2P, standard CMOS process, and consumes 0.38 mW at 5 V. This circuit is simu-lated up to 4 Mbps, and experimentally tested up to 2.5 Mbps with a bit error rate of 10 5, while receiving a 5 10-MHz FSK carrier signal. It is also used in a wireless implantable neural microstimu-lation system. Index Terms—Biomedical implants, CMOS, data rate, demodu-lator, inductive coupling, frequency-shift keying (FSK), radio fre-quency (RF), RF idenitifcation (RFID), wireless. I