Isolator-Less Near-Field RFID Reader for Sub-Cranial Powering/Data Link of Millimeter-Sized Implants

Implants for brain-machine interface (BMI) systems require both wireless powering and data communication to be practical for reliable long-term use. Sub-cranial radio-frequency identification (RFID) readers can receive backscattered data, while providing wireless power to operate the implant. This paper presents a novel reader architecture for an efficient near-field fully integrated RFID reader meant to deliver power to and receive data from BMI implants, where a modified Class-E/Fodd power amplifier (PA) with a current-sense resistor differentially drives a single segmented antenna and acts simultaneously as TX and RX. It operates at 309 MHz and has 54% efficiency. The non-linearity of the switching PA is able to demodulate the backscattered signal to baseband. And the data can be recovered from a current-sense resistor without the need for bulky RF isolators, separate RX/TX antennas, or different frequencies for data/power delivery. The reader, as tested with a proprietary RFID tag through pig-skin and cow-bone, can deliver a maximum of 790 μW to an implant through the skull while consuming 39.4 mW of power. It has a 2-Mb/s data rate with a bit error rate of less than 1e-6.