A Dual Resonant Frequencies Tuning Circuit Based on FSK Modulation for Wireless Power and Data Transmission in Medical Implants

Frequency-shift keying (FSK) is a robust data modulation method that is insensitive to voltage noise and movements of the transmitter and receiver coils of an inductive link. However, the conventional wireless power and data transfer (WPDT) system based on single resonant frequency FSK modulation is difficult to achieve high power transfer efficiency (PTE) because the LC loop works in detuned state. In this paper, we propose a dual resonant frequencies tuning circuit (DRFTC) to improve the PTE of the WPDT system for medical implants. In the proposed technology, the transmitter uses the input data as the control signal of transistor to adjust the equivalent capacitance in the loop, and the receiver adopts the characteristics of series-parallel LC network with dual inherent resonant frequencies to realize resonance at different frequencies of binary FSK modulation. An oscillator with frequency accuracy of 99.84%, which ensures the accuracy of carrier, has also been designed. The transmitter SoC has been fabricated by 0.18-μm CMOS technology and occupies 1.8 mm2. The experimental results of DRFTC-WPDT prototype show that when the two carrier frequencies of binary FSK are 3.952 MHz and 4.516 MHz, the data transmission rate reaches 564 Kbps, and the PTE and power delivered to the load (PDL) are 65.50% and 69.13 mW, respectively.