An Enhanced-Frequency-Splitting-Based Wireless Power and Data Transfer System Achieving 60.2% End-to-End Efficiency and 1 Mb/s Data Rate with a Sub-cm RX Coil for Miniaturized Implants

Implantable medical devices have been scaled down to minimize the invasiveness and complexity of the device-deployment process. In such miniaturization, the main bottleneck is wireless power and data transfer (WPDT), particularly the volume of the receiver (RX) coil. Conventionally, on-off keying (OOK) has been widely used for WPDT over a single inductive link due to its simplicity. However, the OOK scheme restricts the power delivered to the load (POL) as the data rate (DR) increases. To address the trade-off between POL and DR, frequency-shift keying (FSK) and phase-shift keying (PSK) have been utilized. In these WPDT systems, there is an inherent trade-off between the power transfer efficiency (PTE) and DR, driven by the quality factors (Qs) of coils. Recently, to alleviate these trade-offs, a frequency-splitting-based WPDT (FS-WPDT) system that employs a flat-region FSK (FR-FSK) scheme operating at two frequencies $(\mathrm{f}_{\mathrm{H}}, \mathrm{f}_{\mathrm{L}})$ in the flat region of the link gain has been presented [1]. However, the FS-WPDT system still suffers from significant coil size to achieve a coupling coefficient (k) larger than the critical value $(\mathrm{k}_{\mathrm{c}})$ for frequency splitting (FS). This work presents an enhanced-frequency-splitting-based WPDT (EFS-WPDT) system breaking this limitation through the FS enhancement (FSE) enabled by the dynamically controlled LC tank in RX (Fig. 35.6.1). Since $\mathrm{k}_{\mathrm{c}}$ is inversely proportional to the loaded $\mathrm{Q}_{\text{RX}}$, it is proportional to the load resistance $(\mathrm{R}_{\mathrm{L}})$ in the series-series topology. The link-load isolation (LLl) allows the link to see switch on-resistance $(\mathrm{R}_{\text{SW}})$ rather than $\mathrm{R}_{\mathrm{L}}$ I thus lowering $\mathrm{k}_{\mathrm{c}}$ regardless of $\mathrm{R}_{\mathrm{L}}$, resulting in FSE even with fairly small coils. The effect of dynamic LLl on FS is simulated, confirming the feasibility of the EFS-WPDT system. The proposed EFS-WPDT system relieves the trade-offs among POL, PTE, and DR while improving the form factor of the RX coil by 10x.