A Primary Driver with Real-Time Resonance Tracking for Wireless-Powered Implantable Medical Devices

Inductively-coupled wireless powered transfer (WPT) is widely used in implantable medical devices (IMD) [1] to avoid batteries. Flexible coils [2] are desired in this application as they can be attached onto or be implanted into human body. However, flexible coil bending or incoming magnetic shielding material can cause mismatch between LC tank's resonant frequency (mathrm{f}-{text{LC}}) and primary driver's switching frequency (mathrm{f}-{text{SW}}). As the inductive link is a narrow-band system, the link gain and efficiency is very sensitive to the matching quality. To tune mathrm{f}-{text{LC}} back to mathrm{f}-{text{SW}}, auto-tuning techniques [3]-[5] were proposed. [3] uses a capacitor matrix scheme that need several capacitors and relays, and they are not integrated. [4]-[5] proposed the fractional-capacitance (FC) scheme, which only need two capacitors and two LDNMOS. By changing the on-duty of the capacitors, the effective primary capacitance can be tuned. But its system complexity is high and it operates at 2MHz. Besides, zero-voltage switching (ZVS) is not achieved at transient periods, which degrades the efficiency as the primary inductor is perturbed frequently in the IMD scenario.