A Self-Tuning Resonant-Inductive-Link Transmit Driver Using Quadrature Symmetric Delay Trimmable Phase-Switched Fractional Capacitance

The efficiency of inductively coupled power transfer systems is increased when high-Q inductor-capacitor circuits are used, maximizing the magnetic field strength at the transmitter for a given drive amplitude. Such circuits require precise tuning to compensate environmental effects and component tolerances, which modify the resonant frequency. A single zero-voltage-switched fractional capacitance may be used to accurately tune the circuit to resonance, reducing implementation costs compared with classical tuning techniques. However, integration into a chip presents challenges, which must be addressed, such as operating with large voltage excursions and compensating for high-voltage driver delays. We describe here the operation of a self-tuning LC resonant circuit driver using a symmetrically switched fractional capacitance. An architecture for a fully integrated system for operation at 75 kHz-2.6 MHz is presented. Implemented in a 0.18-μm 1.8-50 V CMOS/laterally diffused MOSFET(LDMOS) technology, the integrated circuit uses high-voltage interfaces for capacitance switching and sampling inputs and includes digital phase trimming to compensate propagation delays in large driver devices. Correct operation of the self-tuning functionality is verified across the available frequency range, with results presented for static and dynamic tuning responses.