Abstract
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- $\mu \text{m}$ 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.
Highlights
I NDUCTIVELY coupled systems are becoming increasingly common in a wide range of applications; at one end of the scale, wireless charging systems are focused on power transfer, sometimes at very high levels [1]
The implementation is fabricated in a standard 0.18-μm CMOS/LDMOS process, with timing generation and high-voltage switches integrated into the same die
The system uses zero-voltage switched fractional capacitors in order to reduce the number of bond pads and package pins required compared with the conventional tuning methods using quasi-static switched arrays of weighted capacitors
Summary
I NDUCTIVELY coupled systems are becoming increasingly common in a wide range of applications; at one end of the scale, wireless charging systems are focused on power transfer, sometimes at very high levels [1]. If the transmit frequency is fixed, any tuning technique must take into account of manufacturing tolerances and temperature effects, and detuning due to a varying receiver load and possibly motion of nearby ferromagnetic structures. This problem may be partially sidestepped in some applications by varying the excitation frequency [4]–[6], but this may not be permissible due to band allocation restrictions. Power, low-complexity system with no tuning capabilities and to use a fixed nominal antenna resonant frequency with a modest Q factor to give a satisfactory response despite the impacts of tolerances and environmental effects. Experimental results are shown in a demonstration design, comparing the static tuning performance with a weighted-capacitor tuning system of equivalent specification, as well as looking at the dynamic tuning response of the system to changes in operating frequency, exercising transient detuning behavior
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