Abstract
Inductively coupled power transfer systems often use high- Q antenna circuits to reduce losses and increase transmission range. However, the narrow bandwidth due to the high Q-factor conventionally constrains the modulation rate on the carrier, creating a tradeoff between power transfer efficiency and data rate. In this article, we show how instantaneous tuning of the antenna can permit frequency and phase modulation data rates beyond the Q-factor limitations, provided that the drive and antenna resonance frequencies are kept the same at all times. It is also necessary to ensure that the modulation symbol boundaries are precisely aligned with the tracking of the resonance tuning to ensure phase continuity and optimum power transfer. With instantaneous tuning, phase modulation can be implemented by defined numbers of cycles at an offset frequency, provided the offset is precisely controlled. We describe how the required instantaneous resonance tuning can be achieved using a switched fractional capacitor technique and present a system architecture that can follow abrupt frequency changes due to the modulation while tracking changes to the resonant condi- tion due to environmental detuning effects at each modulation frequency. An integrated mixed-signal driver/modulator/tuner demonstrator system is presented, operating from 10 kHz–2 MHz using a 0.18- µm 1.8–50-V CMOS/laterally-diffused metal-oxide semiconductor (LDMOS) process. The system maintains phase continuity in the antenna