Automatic Tuning Receiver for Improved Efficiency and EMI Suppression in Spread-Spectrum Wireless Power Transfer

In spread-spectrum electromagnetic interference (EMI) suppression, transmitter (
TX
) frequency is continuously modulated with fast speed. Conventional receiver (RX) autotuning methods cannot be used because of their slow response speed. Another limitation of conventional autotuning is their low efficiency if the incoming
TX
frequency is deviated far from
RX
nominal frequency (i.e., boundary of tunable range), even if the
RX
is reconfigured to tuned resonance. To solve the issues, the proposed PWM-tuning
RX
achieves constantly high efficiency even at the boundary of frequency tuning range. The proposed topology boosts the reflected resistance, thereby increasing the
TX
-to-
RX
efficiency compared to traditional variable tunings. We also propose an
RX
feedback loop which can track the fast-varying
TX
frequency and tune the
RX
capacitor accordingly. The step-response of proposed loop is fast (0.1 ms) in order to be suitable for spread-spectrum EMI suppression. The tuning
mosfet
achieves soft switching both at turn-
on
and turn-
off
. A simple grounded gate driving can be used. The measurement results show that the proposed ATR can improve the overall power transfer efficiency (PTE) by 7%–12% point for spread-spectrum ranging from 108 to 137 kHz, enabling 19.9 dB EMI suppression.