Abstract
In spread-spectrum electromagnetic interference (EMI) suppression, transmitter ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TX</i> ) 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TX</i> frequency is deviated far from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</i> nominal frequency (i.e., boundary of tunable range), even if the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</i> is reconfigured to tuned resonance. To solve the issues, the proposed PWM-tuning <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</i> achieves constantly high efficiency even at the boundary of frequency tuning range. The proposed topology boosts the reflected resistance, thereby increasing the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TX</i> -to- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</i> efficiency compared to traditional variable tunings. We also propose an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</i> feedback loop which can track the fast-varying <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TX</i> frequency and tune the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</i> 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 <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> achieves soft switching both at turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> . 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.
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