12.8 Wireless power transfer system using primary equalizer for coupling- and load-range extension in bio-implant applications (2015)

Wireless power transfer (WPT) in the range of 10 to 100mW [1] is widely used in impiantale medical devices (IMDs) to eliminate the use of a battery. Due to load and coupling variations, the output voltage of the rectifier V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> is not steady. In [1-2], a 1X/2X reconfigurable rectifier was reported to uphold V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> when the coupling coils move apart. In [3], V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> is regulated by the transmitter with feedback through a wire, which defeats the purpose of WPT. In [4], V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> is regulated by a resonant regulating rectifier as well as an MCU-controlled transmitter with feedback still through a wire. In [5], a reconfigurable resonant regulating (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) rectifier is reported for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> regulation, but the load and coupling ranges are limited. In the R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> rectifier, the 1X/2X rectifier works as a bridge rectifier in 1X mode with V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> equal to V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1X</sub> , and as a voltage doubler in 2X mode with V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> equal to V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2X</sub> as shown by the dash lines in the HSPICE simulated results in Fig. 12.8.1. V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> is regulated within [V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1X</sub> , V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2X</sub> ] by adjusting the duty cycle of mode-switching through the PWM control under the condition that V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2X</sub> >V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1X</sub> ; otherwise, the PWM control is not stable. This restricts the workable load resistance R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> to be larger than the boundary R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">La</sub> . For a smaller coupling factor k, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">La</sub> is larger (load current is smaller), and thus the coupling range is also limited. In this work, a primary equalizer is introduced to tackle these limitations to extend the load and coupling ranges.