Automatic tuning of a resonant circuit in wireless power supply systems for biomedical sensors

In this paper, a tuning method of a resonant circuit suited for wireless powering of miniature endoscopic capsules is presented and discussed. The method allows for an automatic tuning of the resonant frequency and matching impedance of a full wave rectifier loading the resonant circuit. Thereby, the receiver tunes so as to obtain the highest power efficiency under given conditions of transmission. A prototype receiver for wireless power reception, fabricated in in AMS CMOS 0.35 μm technology, was used to verify correct operation of the proposed tuning. The prototype system produces a stable supply voltage, adjustable in the range of 1.2–1.8 V at a maximum output current of 100–67 mA, which is sufficient to power a typical endoscopic capsule.