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.
 O. Lazaro, G.A. Rincon-Mora, “180-nm CMOS wideband capacitor-free inductively coupled power receiver and charger”, IEEE J. Solid-State Circ., 48 (11), 2839–2849 (2011).
 Ch. Hao, Y. Jia, X. Liu, R.-F. Xue, H.J. Lim, P.B. Khannur, K.L. Chan, A.A. Lee, K. Kang, L.S. Lim, C. He, P. Singh, P. Woo-Tae, J. Minkyu, “An inductively powered implantable blood flow sensor microsystem for vascular grafts”, IEEE Trans. Biomed. Eng., 58 (2), 2466–2475 (2011).
 Ch.-J. Chen, T.-H. Chu, Ch.-L. Lin, Z.-Ch. Jou, “A study of loosely coupled coils for wireless power transfer”, IEEE Trans. Circ. Syst. II: Exp. Briefs, 57 (7), 536–540 (2010).
 K. Fotopoulou, B. W. Flynn, “Wireless power transfer in loosely coupled links: coil misalignment model”, IEEE Trans. Magnetics, 47 (2), 416 – 430 (2011).
 J. Lee Y.-S. Lim, W.-J. Yang, S.-O. Lim, “Wireless power transfer system adaptive to change in coil separation”, IEEE Trans. Antennas and Propagation, 62 (2), 889–897 (2014).
 R.-F. Xue, K.-W. Cheng, M. Je, “High-efficiency wireless power transfer for biomedical implants by optimal resonant load transformation”, IEEE Trans. Circ. Syst. I: Reg. Papers, 60 (4), 867–874 (2013).
 N.Y. Kim, K.Y. Kim, J. Choi, C.-W. Kim, “Adaptive frequency with power-level tracking system for efficient magnetic resonance wireless power transfer”, Electr. Letters, 48 (8), 452–454 (2012).
 A.P. Sample, D.A. Meyer, J.R. Smith, “Analysis, experimental results, and range adaptation of magnetically coupled resonators for wireless power transfer”, IEEE Trans. Industrial Electronics, 58 (2), 544–554, (2011).
 C. Sauer, M. Stanacevic, G. Cauwenberghs, N. Thakor, “Power harvesting and telemetry in CMOS for implanted devices”, IEEE Trans. Circ. Syst. I: Reg. Papers, 58 (12), 2605–2613 (2005).
 G. Blakiewicz, “Bezprzewodowe zasilanie sensorów medycznych”, Przegląd Elektrotechniczny 9, 12–14, (2014).
 W.H. Ko, S.P. Liang, C. Fung, „Design of radio-frequency powered coils for implant instruments”, Medical & Biological Engineering & Computing 15, 634–640, (1977).
 G. Blakiewicz, “Technique to improve CMRR at high frequencies in CMOS OTA-C filters”, Bull. Pol. Ac.: Tech. 61 (3), 697–703 (2013).
 W. Jendernalik, J. Jakusz, G. Blakiewicz, R. Piotrowski, S. Szczepański, “CMOS realisation of analogue processor for early vision processing”, Bull. Pol. Ac.: Tech. 59 (2), 141–147, (2011).