An analytical model to characterize the input stage of a MOSFET based RF energy harvester for improved impedance matching

RF energy harvesting has been widely investigated as a promising method of providing power to passive wireless devices or recharging the battery used in such systems. The AC input signal which is the ambient RF radiation from the available ISM band is received through the coupled antenna and converted into DC output voltage through the energy harvester chip. The energy harvester, which is a novel resonant boost rectifier circuit, typically consists of multiple stages of voltage doubler stacked in series to achieve a desired output voltage level. In order to achieve maximum rectifier conversion efficiency, it is imperative to have impedance matching between the receiving antenna and the harvester circuit. The input of the harvester is frequently modeled as a resistance in parallel with a capacitance [1]. Therefore, a physical model-based derivation of the equivalent input resistance and capacitance of the rectifier is useful to design an appropriate matching network to resonate out the input capacitance and to match the input resistance to the radiation resistance of the antenna. This paper presents an analytical approach to derive the equivalent input impedance of a multistage voltage doubler circuit designed using short-channel diode-connected MOSFETs.