Design Space Exploration of Antenna Impedance and On-Chip Rectifier for Microwave Wireless Power Transfer

Abstract

This paper discusses a design methodology to efficiently determine the best combination of rectenna (rectifier and antenna) to minimize the input power under a given output condition for microwave wireless power transfer (MWPT) without any other external components, such as a matching network, for cost reduction. A linearized equivalent circuit model is expanded upon to include the microstrip line connecting the antenna and rectifier. Based on the model, the design flow is presented that has mainly three steps: (1) Determination of the equivalent rectifier input impedance and the amplitude of input voltage by running SPICE simulation, (2) Drawing contour plots of input power by rectifier candidate on the antenna impedance plane by conducting model calculation and impedance loci of antenna candidates on the contour plots, and (3) Selecting the combination of antenna and rectifier which gives the minimum input power for all the combinations. To validate the equivalent circuit model and design flow, a single-diode (SD) rectifier and a voltage-doubler (VD) rectifier were fabricated in 65 nm CMOS. The input power to generate 100 μA at 1 Vdc was measured and compared. The model, SPICE and measurement are in good agreement with each other that VD has 30–50% lower input power than SD does. In addition, the sensitivity of the parasitic elements, such as the microstrip line and the bonding wires and pads on the input power, are investigated to explore the design space for rectenna.