A comprehensive survey on UHF RFID rectifiers and investigating the effect of device threshold voltage on the rectifier performance

Rectifiers are an integral part of power harvesting systems. In this paper, the literature on RF power rectifiers is surveyed, starting from the well-known voltage doubler. Effects of using low turn-on voltage devices on forward and reverse losses, and therefore, on conversion efficiency, is discussed. Samples of rectifiers with external devices, such as Schottky diodes are presented. Idea of external V th cancellation through a rechargeable battery, self V th cancellation, and floating gate transistors with charge injection onto the gates are demonstrated. Then, standard bridge rectifier and its modified versions, including V th cancellation technique, are explained. Using low voltage devices in other technologies, such as silicon on sapphire and silicon on isolator are also discussed. After literature survey, the bridge rectifier is studied in detail, to extract guidelines for efficiency enhancement. Bridge rectifier has high PCE, because the transistors have a dynamic bias that lowers their forward and reverse losses, simultaneously. Then, the effect of transistor threshold voltages on the bridge rectifier performance is investigated. We propose to shift peak region in the efficiency curve to a desired output voltage, based on which, two modified rectifiers are introduced. A single stage modified bridge rectifier is proposed with 3.3 V transistors, that achieves efficiency of around 80% at 0.9 V output. Then, a two stage modified bridge rectifier is proposed, that uses a combination of 1.8 and 3.3 V transistors to remove the need to source-bulk connection in NMOS transistors (that requires triple-well CMOS technology). Simulations predict around 80% efficiency at 1.7 V output.