Improved efficiency in the CMOS cross-connected bridge rectifier for RFID applications

A bridge rectifier based on the cross-connected NMOS-PMOS bridge that avoids the inherent degradation of power conversion efficiency for increasing input levels is presented. Instead of PMOS switches, the proposed rectifier uses diode-connected MOS transistors with static threshold cancellation and minimised diode reverse leakage. With a simple and power efficient circuit solution the new rectifier allows for low-power, passive tag implementation in standard CMOS for both LF and HF RFID applications. Simulation results of the proposed rectifier in a 0.35 μm CMOS process show a power conversion efficiency over 60% for all input levels above 0.75 V with a 100 kΩ load and an input signal frequency of 13.56 MHz. The simulated DC output voltage at the same conditions is approximately V_in-0.3 V. A model for the PCE of the new rectifier that includes the impact of the V_th-generator is developed and compared with simulated results.