An RF power harvesting system with input-tuning for long-range RFID tags

In this paper, an RF power harvesting system with automatic input tuning for long-range RFID tags is described. The system uses a high quality factor LC-matching network to boost the voltage of the received RF signal. Then a new high-efficiency voltage rectifier is used to extract DC voltage from the signal. In order to maximize the voltage gain of the matching circuit, a tuning loop automatically adjusts the center frequency of the input matching network to achieve the optimum output DC voltage. The loop uses a low-power up/down counter. The power of the counter is optimized by minimizing the number of unnecessary internal transitions. A proof-of-concept system is designed and simulated in a 0.13μm CMOS. It achieves an efficiency of 50% which compares favourably with that of current state-of-the-art RF power harvesting systems.