A Charge Pump System with Controlled Input Impedance for Optimized RFID Energy Harvesting

Efficient energy harvesting is crucial for the seamless operation of passive UHF RFID sensor applications, especially in energy-constrained environments. We present a novel approach to optimize RFID transponder energy harvesting using a carefully designed charge pump system. We pump energy from the transponder's rectified supply voltage to a storage capacitor from which we power the EEPROM and sensors. By regulating the rectifier output voltage, i.e. the input of the charge pump, the maximum energy is extracted without overloading the rectifier. Compared to conventional charge pump output voltage regulation, our approach maintains a minimum supply for the operation of the transponder IC. Our implementation using an analog control loop with a voltage controlled oscillator results in a lower ripple of the rectifier voltage compared to a digital control loop. The entire design is implemented and validated in a commercial 180-nm CMOS technology.