Threshold Compensated UHF Rectifier With Local Self-Calibrator

This letter presents a threshold-compensated UHF rectifier with a local self-calibrator in a 0.18-μm CMOS process. The self-calibrator compensates the intrinsic-Vth voltage for a broad range of input power intensity to decrease the sensitivity of the rectifier's power conversion efficiency (PCE) to the input power fluctuations. This makes the structure suitable for wireless charging applications, where efficient RF-to-DC conversion at different RF intensities is required. The proposed circuitry includes two auxiliary rectifiers and a dummy load. The output voltage of the first auxiliary rectifier generates the required positive compensation voltage for the main rectifier, while the second rectifier limits this voltage for large RF inputs. Thus, the efficiency drop due to the extra compensation voltage is avoided. Measurement results of the prototype at 433-MHz ISM band using various loads show almost constant PCE values over an incident power range of more than 10 dB. The measured maximum PCE is 34%, and the peak short-circuit current is 12 μA at -17 dBm RF power.