Theoretical Analysis of RF-DC Conversion Efficiency for Class-F Rectifiers

In this paper, an analytical model for the Class-F rectifier RF-dc conversion efficiency is presented. This model analyzes each kind of diode power losses in the rectifier due to the diode series resistor, junction capacitor, built-in potential, and breakdown voltage based on the time-domain diode voltage and current waveforms. The model provides a simple calculation routine to determine the threshold input power at which the peak reverse voltage across the diode starts to exceed the diode breakdown voltage and cause the diode efficiency to decrease. Two sets of closed-form equations are derived to calculate the Class-F rectifier efficiency in the input power region where the input power is either smaller or larger than the determined threshold input power, respectively. The implementation of a MATLAB code for the model calculation is also presented. Using this tool, the diode efficiency in Class-F rectifiers of different diode parameters can be easily determined, which provides a useful guideline for the optimal diode selection in various applications. The calculated diode efficiency using this model is compared with the Class-F rectifier ADS simulation at different load conditions, and all the results agree well with the model. To verify the model at different frequencies, two Class-F rectifiers working at 900 MHz and 5.8 GHz, respectively, are designed with the highest measured efficiency of 80.4% for the 900-MHz rectifier and 79.5% for the 5.8-GHz rectifier. Both of the measurement results agree well with the model prediction, which further verified the accuracy of the proposed model.