Switching Behavior of Class-E Power Amplifier and Its Operation Above Maximum Frequency

Abstract

The switching behavior of Class-E power amplifiers (PAs) is described. Although the zero voltage switching can be performed properly, the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> charging process at the switch-off transition cannot be abrupt and the waveform deviates from the ideal shape, degrading the efficiency. For the operation above maximum frequency, the charging process should be even faster but it cannot follow. Moreover, the discharging process is not sufficiently fast and further degrades the efficiency. The discharging process is assisted by the bifurcated current at saturation. The performance of the Class-E PA above the maximum frequency is enhanced by the nonlinear <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> , which helps to shape the voltage waveform. The bifurcated current itself cannot generate enough of a second-harmonic voltage component to shape the required voltage waveform. The performance of the Class-E PA can be further improved by a second-harmonic tuning and a conjugate matched output load, leading to the saturated PA. Compared with the Class-E PA, the saturated amplifier delivers higher output power and efficiency. A highly efficient saturated amplifier is designed using a Cree GaN HEMT CGH40010 device at 3.5 GHz. It provides a drain efficiency of 75.8% at a saturated power of 40.2 dBm (10.5 W).