A time-reduced method for calculation distortions in envelope tracking power amplifiers

Abstract

Pergushev A. O., Sorotsky V. A. "A time-reduced method for calculation distortions in envelope tracking power amplifiers" To increase the efficiency of power amplifiers in wireless telecommunications systems, whose signals have a high peak to average power ratio, the envelope tracking method can be used. This method involves forming of a low-frequency envelope signal by a switched-mode power amplifier (SPA), which is then used as a supply voltage for a RF power amplifier. A specific feature of the SPA is that its output signal has high level of harmonic distortions. To evaluate these harmonic distortions, computer simulation can be used. However, time required to perform one cycle of simulation can be as much as several hours because of high complexity of SPA models. To reduce the simulation time of signal spectrum, approximate method that allows to represent the output voltage of a SPA in analytical form can be used. However, in known publications, the non-zero switching time of transistors is not taken into consideration, which leads to an appreciable error in the determination of the spectral components. This paper presents a method of analytic calculation of SPA output signal spectrum that considers the linear and exponential approximations of non-zero switching times of transistor. It allows to decrease the error in determining the harmonic distortions from 30…35 dB to 1…6 dB and to reduce the time expenditure as compared with computer simulation as much as 300 through 800 times.