Output Voltage PWM Conversion Inaccuracies in Envelope Tracking Power Supply for High Peak-to-Average Power Ratio Applications

Abstract

When amplifying signals with a high peak-to- average power ratio, the envelope tracking method is widely used to increase the efficiency of power amplifiers. When designing a control device for an envelope tracking power supply (ETPS), it is relevant to form control signals using digital methods. The paper considers errors of envelope signal forming with multi-cell ETPS, which are caused by a number of factors. These include: digital representation of control pulses PWM-sequences parameters, inaccuracies of cell synchronization, dispersion of parameters of transistors and elements of low-pass filter (LPF). It is shown that bits number chosen to represent PWM pulses in digital form contributes to the appearance of parasitic components in the output spectrum of the ETPS, which get into the LPF bandwidth. The dispersion of the transistors time parameters, inaccuracies of the PWM forming synchronization and dispersion of LPF inductances lead to a significant increase of the side spectral components that are multiples of the PWM frequency. Satisfying the conditions formulated in the paper, which are associated with increasing the accuracy of control signals forming and decreasing the dispersion of the LPF inductances, will make full use of the multi-cell ETPS advantages.