Modeling and Compensation of Pulse Distortion in All-Digital Transmitters

When amplifying digital pulse signals in an all-digital transmitter (ADTx), the switched-mode power amplifier (SMPA) introduces pulse distortion, which in turn leads to nonlinear distortion. This paper focuses on the nonlinear distortion problem caused by the delay effect in ADTx, analyzing the generation mechanism of pulse distortion during the switching amplification process and establishing a mathematical model based on a five-level RF-PWM outphasing ADTx. Numerical simulations are then conducted using the pulse distortion error model to examine the impact of nonlinear distortion caused by delay errors on the output pulse waveform of the ADTx, as well as on performance metrics such as the error vector magnitude (EVM) and adjacent channel power ratio (ACPR). Pulse distortions are compensated according to the distortion characteristics. After applying the proposed compensation method, the ACPR of the signal improves by 5 dB, and the EVM decreases from 3.4% to approximately 0.4%, resulting in a significant improvement in signal quality.