A Three-Level RF-PWM Method Based on Phase-Shift Control and MPWM for ADTx

Abstract

A radio frequency pulse width modulation (RF-PWM) scheme based on phase-shift control and mapping PWM (MPWM) is described. Pulse coding is the key to improving the coding efficiency, flexibility, and configurability of the all-digital transmitter (ADTx). To solve the problem that the real-time performance of the system is limited by the time resolution, the phase-shift control principle is adopted to constrain the output pulse state. It decomposes the original signal into two phase-modulated constant envelope signals, and directly converts the two-level pulse waveform by MPWM. Finally, the fast generation of the three-level digital RF modulated signal is completed by vector synthesis. In this way, the rear power amplifier can be directly driven, and the difficulty of physical implementation is greatly reduced. Different from the traditional mapping strategy of traversal search, the proposed scheme does not require complicated error calculation and comparison. Simulation and offline experiments show that the proposed scheme has better comprehensive performance than other mapping schemes. For 16QAM modulated signals at a 300 MHz carrier, the proposed scheme can achieve nearly 70% coding efficiency (CE), less than −50 dBc, and 1% adjacent channel power ratio (ACPR) and error vector magnitude (EVM).