A Digital Combining Applied to the Multilevel Pulse Modulated Polar Transmitter

This paper presents a novel digital combining method to implement a multilevel pulse modulation polar transmitter (PMPT) for 5G NR base station applications. Using pulse-width modulation on switch mode power amplifiers (PAs) is a promising method for PA efficiency improvement. Whereas using the interleaved multilevel architecture can eliminate unwanted harmonics. Previous PMPT implementations used passive power combiners to combine multiple PA outputs, this paper proposes combining to be performed digitally prior to the PAs. It was shown the proposed method is no longer susceptible to PA mismatch and is highly suitable for Doherty power amplifiers (DPAs). A transmitter prototype was developed and evaluated with a 256-QAM 5G NR 20-MHz instantaneous bandwidth signal centered at 2140 MHz. The overall system achieved an output level of 39.4 dBm with a power-added efficiency of 39%. It passes the 5G NR adjacent channel leakage ratio (ACLR) downlink spectral requirement with only memoryless digital predistortion.