A Four-Way Series Doherty Digital Polar Transmitter at mm-Wave Frequencies

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Abstract

This article presents an efficient digital polar transmitter (DPTX) at mm-wave frequencies that exploit a novel N -way series Doherty combiner (SDC) to enhance its drain and system efficiency at deep power back-off (PBO). The proposed N -way SDC is scalable and can be implemented elegantly using N transformers and N-1 shunt capacitors. As a proof of concept, a four-way Doherty DPTX is realized with the proposed SDC in which four identical but independent digital phase modulators deliver a phase-modulated constant envelope signal to their corresponding digital power amplifiers to perform the required amplitude modulation. Fabricated in a 40nm CMOS process, the proposed DPTX occupies a core area of 1.1 mathrm {mm^{2}} and exhibits 18.7dBm saturated output power and <-40dBc LO feedthrough. It demonstrates a drain efficiency of 33%/36%/22% at 0/4.5/11.5dB PBO at a 29.5GHz carrier frequency. While transmitting a 300MHz 64-QAM OFDM signal with a peak-to-average power ratio of 10.7dB, the DPTX achieves 18%/8% average drain/system efficiency, -27.6dB error vector magnitude, and -27.5dBc adjacent channel leakage ratio. To the best of our knowledge, this work is the first reported mm-wave Doherty transmitter that includes the entire chain all the way from the binary data stream up to the modulated mm-wave output signal.

Original languageEnglish
Article number9675289
Pages (from-to)803-817
Number of pages15
JournalIEEE Journal of Solid-State Circuits
Volume57
Issue number3
DOIs
Publication statusPublished - 2022

Bibliographical note

Accepted author manuscript

Keywords

  • Digital phase modulator (DPM)
  • digital polar transmitter (DPTX)
  • digital power amplifier (DPA)
  • Doherty design guide
  • millimeter-wave transmitter (TX)
  • power amplifier (PA)
  • series Doherty combiner (SDC).

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