Bandwidth-Expanded High-Linearity Doherty Power Amplifier With Improved AM–AM and AM–PM Characteristics

This article proposes a novel design methodology for a high-efficiency, wideband linear Doherty power amplifier (DPA). A collaborative approach is employed in the design, which introduces phase mismatch between the two branches and incorporates a novel load-matching network (LMN) with additional compensation branches. Through theoretical analysis and derivation, it is shown that this method not only produces predefined nonlinear amplitude-to-amplitude (AM–AM) and amplitude-to-phase (AM–PM) characteristics through LMN but also significantly expands the broadband high-efficiency design space of the DPA. To validate the proposed theory, a linear high-efficiency gallium nitride (GaN) DPA operating between 1.85 and 2.3 GHz with a relative bandwidth of 21.7% is designed and fabricated. The measurement results indicate that the fabricated DPA achieves a saturated output power ranging from 43.2–43.7 dBm, with a saturated drain efficiency (DE) of 60%–68% and a 6-dB back-off DE of 50%–55%. Furthermore, ignoring the performance degradation at the edge frequency of 2.3 GHz, the fabricated DPA exhibits an AM–AM variation of less than 1 dB and an AM–PM variation of less than 3.5° over the 1.85–2.25 GHz range. At an average output power of approximately 35 dBm, the fabricated DPA exhibits an EVM of less than 2.8% and an adjacent channel power ratio (ACRR) lower than −38.1 dBc across the entire operating frequency band without digital predistortion (DPD) when driven by a 60-MHz 5G new radio (NR) signal with a peak-to-average power ratio (PAPR) of 8.1 dB in the TM3.1 test mode. Similarly, under a 100-MHz 5G NR signal at 8.1-dB PAPR in the TM3.1 test mode, the original EVM without DPD in the operating frequency band is less than 3.6% and ACRR is lower than −35.1 dBc.