Single-Input Broadband Hybrid Doherty Power Amplifiers Design Relying on a Phase Sliding-Mode of the Load Modulation Scheme

• Published in: IEEE transactions on microwave theory and techniques Vol. 71; no. 4; pp. 1 - 13
• Main Authors: Liang, Chenyu, Roblin, Patrick, Hahn, Yunsik, Martinez-Lopez, Jose I., Chang, Hsiu-Chen, Chen, Vanessa
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplifier design; Broadband; Broadband communication; Circuit design; Doherty power amplifiers (PAs); Doherty-outphasing continuum; Frequency modulation; Modulation; Orthogonal Frequency Division Multiplexing; Phase shifters; Power amplifiers; Prototypes; Transistors; Transmission lines; Wideband; wideband PAs; Wireless communication
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2022.3222355

This work introduces a novel design theory for a single-input hybrid Doherty power amplifier (PA) inspired by the design space existing within the previously reported dual-input Doherty-Chireix (outphasing) continuum. Unlike the conventional <inline-formula> <tex-math notation="LaTeX">\lambda/4</tex-math> </inline-formula> Doherty PA inverter which only performs the correct load modulation at its center frequency, the hybrid Doherty PA (HD<inline-formula> <tex-math notation="LaTeX">\omega</tex-math> </inline-formula>-PA) combiner network achieves a wideband load modulation using the frequency dependence of the electrical length of the output combiner lines versus frequency for sliding the PA mode of operation. A modified theory is presented in this work to allow for a single-input PA implementation. In this new design, the outphasing angle is only changing with frequency and not the input power. A transmission line phase shifter is used to provide the correct frequency-dependent input phase offset ensuring the correct wideband load modulation performed by the output combiner. A novel methodology is also proposed to select the optimal input phase offset to reduce the variation in the saturation power versus frequency and minimize the circuit size. A proof-of-concept demonstrator PA circuit is designed to operate from 2.5 to 3.3 GHz. When the fabricated PA is excited by a 20-MHz long-term evolution (LTE) modulated signal with 6-dB peak-to-average-power ratio (PAPR), an average efficiency of 45%-59% and adjacent channel leakage ratio (ACLR) less than <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>50 dBc are achieved after digital predistortion (DPD) across the entire band. When the fabricated PA is excited by a 5G-like 50-MHz orthogonal frequency-division multiplexing (OFDM) signal with 10-dB PAPR, an average efficiency of 33%-41% and ACLR less than <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>44 dBc are achieved after DPD across the entire band.