A Compact Doherty-Like Load-Modulated Coupled Amplifier (LMCA) for 5G Phased-Array Applications

In this article, the analysis and design of a millimeter-wave (mm-Wave) Doherty-like load-modulated coupled amplifier (LMCA) are presented. First, the complex-valued behavior of power amplifier (PA) devices during load modulation is investigated. Then, a novel LMCA architecture is developed without a quarter-wavelength line (QTL) to fit the complex-valued behavior of PA devices, thus leading to efficiency enhancement at power back-off (PBO) region. Meanwhile, a shared driver amplifier is implemented for both main and auxiliary amplifier paths, enabling a compact load-modulated PA design. Fabricated in a 55-nm CMOS process, the proposed LMCA achieved a gain of 15 dB and an output $P_{1\,\text{dB}}$ / $P_{\text{SAT}}$ of 14.5/15.2 dBm with the power added efficiency (PAE) of 28.0%/28.3% at 27 GHz with 1.2-V supply voltage. The PAE at 6-/9-dB PBO from P1dB (PAE $_{\text{P1-6\,dB}}$ /PAE $_{\text{P1-9\,dB}}$ ) still maintains 21.8%/15.3%, achieving 1.56 $\times$ /1.55 $\times$ efficiency enhancement over a normalized Class-B PA. Modulation measurement with single-carrier 250-/500-MHz 64-QAM signals, the LMCA achieves 6.49-/5.18-dBm average output power ( $P_{\text{OUT}}$ ) with an average PAE (Avg.PAE) of 17.6%/14.6%. The core area of the prototype PA is only 0.16 mm $<^>{2}$ .