A CMOS 1.2-V Hybrid Current- and Voltage-Mode Three-Way Digital Doherty PA With Built-In Phase Nonlinearity Compensation

Abstract

This article presents a fully integrated hybrid current- and voltage-mode three-way digital Doherty power amplifier (PA) in CMOS using a single supply with builtin large-signal phase nonlinearity compensation. The nonlinear phase responses in both current-mode digital PA (C-DPA) and voltage-mode digital PA (V-DPA) are theoretically analyzed, which are further leveraged to achieve the PA nonlinear phase compensation. To the best of our knowledge, it is the first time the amplitude modulation (AM)-phase modulation (PM) response in V-DPA is explained in detail. The PA exploits the lagging AM-PM distortion of C-DPA and leading AM-PM distortion of V-DPAs, resulting in built-in large-signal phase nonlinearity cancellation without phase pre-distortion. Moreover, the transformer-based Doherty output network provides active load modulation to both C-DPA and V-DPA, achieving a three-way Doherty PA for deep power back-off (PBO) efficiency enhancement without supply modulation. Finally, the 1.2-V single power supply for PA power cells and input drivers reduces supply complexity. As a proof-of-concept, the hybrid three-way digital Doherty PA is implemented in a 45-nm CMOS SOI process. The measurements show a 38.5% peak drain efficiency (DE), 22.4-dBm saturated output power (Psat), and 32.1%/18.7% DE at 3.4-/9.3-dB PBO, achieving ×1.25/×1.46 PBO efficiency enhancement over idealistic class-B PA PBO efficiency at 2.3 GHz. The measured AM-PM distortion is 4.7° which is state-of-the-art among DPAs with PBO efficiency enhancement. The hybrid digital Doherty PA supports 40-/10-MSym/s 64-quadrature amplitude modulation (QAM)/256-QAM at 15.3-/15.2-dBm average output power and 24.7%/23.2% average PA DE while maintaining error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) lower than -32/-32.1 dB and -30.6/-28.9 dBc without phase pre-distortion.