A Compact Broadband Voltage-Combined Doherty Power Amplifier With Shorted Transmission Line for 5G Millimeter-Wave

This article presents a CMOS voltage-combined Doherty power amplifier (PA) based on a broadband compact load modulation network (LMN) for fifth-generation (5G) millimeter-wave (mm-wave) mobile communication applications. By analyzing the frequency response of different types of Doherty power combiner, a novel voltage-combined Doherty LMN with shorted TL and corresponding design procedure are proposed to achieve broadband power back-off (PBO) bandwidth and compact footprint. A compact quadrature hybrid coupler without lumped capacitor is also devised to generate wideband quadrature signals. To improve PBO efficiency, an envelope detector is adopted to produce adaptive DC bias for auxiliary path. For the proof of concept, a dual-driver Doherty PA is implemented in 65-nm bulk CMOS technology with a chip size of 0.42 mm2 including all pads. The PA achieves a 3-dB small-signal $S_{21}$ bandwidth from 21.1 to 30.4 GHz and a 1-dB saturated output power ( $P_{\text {sat}}$ ) bandwidth from 24 to 30 GHz. The measured $P_{\text {sat}}$ , output 1-dB compression point ( $OP_{\text {1dB}}$ ), peak power-added efficiency (PAE) and PAE at 6dB-PBO are 20.0 dBm, 19.1 dBm, 24.6% and 20.0% at 27 GHz, respectively. For modulation measurements, the proposed PA under 64-quadrature-amplitude-modulated (64-QAM) signal at a data rate of 0.6/2.4 Gb/s achieves average output power ( $P_{\text {avg}}$ ) of 11.5/4.8 dBm and average drain efficiency of 14.1%/3.9% with −25/−24.5 dB of error vector magnitude (EVM) and −29/−25.6 dBc of adjacent channel leakage ratio (ACLR) at 28 GHz, respectively.