A Broadband Linear Ultra-Compact mm-Wave Power Amplifier With Distributed-Balun Output Network: Analysis and Design

This article presents a broadband power amplifier (PA) with a distributed-balun output network that provides the PA optimum load impedance over a wide bandwidth. The proposed output network comprises two coupled-line sections and absorbs the device output capacitance. It employs a scalable coupled-line modeling approach that captures both the magnetic (inductive) and electric (capacitive) couplings between windings with fewer parameters and supports a rapid design process. Closed-form design solutions, design space limitations, bandwidth limits, and design tradeoffs are derived and analyzed comprehensively. Its extension to differential output and common-mode response is also discussed in detail. As a proof of concept, a prototype PA is implemented for multiband fifth-generation (5G) applications in 45-nm SOI CMOS. With no biasing retuning or network reconfiguration, the PA consistently achieves >19.1 dBm P
_sat
, >37.3% peak power-added efficiency (PAE), 17.8-19.6 dBm P
_1dB
, and 36.6%-44.3% PAE
_P1dB
over 24-40 GHz, verifying the truly wideband large-signal matching. The PA demonstrates 5G new radio (NR) frequency range 2 (FR2) modulation signals over 24-42 GHz, covering n257/n258/n260 5G bands. For 5G NR FR2 800-MHz 2-CC 64-QAM signals (11.78-dB PAPR), the PA achieves 11.3-dBm/16.6% average P
_out
/PAE with -25.1-dB rms EVM at 28-GHz and 10.2-dBm/13.6% average P
_out
/PAE with -25.1-dB rms EVM at 37 GHz.