A Coupler Balun Load-Modulated Power Amplifier With Extremely Wide Bandwidth

Next-generation millimeter-wave (mm-Wave) power amplifiers (PAs) need to support multistandard communication systems with wide bandwidth, complex modulation, and high energy efficiency. Most existing mm-Wave PA architectures with power backoff (PBO) efficiency enhancement, such as Doherty and outphasing PAs, typically only support limited carrier bandwidth. In this work, we propose and demonstrate that a 180° coupler balun structure can serve as an extremely wideband active load modulation network for broadband PBO efficiency enhancement and further realize a coupler balun load-modulated PA (CBMA). Moreover, compared to load-modulated balanced amplifiers (LMBAs), the proposed CBMA supports natural single-ended-to-differential balun conversion, differential power cells, and wideband capacitive neutralization, ideal for integrated mm-Wave PAs. Furthermore, we propose a continuous-mode CBMA operation with role exchanges to attain a nearly 3:1 carrier bandwidth. A prototype CBMA is designed and fabricated in a 45-nm RF CMOS SOI process, which achieves an OP1 dB PAE of 39.9%–20.4% with OP1 dB of over 21.6–18.3 dBm from 26 to 60 GHz. The PA also achieves a 32.8%–13.4% 6-dB PBO (from OP1 dB) efficiency with its best $1.75\times /3.51\times $ efficiency enhancement over an ideal Class-B/-A PA. Using a single-carrier 64-QAM signal with 0.5 GSym/s (3 Gb/s), the PA supports an average $P_{\mathrm {out}}$ of 15.8–11.3 dBm with an average PAE of 27.15%–8.58% with −23-dB rms error vector magnitude (EVM) over 26–60 GHz. The PA also supports 5G NR modulation using 5G new radio (NR) FR2 200-MHz 1-CC 64-QAM signals, achieving 18.22%–6.55% average PAE at 10.72–7.1-dBm average $P_{\mathrm {out}}$ with rms EVM of −23 dB over 26–60 GHz.

I. Introduction

Millimeter-wave (mm-Wave) spectrum offers wide frequency bands to support a large range of next-generation wireless communication and sensing applications. In particular, mm-Wave wireless communication links primarily aim at providing massive data throughputs among wireless nodes. The fifth-generation (5G) communication is expected to achieve a 10– data rate increase compared to 4G wireless for enhanced mobile broadband (eMBB). The 3GPP 5G new radio (NR) standard [1] specifies the n257 band (26.50–29.50 GHz), n258 band (24.25–27.50 GHz), and n260 band (37.00–40.00 GHz) as the frequency range 2 (FR2) allocation [2], [3]. Multistandard 5G mm-Wave systems need to cover these noncontiguous FR2 frequency bands, necessitating wideband mm-Wave 5G front-end modules (FEM) and systems to support cross-country/region roaming, especially for user equipment (UE) devices.