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 1.75x/3.51x 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-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-out with rms EVM of -23 dB over 26-60 GHz.

Automated summary

In this work, a 180° coupler balun structure is proposed as a wideband active load modulation network for broadband power backoff (PBO) efficiency enhancement. This structure, called coupler balun load-modulated PA (CBMA), supports natural single-ended-to-differential balun conversion, differential power cells, and wideband capacitive neutralization, making it ideal for integrated mm-Wave PAs. A continuous-mode CBMA operation with role exchanges is also proposed to achieve nearly 3:1 carrier bandwidth.