5G needs better amplifier efficiency

Power amplifier efficiency too center stage at the 2020 International Microwave Symposium’s 5G Summit. In this video interview, Naveen Yanduru of Renesas, one of the summit’s presenters, explains why engineers need to continue working on the problem.

For the last several years, the IEEE International Microwave Symposium has featured a 5G summit. In the early years, the 5G Summit was a report on 5G concepts as engineers were formulating technologies such as beamforming and trying to decide on which form of modulation to use.

In 2020, 5G is in deployment. Engineers at the IMS 5G Summit virtual event no longer gave presentations on how the wireless aspects of 5G work. It’s now about improving on those designs. In “IMS 5G Summit: Design challenges remain” part 1 and part 2, 5G Technology World reported on the summit, which focused on problems such as power amplifier (PA) efficiency, or lack thereof.

In his presentation, “Sub-6 GHz and mmWave RFICs for 5G Wireless Infrastructure RF Front Ends,” Naveen Yanduru, vice president and general manager at Renesas Electronics discussed the need for better PA efficiency. Yanduru spoke with 5G Technology World following the conference.

Figure 1. Envelope tracking improves PA efficiency.

In the video, Yanduru explains the problem with power amplifiers in that they reach maximum efficiency when the output signal nears the amplitude of the PA’s power supply, it’s saturation region. At low amplitudes, the PA operates in its linear region and efficiency drops. One of the early techniques that Yanduru mentions for improving efficiency is envelope tracking (Figure 1), where the power supply tracks the signals amplitude, thus keeping it close to saturation.

Yanduru also explains why PA efficiency has gained in importance as beamforming increases in use; antennas are arrays rather than a single object. Thus, 5G antennas need multiple PAs. He discusses the difference between digital and hybrid beamforming (hybrid beamforming shown in Figure 2). He also discusses the pros and cons of different semiconductor technologies used in PAs and efficiency issues at sub-6 GHz and mmWave frequencies.