Some new changes that 5G brings to PA

btty038

Some new changes that 5G brings to PA [Copy link]

The 5G wireless revolution is bringing big changes to the world of RF design, and the power amplifiers for cell phones and radio base stations are no exception. First, the power amplifier chips in 5G wireless applications are very different from those used in 4G networks.

This is mainly because the broadband modulation of 5G transmission requires power amplifiers to provide higher efficiency and stricter linearity; in addition, 5G networks will use phased array antennas to focus and steer multiple beams, which places extremely high demands on the ability to divide transmission tasks among multiple beams.

For example, a 4×4 array of phased array antennas must have a power amplifier that is much lower in power than the amplifier required to amplify the single-beam omnidirectional signal used in current cellular systems.

It is worth mentioning that 5G networks were initially implemented in the Sub-6GHz frequency range. However, the real commercial prospects of 5G will be reflected in millimeter wave (mmWave) bands including 24 GHz, 28 GHz and 39 GHz bands. In other words, mmWave will also bring severe challenges to RF design.

Therefore, multiple-input multiple-output (MIMO) antennas serving a variety of devices in densely deployed environments will require power amplifier chips with high efficiency and strict linearity. Phased-array MIMO antennas with numerous RF front ends will also require power amplifiers with higher integration to further reduce the cost of chip solutions.

This situation can be seen in the PA devices including PA modules, PA duplexers, switched power amplifiers and duplexers (S-PADs), PA module integrated duplexers (PAMiDs) and total radio modules (TRMs).

New integration milestone

The PA module has become the cornerstone of integration because its presence further reduces the number of components in the 5G RF front end. 5G networks have more frequency bands and require more RF switches, filtering, and power amplifier components in the PA module. Therefore, as 5G networks develop, the complexity of the PA module will continue to increase.

In the 4G wireless space, the pressure to integrate components that cover multiple frequency bands and technologies into a PA module has already driven many small suppliers out of business. In the 5G era, the pressure to pack more components into a PA module is likely to increase further.

A view of power amplifier circuitry for sub-6 GHz communications.Image: Qorvo

As a major supplier of 5G PA modules, Qorvo is also meeting the challenges brought by 5G power amplifiers. In 2016, they established a partnership with NanoSemi, a linearization software developer. They hope to use NanoSemi's machine learning-based digital pre-distortion (DPD) algorithm to enhance Qorvo's PA modules and ensure ultra-wideband linearization in power amplifiers.

Multi-carrier configurations present significant challenges to power amplifiers serving multi-band 5G designs, and NanoSemi’s digital compensation technology helps power amplifiers adjust power and capacity requirements based on available resources.

PA Basic Technology

Another valuable comparison with 4G involves the underlying technology of power amplifiers.

In the 4G era, gallium arsenide (GaAs) has been the leading technology for power amplifier chip manufacturing. This is because GaAs can easily support the high voltages required by power amplifiers. After the wireless industry has entered Sub-6 GHz communications, GaAs devices can still dominate, but new semiconductor solutions are competing for a place in mmWave PA manufacturing.

The block diagram showing an RF front-end module for mmWave RF design.Image: Qorvo

For example, a new RF silicon-on-insulator (SOI) technology developed by the University of California, San Diego (UCSD) is making waves. They connect silicon-based transistors in series to achieve higher voltages in power amplifiers. Stacked transistors (four transistors arranged in series) can provide the necessary output power for 5G power amplifiers. The stacking of transistors not only enhances the overall voltage handling, but also eliminates parasitic issues related to body effect and substrate capacitance.

Other candidates for 5G power amplifiers include gallium nitride (GaN) and silicon germanium (SiGe). GaN technology relies on advantages in capacity and thermal efficiency to improve PA performance, efficiency and power. According to Yole Développement, the RF market for GaN devices is expected to grow from $380 million in 2017 to $1.3 billion in 2023.

The 5G design world is in a state of flux, and as this article shows, power amplifier chips are fully part of this transformation. It is also clear that the 5G capacity revolution journey will impact all major aspects of power amplifier design: physical size, efficiency, linearity, and reliability.

btty038

Mobile Internet and Internet of Things are the two major driving forces for the development of mobile communications in the future. The number of users, the number of connected devices, and the amount of data continue to grow exponentially. New mobile services are emerging in an endless stream. Various applications such as cloud operations, virtual reality, augmented reality, smart devices, smart transportation, telemedicine, and remote control have increasing requirements for mobile communications, and user experience requirements are constantly improving. However, 4G mobile communication technology can no longer meet the future business and user experience needs. Compared with 4G, 5G will support more diverse scenarios, integrate multiple wireless access methods, and make full use of spectrum resources such as low-frequency and high-frequency. At the same time, 5G will also meet the needs of flexible network deployment and efficient operation and maintenance, greatly improve spectrum efficiency, energy efficiency, and cost efficiency, and achieve sustainable development of mobile communication networks. In 2017, the 5G standard accelerated its formation, and the popularity of related topics continued to remain high, but this technology is not yet mature and there is still considerable room for research and development. From the perspective of operators, the construction and operation of future 5G networks face many challenges. It is necessary to conduct in-depth discussions at this stage. On the one hand, we should be prepared in the design and development of networks and equipment ; on the other hand, operators can plan ahead and clarify the functional requirements of equipment and operation systems in the deployment of 4G evolution technology and future 5G, and do a good job in the reserve of knowledge and talents. This article gives some preliminary considerations on several key issues, hoping to play a role in inspiring others.