The telecommunications industry connects billions of people and millions of companies worldwide. The growth of the telecommunications industry is based on new technologies. These new technologies make interconnection possible, provide users with attractive new features, and justify investments in upgrading and expanding cellular network infrastructure. With the advent of early 4G LTE technology-enabled data communications, communications services have exploded, making mobile phones and cellular networks ubiquitous in developed countries. The next-generation telecommunications technology, 5G, is expected to bring another revolution in interconnected services. It will surpass telephones, text messages, and simple Internet, and may usher in a true information age.
To be able to meet the necessary network throughput and reliability required by these new applications, new technologies are needed. Part of the problem in achieving the next level of interconnection is the cost and complexity of transmitting and receiving high-quality radio frequency signals at higher frequencies while providing services for an order of magnitude or more additional user equipment in the same area. Two key enabling technologies that can help solve these challenges are GaN-on-SiC power amplifiers and large-scale multiple-input multiple-output (mMIMO) antennas.
The purpose of this article is to introduce readers to relevant backgrounds such as demand changes and design challenges brought by 4G to 5G ready and 5G technology services and base station upgrades. The discussion included some key details that explain how mMIMO antennas have become the new normal, and new communication technologies (such as silicon carbide-based gallium nitride power amplifiers) are deploying 5G services to meet 3GPP specifications and the growing number of users It is essential when expecting.
5G base station trends
Many people may think that since 5G has begun to roll out, then 4G technology is about to withdraw from the stage of history. But this is by no means a fact, because there are still plans to provide 4G services to many areas that use older 3G/4G technologies, as well as upgrade and maintain 4G services in order to prepare for the future installation of 5G base stations. The network infrastructure built for 4G is also likely to continue to be used and integrated into the deployment of 5G, just as 2G and 3G are integrated into 4G services. Therefore, 4G technology still has a market, including LDMOS power amplifiers for 4G cellular bands.
However, the development of 5G services also requires new technologies and methods to meet the expectations of 5G, that is, to transmit data at a speed of hundreds of megabits per second (Mbps) in highly congested areas, while improving reliability and reducing latency. Therefore, the discussions and planning for large-scale 5G deployments mostly involve the installation of small cells. These small base stations will be more densely distributed in urban and suburban areas. Moreover, there are currently 4G systems that are being upgraded from 2T2R and 8T8R MIMO to 32T32R and 64T64R mMIMO antennas. Before the full spectrum 5G (sub-1 GHz, sub-6 GHz and millimeter wave spectrum) is deployed, mMIMO technology is expected to help upgrade 4G services to meet 5G expectations.
These new 5G base stations and 5G-ready 4G upgrades require more antenna units and more cellular signal transmitters. In order to minimize the size and weight of these new mMIMO antennas, the RF components need to be carefully designed and selected. In order to reduce the size and weight of the mMIMO antenna, a common design decision is to replace the existing 4G antenna with a 4G/5G mMIMO combined antenna with embedded RF hardware. This type of densification can greatly reduce the cost, especially when it involves tower space and wind-loaded charges, but at the cost of requiring a higher power density RF transmitter, this transmitter must be very reliable to reduce due to components Failure may result in increased maintenance and service failures.
These matters are very important for sub-6 GHz 5G systems, and even more important for current prototypes and future millimeter wave 5G systems. Even for sub-6 GHz 5G systems, the 3.5G to 5 GHz 5G New Air Interface (NR) cellular band faces greater frequency-related RF losses than the 4G cellular band below 3 GHz. These larger losses also require higher amplifier efficiency to accommodate the more complex, higher peak-to-average ratio (PAPR) modulation signals used in the latest communications technologies. Therefore, the demand for RF power amplifiers is even greater. RF power amplifiers need to be able to provide high-efficiency bandwidths of several gigahertz, which can exhibit high reliability even with higher power density, and are sufficiently cost-effective and small enough to be assembled into embedded mMIMO with embedded hardware antenna.
5G RF front-end technical specifications
The mMIMO 5G antenna system has many similar performance considerations as 4G, as well as many additional additional considerations and limitations, and more stringent performance standards. Since mMIMO transmit and receive antennas are placed at very close distances, performance factors such as isolation and adjacent channel power ratio (ACPR)/adjacent channel leakage ratio (ACLR) need to be considered. ACPR/ACLR is a measure of power leakage from the transmitter to the adjacent radio channel. The main function of ACPR/ACLR is the linearity of the transmitter power amplifier. A more linear power amplifier will exhibit less distortion, which in turn causes less distortion products to appear on adjacent channels.
The linearity and distortion (especially amplitude distortion and phase distortion) of the power amplifier will have other effects on the deeply modulated communication signal. Even if the transmission mask required by the US Federal Communications Commission (FCC) or other global telecommunications regulations is met, excessive distortion can cause the power amplifier's own transmission performance to degrade. The error vector magnitude (EVM) is used to measure the deviation between the constellation point and the ideal point. Its magnitude is related to the nonlinearity, phase noise and amplifier noise of the power amplifier. Therefore, the key is to use power amplifier technology to maintain high standards of linearity and noise, even under high loads and high temperatures.
However, more linear power amplifiers may not necessarily provide better isolation specifications-transmitter to transmitter, transmitter to receiver, or receiver to receiver. High isolation is essential for mMIMO systems. It prevents unwanted signals from other spatially multiplexed signals from appearing in adjacent MIMO antenna elements. Although time domain duplexing (TDD) used with 5G technology is less susceptible to transmitter-to-receiver isolation considerations, this still does not solve the problem of transmitter-to-transmitter or receiver-to-receiver isolation. To solve the isolation problem, careful circuit and package design is necessary, and it is only possible if large and high-power components (such as transmitter power amplifiers) are compact and flexible enough to allow creative configurations designed to meet strict isolation requirements achieve.
Other considerations for power amplifiers include low current consumption and high power added efficiency (PAE). Since mMIMO antenna systems require arrays of transmitters and receivers, the power consumption and efficiency of each element has become a key performance standard. With future plans for 5G deployment including laying a large number of dense networks throughout urban and suburban environments, from macro base station towers to building sides/tops and telephone poles, to street lights and tunnels/subway structures, this effect has been amplified. As more 5G base stations are planned to be built, the pressure to reduce overall power consumption is increasing, and the power amplifier of the transmitter is one of the components with the highest power consumption.
In the case of the same output power, higher PAE (high power additional efficiency) amplifiers can not only reduce the overall energy consumption, but also have other beneficial effects. The higher the PAE, the less heat is generated by the amplifier. More amplifier power is used to increase the signal energy instead of being converted into waste heat. The advantages of reducing waste heat also include the need for less heat dissipation materials, which will greatly increase the weight, size and cost of the transmitter components. In addition, lower heat generation will bring lower operating temperature. For semiconductors, this usually results in a longer life and even more linear performance under high load.
5G transmitter requirements
The above RF front-end technical specifications impose substantial restrictions on 5G transmitters, especially those used with mMIMO antenna systems. This is why there is extensive research and industry investment to develop power amplifier technologies that can meet these stringent requirements under 5G operating conditions and within the new 5G spectrum range. Traditional power amplifier technologies, such as laterally diffused metal oxide semiconductor (LDMOS) and gallium arsenide (GaAs) power amplifier technologies, cannot meet the power density, energy efficiency, linearity, and cost/space requirements required by 5G mMIMO systems.
Taking gallium arsenide amplifiers as an example, these devices are very suitable for low-noise receiver applications, but the bandgap voltage is lower. This means that the gallium arsenide amplifier must have a lower operating voltage, which makes it challenging to achieve high power density, and the gallium arsenide amplifier has lower efficiency at higher power. The result is a hotter and relatively more power-hungry device. This is less attractive for 5G mMIMO applications that require higher power density and higher energy efficiency levels.
Although LDMOS amplifiers have been used in high-power applications below 3 GHz for some time, the thermal conductivity of LDMOS amplifiers is relatively limited and the efficiency at higher frequencies is relatively lower. Ultimately, this results in LDMOS amplifiers consuming more power and generating more heat at frequencies above 3 GHz, while also sacrificing other factors that need to be considered, such as linearity and noise (related to the temperature of most materials).
This leaves a lot of room for GaN semiconductor materials to fill the gap. There has been a lot of publicity about the application of GaN technology in radio frequency. In many ways, GaN devices have significantly improved the performance of various devices, from telecommunications to radar. This is because gallium nitride is usually superior to most other common semiconductor materials in terms of power amplifier quality factor (PAFOM), that is, power density, reliability, thermal conductivity, linearity, and bandwidth.
GaN semiconductors have some subtle differences because gallium nitride is usually grown epitaxially on an insulating substrate. Therefore, GaN devices can be based on many different substrates, such as sapphire, silicon, silicon carbide, gallium nitride, and even diamond. Due to process maturity, cost, and other design limitations, widely available GaN for radio frequency typically includes GaN on silicon or GaN on silicon carbide.
It is roughly the same reason that gallium nitride is superior to silicon-based LDMOS devices in high-frequency RF applications. In 5G mMIMO applications, silicon carbide-based gallium nitride is superior to silicon-based gallium nitride. Many performance advantages of silicon carbide-based gallium nitride over silicon-based gallium nitride come from the fact that silicon carbide is a more stable and durable material, has better thermal conductivity, and has a better lattice match with gallium nitride. This means that under high load conditions, silicon carbide-based gallium nitride devices are more heat-resistant, have fewer losses during operation, and have higher power efficiency. Moreover, this means that for the same power output, the silicon carbide-based GaN power amplifier may be smaller than the silicon-based GaN device, and the required heat sink size is also smaller. Not only that, the reliability of GaN-on-Silicon Carbide has also been fully reviewed and approved by the US Department of Defense (DoD) and aerospace applications.
Summary
The deployment of 4G and 5G systems is likely to use mMIMO technology to provide the best coverage and capacity for users who have higher expectations for modern communication services. Compared with GaN-on-silicon and LDMOS technology, GaN-on-SiC power amplifier technology provides the best performance and cost requirements for mMIMO systems. Wolfspeed GaN-on-silicon carbide technology has been approved for high-reliability telecommunication, military, defense, and aerospace applications, and provides lower life-cycle costs than GaN-on-silicon and LDMOS.