"This knowledge is not too cold" Exploring 5G radio frequency technology (Part 2)

The "This Knowledge Isn't Too Cold" series aims to help friends awaken their memory of knowledge. It will select some of Qorvo's key knowledge points and interpret them based on the current status of the industry, so as to review the past, learn new things, and find out what is missing. This tweet continues to talk about 5G radio frequency~

Click here to view the exciting content of 5G radio frequency technology ( Part 1 )

The true realization of the 5G vision requires more innovation. Network base stations and user devices (such as mobile phones) are becoming thinner and smaller, and consume less energy. Printed circuit boards (PCBs) used in many RF applications are also being reduced in size to fit into smaller devices. Therefore, RF application suppliers must develop new packaging technologies to minimize the footprint of RF components. Going a step further, some suppliers have begun to develop system-in-package (SiP) solutions to reduce the number of RF components, although this approach will increase packaging costs .

System-in-package approaches are being used for RF front-ends, which include all components between the base station and the antenna .

A typical RF front-end consists of switches, filters, amplifiers and tuning components. These technological devices continue to decrease in size and become more integrated with each other. As a result, in 5G applications such as mobile phones, small cells, antenna array systems, Wi-Fi, etc., the RF front-end is becoming a complex, highly integrated system package.

In any case, the realization of the 5G vision requires disruptive innovations in radio frequency technology and packaging technology.

Gallium nitride (GaN) is a binary III/V bandgap semiconductor that is well suited for use in high-power, high-temperature transistors. The potential of gallium nitride power amplifier technology for 5G communications is only just emerging. Gallium nitride has the advantages of high RF power, low DC power consumption, small size and high reliability, allowing equipment manufacturers to reduce the size of base stations. This, in turn, helps reduce the weight of the antenna array systems installed on 5G base station towers and therefore reduces installation costs. In addition, gallium nitride can easily support high throughput and wide bandwidth at various millimeter wave frequencies.

Gallium nitride technology is best suited to achieve high effective isotropically radiated base station power (EIRP), as shown in the figure below. The US Federal Communications Commission has defined very high EIRP limits, stipulating that for the 28GHz and 39GHz frequency bands, 75dBm power per 100MHz of bandwidth is required. What challenges does this bring? The equipment must be built to meet these objectives while keeping cost, size, weight and power within the mobile network operator's budget. Gallium nitride technology is key; compared to other technologies, gallium nitride technology uses fewer components and has higher output power to achieve the above high EIRP values.

Comparison of the adaptability of semiconductor technology to EIRP requirements

For high-power base station applications, compared to other power amplifier technologies such as silicon germanium (SiGe) or silicon (Si), under the same EIRP target value, the total power dissipation of gallium nitride technology is lower, as shown in the figure below. Gallium nitride reduces overall system weight and complexity while still maintaining low power consumption, making it more suitable for tower-mounted system designs.

Gallium Nitride reduces base station design complexity and costs

• Reliability and robustness: Gallium nitride is more power efficient, thus reducing heat outputGallium nitride's wide bandgap allows it to withstand higher operating temperatures, thus reducing cooling requirements in compact areas. Because Gallium Nitride is able to operate at the high temperatures found in tower applications (e.g., antenna array systems), cooling fans may not be required and/or the size of the heat sink may be reduced. Historically, cooling fans have been the leading cause of field failures due to their mechanical nature. Not only do large radiators constitute a significant cost in terms of hardware themselves, but there may also be additional labor costs due to weight. The use of gallium nitride eliminates the need for these high-cost heat dissipation methods.
  
  
• Low current consumption: Gallium nitride reduces operating costs and generates less heat. Additionally, low current helps reduce system power consumption and lower power requirements. Furthermore, service providers also reduce operating expenses due to reduced power consumption.
  
  
• Power capabilities: GaN devices provide higher output power compared to other semiconductor technologies. The development trend of the market and the demand for high power output of base stations are more conducive to the development of gallium nitride technology.
  
  
• Frequency bandwidth: GaN has high impedance and low gate capacitance, enabling greater operating bandwidth and higher data transmission speeds. In addition, gallium nitride technology also has good RF performance above 3GHz, while other technologies (such as silicon) do not perform well in this frequency range. The broadband performance provided by today’s gallium nitride modules and power amplifiers can support the unprecedented bandwidth requirements of 5G.
  
  
• Integration: 5G requires smaller solutions, which has prompted vendors to replace large-scale, discrete RF front-ends containing multiple technologies with single, fully integrated solutions. GaN manufacturers are beginning to capitalize on this trend by developing fully integrated solutions that consolidate the transceiver chain into a single package. This further reduces system

Because of new frequency bands and carrier aggregation, plus the fact that cellular communications must coexist with many other wireless standards, interference problems are more serious than ever. To reduce interference between frequency bands and standards, filter technology is key.

• Surface acoustic wave filters and bulk acoustic wave filters have the advantages of small footprint, excellent performance, economical and applicable, and dominate the mobile device filter market.

  
  

• Bulk acoustic wave filters are best suited for frequency bands from 1GHz to 6GHz, and surface acoustic wave filters are best suited for frequency bands below 1GHz. Therefore, the 5G “sweet spot” for bulk acoustic waves is the frequency band below 7GHz.

  
  

• Bulk and surface acoustic waves can reduce interference in LTE, Wi-Fi, autonomous communications and new sub-7GHz 5G frequencies while meeting manufacturers' strict size and performance standards.

For smartphone designers, the launch of 5G is another challenge for battery life and motherboard space. With each new generation of products, the pressure to integrate and shrink continues to increase. Operating at higher frequencies means that the power amplifier efficiency is reduced, while antenna and line losses increase. In addition, 5G mobile phones also need to add radio frequency switches, thus causing more link budget losses. (The so-called "link budget" refers to the sum of all gains and losses incurred in a telecommunications system from the transmitter through cables, traces, etc. to the receiver.)