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| 4 | | 28 | Higher PAE also indicates that there is less heat generated by the amplifier, as more amplifier power is used to gain up the signal energy and isn't converted to waste heat. Less waste heat also has the benefit of requiring less heat-sinking material, which can add a significant amount of weight, size, and cost to a transmitter assembly. Moreover, lower heat generation can also lead to lower operating temperatures, which, for semiconductors, will often lead to longer lifespans and even more linear performance under high- load situations. 5G Transmitter Requirements RF front-end specifications place substantial constraints on a 5G transmitter, especially 5G transmitters used with mMIMO antenna systems. This is why extensive research and industry efforts are under way to develop power amplifier technologies that can meet these stringent requirements under 5G operating conditions and across the new 5G spectrum. Legacy power amplifier technologies, such as LDMOS and gallium arsenide (GaAs) power amplifier technologies, don't deliver on the necessary power density, energy efficiency, linearity, and cost/ space requirements of 5G mMIMO systems. In the case of GaAs amplifiers, these devices are well-suited to low-noise receiver applications but have a low bandgap voltage. This means that GaAs amplifiers have necessarily low operating voltages, which makes attaining high power densities challenging, and GaAs amplifiers are less efficient at higher power levels. The result is a much hotter and comparably higher-power-consuming device, which is less attractive for 5G mMIMO applications that demand more power density at higher efficiency levels. Although LDMOS amplifiers have been used for high-power applications below 3GHz for some time, LDMOS amplifiers also suffer from relatively limited thermal conductivity and comparably more reduced efficiency at higher frequencies. Ultimately, this results in LDMOS amplifiers using more power and generating more heat at frequencies beyond 3GHz while also sacrificing other considerations, such as linearity and noise (which is related to temperature for most materials). This leaves a lot of room for a new semiconductor material to fill that being gallium nitride (GaN). There has been much hype over GaN technology for RF applications. In many respects, GaN devices have led to dramatic performance increases in devices ranging from long-range communications to radar. This is because GaN generally outperforms most other common semiconductor materials in power amplifier figure of merit (PAFOM)—namely, power density, reliability, thermal conductivity, linearity, and bandwidth. There are some nuances to GaN semiconductors, as GaN is generally epitaxially developed on an insulating substrate. GaN devices could use a variety of substrates, such as sapphire, silicon (Si), SiC, GaN, and even diamond. Because of process maturity, cost, and other design constraints, GaN for RF applications is typically widely available as either GaN on Si or GaN on SiC. For much the same reasons that GaN is superior to Si-based LDMOS devices for high-frequency RF applications, GaN on SiC is superior to GaN on Si for 5G mMIMO applications. Much of the performance advantages of GaN on SiC over GaN on Si derive from SiC being a much more rugged material, with better thermal conductivity and a better lattice match to GaN. This means that under a high load, GaN on SiC devices can be run hotter, with less wear and tear and with higher power efficiency than GaN on Si. This implies that for the same power output, GaN on SiC power amplifiers can be smaller and require smaller heat sinks than GaN on Si devices. The reliability of GaN on SiC has been thoroughly examined and approved for critical U.S. Department of Defense (DoD) and aerospace applications. WOLFSPEED / CREE 5G RF TRANSISTORS • Integrated ESD protection • Broadband internal input and output matching • Low thermal resistance Learn more > Learn more > Learn more > The deployments of 4G and 5G systems are likely to leverage mMIMO technology to offer the best coverage and capacity to customers with ever- higher expectations from modern communication services. GaN on SiC power amplifier technology provides the best performance and cost requirements for mMIMO systems compared to GaN on Si and LDMOS technologies. Wolfspeed's GaN on SiC technology has received approvals for use in high-reliability telecommunications, military, defense, and aerospace applications. It offers lower total life-cycle costs than both GaN on Si and LDMOS. CONCLUSION

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