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Recognize the Flavors of RF Power Transistors

May 31, 2018
This technical brief focuses in on RF power transistor technologies, helping readers to determine the best choice when designing a high-power amplifier.

When designing a solid-state high-power amplifier (HPA), the appropriate RF power transistors must be used. An RF power transistor can be categorized by its semiconductor technology. Among them are silicon (Si) bipolar, laterally diffused metal oxide semiconductor (LDMOS), and gallium-nitride (GaN). In the technical brief, “Zero-in on the Best RF Transistor Technology for Your Radar’s High Power Amplifier Designs,” Integra Technologies examines these three technologies, explaining the advantages and disadvantages of each one in terms of HPA design.

The tech brief begins by noting that an RF power transistor is usually characterized based on the type of signal it will handle, i.e., continuous-wave (CW) or pulsed. The document also states that no “silver bullet” technology exists for all high-power amplification requirements. Rather, the solution involves determining how a transistor’s key characteristics correspond with the important requirements of the given application.

Discussion then turns to Si bipolar-junction transistors (BJT). Although Si BJT technology is the oldest among those used in pulsed applications, it’s not obsolete. Si BJT devices offer some benefits, which are listed in the tech brief. However, it also mentions that newer HPA designs generally don’t include Si BJT devices due to their low gain, as well as their need for expensive and environmentally unfriendly beryllium-oxide (BeO) packages.

The brief subsequently delves into Si LDMOS technology. Newer than Si BJT, this technology has achieved widespread usage in high-linearity communication applications and broadband CW amplifiers. The document notes that Si LDMOS is a good choice for pulsed applications at frequencies up to L-band.

Wrapping up the brief is a discussion on GaN technology. GaN high-electron-mobility-transistors (HEMTs) represent the latest in RF/microwave power transistors. They offer benefits like high gain and high power levels at S-band frequencies and higher. Product examples for each of the three technologies under investigation are included in the tech brief. In addition, there’s a table that lists various attributes of each, allowing readers to see their advantages and disadvantages.

Integra Technologies, 321 Coral Circle, El Segundo, CA 90245-4620; (310) 606-0855.

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