RF transistors fall under a variegation of technologies that have been developed over recent years. The different technologies that are available from RF power transistor suppliers come with different advantage and disadvantages, depending on the power levels and frequency ranges of your applications. Thus, makers of RF power transistors continue to make many different types.

Some of the most common types of RF transistors include metal oxide semiconductor field effect transistors (MOSFET), laterally diffused metal oxide semiconductor (LDMOS), gallium arsenide (GaAs) and bipolar junction transistors (BJT). Different RF power transistor manufacturers focus on different types of devices. When searching suppliers of RF transistors to find the right device(s) for your application, consider the following:

1. For moderately high frequency, low voltage applications, buy MOSFET RF transistors.

2. For a combination of high frequency and high power, check the LDMOS aisle.

3. When you're working at frequencies beyond what LDMOS will handle, GaAs RF transistors are still an option.

4. For lower-frequency RF, TV deflection circuits, and lighting, go with bipolar junction RF transistors.

Action Steps
The best contacts and resources to help you get it done

Consider MOSFET power transistors for really high power RF applications

MOSFET transistors are designed for high power applications. Use them when you need high switching speed and good efficiency at low voltages. The RF power MOSFET is the most commonly employed power transistor device. Radio transmitters, television monitors and stereo system amplifiers commonly employ MOSFET RF power transistors.

I recommend: RF power transistor manufacturer Integra Technologies carries a line of MOSFET RF power transistors they call VHF-VDMOS, as they're made for VHF use. They're sported as having the smallest footprint of hi-power transistors. IXYS RF, another maker of RF power transistors, is a great source for high voltage, high power, bias-stable RF transistors covering HF and VHF frequency ranges.

Try LDMOS RF transistors for the highest frequency and power applications

LDMOS RF power transistors have very high electron mobility and are thus well suited for very high frequency operation, finding extensive uses in RF and microwave power amplifiers. As cell frequencies were rising, GaAs makers thought they'd have an easy win, but LDMOS overtook much of the GaAs market, with components already passed 3.5 GHz at 100 Watts.

I recommend: Freescale Semiconductor has a complete line of LDMOS RF transistors, covering frequencies from mobile to beyond 2.2 GHz. They recommend their LDMOS transistors for PCS, digital television, GSM, and 900 MHz linear cellular, etc. RFMD has a similarly extensive collection of LDMOS RF power transistor devices.

Employ GaAs RF power transistors for frequencies beyond 3.5 GHz

Due to higher electron mobility than silicon, GaAs RF power transistors are quiet and are suitable for applications involving frequencies up to 250 GHz and for those requiring high power. Therefore, GaAs RF power transistors are a great choice for satellite communications, mobile phones, radar systems and microwave point-to-point links.

I recommend: RF power transistor supplier Triquint carries a few models of SOT-89 style MESFETs and HFETs, with operating frequencies ranging to 4 GHz. The HFETs are higher-current devices than the MESFETs. Avago has an impressive list of GaAs FETs with test frequencies well into the gigahertz.

Save money in lower frequency RF applications with bipolar RF transistors

The bipolar junction transistor (BJT) is useful in lower-frequency RF amplifiers because emitter and collector currents are controllable by the relatively small base current. They are commonly used in television deflection circuits and in lighting applications.

I recommend: Northrup Grumman carries bipolar RF transistors that feature optimal internal matching, operate well into the GHz, have low thermal resistance, and are suitable for high performance communications systems. Mouser Electronics carries numerous bipolar RF transistors to choose from, covering frequencies up to 42 GHz.

Tips & Tactics

Helpful advice for making the most of this Guide

• •  For output stages, use LDMOS or gallium nitride (GaN) transistors because of higher gain, improved linearity, and very low on-resistance. High gain reduces the number of amplifier stages needed, compared to older systems employing bipolar transistors.