Radio frequency (RF) transistors are a type of transistor that is used in audio systems, TVs and radio transmitters to manipulate large radio frequency signals. Bipolar RF transistors, RF field effect transistors, MOSFET RF transistors, heterojunction field-effect transistors (HFET), pseudomorphic high electron mobility transistors (PHEMT) are all configured for use as RF transistors.
RF transistors are similar to other semiconductor devices as they are made of various materials such as silicon (Si) and germanium (Ge). These transistors are also doped with impurities to create changes in electrical properties. There are several basic types of RF transistors. Bipolar RF transistors are made of an N-type or P-type layer that is sandwiched between two layers of the opposite type. Both NPN and PNP types are available. MOSFET RF transistors are metal-oxide field effect transistors (MOSFETs) that consist of a channel which is made of either an N-type or P-type material. Heterojunction field effect transistors (HFETs) need a negative power supply and they are generally used for driver or power amplification applications.
Pseudomorphic high electron mobility transistors (PHEMTs) are typically used in satellite communication systems and wireless devices.
These transistors are sorted by their application such as: commercial grade, industrial grade, military grade and automotive. They are available as PNP, NPN, N Channel, P Channel or a combination of these types. Certain RF transistors support a temperature range and consist of mechanical and electrical specifications that are ideal for commercial or industrial applications. Other transistors meet the screening levels for military specifications (MIL-SPEC).
While selecting a RF transistor, you need to specify certain factors such as:
- The range of ambient operating temperature
- The output power: the amount of power in watts that is produced by the transistor
- The power gain: the output power divided by the input power
- The noise figure: the amount of noise that is generated along with the output and the operating frequency
RF Transistors are packaged and designated as TO-3, TO-8, TO-202, and are available as tape reel, rail, bulk pack and tube. The tape reel process packages the transistors in a tape system by reeling specified lengths or quantities for shipping, handling, and configuration in industry standard automated board-assembly equipment. The rail method is generally used in production settings only. Bulk pack units are shipped as individual parts and tray units are distributed in trays. The tube or stick magazine method is usually used to feed bipolar RF transistors into automatic placement machines for through-hole or surface mounting.