RF transistors are designed to handle high-power radio frequency (RF) signals in devices such as stereo amplifiers, radio transmitters, and television monitors. Like other semiconductor devices, they are made of materials such as silicon (Si) or germanium (Ge) and doped with impurities to induce changes in electrical properties. There are several basic types of RF transistors. Bipolar RF transistors consist of an N-type or P-type layer sandwiched between two layers of the opposite type. Both NPN and PNP configurations are available. MOSFET RF transistors are metal-oxide field effect transistors (MOSFETs) with a channel made of either an N-type or P-type material. Heterojunction field effect transistors (HFETs) require a negative power supply and are used mainly for driver or power amplification applications. Pseudomorphic high electron mobility transistors (PHEMTs) are used mainly in wireless devices and satellite communication systems.
Selecting RF Transistors
Selecting RF transistors requires an analysis of performance specifications. Power gain, a measure of power amplification, is the ratio of output power to input power. Noise figure, a measure of the amount of noise added during normal operation, is the ratio of the signal-to-noise ratio at the input and the signal-to-noise ratio at the output. Both power gain and noise figure are expressed in decibels (dB). Other performance specifications for RF transistors include output power, operating frequency, and operating temperature. Some RF transistors support a temperature range and feature mechanical and electrical specifications that are suitable for commercial or industrial applications. Other devices meet screening levels for military specifications (MIL-SPEC).
IC Package Types
Basic integrated circuit (IC) package types for RF transistors are transistor outline (TO), small outline (SO), and small outline transistor (SOT). For each package type, many variants are available. Transistor outline packages include TO-92, a single in-line package often used for low power devices; TO-220, which is suitable for high power, medium current, and fast-switching power devices; and TO-263, the surface-mount version of the TO-220 package. Small outline transistor packages include SOT23, which is often used in home appliances, office and industrial equipment, personal computers, printers, and communication equipment; SOT89, a plastic, surface mounted package with three leads and a collector pad for good heat transfer; and SOT223, an encapsulated package that provides excellent performance in environments with high temperatures and humidity levels. IC package types that use flat packaging (FPAK) are also available.
Packing methods for RF transistors consist of tape reel, rail, bulk pack, and tube technologies. The tape reel method packs components in a tape system by reeling specified lengths or quantities for shipping, handling, and configuration in industry-standard automated board-assembly equipment. Rail, another standard packing method, is typically used only in production environments. Bulk pack devices are distributed as individual parts, while tray components are shipped in trays. Typically, the tube or stick magazine method is used to feed bipolar RF transistors into automatic placement machines for through-hole or surface mounting.
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Bipolar RF Transistors
Bipolar RF transistors consist of an N-type or P-type layer sandwiched between two layers of the opposite type. They are designed to handle high-power radio frequency (RF) signals in devices such as stereo amplifiers, radio transmitters, and television monitors.
Insulated Gate Bipolar Transistors (IGBT)
Insulated gate bipolar transistors (IGBT) are bipolar transistors with an insulated gate. They combine the advantages of the bipolar transistor (high voltage and current) with the advantages of the MOSFET (low power consumption and high switching).
Metal-Oxide Semiconductor FET (MOSFET)
Metal-oxide semiconductor field-effect transistors (MOSFETs) are electronic switching devices with a conducting channel as the output. An electrode called a gate controls the width of the channel and determines how well the MOSFET conducts.
Power Bipolar Transistors
Power bipolar transistors are semiconductors in which a base n-type or p-type layer is sandwiched between emitter and collector layers of the opposite type. The junctions between the semiconductor sections amplify weak incoming electrical signals.
Power MOSFETs are majority carrier devices which have high input impedance and do not exhibit minority carrier storage effects, thermal runaway, or secondary breakdown. Power MOSFETs have higher breakdown voltages than bipolar junction transistors (BJTs) and can be used in higher frequency applications where switching power losses are important.
RF MOSFET Transistors
MOSFET RF transistors are metal-oxide semiconductor field-effect transistors (MOSFETs) that are designed to handle high-power RF signals from devices such as stereo amplifiers, radio transmitters, TV monitors, etc.
Small-Signal Bipolar Transistors (BJT)
Small-signal bipolar transistors (BJT) are semiconductors that amplify small AC or DC signals. They consist of a base n-type or p-type layer sandwiched between emitter and collector layers of the opposite type.