Bipolar RF Transistors

RF bipolar 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. Like other semiconductor devices, RF bipolar transistors are made of materials such as silicon (Si) or germanium (Ge) and doped with impurities to induce changes in electrical properties. The junctions between the semiconductor sections cause a weak input to be amplified. Varying the current between the base and the emitter varies the current flow between the emitter and the collector. In normal operation, the emitter-base junction is forward-biased and the base-collector junction is reverse-biased. In the linear region, the collector-emitter current is approximately proportional to the base current, but many times larger. In the cut-off region, the base-emitter voltage is too small for any significant amount of current to flow. 

Selecting RF bipolar transistors requires an analysis of performance specifications. Collector-to-emitter breakdown voltage is the maximum voltage than can be applied continuously in the reverse direction of the collector junction when the emitter is open. Similarly, collector-to-base breakdown voltage is the maximum voltage that can be applied continuously in the reverse direction of the collector junction when the base is open. 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). Power dissipation, a measure of total power consumption, is expressed in watts or milliwatts. Other performance specifications include maximum collector current, current gain bandwidth, operating frequency, and output power. Some RF bipolar 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).

RF bipolar transistors vary in terms of polarity, packaging, and packing methods. NPN is a physical bipolar junction transistor (BJT) arrangement in which the emitter and the collector are made of N-type material and the base is made of P-type material. By contrast, PNP is a BJT arrangement in which the emitter and the collector are made of P-type material and the base is made of N-type material. In terms of packaging, RF bipolar transistors are available in small outline (SO), transistor outline (TO), small outline transistor (SOT), and flat packaging (FPAK). Devices use either surface mount technology (SMT) or through hole technology (SMT) and vary in terms of the number of leads. Packing methods for RF bipolar transistors include tape reels, rails, bulk packs, tubes, and trays.

• Biasing MSA Series RF Integrated Circuits - App Note
  Like discrete transistors, the MSA Series of RF Integrated Circuits can be operated at different bias points to achieve different performance results. These Monolithic Silicon Amplifiers have an...
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Part Numbers for Bipolar RF Transistors