Bipolar transistors

What does the transition frequency fT of a bipolar transistor mean?

  1. AThe frequency of the power supply
  2. BThe frequency at which the common-emitter current gain falls to 1
  3. CThe frequency at which a circuit oscillates
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Answer: B. The frequency at which the common-emitter current gain falls to 1

A transistor's current gain decreases at higher frequencies. The frequency at which the common-emitter current gain becomes 1 is called the transition frequency fT, and it is an indicator of the transistor's high-frequency performance.

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  2. Which is a characteristic of a SiGe HBT (heterojunction bipolar transistor)?
  3. What is the typical collector-emitter voltage of a silicon bipolar transistor in the saturation region?
  4. Which circuit uses two matched transistors to make the current in one transistor equal to the current in the other?
  5. What does a differential pair, with the emitters of two transistors connected to a common current source, do?