Bipolar transistors

Which correctly describes the Miller effect that degrades the high-frequency performance of a common-emitter amplifier?

  1. AThe base-collector capacitance appears, from the input, as a much larger capacitance in proportion to the voltage gain
  2. BThe emitter resistance changes with temperature
  3. CThe collector current fluctuates due to thermal noise
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Answer: A. The base-collector capacitance appears, from the input, as a much larger capacitance in proportion to the voltage gain

In a common-emitter amplifier, the collector voltage swings widely in antiphase with the base, so the base-collector capacitance Cμ appears from the input as about (1 + |Av|) times larger. This large input capacitance, together with the source resistance, narrows the bandwidth. Countermeasures include the cascode configuration.

  • A. Correct. The feedback capacitance multiplied by the gain is the Miller effect.
  • B. A temperature-dependent resistance change is not the Miller effect.
  • C. Thermal noise is a separate phenomenon from the Miller effect.
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More Bipolar transistors questions

  1. What is the aim of a transistor with a Schottky barrier diode connected across its base-collector junction (a Schottky clamp)?
  2. Which bias condition is correct when an NPN transistor is used for amplification (operated in the active region)?
  3. Which expression gives the DC current gain hFE of a bipolar transistor? (IC: collector current, IB: base current, IE: emitter current)
  4. What is the main reason for making the base of a bipolar transistor thin?
  5. When a bipolar transistor is used as a switch, which operating region corresponds to the on state?