Bipolar transistors

How does the phase of the output voltage of a common-emitter amplifier compare with the input voltage?

  1. AIn phase
  2. BInverted by 180°
  3. CLeading by 90°
Show answer and explanation

Answer: B. Inverted by 180°

In a common-emitter amplifier, when the input (base) voltage rises, the collector current increases and the voltage drop across the collector resistor grows, so the output (collector) voltage falls. The output is therefore 180° out of phase with the input.

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More Bipolar transistors questions

  1. What is the main reason for making the emitter of an NPN transistor more heavily doped than the base?
  2. What is the approximate common-emitter current gain β of a bipolar transistor whose common-base current gain α is 0.99?
  3. Which correctly describes the Early effect in a bipolar transistor?
  4. Which is a characteristic of a Darlington connection of two transistors?
  5. In a PNP transistor, which carriers are injected from the emitter into the base and mainly carry the current?