Analog and electronic circuits

What condition must a feedback oscillator satisfy to sustain oscillation?

  1. ALoop gain of 0 and a 180° phase shift
  2. BLoop gain of 1 or more and a total phase shift of 0° (360°) around the loop
  3. CThe input signal is always 0
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Answer: B. Loop gain of 1 or more and a total phase shift of 0° (360°) around the loop

To sustain oscillation, a signal going once around the amplifier and feedback network must return in phase with the original and at least as large (the Barkhausen criterion). In practical oscillators, the loop gain is made greater than 1 at start-up and settles to 1 as the amplitude grows.

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