What fundamental requirement must be met for a circuit to sustain oscillations?

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Multiple Choice

What fundamental requirement must be met for a circuit to sustain oscillations?

To keep an oscillator going, the feedback around the amplifier loop must reinforce the signal. This reinforcement comes from positive feedback, where the returned signal is in phase with the original and adds to it. For a steady oscillation, the loop gain at the oscillation frequency needs to be at least one in magnitude so that the energy fed back to the input compensates for any losses in the circuit. If the loop gain is less than one, the oscillation fades away; if it’s more than one, the amplitude would grow until nonlinearities limit it, but the system tends to settle where the loop gain effectively becomes unity. The phase around the loop also has to align so the feedback adds in phase (typically a net 0 or 360 degrees) at that frequency. Negative feedback or insufficient positive feedback would suppress or kill oscillations, while neutralizing feedback isn’t what sustains them. So the essential requirement is sufficient positive feedback.

To keep an oscillator going, the feedback around the amplifier loop must reinforce the signal. This reinforcement comes from positive feedback, where the returned signal is in phase with the original and adds to it.

For a steady oscillation, the loop gain at the oscillation frequency needs to be at least one in magnitude so that the energy fed back to the input compensates for any losses in the circuit. If the loop gain is less than one, the oscillation fades away; if it’s more than one, the amplitude would grow until nonlinearities limit it, but the system tends to settle where the loop gain effectively becomes unity. The phase around the loop also has to align so the feedback adds in phase (typically a net 0 or 360 degrees) at that frequency.

Negative feedback or insufficient positive feedback would suppress or kill oscillations, while neutralizing feedback isn’t what sustains them. So the essential requirement is sufficient positive feedback.

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