What condition must exist for a circuit to oscillate?

• A. Have sufficient positive feedback
• B. Have a gain less than 1
• C. Be neutralized
• D. Have sufficient negative feedback

Answer: (A)

Oscillation can continue only when the feedback reinforces the signal rather than opposing it. That means the feedback must be positive and strong enough to overcome losses in the circuit. If the loop gain is at least one and the total phase shift around the loop is an integer multiple of 360 degrees at the oscillation frequency, energy is fed back constructively and the signal sustains itself. If the gain is less than one, the oscillations die out because energy is lost each cycle. Negative feedback tends to reduce or cancel the signal instead of reinforcing it, so it would suppress oscillation. Neutralization isn’t about starting oscillation; it’s a technique used to cancel unwanted feedback in some circuits, not to enable sustained oscillation.