What condition is necessary for a circuit to oscillate?

For a circuit to oscillate, it is essential that it has sufficient positive feedback. Oscillation occurs when the output of a circuit is fed back to the input in such a manner that it reinforces itself. This positive feedback is crucial because it builds up the voltage or current in the oscillating circuit to sustain a continuous signal. Without enough positive feedback, any small signal present in the circuit would dissipate rather than amplify, preventing oscillation from occurring.

The characteristic of sufficient positive feedback is a fundamental principle in oscillator design, ensuring that the signal reaches a level that sustains the oscillation process. Other factors might enhance the performance or efficiency of oscillators, but the condition of positive feedback is necessary for the initiation and maintenance of oscillatory behavior.