A circuit depending on positive feedback for its operation would be a:

An oscillator relies entirely on positive (or regenerative) feedback to function. By taking a portion of the output signal and feeding it back into the input in phase with the original signal, the circuit sustains continuous oscillations at a specific frequency. In contrast, audio amplifiers generally utilize negative feedback to improve stability, widen bandwidth, and reduce distortion. Mixers and detectors are used to combine or extract signals and do not rely on positive feedback to generate their own sustained RF signals.