Really, phase locked loops (phase detector/oscillator) and ringing circuits can both be analyzed to determine the important operating characteristics of noise bandwidth, and phase shift vs. frequency offset. The only major difference is that the ringing circuit has no positive feedback to sustain output indefinitely in the absence of input. It is also possible to use an oscillator without a phase detector and lock the oscillator by injecting the burst (which some Motorola chassis did). Such injection-locked oscillators can also be analyzed to determine the same performance characteristics.
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