In the phase-locked loop, the output signal is not processed by the input signal, but generated by the internal oscillator itself. Even if there is no input signal, there is still an output.

When CD4046 is a digital phase-locked loop, the output is a square wave with an amplitude equal to the power supply voltage. If the loop is locked, the output frequency is determined by the frequency division parameter of the feedback loop, and the circuit in the figure should be equal to the input frequency 10kHz. If there is no lock, the free oscillation frequency is determined by C 1, R 1 and R2, and a certain value is pulled in the direction close to the input frequency.