Phase-locked loop

The invention relates to the technical field of electronic communication, and discloses a phase-locked loop, which comprises a tuning voltage generation unit, a tuning voltage detection unit, a bidirectional sub-band counting unit, an adjustment amplitude control unit and a voltage-controlled oscillator; in actual use, the output frequency sub-band of the voltage-controlled oscillator is controlled through an output signal of the bidirectional sub-band counting unit; then an output signal of the bidirectional sub-band counting unit is determined by a counting direction and an adjusting amplitude, the counting direction is input by the tuning voltage detection unit, and the adjusting amplitude is input by the adjusting amplitude control unit, so that the frequency of the phase-locked loop does not need to be adjusted one by one; and therefore, the sub-band selection time of the phase-locked loop can be shortened according to the multi-stage adjustment of the difference between the reference frequency and the output frequency of the voltage-controlled oscillator.