Phase-locked loop with protection circuit

The invention provides a phase-locked loop with a protection circuit, comprising a first programmable feedback frequency divider and a voltage controlled oscillator. The protection circuit comprises a frequency divider, a second programmable feedback frequency divider, an inverter, a counter, a trigger and an automatic controller. The input terminal of the frequency divider is in electric connection with the input terminal of the first programmable frequency divider, and the output terminal is in electric connection with the input terminal of the second programmable feedback frequency divider; the output terminal of the second programmable feedback frequency divider is respectively in electric connection with the input terminal of the inverter, and the clock terminal of the trigger; the output terminal of the inverter is in electric connection with the reset terminal of the counter; the clock terminal of the counter is in electric connection with the output terminal of the second programmable frequency divider; the output terminal of the counter is in electric connection with the input terminal of the trigger; the output terminal of the trigger is in electric connection with the input terminal of the automatic controller; the output terminal of the automatic controller is in electric connection with the control terminal of the voltage controlled oscillator. The phase-locked loop employs a digit protection circuit, and reduces phase-locked loop power consumption and circuit manufacturing cost.