APLL NO INPUT SIGNAL COMPENSATION CIRCUIT

PURPOSE:To attain immediate lock-in when an input signal is intermitted and a data is restored again by providing a specific circuit holding the state of a point of time when the last data is inputted. CONSTITUTION:In the APLL circuit comprising a phase comparator 1, a voltage controlled oscillator 5 connected to an output of the comparator 1, and a feedback path connecting the output of the voltage controlled oscillator 5 and the one input of the phase comparator, an integration means 2 integrating the output of the phase comparator 1, an input signal detection circuit 4 detecting the presence of an input signal to the phase comparator 1, a switch 6 controlled by the input signal detection circuit 4 and a hold means 3 holding two outputs of the integration means while being connected to the output of the integration means 2 via the switch 6 are provided between the phase comparator 1 and the voltage controlled oscillator 5. Thus, when the input signal is interrupted and then restored again, the immediate lock-in is attained.