JPS644117A - Phase locked loop oscillator - Google Patents

Abstract

PURPOSE:To prevent a reception fault due to out of phase after the next and succeeding stages from being caused at the restoration from a fault by decreasing the open loop gain of a phase locked loop oscillator more than the open loop gain of other phase locked loop oscillator at the restoration from the fault. CONSTITUTION:An input signal 1 is fed to a phase comparator 4 together with an output signal 3 of a voltage controlled oscillator 2 and a voltage 5 proportional to the phase difference of the both is outputted. The said voltage 5 is fed to an oscillator 2 via a filter 6 and a gain limit circuit 7 to vary the oscillating frequency of the oscillator 2 in a direction that the phase difference between the input signal 1 and the output signal 3 is decreased. On the other hand, when the input signal is interrupted and another input signal arrives again, the gain limit circuit 7 is controlled by an input signal interruption detecting circuit 8 and a timer 9 so as to keep the open loop gain of the said phase locked oscillator to a smaller value in comparison with the value at the normal operation for a prescribed time elapsed after the input signal interruption and the re-arrival of the input signal.