| 摘要 |
PURPOSE:To prevent a jump of a frequency of a VCO at the restoration of an input clock by using a N/2 frequency division pulse of the VCO so as to keep an output of a coupling circuit to a required control voltage level at the clock input interruption. CONSTITUTION:When an input interruption detection circuit 1 detects a clock interrupt, A phase comparator circuit 4 segmenting a signal with a pulse of 1/N frequency division via a 1/N frequency divider circuit 2 segments an output of a VCO 9 by using a pulse of N/2 frequency division by a N/2 frequency divider circuit 10. On the other hand, a phase comparator 5 inhibits the set of an FF 21 at the interruption and uses the N/2 frequency division pulse of the VCO 9 to repeat the inversion of a FF 21. Thus, a duty of an input pulse to a coupling circuit 8 is close to 50% and an output level of the circuit 8 reaches a level at which the VCO 9 outputs a center frequency and jump of an output frequency is prevented when the input clock is restored. |
