| 摘要 |
PROBLEM TO BE SOLVED: To provide a synchronizing source signal changeover circuit that selects and switches any of the clock signals supplied from each of transmission lines to generate an in-device frame signal. SOLUTION: A clock signal selection circuit 120 selects any of clock signals 201 or the like supplied from transmission lines and produces a selected clock signal 220. A frequency divider circuit 130 frequency-divides the selected clock signal 220, to produce a synchronizing source frame signal 220. A phase locked loop oscillator, consisting of a phase comparator circuit 140, a voltage controlled oscillator(VCO) circuit 150 and a frequency divider circuit 160, has the frequency divider circuit 160 and the VCO circuit 150 produce an in-device frame signal 240 and an in-device clock signal 250. A clock signal fault detection circuit 201 or the like detecting a fault in the clock signal 201 or the like allows the clock signal selection circuit 120, to newly select a normal clock signal through a clock signal selection control circuit 110. |
