| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem of a conventional phase frequency synchronizing circuit that it takes a long time to reach synchronization from an asynchronous state, because a loop filter constant suitable for the asynchronous state cannot be selected. SOLUTION: This phase frequency synchronizing circuit is consists of a phase comparator 10, that outputs a voltage in response to the phase difference of a clock based on an input signal as a reference, a frequency comparator 20 that discriminates the magnitude relation of a clock frequency by using a transmission speed of the input signal as a reference and provides an output of a binary signal, a synchronization discriminating device 30 that discriminates synchronization of phase and frequency, a 1st switch that receives the output of the phase comparator 10, is closed when the synchronization discrimination device 30 discriminates synchronization and opens, when the synchronization discrimination device 30 discrimination asynchronization, a 2nd switch that receives the output of the frequency comparator 20, is closed when the synchronization discriminating device 30 discriminates synchronization and opens, when the synchronization discriminating device 30 discriminates asynchronization, a loop filter 40 that receives the outputs of the 1st and 2nd switches, and a voltage-controlled oscillator 50 that oscillates on the basis of the output of the loop filter 40. |
