| 摘要 |
PURPOSE:To obtain a phase synchronizing loop circuit which can perform simply and surely the function check for a digital phase comparator and does not require to provide additionally pins for checking specially in case that this circuit is made into an IC. CONSTITUTION:Switching circuit 16 is provided between reference oscillator 11, variable frequency divider 13 and digital phase compartor 14a, and signals supplied to each input terminal of digital phase comparator 14a are switched from fr and fo signals of reference oscillator 11 and variable frequency divider 13 to signals for checking by giving switching instruction signals to this switching circuit 16 from switching instruction circuit 17 utilizing the external data input line which is provided for setting the frequency division ratio of variable frequency divider 13. Here, in case that reference oscillator 11, variable frequency divider 13 and digital phase comparator 14a are made into an IC in one body, switching circuit 16 and switching instruction circuit 17 are incorporated in the IC. |
