| 摘要 |
PURPOSE:To detect a prescribed frequency with high accuracy by allowing one set of circuits comprising an SCF, a PLL and a variable frequency divider to switch the setting of the variable frequency divider. CONSTITUTION:An input clock pulse frequency compared by a phase comparator 23 is a clock pulse frequency obtained from an output of a VCO26 applied with frequency division to 1/M by a frequency divider 27. An output based on the phase difference of the frequency compared by a phase comparator 23 is integrated by a filter 24, fed to the VCO26 and becomes a control signal input making the frequency or phase constant. Thus, when the frequency and phase of the signal to be detected being an output of the SCF22 and of an output signal of the frequency divider 27 are coincident, a prescribed single frequency is detected at an output terminal.
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