| 摘要 |
In a phase lock loop circuit comprising a charge pump circuit (13), a loop filter (14), and a voltage controlled oscillator (15), a subsidiary loop filter (20) is connected to the charge pump circuit and the loop filter in a phase lock operation through first and second switching circuits (21) and (22). The loop filter comprises a filter capacitor (Cl) and delivers a filtered signal to the voltage controlled oscillator. In the phase lock operation, the subsidiary loop filter reduces a charge duration and a discharge duration of the filter capacitor. As a result, a voltage of the filtered signal varies rapidly. For the reason, the phase lock operation is carried out in high speed.
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