| 摘要 |
The invention provides a PLL circuit which can form a phase difference between input and output signals with a high degree of accuracy without employing a current source for a very weak current and eliminates dependency of the phase difference upon the input signal frequency. In the PLL circuit, phase difference forming current is added within a term of a fixed period to a selected one of charge-up current and charge-down current, selected by a phase comparison circuit, of a charge pump circuit, which charges up or charges down a loop filter under the control of an output signal of a phase comparison circuit, to form a phase difference between input and output signals of the PLL circuit which are to be compared in phase by the phase comparison circuit. The magnitude of the phase difference depends upon and is controlled by a term within which the phase difference forming current.
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