| 摘要 |
PROBLEM TO BE SOLVED: To provide a circuit and a method for evaluating a PLL circuit, with which the characteristics of a PLL circuit can be easily and accurately measured. SOLUTION: A low-pass filter 13 generates an oscillation control signal VCTRL on the basis of an output from a charge pump circuit 12. An analog/ digital converter 16 converts the supplied oscillation control signal VCTRL to a digital oscillation control signal VCTRL-D and supplies it to a lock detecting means 17. The lock detecting means 17 compares the supplied digital oscillation control signal with a digital oscillation control signal supplied the last time and when these values match continuously (m) times, a lock detecting signal MATCH ALL is turned to 'H' and outputted. As a result, the time from the input start of a reference signal CLK to the time when the lock detecting signal MATCH ALL is turned to 'H', can be detected as lock-up time T. |
