| 摘要 |
PROBLEM TO BE SOLVED: To switch a frequency without affecting the characteristics of a PLL itself by electric change in switching the frequency by controlling the loop gain of a digital filter by control information from the outside. SOLUTION: The digital filter 6 is adopted as a loop filter. Then, a cut-off frequency is specified by the control information from an external control terminal 11. Thus, the band and gain of a loop are arbitrarily changed even though it is physically single constitution. As a result, since no plural loop filters are physically required, the probability that frequency lock is released by noise or the like is lowered.
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