| 摘要 |
PROBLEM TO BE SOLVED: To limit the frequency of an oscillated output from a PLL circuit having same dispersion within a prescribed range of an upper limit frequency and a lower limit frequency. SOLUTION: A horizontal period measurement section 5 uses a horizontal period measurement clock signal Sm, to measure the period of a horizontal synchronizing signal Sh as a reference signal and provides an output of a measured value A. A frequency division ratio calculation section 6 calculates the oscillation frequency of a voltage controlled oscillator 4, calculates a frequency division ratio set to the upper limit frequency and calculates a frequency division ratio set to the lower limit frequency according to a prescribed calculation equation on the basis of a preset upper limit frequency, lower limit frequency and the measured data. A frequency division ratio calculation section 6 sets a frequency division ratio set to a frequency divider 1, so that the oscillation frequency of the voltage controlled oscillator 1 that is calculated in the above will not exceed the upper limit frequency or the lower limit frequency. |
