| 摘要 |
In a phase locked loop (PLL) circuit having a function of automatically adjusting the free-running frequency of a voltage controlled oscillator (VCO), the number of pulses of a pulse signal output from the VCO in a period in which a comparison signal output from a phase comparator is at a predetermined level is counted, and a microcomputer updates digital data based on the counted value. The digital data is converted into an analog signal by a digital-to-analog converter. A combiner combines the analog signal with a signal obtained by smoothing the comparison signal of the phase comparator by a low-pass filter so as to generate a frequency control signal of the VCO. |
