| 摘要 |
PURPOSE:To lock a voltage-controlled oscillator at a desired frequency in a short time by supplying a high voltage to the voltage-controlled oscillator when the oscillator in an unlocked state is set to the desired frequency, and setting the frequency division ratio of a frequency divider to a different value and then setting the frequency division ratio again so that the desired frequency is obtained. CONSTITUTION:When the voltage-controlled oscillator VCO 5 in the unlocked state is locked at a frequency f2, a high voltage supply circuit 8 is put in operation to apply the high voltage to a charge pump 3, and the frequency division ratio of the frequency divider 6 is set by a frequency division ratio setting circuit 7 so as to obtain the maximum frequency f1' and also set again so that the output frequency of the VCO 5 is the desired frequency f2. Thus, the maximum frequency of the VCO is increased temporarily and then the frequency divider is set again so as to obtain the desired frequency. Consequently, the time in which the frequency can not be pulled in can be shorten and the time up to the locking at the desired frequency can be shortened. |
