#### Abstract

A PLL frequency synthesizer which is provided with a voltage detector which detects the present value of a control voltage applied to a voltage-controlled oscillator, a storage device which stores inadvance the set values of a plurality of control voltages corresponding to the set values of a plurality of frequency dividing numbers set in a frequency divider and outputs the set value of the control voltage corresponding to the frequency dividing number set in the frequency divider by selecting the set value out of the set values of the control voltages, a voltage value comparator which compares the present value of the control voltage detected by the detector with the set value of the control voltatage outputted from the device, and a switching circuit which outputs either the phase difference signal generated by means of a phase comparator and representing the phase difference between the phase of a frequency dividing signal outputted from the divider and that of a reference frequency signal or the output signal of the comparator by switching. The comparator controls the circuit so that a charge pump can be driven with its own output signal when the difference between the present value of the detected control voltage and the set value of the control voltage from the device is larger than a prescribed value or with the phase different signal from the phase comparator when the difference is not larger than the prescribed value.

一种PLL频率合成器,包括:电压检测器(9),检测施加给电压控制振荡器(6)的控制电压的当前值;存储装置7,在其中预先存储与设定在分频器(2)中的多个分频的设定值对应的多个控制电压的设定值,从多个控制电压的设定值中选择输出与设定在分频器的分频对应的控制电压的设定值;电压值比较器(8),对由电压检测器(6)检测的控制电压的当前值和从存储装置(7)输出的控制电压的设定值进行比较;和转换电路(10),对相位比较器(3)生成的表示分频器(2)输出的分频信号的相位与基准频率信号的相位差的相拉差信号和电压值比较器(8)的输出信号进行转换,并输出给电荷泵(4);在检测的控制电压的当前值与来自存储装置(7)的控制电压的设定值之差比预定值大的情况下,电压值比较器(8)利用自身的输出信号驱动电荷泵(4),而在除此之外的情况下,电压值比较器(8)控制转换电路(10),以便由来自相位比较器(3)的相位差信号驱动电荷泵(4)。