FREQUENCY SYNTHESIZER

PURPOSE:To always generate a stable output frequency by detecting the temperature change of a voltage controlled oscillator (VCO), stopping intermitting operation when the temperature change is larger than a prescribed change and continuously operating a reference signal oscillator, phase comparator and frequency divider. CONSTITUTION:When a power source 9 is turned-ON, power supply control parts 20-1 and 20-2 of a power supply control circuit 20 are turned-ON and simultaneously, the frequency dividing ratio of a frequency divider 5 is set. Next, a control circuit 19 inputs an output to detect the temperature change of a VCO 4 from a temperature detecting circuit 13. When it is judged by the control circuit 19 that the detecting output of the temperature detecting circuit 13 to be previously inputted and a detecting output to be newly inputted exceed the range of temperature difference determined in advance, the control circuit 19 turns-OFF the power supply control part 20-2 and stops the intermitting operation. Then, a reference signal oscillator 1, phase comparator 2 and frequency divider 5 are continuously operated and a frequency synthesizer is operated in a locking state.