| 摘要 |
PURPOSE:To stop automatic frequency control by grounding the output of an operational amplifier by means of the control of a judgement signal when the detection signal of a level detection circuit and an input voltage cut signal from an external part are inputted. CONSTITUTION:The level detection circuit 4 detects whether an output voltage 104 exceeds a prescribed voltage Vm or not. A deciding circuit 5 outputs a detection signal 105 with effect that the circuit 4 exceeds the prescribed voltage Vm. When the signal of the input voltage cut signal 108 is inputted, a switch 6 is controlled by the judgement signal 106 and the output voltage 104 for a VCO part is set to 0V. When the output voltage 104 becomes less than the prescribed voltage Vm on the other hand, the output voltage for the VCO part 7 is left to be + or - vo, as it is. When there is the input voltage cut signal, the output voltage 104 in the state is inputted to VCO 7 and an automatic frequency control operation is continued. Consequently, the output phase 107 of the VCO part 7 is returned to a phase comparator and the same operation is repeated. Then, automatic frequency control can be executed so that the output voltage V0 for the VCO part 7 is settled within a certain level. |
