| 摘要 |
PURPOSE:To eliminate unstableness at the time of switching and to realize high-speed lead-in by changing a constant of a loop filter continuously by using an element that can change resistance electrically. CONSTITUTION:An output signal of a phase comparator is applied to the input terminal 101 of a loop filter, and an output terminal 113 is connected to the control terminal of a voltage control oscillator. The loop filter in steady consists of resistances R1, R2 and capacity C. Elements 107, 108 resistance value of which can be varied (electronic volume) by a signal from outside and resistances R3, R4 are connected to both ends of resistances R1, R2. A resistance value controlling circuit 109 is provided to make resistance values Rv1, Rv2 of resistances 107, 108 variable continuously with time, and a terminal 110 detects the time of application of power source and frequency switching and sends out a starting signal to the resistance value controlling circuit 109. |
