| 摘要 |
PURPOSE:To stabilize a loop, by overshoot-controlling the high-low relation between the frequency of output signal of a voltage controlled oscillator and the frequency of a signal contolling a mixer so as not to change the relation at the locking time of a PLL circuit at a power supply is turned on, etc. CONSTITUTION:A phase comparator 11 compares the modulated signal of a frequency fM with a frequency fS-fT in terms of the frequency and phase, and outputs a difference signal Vd in accordance with the difference in phase, assuming that the frequency fT is the output of a voltage controlled oscillator 13 and fS is the frequency of a signal which controls a mixer 14 the voltage Vd increases when the frequency fM is lower than the frequency fS-fT and it decreases when higher. Moreover, when it is judged that the voltage Vd goes to larger than a prescribed voltage, an overshoot controller 16 closes a switch circuit SW1 for a specified time to discharge a capacitor C and opens another switching circuit SW2 to make the time constant and damping constant of an LPF12 large, and thus, a loop is stabilized. |
