| 摘要 |
PURPOSE:To prevent the locking with an image frequency by switching a reference frequency oscillating source so as to control the output of a VCO to move in the direction of an inherently desired frequency. CONSTITUTION:A comparator 15 compares the voltage of a control signal VT to a VCO 1 and a reference voltage VR, and at the time of VT<KT, a comparator output signal 17 of L is outputted. The signal 17 of L comes to H through an inverter 18, an analog switch 20 is turned on, 19 is turned off, and a reference signal fref of a frequency fR2 is supplied from a reference frequency oscillator 21 to a phase comparator 11. Here, the frequency fR2 of the oscillator 21 is set so as to come to FR2>>fR1 compared with a frequency fR1 of a reference oscillator 9. Thus, to a frequency-divided 7 frequency signal f1, fref is f1<fref, therefore, the signal VT becomes higher. VT>=VR is obtained, the signal 7 comes to H, the switch 19 is turned on, fref=fR1 is obtained, the signal VT arrives at the desired value in a short time, then, f1=fref is obtained and stabilized. |
