| 摘要 |
PURPOSE:To stabilize the frequency characteristic of a phase leveling loop (PLL) circuit by providing the electrostatic capacity of a diode having variable capacity with a value coincident with the load capacity/oscillating frequency characteristics of a voltage controlled type oscillator. CONSTITUTION:In the voltage controlled oscillator (VCO) 4, the capacitance of the variable capacity diode 42 is changed by a control voltage Vc and the oscillating frequency of a piezoelectric vibrator 43 is also changed is response to said change to obtain output frequency fVCO. The characteristics of the diode 42 are made coincide with the load capacity/oscillating frequency characteristics of the VCO 4 so that the output frequency fVCO having high linearity corresponding to the change of the control voltage Vc is obtained. In addition, the piezoelectric vibrator 43 reduces the changing range of the frequency fVCO as compared with the change of the voltage Vc. Consequently, influences due to the change of voltage, noise, etc. can be reduced and the PLL circuit can execute stable operation as a whole.
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