| 摘要 |
PURPOSE:To obtain a small frequency step and to vary a frequency continuously, by providing a local oscillator st the outside of a PLL. CONSTITUTION:A frequency mixer 8 mixing two input signals, and a local oscillator 9 varying an oscillation frequency with a crystal oscillator 10 and a variable reactance element 11 are arranged at the outside of a PLL, and the frequency mixer 8 mixes the output frequency of the PLL and the local oscillator 9. Further, a digital circuit 13 which takes up frequencies under a reference frequency and producing an arbitrary number of digits of digital signal, and a D/A converter 12 are provided and an output from the digital circuit 13 is converted into a DC voltage, which is applied to the variable reactance element 11, to control the oscillating frequency of a local oscillator 9. Moreover, a digital signal at higher-order digit from the digital circuit 13 is applied to a variable frequency divider 6 to control the frequency dividing ratio of the said frequency divider. |
