| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To improve the signal-to-noise characteristics and distortion characteristic of a frequency modulated wave. <P>SOLUTION: A frequency divider 28 divides the frequency of an output signal of a voltage controlled oscillator 30, an integrating circuit 29 integrates a modulated signal, a reference frequency divider 24 divides the frequency of a reference clock 23, and a variable delay circuit 25 is then used to apply phase modulation to the reference clock 23 by using an output signal of the integrating circuit 29. A phase comparator 26 compares the phase of an output signal of the frequency divider 28 with that of an output signal of the variable delay circuit 25, a loop filter 27 extracts the low-pass components of the output signal of the phase comparator 26 and gives the low-pass components as a frequency controlled voltage to the voltage controlled oscillator 30. The variable delay circuit 25 comprises a differential transistor in which a current source is connected to the collector side and the emitter side, capacitors connected to the collector of the differential transistor, and a current source with a switch for limiting the upper limit value and lower limit value of the voltage of the collector of the differential transistor to a predetermined value. <P>COPYRIGHT: (C)2004,JPO</p> |
