| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an oscillation frequency control circuit capable of stably keeping an oscillation frequency by correcting its own frequency, even without inputting a highly stable reference signal and even during self-running. <P>SOLUTION: The oscillation frequency control circuit includes: a voltage controlled oscillator 15; a frequency divider 16; a phase comparator 12; a loop filter 14; a detection circuit 17 for detecting an external reference signal; a PWM circuit 22 which generates a pulse and outputs it to the loop filter 14 when pulse generation information is input; a memory 21 for storing pulse generation information corresponding to voltage information; a switch 13 for turning on/off the connection of the phase comparator 12 and the loop filter 14; and a CPU 20 which turns on the switch 13 when the level of the external reference signal detected by the detection circuit 17 is within a proper range, or turns off the switch 13 when the level is out of the proper range, and outputs to the PWM circuit 22 the pulse generation information stored in the memory 21. <P>COPYRIGHT: (C)2008,JPO&INPIT |
