| 摘要 |
<p>Provided is an oscillation frequency control circuit, which corrects its own frequency so that it can hold an oscillation frequency stably even when it does not have an input of a highly stable reference signal but makes a self-run. The oscillation frequency control circuit comprises a voltage-controlled oscillator (15), a frequency divider (16), a phase comparator (12), a loop filter (14), a detecting circuit (17) for detecting an external reference signal, a PWM circuit (22) for generating pulses, when pulse generating information inputs, to output the pulses to the loop filter (14), a memory (21) for storing the pulse generating information corresponding to voltage information, a switch (13) for turning ON/OFF the connection between the phase comparator (12) and the loop filter (14), and a CPU (20) for turning ON the switch (13), if the level of the external reference signal detected by the detecting circuit (17) is within a proper range, but OFF the switch (13), if the level is outside of the proper range, thereby to output the pulse generating information stored in the memory (21), to the PWM circuit (22).</p> |
