| 摘要 |
<p>An oscillation frequency control circuit for correcting its frequency, keeping the oscillation frequency stable when self-oscillating, and oscillating with a control voltage generated by making a fixed voltage given from outside variable. The oscillation frequency control circuit comprises a voltage-controlled oscillator (15), a divider (16), a phase comparator (12), a loop filter (14), a detecting circuit (17), a PWM circuit (22), a memory (21), a control voltage varying circuit (26), a selection switch (13) for connecting/disconnecting the phase comparator (12) and the loop filter (14) and selecting/outputting a control voltage from the control voltage varying circuit (26), and a CPU (20). The CPU selects/outputs the control voltage preferentially according to the command of the control voltage selection. If the command is not given and the level of the outside reference signal detected by the detecting circuit (17) is within an adequate range, it turns the selection switch (13) on. If the command is not given and the level of the outside reference signal is out of the adequate range, it turns the selection switch (13) off and outputs information about pulse generation stored in the memory (21) to the PWM circuit (22).</p> |
