| 摘要 |
<p>A present invention provides a frequency determination circuit (204) to determine whether the frequency of a clock signal is higher or lower than a reference frequency with a high precision. A capacitor element (251) is charged/discharged with a power supply voltage that is cycled by a switching transistor (252) according to a clock signal. A comparator circuit (253) compares a constant reference voltage produced by a bad gap regulator circuit (211) from the power supply voltage with a voltage stored in the capacitor element (251). A high/low determination circuit (216) determines, from the output signal of the comparator circuit (253), whether the clock signal frequency is higher or lower than a predetermined reference frequency. This makes it possible to determine whether the clock signal has a low frequency or a high frequency with precision. FIG.3</p> |
