| 摘要 |
A frequency determination circuit (204) determines, with a high precision, whether the frequency of a clock signal (CLK) is higher or lower than a reference frequency. A capacitor element (251) is charged/discharged with a power supply voltage (VDD) that is cycled by a switching transistor according to the clock signal. A comparator circuit (215) compares a constant reference voltage produced by a band-gap regulator (211) circuit from the power supply voltage with a voltage stored in the capacitor element. A high/low determination circuit (216) determines, from the output signal of the comparator circuit, whether the clock signal frequency is higher or lower than a predetermined reference frequency. This makes it possible to determine with precision whether the clock signal has a low frequency or a high frequency. <IMAGE> |
