| 摘要 |
As a countermeasure against operating an LSI with a frequency out of an allowed range, there is a frequency sensor that generates reference clocks and detects the frequency by counting the reference clocks. In this method, however, power consumption and circuit scale are undesirably increased. So, in the present invention, a resistor element (13) and a capacitor (14) are provided, and a frequency is detected according to a charging/discharging time to/from the capacitor (14), thereby realizing a frequency sensor with reduced power consumption and reduced circuit scale. Further, when plural resistors and plural capacitors are provided and switches are connected to the respective resistors and capacitors, the time constant can be adjusted after production, whereby variations in production can be reduced. Furthermore, when a self-diagnosis circuit for determining whether the frequency sensor itself operates normally or not is provided, a highly-reliable frequency sensor can be realized.
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