| 摘要 |
PURPOSE:To eliminate the dependence of a power source voltage of a frequency detector, by arranging first and second constant current sources, a potential comparison means, a reference potential generation means and the like to reduce variations in the frequency of a pulse signal. CONSTITUTION:A capacitance 17 of a pulse current detection circuit is charged with current of a first constant current source 15 and the discharge of the capacitance 17 is controlled with a first transistor TR11 which is turned ON or OFF by a pulse signal. The charge/discharge potential of the capacitance 17 is compared with a reference potential with a comparator 22. A second constant current source 23 is provided to output a current at a specified ratio with respect to current of the current source 15 and a reference potential generation circuit 28, which comprises a second TR25 to be fed with a specified bias current and a resistance 24. A connection point potential between the constant current source 23 and the resistance 24 is applied to the comparator 22 as reference to reduce variations in the frequency of a pulse signal. Thus, a current detection circuit is built without dependence on a power source voltage.
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