| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal detecting circuit which sets a decision threshold voltage to an arbitrary value to reduce the influence of an offset component contained in output, thereby assuring a high precision detection. SOLUTION: The signal detecting circuit is provided with: an amplifier 2; a switch unit 1 which supplies signals to the amplifier 2 such that the polarity thereof is reversed between first and second periods; a capacitor 3 connected with a terminal 2a; a capacitor 4 connected with a terminal 2b; a switch S1 connected to the capacitor 4; a comparator 5 connected with the capacitor 3 and the switch S1; a switch S3 connected between an output terminal 5c and an inverting input terminal 5b; a switch S2 connected with a terminal 4b; a switch S4 connected to a non-inverting input terminal 5a; and a threshold voltage source Vref connected between the switch S2 and the switch S4. In the first period, the switch S1 is off, and the switches S2-S4 are on. In the second period, the switch S1 is on, and the switches S2-S4 are off. COPYRIGHT: (C)2009,JPO&INPIT
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