| 摘要 |
PURPOSE:To eliminate noise of a low frequency, and to exactly measure a distance by connecting an auto offset circuit to an operational amplifier for amplifying an output of a photodetector, and inputting a voltage corresponding to a noise component to the operational amplifier, as an offset voltage. CONSTITUTION:A pulselike photocurrent corresponding to a light emission of a light emitting diode 10 is generated in a photodetector 16, and a pulse like voltage is outputted from an output terminal of an operational amplifier 20. A differential amplifier 22 calculates a difference of an output voltage of an operational amplifier 21 and a reference voltage V1, stores an obtained voltage in a capacitor 24, and also, inputs this voltage as an off set voltage to a plus input terminal of the operational amplifier 21. In such a case, a switching circuit 23 is turned on in the course of a dormant period of the light emitting diode 10, therefore, sampling is executed in a period in which the differential amplifier 22 is outputting a voltage corresponding to a difference of a voltage of a noise component and the reference voltage V1. In such a way, a variation quantity from the reference voltage V1 is outputted from the operational amplifier 21, and the noise component is eliminated. |
