| 摘要 |
PURPOSE:To amplify and output only an AC component corresponding to changes in impedance of a photodetecting element as a signal by comparing the output of the photodetecting element with a reference voltage and amplifying the difference voltage to output the amplified voltage. CONSTITUTION:When impedance is changed by the change of a photodetecting variable of the photodetecting element 2 and an output voltage from the output terminal of a current/voltage converter consisting of an operational amplifier 10 and a resistor 11 is changed, the output held in a voltage holding circuit consisting of a capacitor 19 and a resistor 20 is continuously applied to a buffer circuit consisting of an operational amplifier 13 if the output of a comparator consisting of an operational amplifier 15 is a reversed voltage to a rectifier circuit consisting of a diode 17. The output voltage of the current/voltage converter is changed in accordance with the change of the impedance of the photodetecting element 2. The difference voltage between the output voltage of the current/voltage converter and the reference voltage VS is amplified and outputted by a differential amplifier circuit consisting of an operational amplifier 14 and resistors 21, 22. Consequently, only an AC component corresponding to the change in the impedance of the element 2 is outputted to an output terminal as a signal.
|
