| 摘要 |
PURPOSE:To detect the magnitude of a signal with good accuracy, by holding the first signal of the first current mirror circuit when an input signal is a peak value as the second signal of the second current mirror circuit and setting the second signal to a reference value to discriminate the magnitude of the input signal on the basis of the difference between both signals. CONSTITUTION:The movement of the slit member 24 between a light emitting diode 1 being a light projecting element and a phototransistor 7 being a light receiving element is optically detected and the output current based on said movement is detected. When the member 24 is not inserted and the slit thereof is positioned between both elements, a peak current flows and a capacitor 20 is charged up to a constant voltage. This peak current flows through the first current mirror circuit constituted of transistors 3-6 and, when the capacitor 20 reaches the constant voltage, the current equal to that from the transistor 6 flows through the transistor 13 of the second current mirror circuit to become an equilibrium state. Further, a comparator 11 comparing the signals of both circuits is provided and the magnitude of the input signal is discriminated on the basis of the difference between both signals.
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