| 摘要 |
PURPOSE: A projection type video display device having a photo transistor sensor is provided to make raster edge measurements easy by detecting light emission from a first edge of a measured image moving in a first direction and light emission from a second edge of a measured image moving in a second direction and combining the motions of the first and second edges in the detected state. CONSTITUTION: Most of a reference current is given to a sensor detector(275) as a current(Isw). The current(Isw) biases the detector(275) in a state that an output state is low, that is, in a selecting state to represent no light reception or a sensor not lighted. When a phototransistor(TR) is irradiated, electric charges produced by light make the photo(TR) conductive to introduce its current from the reference current. Since a constant current source(250) generates the reference current, the sensor current is deviated from the current(Isw) of the sensor detector(275). The photo(TR) deviates a sufficient current from the sensor detector(275) at a prescribed lighting level to turn off the sensor detector(275).
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