| 摘要 |
PURPOSE:To stabilize the capacity of each detecting element and reduce the cost by controlling a light emitting diode with a control signal form the external and irradiating the light from the light emitting diode to the detecting element for a certain time with a bias applied. CONSTITUTION:A light emitting diode LED 7 is driven by an LED control circuit 10 controlled by the pulse signal form a pulse generator 9. The pulse generator 9 emits light for a certain time periodically. The pulse generator 9 emits light for a certain time periodically. The pulse generator 9 sends signal corresponding to this pulse signal to a position operating circuit 8 to control it so that the processing function of position operation or the like is stopped temporarily while the 1ED 7 emits light. Thus, the leak current in a substrate 1 is prevented form increasing the circuit noise to have an influence upon the capacity of the detecting element. The light is irradiated from the LED 7 while applying a high voltage bias. Since the light is irradiated from the LED 7 to the substrate 1 with the bias applied, the polarizing effect is held relatively to reduce the quantity of irradiated light.
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