| 摘要 |
PURPOSE:To detect accurately the quantity of photodetection and to reduce the size of the circuit by providing plural transistors (Tr) for expansion. CONSTITUTION:Plural Trs 11' and 11'' which have a common base, emitter, and collector with a Tr11 are provided. Therefore, the signal of a photocurrent generated by a photodiode PD1 and converted into a voltage through Trs 11, 11', and 11'' connected to an operational amplifier 10 through a diode 12 is charged in a capacitor 12' as a current expanded through the plural Trs 11, 11', and 11''. Therefore, a logarithmic relation is born between the terminal voltage of the capacitor 12' and the quantity of light incident on the PD1, and even when the quantity of light incident on the PD1 is extremely small, the optical integration circuit is combine with a dimming circuit which raises the voltage of a reference voltage source by a specific value every time a dimming level is doubled, thereby reducing an error. |
