| 摘要 |
PURPOSE:To enhance the offset of an amplifier, by removing the signal current of background light by utilizing the saturation characteristics of MOSFET and amplifying said current to take out the same. CONSTITUTION:Transistors Q3a, Q3b amplifying a signal current, MOSFETQ2a, Q2b removing background light and depression type MOSFETQ1 for supplying a constant current are formed on the substrate of a semiconductor position detector PSD having a strip like photodiode receiving incident light formed thereto. At first, a background light level is stored in the electric field effect type transistors of the memory condensers 20a, 20b respectively preliminarily connected to the gates of FETQ2a, Q2b. Next, when a light emitting diode is allowed to emit light, the signal current superposed to a background photocurrent is extracted by utilizing saturation characteristics of this circuit by FETQ2 a, Q2b and amplified by amplifiers Q3a, Q3b and taken out to be sent out to the next stage. The amplifies photocurrent receives logarithmic conversion by a logarithmic converters 21a, 21b to be converted to the signal of an incident position by a converter 25. |
