| 摘要 |
PURPOSE:To obtain sample hold in accurately response to amount of photo detection, by connecting an auxiliary FET to a switching FET for sample hold and correcting the effect of the capacitance of the FET. CONSTITUTION:A switching FET18-1 for sample turns on with a sample hold signal via an inverter 33-1 of a sample hold circuit 11-1, and a voltage at point X corresponding to the amount of photo detection via a capacitor 13-1 and a photodetector 12-1 is sampled and stored in a capacitor 19-1. An auxiliary FET 31-1 which is the same characteristics as those of the FET18-1 and in which the source and the drain are shortened is connected in series between the FET18-1 and the capacitor 19-1, and a signal opposite to a sample hold signal applied to the gate of the FET18-1 is applied to the gate of the FET31-1. Thus, the storage charge due to capacitors between the gate and source and the gate and drain of both the FETs18-1 and 31-1 is cancelled with each other, allowing to avoid the generation of noise and obtain sample hold a voltage in accurately response to the amount of photo detection. |
