| 摘要 |
PURPOSE:To provide a photo-detection circuit, wherein a constant voltage corresponding to the level of dark voltage generated in a photo-electric converter when the same does not receive any light is inputted to the input terminal of a differential amplifier to exclude external noise thereby to ensure a high quality of the photo-detection output signal. CONSTITUTION:A differential amplifier A includes the following parts: first and second voltage generating circuits 1 and 2 which function as a pair of level shift circuits of basically matching characteritics; first and second high-gain phase inversion amplifier circuits 11 and 12 adapted to receive the level shift outputs from corresponding voltage generating circuits; a negative feedback connection leading from the first phase inversion amplifier circuit 11 to the first voltage generating circuit 1; and an auxiliary negative feedback circuit 22 leading from the first phase inversion amplifier circuit 11 to the second voltage generating circuit 2. The amplification factor of the differential amplifier circuit can be changed freely by changing the amplification factors of the first and the second voltage generating circuits and, hence, to easily and stably obtain a small amplification factor of the differential amplifier circuit. It is also possible to attain a high-speed operation by using, as the voltage generating circuit of the push-pull type phase inversion amplifier, a voltage generating circuit having the same characteristic as that of the first and second voltage generating circuits 1 and 2. |
