| 摘要 |
PURPOSE:To eliminate the need for offset adjustment by removing the effect of the input offset voltage of MOSFETs upon their outputs by using an operational amplifier of single input type. CONSTITUTION:When arbitrary light falls onto a photo diode SPD2, the photoelectric current IL corresponding to the quantity of light flows through MOSFET4 SPD2 NPN transistor 11. The collector potential of the NPN transistor 11 is automatically set at the potential voltage VA determined by the threshold voltage Vth of the MOSFET3 and source voltage Vcc. The cathode side of the SPD2 is equal to VA since the gate and drain of the MOSFET4 are connected and the photocurrent IL is flowing. In this way, the potentials of the anode and cathode of the SPD2 are made nearly equal by the Vth of the MOSFET3, 4 and the photocurrent in this state becomes the collector current of the NPN transistor 11. Hence, the input offset voltage of the MOSFETs is not included in the voltage VO of the output terminal 14 and therefore the need for offset adjustment may be eliminated. |
