Double-Type Photocoupler Negative Feedback Circuit for Very Low Level DC Current Amplifier

To obtain fast response in a very low level dc current amplifier, the amplifier using a single-type photocoupler negative feedback circuit has been developed; however, it has an offset drift problem because of the electrical property of the photocoupler. In this study, we proposed a very low level dc current amplifier using a double-type photocoupler negative feedback circuit that has two functional parts, that is, a negative feedback part and an offset controller. The experimental results show that the response speed of this amplifier is as high as that of the amplifier using the single-type circuit, and that the offset voltage drift of the amplifier using the double-type circuit is markedly improved.