| 摘要 |
PURPOSE:To reduce the offset voltage at SEPP amplifier, by controlling the current in the current source circuit in which the current changes with the offset voltage, by means of the output of the operational amplifying circuit. CONSTITUTION:The signal from the input terminal IN is output via the SEPP amplifying circuit consisting of FETQ1, transistors TRQ2 and TRQ3, Q4. TRQ5, Q6 and Q7, Q8 respectively form the current Miller and also form the constant current circuit, and TRQ5, Q7 are in cascode connection between the power supplies of negative and positive polarities. Since the output terminal OUT is connected to the noninverting terminal of the operational amplifier OP, the offset voltage is compared with the ground potential and fed to the connecting point A after amplification. Accordingly, when the offset voltage is shifted, the current source circuit is controlled with the output of the amplifier OP and the offset voltage is kept around the ground potential. Thus, even if a FET is used at the first stage, the offset voltage can be kept around the ground potential. |
