The operational amplifier circuit of the present invention comprises: a first differential input section having a first differential input pair for receiving a differential input signal and a differential output pair including first and second differential outputs; A second differential input pair coupled to the first differential output pair of the input section, a first cascode current source coupled to a first output of the operational amplifier circuit, and a second cascode current source coupled to a second output of the operational amplifier circuit, A cascode current source having a current source; A cascode current mirror portion having a first mirror current source coupled to the first output of the op-amp circuit and a second mirror current source coupled to the second output of the op-amp circuit; And a second cascode current source for receiving the voltages of the first and second outputs of the operational amplifier circuit such that when the DC bias levels of the first and second outputs are higher or lower than a desired level, And a bias adjusting unit for generating a control signal for adjusting the amount of current flowing through the plurality of transistors.
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