JPH0626288B

PURPOSE:To obtain a sufficient output voltage even when a supply voltage is low concerning a operational amplifier for which the output is variable from positive to negative. CONSTITUTION:In transistors TR7 and 8, when an output voltage VOUT of an operational amplifier is lower than the ground voltage, assuming a forward direction voltage drop between the base emitters of a TR7 is VBE, the current, which becomes I1=(VOUT+VBE)/R1, flows at the collector of the TR7. Here, an R1 is a first resistance value. A first current mirror outputs a current I1' to mirror a current I1 for a positive power source and a second current mirror mirrors an I1' for a negative power source. The second mirror is an amplification factor alpha(alpha>1) and an output current is alphaI1''. For the output terminal of the second current mirror, the output voltage of the operational amplifier is pulled up to the action limit of the second current mirror and can be outputted up to the vicinity of a negative voltage VSS. In the same way, when the output voltage of the operational amplifier is higher than the ground voltage, the current flows at the second TR and this is outputted up to near a voltage VDD.