| 摘要 |
PROBLEM TO BE SOLVED: To provide an operational amplifier, an analog arithmetic circuit and an analog-digital converter that have a compact output stage.SOLUTION: The operational amplifier of a folded cascode type includes: a constant current source for outputting a constant current; a differential input stage connected to the constant current source to output part of the output current of the constant current source as a differential current in accordance with a difference between voltages input into an inverting input terminal and a non-inverting input terminal; and the output stage connected in parallel with the differential input stage with respect to the constant current source to output as an output stage current a current remaining after subtracting the differential current from the output current of the constant current source. The output stage satisfies Ka=Iout/Idiff<1 and |&Dgr;V/2 Vod|<1, where &Dgr;V is the input voltage difference of the differential input stage, Idiff is the differential current, Iout is the output stage current and Vod is an overdrive voltage of input transistors of the differential input stage. |
