OPERATIONAL AMPLIFIER, ANALOG ARITHMETIC CIRCUIT AND ANALOG-DIGITAL CONVERTER

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