OPERATIONAL AMPLIFIER

An operational amplifier 1 comprises transistors Q and Q forming an input stage, and input resistors R and R which form a filter together with parasitic capacitors C and C accompanying the transistors Q and Q Resistance values R of the resistors R and R may be set to R=1/(2π·fc·C), where C is the capacitance value of each of the parasitic capacitors C and C and fc is the target cutoff frequency of the filter. The operational amplifier may also include a power supply resistor R which forms a filter together with a parasitic capacitor C accompanying a power supply line.