is no input signal inputted on the other hand when a differential signal is inputted into the operational amplifier 300 the voltage difference v ab can be controlled to be a smaller value through appropriately assigning the sum of the currents outputted from the input stage 310 to the biasing circuit 320 such that the operational amplifier 300 can have a better linearity of the amplified signal and the input signal when the operational amplifier 300 performs an amplifying operation in other words when the input differential voltage is 0 because the sum of the currents i pp and i pn outputted from the class ab input stage 310 to the biasing circuit is a known value if the gate voltages v bn and v bp of the transistors m 19 and m 20 or the current ibp and ibn are well designed an optimized static current iq can be obtained on the other hand when a differential signal is inputted into the operational amplifier 300 because the sum of the currents i pp and i pn outputted from the class ab input stage 310 to the biasing circuit change if the parameters of the class ab input stage 310 is well designed to make the voltage difference v ab smaller such that the entire circuit 300 can have an optimized linearity please refer to fig5 fig5 is a diagram showing the characteristic curves of the present invention output stage circuit 330 and the prior art output stage circuit 130 please note that in.