Q. Input bias current of operational amplifier?

When operated at extremely low quiescent current values, the base bias currents will be low; but they do have to be taken into consideration. The input bias current IB for an op amp is defined as the average of the two input currents with the inputs grounded, i.e.,

A typical value for a µA 741 is 80 nA; for a µA 771 it is 50 pA.When the resistance of the source feeding the op amp is large enough, the input bias current may have an adverse effect. As shown in Figure, where the noninverting input is grounded and the inverting input is connected to a source of 1-M resistance and of voltage vS momentarily at 0 V, the bias current of 80 nA generates a voltage of -80 mV on the noninverting input.