This picture is from http://www.ecircuitcenter.com/Circuits/op_ibias/op_ibias.htm I am not very sure if I am getting the right idea of how the IB+ and IB- works, but when i solve it open up one of the IB to solve the problem. for IB+, (IB- is opened) Vout = V-( 1 + R2/R1), ..... V- = IB+R3 Vout = IB+R3( 1 + R2/R1) for IB- (IB+ is opened) IB- = (V- - 0) / R1 + (V- - Vout) / R2 Vout = V-(1+ R2/R1) + IB-....can i consider that when IB+ is opened, V+ = 0 = V- ? if I assume that I am right, i get what the page gives: Vout = -R2(IB-) one more thing, the IB+ is positive input biase current while the IB- is the negative input bias current? And the Iinput offset = difference of IB- and IB+ ->|IB+ - IB-| ? These two input bias current and input offset current are the parameters that always appear in the datasheet right?