Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
What operational amplifier? You mean inverting and noninverting inputs.
Current feedback operational amplifiers has genericaly different input impedances(as you are questioning) as oposed to voltage feedback operational amplifiers which has equal input impedances.
In the non-inverting amp configuration the input goes directly to the op amp (+) input which is normally very high impedance.
In the inverting amp configuration the input goes through the input resistor to the virtual ground point at the (-) input so the input impedance is equal the the input resistor value. That is almost always less than the (+) op amp input impedance.