Question

why do op-amps have high input impedance can anyone explain clearly?

Answer 1

OpAmps have a differential amplifier input and because of high gain can only be used in negative feedback configuration. Because of the high gain the differential input can't be more than about a microvolt which represents high input impedance. Analysis generally use what's called a virtual ground of the - input equal to the + input.

Answer 2

opamps have high input impedence in order to ensure that all the signal gets into the amplifier without a drop ideally it is assumed infinity(based upon the configuration of opamp)

Answer 3

Op amps are designed with high input impedance so that they do not load the input network, the feedback network, or the preceeding stage. In an ideal world, the op amp input impedance would be infinitely high. Whatever stage preceeds the op amp will have a non-zero impedance. And the input network of the stage in question and its feedback network have non-zero impedance. Therefore, whatever input impedance the op amp exhibits will "load" the preceeding stage and the input and feedback networks. If the preceeding stage were to have zero output impedance and the stage in question were to have infinitely high impedance, each stage could be designed completely on its own - without regard to adjacent stages. In the real world, this cannot be absolutely achieved. However, op amps allow us to get close to that ideal by offering us very high input impedance and very low output impedance.

Answer 4

I just re-read my previous post and it didn't seem very clear to me. So please allow me to try again.

A perfect amplifier has infinitely high input impedance so the amplifier will not have any effect on the signal it is supposed to amplify.

A perfect amplifier also has a zero output impedance so that whatever it is connected to will not have any effect on the signal coming out of the amplifier.

Op amps are as close as we can get to a perfect amplifier.