When does the really high input resistance of the OpAmp go away? ..... I remember the 3 OpAmp Instrumentation amplifier.... and I believe I recall the final stage OpAmp being a differential OpAmp, and that it had a low input impedance, so there's the other 2 OpAmps as buffers feeding into the differential OpAmp....
is that right?
so, I was wondering... for example in a regular inverting amplifier with the gain of -Rf/Ri...... and the non-inverting input grounded..... is my input resistance of the op-amp still that really high input resistance... the Meg or Gig Ohm range that's associated with OpAmps? or have the resistors brought it down?
thanks!