# Inverting Operational amplifier

#### Amith2006

1. Homework Statement
1) Consider an inverting operational amplifier as shown in figure. Suppose R1= 1000 ohm & Rf = 10^6 ohm. It is said that the input impedance=R1=1000 ohm and the Output impedance= 0.

2) Consider a non inverting operational amplifier as shown in figure. Suppose R1= 3500 ohm & Rf = 15000 ohm. It is said that the input impedance=infinite. Why is it so? Here Rf is the feedback resistor.But only for an ideal Op-Amp, the input impedance is infinite and not for a real one, isn’t it? So, can R1 be taken as the input impedance of the Op-Amp in both cases?

2. Homework Equations

3. The Attempt at a Solution

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#### ranger

Gold Member
These are a couple of links that explain the input impedance for both op amps.
http://www.phys.ualberta.ca/~gingrich/phys395/notes/node102.html [Broken]
http://www.phys.ualberta.ca/~gingrich/phys395/notes/node103.html [Broken]

For a real non inverting op amp, the input impedance is somewhere between 1 MΩ to 10 TΩ.

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