Inverting Operational amplifier

[Amith2006]

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?

Homework Equations

The Attempt at a Solution

 

[ranger]

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
http://www.phys.uAlberta.ca/~gingrich/phys395/notes/node103.html

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

 

[piercas]

Firstly, it is important to note that the term "inverting" refers to the fact that the output signal of the operational amplifier is an inverted version of the input signal. This is due to the negative feedback loop created by the resistor Rf.

Regarding the input and output impedances, it is true that for an ideal operational amplifier, the input impedance is infinite and the output impedance is zero. This is because an ideal operational amplifier has infinite gain and no internal resistance, allowing it to amplify the input signal without affecting the input impedance.

However, in real-world operational amplifiers, there will be some non-idealities such as finite gain and input impedance. In the first scenario, where R1=1000 ohm and Rf=10^6 ohm, the input impedance of the operational amplifier can be approximated as R1, which is 1000 ohm. This is because the large value of Rf will essentially "short out" the input impedance of the operational amplifier.

In the second scenario, where R1=3500 ohm and Rf=15000 ohm, the input impedance can be approximated as infinite. This is because the non-inverting configuration creates a virtual ground at the input of the operational amplifier, causing the input current to be nearly zero. As a result, there is no voltage drop across R1, making the input impedance effectively infinite.

In conclusion, the input and output impedances of an operational amplifier can vary depending on the circuit configuration and the values of the resistors used. For an ideal operational amplifier, the input impedance is infinite and the output impedance is zero, but for real-world operational amplifiers, these values may differ.