# Inverting Operational amplifier

• Amith2006
This is because the input voltage is equal to the output voltage multiplied by the feedback resistor divided by the input resistor. As the input resistor increases, the input impedance also increases. However, for an ideal op amp, the input impedance is infinite because the input voltage is directly proportional to the output voltage, regardless of the input resistor.In summary, the input impedance of an inverting operational amplifier is equal to the value of the input resistor, while the output impedance is 0. For a non inverting operational amplifier, the input impedance is typically between 1 MΩ to 10 TΩ for real op amps, but infinite for ideal op amps. R1 can be taken as the input impedance in both cases, but only for ideal
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?

## The Attempt at a Solution

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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.

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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.

## 1. What is an inverting operational amplifier?

An inverting operational amplifier is a type of electronic circuit component that amplifies an input signal while inverting its polarity. This means that the output signal will be the opposite of the input signal.

## 2. How does an inverting operational amplifier work?

An inverting operational amplifier works by using a negative feedback loop. The input signal is fed into the inverting input terminal of the amplifier, while a portion of the output signal is fed back to the inverting input through a feedback resistor. This causes the output signal to become the opposite of the input signal and amplifies it according to the gain of the amplifier.

## 3. What are some common applications of inverting operational amplifiers?

Inverting operational amplifiers are commonly used in audio amplifiers, signal processing circuits, and voltage regulators. They are also used in instrumentation and control systems, as well as in active filters and oscillators.

## 4. What are the advantages of using an inverting operational amplifier?

One of the main advantages of using an inverting operational amplifier is its high gain and accuracy. It also has a low input impedance and high output impedance, making it suitable for use in a variety of circuits. Additionally, inverting amplifiers have a simple design and can easily be cascaded to increase the overall gain.

## 5. What are some key considerations when using an inverting operational amplifier?

When using an inverting operational amplifier, it is important to consider the input and output voltage ranges, the power supply voltage, and the desired gain. The choice of feedback resistor and the type of amplifier used can also affect the performance of the circuit. Additionally, proper grounding and decoupling techniques should be employed to minimize noise and ensure stability.

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