# New impedance after feedback

• tanaygupta2000
In summary, the conversation discusses the effect of feedback on voltage gain and impedance in a circuit. The formula for voltage gain is mentioned and it is stated that the input and output impedances change when feedback is applied. The question of how to measure input and output impedance is also raised. The conversation also mentions the importance of drawing a schematic of the circuit and suggests looking for answers in relevant textbooks.

#### tanaygupta2000

Homework Statement
An amplifier has a voltage gain Av = 1000 , input impedance 1 kΩ and output impedance 500Ω A
fraction βv = 0.1 of the output voltage is fed back in the series in opposition to the input voltage. The
input and output impedance after the feedback are given respectively by the approximate values ?
Relevant Equations
A' = A/(1-βA)
I know that when the feedback is connected, the voltage gain changes by the above formula. But I don't know how to find final values of input and output impedances.

How do input and output impedance change when you apply feedback? Have you studied that point?

How would you measure the input impedance (i.e. what information about this circuit do you need to calculate this)? How would you measure the output impedance?
Have you drawn a schematic of this circuit yet?

berkeman
You have mentioned a formula for the gain A´ with feedback ...when you insert the mentioned value βv = 0.1 , will the gain be larger or smaller than A (without feedback)? What do you expect ?

(By the way: An answer to your question can be found in each relevant textbook...did you already spend some time for searchnig?)

## 1. What is "New Impedance after Feedback"?

"New Impedance after Feedback" refers to the change in electrical impedance that occurs in a circuit after a feedback loop is added. Impedance is a measure of the opposition to an electric current, and feedback is a technique used to modify the behavior of a circuit. Therefore, "New Impedance after Feedback" is the resulting impedance value after the feedback loop has been applied.

## 2. How does feedback affect impedance?

Feedback can either increase or decrease the impedance of a circuit, depending on the type of feedback used. Negative feedback, where the output signal is inverted and fed back into the input, tends to decrease impedance. Positive feedback, where the output signal is in phase with the input, tends to increase impedance.

## 3. Why is "New Impedance after Feedback" important?

"New Impedance after Feedback" is important because it allows us to predict and control the behavior of a circuit. By understanding how feedback affects impedance, we can design circuits with specific characteristics and ensure stable operation.

## 4. What are some common applications of "New Impedance after Feedback"?

One common application of "New Impedance after Feedback" is in audio amplifiers. By using negative feedback, the impedance of the amplifier can be reduced, resulting in improved linearity and reduced distortion. Feedback is also commonly used in control systems, such as in electronic amplifiers, to regulate the output and improve stability.

## 5. How is "New Impedance after Feedback" calculated?

The calculation of "New Impedance after Feedback" can be complex and depends on the specific circuit and type of feedback used. In general, it involves analyzing the circuit using circuit analysis techniques, such as Kirchhoff's laws and Ohm's law, and incorporating the effects of the feedback loop. Computer simulations and specialized software can also be used to calculate "New Impedance after Feedback" for more complex circuits.