# Electronics Determining Op Amp Gain.

• OmniNewton
In summary, the conversation discusses determining the Op amp gain of a given circuit. The homework equations and attempt at a solution are provided, but it is noted that the answer obtained is off by a factor of 4. There is a discussion about the circuit not making sense and if there may be any errors. It is suggested to approach the problem assuming the op-amp is not ideal and re-evaluate the solution. It is ultimately determined that the correct answer is A = 4004, but the previous editions of the textbook show the answer as 1001, indicating a possible error in the book.
OmniNewton

## Homework Statement

Determine the Op amp gain of the following circuit.

V1 = 1v Vo = 4 V

A = Vo/ VI

## The Attempt at a Solution

Using voltage division I determined the voltage for the node at the +ve terminal

VI = V1(1k/ ([1000 + 1]k)) = 1/1001 V
Vo = 4v Given

Therefore A = Vo/VI = 4/(1/1001) = 4(1001)

However the answer is A = 4/(4/1001) = 1001

So somehow I'm off by a factor of 4. I am really unsure why VI is 4/1001.

Thank you so much for your time.

The circuit does not make sense to me. Are you sure you don't have a feedback resistor somewhere? Also, are you sure the "-" terminal is connected to ground? Perhaps someone else can figure it out, but to me, it looks like it is missing something.

OmniNewton
The circuit does not make sense to me. Are you sure you don't have a feedback resistor somewhere? Also, are you sure the "-" terminal is connected to ground? Perhaps someone else can figure it out, but to me, it looks like it is missing something.

I strongly felt the same way as well Charles. But this is a problem directly from my textbook and it has not been modified for the last 3 editions so I'm assuming it is correct. Thank you so much for the response though.

EDIT: It is definitely very strange compared to the Operational amplifier problems I am used too. I am seeking enlightenment

The circuit is okay, it's just that the op-amp depicted is not an ideal op-amp. Perhaps it would be better to think of it in terms of some general amplification stage with a finite gain. The idea is to find that gain given the "measured" input and output voltages.

OmniNewton
OmniNewton said:
I strongly felt the same way as well Charles. But this is a problem directly from my textbook and it has not been modified for the last 3 editions so I'm assuming it is correct. Thank you so much for the response though.

EDIT: It is definitely very strange compared to the Operational amplifier problems I am used too. I am seeking enlightenment
Taking the circuit as is, for a small positive input voltage, the output voltage would be pinned at +12 Volts or whatever bias you use for it. For a small negaive input voltage, the output would pin itself at -12 volts.

OmniNewton
Charles thanks for taking to the time to help out as well. I think gneill has the right idea of how to approach this problem so if we are to approach the problem assuming it is not an ideal OP amp what would I have to change in my solution?

From what is given it appears to me that your result of A = 4004 is correct. Is the question complete as shown or were there other "characteristics" of this amplifier, such as input impedance?

gneill said:
From what is given it appears to me that your result of A = 4004 is correct. Is the question complete as shown or were there other "characteristics" of this amplifier, such as input impedance?

Yes you are absolutely right my A will be 4004 but the correct answer is indicated to be 1001 in all previous editions. the circuit provided is all information. The only additional information says Vo = 4 V and v1 = 1.0 V

There is nothing provided in the given circuit to account for a factor of 4 other than the gain itself, so I'm thinking that there's an error in the book.

OmniNewton said:
Charles thanks for taking to the time to help out as well. I think gneill has the right idea of how to approach this problem so if we are to approach the problem assuming it is not an ideal OP amp what would I have to change in my solution?
I had difficulty reading the line in your OP where you have ## V1=+1.0 ## Volts and ## V_{out}=+4.0 ## Volts. I am glad that @gneill was able to help get the correct solution.

## 1. How does an op amp determine gain?

An op amp determines gain through its internal circuitry, which includes a differential amplifier, feedback resistors, and power supplies. The differential amplifier amplifies the voltage difference between its two inputs, and the feedback resistors control the amount of output voltage that is fed back to the input, resulting in the desired gain.

## 2. How is op amp gain calculated?

Op amp gain is calculated by dividing the output voltage by the input voltage. This can be represented by the equation: Gain = Vout / Vin. The gain can also be determined by the values of the feedback resistors, as the ratio between the feedback and input resistors determines the overall gain of the op amp.

## 3. What are the different types of op amp gain configurations?

The most commonly used op amp gain configurations are the inverting, non-inverting, and differential configurations. In the inverting configuration, the input is connected to the inverting terminal of the op amp and the output is fed back to the inverting input through a feedback resistor, resulting in a negative gain. In the non-inverting configuration, the input is connected to the non-inverting terminal and the output is fed back to the input through a feedback resistor, resulting in a positive gain. In the differential configuration, the op amp has two inputs and two outputs, and the gain is determined by the ratio between the feedback and input resistors.

## 4. What factors affect op amp gain?

Several factors can affect op amp gain, including the input and output voltage ranges, the power supply voltage, and the feedback resistance values. Additionally, the frequency of the input signal and the characteristics of the op amp itself, such as its bandwidth and slew rate, can also impact the gain.

## 5. How can op amp gain be adjusted?

Op amp gain can be adjusted by changing the values of the feedback resistors, which can be done by using potentiometers or variable resistors. Additionally, the gain can be adjusted by changing the power supply voltage or by using external circuitry, such as a voltage divider, to adjust the input voltage. Some op amps also have built-in gain adjustment features.

Replies
13
Views
2K
Replies
3
Views
1K
Replies
34
Views
2K
Replies
5
Views
4K
Replies
9
Views
2K
Replies
2
Views
2K
Replies
1
Views
1K
Replies
18
Views
3K
Replies
11
Views
3K
Replies
13
Views
2K