Solving OP AMP Structure Problems: Inverting & Non-Inverting Inputs

In summary, the conversation discusses the problem of determining which inputs of a differential stage in an op amp are inverting and non-inverting. The person has tried to find the answer through online research and books, but has not found a clear explanation. The conversation then goes on to explain how to determine which input is which, using a specific circuit as an example. Increasing the voltage at the inverting input will cause the output to drop, while increasing the voltage at the non-inverting input will cause the output to rise. This allows for the determination of which input is inverting and non-inverting.
  • #1
Drao92
72
0
Hello everyone. I am studying internal structure of op amp and i don't know to solve some problems.
The problem is that i have to specify and justify which inputs of the differential stage are inverting and non-inverting input and i don't know how to do it. I tried to find the answer on google and on many many books but i didnt find anything to give me a clearly answer. Only thing i found is that we use the maximum and minimum value of common mode voltage but i didnt understand how.
I`ll also post some circuits if anybody can help me.
https://www.physicsforums.com/attachment.php?attachmentid=66211&stc=1&d=1391287797
https://www.physicsforums.com/attachment.php?attachmentid=66212&stc=1&d=1391287797
 

Attachments

  • circuit 1.jpg
    circuit 1.jpg
    23.5 KB · Views: 583
  • Circuit 2.png
    Circuit 2.png
    16 KB · Views: 629
Physics news on Phys.org
  • #2
First I must ask you a question, do understand how BJT work and also how the basic BJT amplifier configuration work?
Also can you tell me how the output voltage will behavior if you increase voltage at inverting input?
 
  • #3
You can quite easy determine which input do what.
Let as exam this circuit.

https://www.physicsforums.com/attachment.php?attachmentid=66212&stc=1&d=1391287797

If we increase the voltage at Vin1 (Q1 base), Q1 will turn-on more, this means that the voltage at Q1 collector will drop. Because Q4 base is connect to Q1 collector. Q4 base voltage will also drop. This of course will open more Q4 transistor. So voltage at Q4 collector and Q7 base will rise.
This voltage rise at Q7 base will turn-on Q7 more. So the voltage at point A and at output will drop.
So form our analysis we can tell that Vin is inverting and Vi2 is non-inverting input.
 
  • #4
Well, i got the idea. So if an increase in one of the input is droping the output it means it is inverting and if it increase the output it means it is non-inverting?
 
  • #5
Drao92 said:
. So if an increase in one of the input is droping the output it means it is inverting and if it increase the output it means it is non-inverting?

attachment.php?attachmentid=46245&stc=1&d=1334484384.png


Yes, exactly as you said.
 
  • #6
Thanks a lot!
 

1. What is an op amp?

An op amp, short for operational amplifier, is an electronic device used to amplify a signal. It consists of several transistors, resistors, and capacitors arranged in a specific configuration to provide high gain and high input impedance.

2. What is the difference between inverting and non-inverting inputs in an op amp?

Inverting inputs are connected to the inverting (-) input terminal of the op amp, while non-inverting inputs are connected to the non-inverting (+) input terminal. Inverting inputs reverse the polarity of the input signal, while non-inverting inputs maintain the same polarity.

3. How do I solve for the output voltage in an inverting op amp circuit?

To solve for the output voltage in an inverting op amp circuit, you can use the formula Vout = -Rf/R1 * Vin, where Rf is the feedback resistor and R1 is the input resistor. This formula assumes an ideal op amp with infinite gain and zero input current.

4. What is the gain of an inverting op amp circuit?

The gain of an inverting op amp circuit is determined by the ratio of the feedback resistor (Rf) to the input resistor (R1). It is expressed as a negative value, as the output voltage is inverted compared to the input voltage.

5. How do I choose the appropriate values for the resistors in an inverting op amp circuit?

The values of the resistors in an inverting op amp circuit can be chosen based on the desired gain and input impedance. A higher gain can be achieved with larger resistor values, while a lower input impedance can be achieved with smaller resistor values. It is important to also consider the specifications of the op amp being used and choose resistor values within its operating range.

Similar threads

Inverting Op-amp signals and Sawtooth waveform generation
    • Engineering and Comp Sci Homework Help
2
Replies
44
Views
3K
Op Amp Vout Calculation for Non-Inverting Configuration
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
Engineering Circuit input impedance with ground in an OP Amp circuit
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
Output Impedance of an Inverting Op Amp
    • Engineering and Comp Sci Homework Help
Replies
10
Views
4K
Opamp Voltages: Finding Output Voltage with Inverting and Non-Inverting Amps
    • Engineering and Comp Sci Homework Help
Replies
2
Views
2K
Finding closed loop gain in ideal op amp
    • Engineering and Comp Sci Homework Help
Replies
5
Views
2K
Solving for Output Voltage of Op Amp
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
How can I analyze this transimpedance amplifier?
    • Engineering and Comp Sci Homework Help
Replies
13
Views
2K
Engineering Op Amp Circuit - Simple non-inverting circuit question
    • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
Engineering Op Amp Simple Circuit Model
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top