# Differential Amplifier using pspice

Discussion in 'Homework Help' started by Wend, Dec 29, 2011.

1. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
hi there

I have a circuit in Microelectronic Circuits book

I need to do simulation on it

the page is below

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2. ### jegues Well-Known Member

Sep 13, 2010
735
43
Okay...

So what's the problem that your having?

This question provides insight on the various configurations one can achieve using an op amp.

3. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
the quistion and the solution in the attach

I want pspice simulation for the circuit in the attach

4. ### jegues Well-Known Member

Sep 13, 2010
735
43
So preform the simulation yourself.

We are not here to do your homework for you.

If you post some work or attempts at either doing the question on paper or simulating it, then we can further assist you.

5. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
I try to do simulation for it put I neve had a pspice before because I am a computer engineering not electrical and this subject called electronics it's new for me
and I have the solution of this circuit

6. ### crutschow Expert

Mar 14, 2008
13,511
3,385
So show us the pspice circuit schematic and results of your simulation.

7. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
thats what I did in attach

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8. ### jegues Well-Known Member

Sep 13, 2010
735
43
You don't have any connections at the other ends of R3 and R4.

Hook them up to something. (Whether it be a source, another node, or ground)

EDIT: Also, it doesn't look like that is the op amp you want. You only have one connection, where are the connections for the inverting and non-inverting terminals? There should be 2 connections for the threshold voltages as well. (usually)

You want to use the INA105 as mentioned in the question.

9. ### crutschow Expert

Mar 14, 2008
13,511
3,385
The 1NA105 already has the resistors internally so you wouldn't want to use it in the circuit shown.

There also needs to be power connections (unless it's an ideal 3-terminal op amp model that doesn't require power).

What is a 74126? That appears to be a digital gate part number.

10. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
guys I am a computer engineering and I can not deal with electrical E.
and this subject does not important to me
so plz any one can solve this

11. ### jegues Well-Known Member

Sep 13, 2010
735
43
If you don't care about this why should anyone even bother helping you? You don't care, so why should I?

This is pathetic, we are NOT going to do your homework for you.

Posts like this should be bannable offenses on these forums, as they are against everything that these forums are about.

12. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
I mean that my major does not care about elctronics, but I have to pass the course
and I said that to let you knew I can not do the pspice simulation

13. ### crutschow Expert

Mar 14, 2008
13,511
3,385
You apparently haven't tried any of the changes we have mentioned or answered my question. Therefore I see no reason to help you any further.

14. ### jegues Well-Known Member

Sep 13, 2010
735
43
You are a COMPUTER ENGINEERING STUDENT and you don't think you should care about anything electronics related?

It seems as though you are on the path to becoming quite a lousy engineer...

I find your "just pass the course" mentality to be embarrassing and disgraceful towards other engineers/engineering students such as myself.

If all you care about is passing the course I sincerely pity your career choice as becoming an engineer.

Last edited: Dec 29, 2011
15. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
I'm good in programing and Computer Architecture and I love my major
and I never had electrical course before it's the only course in electronics

16. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
We don't need to launch blames here. Things are simple:

AAC's Homework Help (and AAC in general) place learning above answers.
We strongly believe that for a member to be entitled to a solution, he must have shown some effort on his own.
If he doesn't, the thread stalls, after he gets some suggestions, and we part ways.

Don't get upset about differences in viewpoints.

17. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
Georacer first of all I respect you .

and I did nothing here I told them the truth I'm not good in electrical as well
just like them in CE

18. ### linda-ethel New Member

Dec 30, 2011
2
0

Single-stage transistor amplifier
Figure 3: FET feedback amplifier

Consider the simple FET feedback amplifier in Figure 3. The aim is to find the low-frequency, open-circuit, transresistance gain of this circuit G = vout / i in using the asymptotic gain model.
Figure 4: Small-signal circuit for transresistance amplifier; the feedback resistor Rf is placed below the amplifier to resemble the standard topology
Figure 5: Small-signal circuit with return path broken and test voltage driving amplifier at the break

The small-signal equivalent circuit is shown in Figure 4, where the transistor is replaced by its hybrid-pi model.
 Return ratio

It is most straightforward to begin by finding the return ratio T, because G0 and G∞ are defined as limiting forms of the gain as T tends to either zero or infinity. To take these limits, it is necessary to know what parameters T depends upon. There is only one dependent source in this circuit, so as a starting point the return ratio related to this source is determined as outlined in the article on return ratio.

The return ratio is found using Figure 5. In Figure 5, the input current source is set to zero, By cutting the dependent source out of the output side of the circuit, and short-circuiting its terminals, the output side of the circuit is isolated from the input and the feedback loop is broken. A test current it replaces the dependent source. Then the return current generated in the dependent source by the test current is found. The return ratio is then T = −ir / it. Using this method, and noticing that RD is in parallel with rO, T is determined as:

T = g_m \left( R_D\ ||r_O \right) \approx g_m R_D \ ,

where the approximation is accurate in the common case where rO >> RD. With this relationship it is clear that the limits T → 0, or ∞ are realized if we let transconductance gm

Last edited by a moderator: Jan 2, 2012
19. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
@linda-ethel

Which figures are you referring to?

20. ### Wend Thread Starter New Member

Dec 29, 2011
10
0
gentlemen please I need this project so help me out