Hi , I've been trying to solve this question. I know , the gain till the M5's gate is gmn(ron//rop) but I could not accomplish the last part.
Could you help please ?

solution:

 

I remember this problem from my feedback circuits course. Not simple at all.

 

I remember this problem from my feedback circuits course. Not simple at all.

I could not find explaination for M5 part i guess it was called front amplifier or smt

 

yo , can anyone help ?

 

i solved it okkey

 

Calculating the gain of a feedback system is seldom simple. That was a "300 level" class back in the technical institute. And I never had to do it in the real world.

 

See

 

I think, it is not too complicated....

Finding the loop gain Aol of a circuit with feeedback is a straightforward matter: It is the product of the the forward (main) amplifier open-loop gain Ao and the feedback factor k.

1.) The gain Ao of the shown diff. amplifier is product of the transconductance gm1=gm2 and the relevant drain resistance which is the parallel combination ro2||ro4 (to be varified in the circuit diagram). The input impedance of M5 is assumed to be infinite.
Hence, we have Ao=gm1*(ro2||ro4)

2.) The feedback circuit consists of the common drain stage M5 with the gain (identical to the feedback factor k)
k= gm5*ro5/(1+gm5*Ro5)
This expression results from the classical gain formula for a common drain stage with (a) an ideal current source between source and ground and (b) a finite transistor drain-to-source resistance ro5.

3.) Therefore: Aol=Ao*k=[gm1*(ro2||ro4)]*[gm5*ro5/(1+gm5*ro5)]

4.) The closed-loop gain (related to the node between M2 and M4) is
V2/Vin=Ao/(1+Aol).
Therefore, the closed-loop gain related to the source node of M5 is
Acl=Vout/Vin=[Ao/(1+Aol)]*[k]

Comment: If, from the beginning, the stage M5 is considered as part of the forward path (part of the gain Ao), the feedback factor is, of course, k=1.

 

And what's the point of a math exercise? To get a fundamental formula that will be used all over the world. My opinion is that while there are no numerical results at the end of the conversion, it is a waste of time. Where is the numerical result? And where are the initial data: output conductivity and steepness, currents of current sources. The first pair of parameters depend on the operating current. And it all looks like child's play. After all, there are a lot of simulators of electronic circuits!
I did similar calculations 40 years ago. When I didn't have a computer and the Spice program.

 

And what's the point of a math exercise? To get a fundamental formula that will be used all over the world. My opinion is that while there are no numerical results at the end of the conversion, it is a waste of time. Where is the numerical result? And where are the initial data: output conductivity and steepness, currents of current sources. The first pair of parameters depend on the operating current. And it all looks like child's play. After all, there are a lot of simulators of electronic circuits!
I did similar calculations 40 years ago. When I didn't have a computer and the Spice program.

For my midterms , i must be able to get over this kind of problems

 

[MODERATION]

After more then 300 posts you should already be aware that ALL COURSEWORK RELATED POSTS MUST BE MADE TO THE HOMEWORK HELP FORUM.

This is because members are constrained by AAC rules to providing guidance based on the student’s efforts not direct solutions. When posts are made outside the Homework Help forum members may not detect their nature and inadvertently violate this rule.

As a courtesy, and giving you the benefit of the doubt, you thread was moved rather than deleted. Please take care in the future to follow this rule.

 

[MODERATION]

After more then 300 posts you should already be aware that ALL COURSEWORK RELATED POSTS MUST BE MADE TO THE HOMEWORK HELP FORUM.

This is because members are constrained by AAC rules to providing guidance based on the student’s efforts not direct solutions. When posts are made outside the Homework Help forum members may not detect their nature and inadvertently violate this rule.

As a courtesy, and giving you the benefit of the doubt, you thread was moved rather than deleted. Please take care in the future to follow this rule.

Sir , in summer i was designing opamp here. This is not homework or smt I want to learn it...

 

Sir , in summer i was designing opamp here. This is not homework or smt I want to learn it...

It is difficult to distinguish this from homework because what you started the post with is clearly a homework problem, and you are a student. Because we are very sensitive about students using AAC resources for cheating, it is difficult to simply take your word for this.

However, I am going to move this thread back based on your response. If in the future it becomes clear that you are using AAC instead of help provided by your institution, you will face a ban.

I apologize for the inconvenience if your post is, in fact, self-directed study. For now, I will accept your word on this and my apology stands. Please excuse the apparent harshness of my response and my congratulations on making the effort to extend your knowledge independently.

 

And what's the point of a math exercise? .......... it is a waste of time. ......And it all looks like child's play.

Nevertheless, from the OP`s comments I have got the impression that the OP could be helped somewhat.

 

A theoretical circuit is not what I would call "a system". Not even close.