op amp design

[audioguru]

-1.2m is meaningless. Maybe it is -1.2mV?

475 m is also meaningless. Maybe it is 475mV?

Why is the amplitude of your signals so low??

Why don't you correct the negative supply? It shows +15V but its text is -15V. The symbol is also upside down.

 

[BrownOut]

i really not sure why my vee got problem.it is connected to -15v.i am really a beginner,maybe i cannot follow your meaning,can you modify the circuit for me?

Try this for vee. You also have "neg" and "pos" inputs backwards. Could fix that by the 1st stage modifications I suggested.

 

[prescott2006]

it does not make any difference after the vee is changed.i wonder why?

 

[BrownOut]

Re-read my last post. I made some edits.

 

[prescott2006]

i really cannot follow your instruction.maybe a picture is better than thousand word.

 

[BrownOut]

Why are you doing this? You need to know something about the thing you are designing.


It seems to be working now. I'm not sure what I did.

PS: Transient analysis show alot of clipping.

 

[prescott2006]

why my waveform not same as yours?i running ac analysis.

 

[BrownOut]

I changed one of your output transistors to a generic PNP, because my LTSpice didn't have a model for yours. That's the only change besides correcting vee. Try running my .asc file. It that doesn't work, then I just don't know.

BTW, your differential stage was OK. I am just used to seeing it drawn differently.

 

[prescott2006]

ya,the problem is the pnp.after change it i gt the same waveform like your.by the way,what is the gain of the circuit?seem not achieve gain 4000.

 

[BrownOut]

I diasgree. It achieves more than 4000.

 

[prescott2006]

how to know the gain by bode plot?can i make the gain exact 4000?

 

[BrownOut]

Don't worry about making the gain exactly 4000. If that is your target, it should be a minimum number.

Gain = 101*Vout/Vin

Vout/Vin(db) = 20*log*(Vout/Vin)

 

[prescott2006]

how should i modify the current sink circuit to obtain other current value?and one stupid question,can the op amp above amplify dc voltage?

 

[BrownOut]

At some point, you need to do some research.

 

[audioguru]

At some point, you need to learn about electronics.

 

[prescott2006]

ok,you already help me alot.i really appreciate it.thanks alot ya.
PS:how to achive the same electronic level like you...?

 

[BrownOut]

You never answered my question: Why are you doing this? Is it a school assignment? If so, what kind of program are you in. I whet to school for a VERY long time, and have been working in the field for almost 30 years. If you want this, you have to make a commitment.

 

[audioguru]

Many of us learned Electronics in school and in university.
A few of us learned electronics themselves.
Since you know such a little amount of electronics then maybe you should do something else (gardening, catching butterflies?).

 

[BrownOut]

Don't worry about making the gain exactly 4000. If that is your target, it should be a minimum number.

Gain = 101*Vout/Vin

Vout/Vin(db) = 20*log*(Vout/Vin)

Oooooopssssss... that first equation should have been:

Gain = 101*vout/vx

And vout/vx(db) = 20log(vout/vx)

 

[Roff]

Prescott2006 got that .asc file from me on the All About Circuits forum.
Thanks for the credit (not!).

EDIT: Upon further reflection, perhaps you didn't understand the etiquette of this situation. Now you do.

EDIT: Prescott2006 has added credit to his post. No harm done.