[MOVED] BJT op amp design (help me plz)

godfreyl said:

Agreed. I did mention earlier that an output stage will need to be added, to improve the gain and phase margin (and as you say, the output current capability, if that's important).

I just thought it would be easier for the OP if he starts by analyzing and understanding this part first, before adding more complexity. i.e. do it one step at a time.

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thank u so much keith & godfreyl ,
so i try to download SIMetrix for analyze this circuit........


and one question ,If the nodes are not automatically connected in pspice , so what is the solution ?

farzin0123 said:

If the nodes are not automatically connected in pspice , so what is the solution ?

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I don't know how PSpice works, but there are two funny things in the picture you showed.

Firstly, there are two pink squares next to Q9. Perhaps they show where the connections are missing?

Secondly, there are two green circles next to Q6. All the other transistors only have one.

farzin0123 said:

and one question ,If the nodes are not automatically connected in Pspice , so what is the solution ?

Click to expand...

Find the two nets that are the problem - you can search for nets from the "find" menu. Then, I suggest you delete the offending nets and re-draw them. You can add junctions manually by simply hitting the letter J and then clicking where you want the junction.

There is not much point switching simulators - Pspice will do the job fine once you get the drawing fixed (although as it happens I use SIMetrix).

Keith.

---------- Post added at 14:44 ---------- Previous post was at 14:42 ----------

I don't think the two squares are significant - they are just the currently selected net. The transistor with two circles next to a connection could be the problem though.

Keith

godfreyl said:

I don't know how PSpice works, but there are two funny things in the picture you showed.

Firstly, there are two pink squares next to Q9. Perhaps they show where the connections are missing?

Secondly, there are two green circles next to Q6. All the other transistors only have one.

Click to expand...

hi godfreyl ,
in this circuit that u suggested to me , how can i define input common mode and diffrential voltage ?
tnx

farzin0123 said:

how can i define input common mode and diffrential voltage ?

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The same as with a 741, or any other opamp.

thank u bro .....
truly i dont have enough time for designing ... because i have finall exams in university , and my teacher didnt gave me enough time for designing , and now im in trouble for this problem , so do u have any designed circuits with about 100 db gain and rail-rail input ?.....

tnx alot ....

This circuit doesn't have rail to rail inputs. If the input voltage be between 0.7 and -07 the circuit does not work Properly!!!!!!