Hello to everybody, i need some help to study about opamps, i will have some exams soon, and here is a circuit about i would have some questions, i know that the image is not very clear, and i'm really sorry about that, i hope you can read it: http://tinypic.com/view.php?pic=11v3cz5&s=5 . First question about this: what type of circuit is this?

Question

anonymous · Answer

What image?

anonymous · Answer

The image from the url, but i will attach it here again.

anonymous · Answer

Why don`t you get help from the text book of Sir Anant? I think it may help you.

anonymous · Answer

Does anybody know what is the fee for getting certificate from MITx and when exactly is to pay?

anonymous · Answer

i thought that the certificate is free... ?!

anonymous · Answer

To answer the OP's question, the circuit is what the first part of a very simple opamp looks like "under the hood".  It shows how one can be made using bipolar junction transistors hooked up as a differential amplifier with a current source.  It's missing the gain stage and the output push-pull stage needed to make an opamp though.  

If you want to learn about opamps, unless you already know a lot about BJT devices (and you probably don't; opamps are taught first because they're conceptually much simpler) you'll be better off ignoring the diagrams like this and going through the course text in the order presented.  What takes a page of calculations using the underlying BJT models take just a single equation taking advantage of the ideal opamp model abstraction.  Once you get a good feeling of how opamps actually work, you'll be much better able to digest how their idealized model is approximated using BJTs.