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Tutorial about feedback circuits

Started by Boops May 8, 2004 at 12:58 PM 4 replies 450+ views

Original Post

May 8, 2004 at 12:58 PM

We have a course about feedback circuits (with opamps or other amplifiers), but the prof is so smart that he doesn''t realize he isn''t getting to the point. He gives tons of examples, but goes over they way too quickly and never really sais how to actually solve it (= find open loop gain, input resistance and output resistance), he only focuses on some details and explains that without actually making clear why he''s doing it. So is there good info about this on the web? Someone here must know

Conner McCloud

May 8, 2004 at 1:07 PM

I failed that class, and have to retake it in the fall. This puts a serious dent in my graduating next May. So I wish you the best of luck in finding a good resource, and I hope that you find it here so I have access to it as well.

CM

Man_with_a_Plan

May 8, 2004 at 1:49 PM

well an ideal op amp has infinite input resistance and zero ouput resistance and the voltage between the polarities of the op amp are the same. Open gain is given by V0/Vi. Just use nodal analysis to find V0/Vi.

Boops

May 8, 2004 at 2:05 PM

quote:
Original post by Man_with_a_Plan
well an ideal op amp has infinite input resistance and zero ouput resistance and the voltage between the polarities of the op amp are the same. Open gain is given by V0/Vi. Just use nodal analysis to find V0/Vi.

It''s not as simple as this

It''s some technique where you break the circuit somewhere, and then you add a "test voltage". In the technique you have to do something weird like "calculating the impedance of a point", between a ground which is appearantly not necessarily the ground of the circuit as it''s given. And then a lot of things can be neglected, but we never really saw when you can neglect something and when not.

Boops

May 9, 2004 at 8:41 AM

I found something quite interesting:

http://www.ece.sunysb.edu/~pacelli/ese311/notes/fb.pdf

benryves

May 9, 2004 at 10:24 AM

Input and output impedance, not resistance.

Use the funky terms if available.
Typically an op-amp has about a 2M input impedance.
You can force it to have a particular resistance by tying the input to 0V with a resistor.
I don''t know, there''s so much you can say about op-amps than can fit in a single reply

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