Who can help me think about the negative feedback in analog circuit?

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zhenyuanwu@gmail.com - 31 Mar 2006 04:17 GMT

In the voltage-current negative feedback,what is the value of the
negative feedback voltage of the output voltage?
It says that "Vref=Vo*Re1/(Re1+Rf)" in the text book,why is that?
Should I consider the output resistance of the emission pole of the
first transistor?I think the Re1 should be taken place by
Re1//(rbe/(ß+1)),and there also should be an equivalent negative
voltage that equals to be vi*rbe/(Re1*(ß+1)).
I think there may be something wrong with my consideration, who can
help me?
Is there any way to upload the schematic?
Thanks in advance!

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Noway2 - 31 Mar 2006 15:42 GMT

In a bipolar transistor, using an emitter resistor acts as a form of
negative feedback.

The input to the transistor can be thought of as the Vbe minus a
portion of the Ie*Re product. Hence the emitter resistance provides
negative feedback. In order to understand this, you need to thoroughly
undertand the transistor models. It has been a long time since I have
studies this, but some searches into the "Ebers-Moll" model and the
"Early Effect" may help shed some light on this subject.

It is my opinion that most text books do a poor job of teaching
transistors with respect to real world applications because they
concentrate too heavilly on properties such as Beta and other process
dependant features. I would sugges the book, The Art of Electronics
for a more realistic discussion of transistor circuits.

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Electronics Forum / Basics / March 2006

Who can help me think about the negative feedback in analog circuit?