feedback amplifier DC analysis thevenize solve for Ro of 2 stage transistor amp
1page 707 , I solve the rather large Eq. of Ro , for the CCCS
2 stage feedback amp.
based on Microelectronic Circuits second edition
ISBN 0-03-007328-6
page 707 ,
Ro is the output resistance Eq. of a 2 stage CCCS negative feedback transistor amp., from chapter 12 ,
page 707
The book only gives the symbolic solution Eq. for Ro ,
with No explaination .
I just solved this, that's why it isn't in part 1 .
Out of the 4 circuits analyzed in chapter 12, this
Ro Eq. is a bit tricky.
It's tricky because:
part of stage 1 is still available to stage 2's output .
the Emitter of Q2 is NOT grounded,
the Vin of stage 2 is still present .
the input----output is NOT isolated.
The other 3 amps. in chapter 12 have isolated
input-----output sections .
So, I just had to solve this one.
The circuit model must be correct. If our circuit
model is in-correct, then all we can do is analyze junk.
Even after we have a correct circuit model, we need to
find a good\best approach for analysis. KVL, KCL ,
mesh currents, node analysis, general loop currents,
general node analysis, Theven-ize or Norton-ize ,
Test current , or Test voltage , or an appropriate
combination of the above techniques.
to find the equation of Ro I used:
1. Test Current method to find R Thevenin ==== Ro
2. a simple node Eq.
3. a generic KVL Eq.
4. ohms law
5. Voltage divider Eq.
6. basic algebra , substitutions, and observations .
It can't be faked.
We have a correct model or we don't .
We have the ability to analyze the model, or we don't .
at first, I see in the book's Ro Eq. that ( gm * ro2 )
is part of the equation. well, I want an easy fast way to hack
the equation together. Well, shot-gunning it , didn't work.
I wasted more time that way.
Just, set up the correct model and analyze it and let the
math fall into place. At times we may observe equalities or
identities, however. ie; we still need to interpret results .
I show the model with a complete descriptive set of notes.
Then I analyze it by writing all needed equations, finally
putting them all together to get the final equation for Ro,
the same as the book's Eq.
After doing the lenghty crunch, I see why the solution is
not part of the book. Having the final solution in the book
was still helpfull.