I'm not interested in spending a lot of time on this, right now. Other work needs doing today. But I can offer a thought or two on the basis that you are discussing NFB.
NFB linearizes. It's amazing at it. You should play around with it, using paper and pencil. You'll gain a lot from taking some arbitrary equation, applying NFB, and then seeing the new closed equation.
For example, start with:
$$y=e^x$$
Apply 10% NFB to that to get:
$$\begin{align*}
y &= e^{x-10\%\,\cdot\, y}\\\\
&= 10\cdot\operatorname{LambertW}\left(10\%\cdot e^x\right)
\end{align*}$$
The original and resulting curves are:
Well, one looks more linear than the other to me. (See LambertW Appendix below for derivation of the closed equation.)
Suppose we do something trickier:
$$y = e^{\sin(5\,x)+1}$$
(The above equation isn't too far from what you might get from a BJT operated as a grounded-AC CE arrangement.)
And apply 30% NFB to it? We get this:
Notice the nice recovery of the sine wave? This is why global NFB is critical when you are using a grounded-AC BJT amplifier to get high voltage gain!
I've taken a few examples based upon what I consider to be kind of crazy -- functions that are exponentials of other functions -- just to exaggerate the problem a bit.
But don't stop there. You can do this to polynomials, too. Or anything, really.
Suppose this polynomial:
$$y = 4\,x^2 - 6\,x + 3$$
Apply 10% feedback to it (there will be two solutions) and get:
And so it goes.
NFB is very, very powerful.
LambertW Appendix
The LambertW function is also known as the product-log function. In the first case I listed above, I followed this derivation:
$$\begin{align*}
y &= e^{x-10\%\cdot y}\\\\
y &= e^{x}\cdot e^{-10\%\cdot y}\\\\
y\cdot e^{10\%\cdot y} &= e^{x} \\\\
10\%\cdot y\cdot e^{10\%\cdot y} &= 10\%\cdot e^{x} \\\\
\operatorname{LambertW}\left(\left[10\%\cdot y\right]\cdot e^{\left[10\%\cdot y\right]}\right) &= \operatorname{LambertW}\left(10\%\cdot e^{x}\right) \\\\
10\%\cdot y &= \operatorname{LambertW}\left(10\%\cdot e^{x}\right) \\\\
y &= \frac1{10\%}\cdot \operatorname{LambertW}\left(10\%\cdot e^{x}\right) \\\\
y &= 10\cdot \operatorname{LambertW}\left(10\%\cdot e^{x}\right)
\end{align*}$$
As exponentials (and logarithms) appear frequently, it's a function worth learning about. Anytime a variable appears both inside and outside of a logarithm or an exponential, you should think about it.
There's an odd history to it. Leonhard Euler investigated it. But in that paper he refers to Johann Lambert and as there were already lots of stuff named after Euler. So the function got Lambert's name assigned to it.
Footnote: Images above were generated using Wolfram Alpha.
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