[circuit theory] Transfer function of feedback network

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In the system with negative feedback, what is described by G(s) actually? is it G(s)=A(s)/Y(s) ?

If I want to derive Y(s)/X(s), is it a correct way to derive G(s)=A(s)/Y(s) and then I can plug it in to the equation (8.2)?

With simple resistor as feedback, I usually derive the transfer function directly.
But right now, I have a quite complicated feedback network with some frequency-dependent components.
That's why I want to derive G(s) first.




 

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danadakk said:
Just derive the G(s) element expression, and plug that
into 8.2, just as you do for H(s).
Click to expand...

sorry it is a bit unclear for me.
I think I should derive G(s)=A(s)/Y(s) when the feedback network is detached from the feedforward. Is this correct?


I will check your links. Thanks
 

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Yes, you treat G(s) as a stand alone network with an input
and output. But dont use Y(s) as input because that would make
it a f( G(s), X(s), Y(s) ). So make input Z(s), output A(s), and then
solve for is T(s) = A(s) / Z(s) and plug that into the general T(s)
for the overall problem.

Regards, Dana.
 
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I wonder what you mean with "derive G(s)"? The feedback factor is intentionally chosen in the design process.
 

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You are stating in post #1:
I have a quite complicated feedback network with some frequency-dependent components.
That's why I want to derive G(s) first.
Click to expand...
In this case, G(s) will be described by a rational function with numerator and denominator coefficients (zeros and poles). Consider that the "detached" feedback network must be loaded similarly to the final circuit.
 

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