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Below are all of the forum threads, including all
the responses to the original posts.
Post subject: available noise power consistency check
Posted: Sat Sep 10, 2005 8:42 am
Sep 10, 2005 8:04 am
I was reading up
on noise power and etc, and I understand that 4KTR*delta_f is the maximum
power transmitted(available noise power) for a resistor with a matching
load resistance. Unless I miss read between the lines, if the load resistance
is NOT = to the source resistance, then the above equation is no longer
Now the problem I ran into is this: after a few more pages,
I found a simple Thevenin eq circuit containing Source V and R, and
a load C. Now Vo^2 is the noise power across the Capacitor and Vs^2
is the noise power input. Thus, Vo^2 = Vs^2 / (1 + jwRC)^2. Now my first
I thought P(load) = Vs^2 x Resistance(load) / Impedance(total),
and since the output impedance is modeled by just the capacitor, there
shouldn't be a real resistance value at all, but the above equation
applies (1/sC) as the output resistance and I don't know why. I thought
(1/sC) is the complex part of the impedance and should not be utilized
in the above Noise power equation?
And then the book replaces
Vs^2 with 4KTRdf, so:
[b] I thought 4KTRdf is only valid when
the R_load matches the R_S, so what makes the author perform the above
I am a fourier illiterate...