relation b/w noise and output impedance

[shiva20587]

Hi,,
I have read it one of the textbooks that amplifiers with low output impedance are less sensitive to noise,can anyone point out the relation between output impedance and noise ??

Regards,
Shiva

 

[goldsmith]

Dear SHiva
Hello
we have the noise that called temperature noise or white noise that will given by : (4*K*BW*R*T) under radical .
K is boltzman coefficient that is about 1.38*10^-23 . and BW is your band width . and T is temperature at kelvin . and R is your impedance . if the R become higher , thus the noise will increase.
Best Wishes
Goldsmith

 

[chuckey]

shiva20587, the output impedance of an amplifier has nothing at all with the noise performance of THAT amplifier. If however if it feeds another amplifier, then if the first amplifier has a low output impedance then less noise will be picked up in the connection to the next amplifier. It is the input impedance of an amplifier that can generate noise if it is higher then it needs be.
Frank