hi

thermal noise from its nature is power, not voltage.

Pn = k * T * B
k boltzmann constant 1.380662E-23 J/K (VAs/K) 
T absolute Temperature (Kelvin)
B bandwidth Hz 

this power is delivered from any resistor, regardless of its 
resistance.
(assumed "white", i.e. frequency independent noise)
so noise denisty is Pn/B = kT in Watts/Hz

as power is P = U * U / R or P = I * I * R
(voltage or current squared)

you get the sqrt of bandwidth (i.e. Hz^0.5) when you go from power to 
voltage at a known resistance.
U = sqrt(P * R)

(with "white", thermal noise the noise denity is frequency 
independent. Otherwise you would have to integrate over frequency)

regards 
Alois

> Hi all
> 
> I have to fill up a knowledge gap about noise.
> 
> The unit of the noise density is mostly nV/"sqrroot"HZ and I don't
> really what this likes to tell me.
> 
> Anyone has a good article about this?
> 
> TIA
> Edi
> 
> -- 
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Alois Bauer
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Author: Alois Bauer
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