DAC11001A: Why use nV/sqrt(Hz) as the unit of noise density?

Hi Jim,

Since noise has energy spread across frequencies (aka power spectrum), we need to consider bandwidth as well. For example , thermal noise in a resistor represented as V^2 / R = 4*K*T*ΔF

where K is Boltzmann's constant in joules per kelvin, and T is temperature in kelvin. Δf is the bandwidth in Hz

V^2/R  = power in a resistor, in order to get the voltage V = Sqrt (4*K*T*R*ΔF), that is the reason you have the Sqrt (Hz) term in the noise 

Alternatively if we express the noise in terms of power , we will not have Sqrt(Hz) 

For more info you can look into the below link.

http://www.ecircuitcenter.com/Circuits/Noise/Noise_Analysis/res_noise.htm

Regards,

AK