Calculation of noise figure

[heritage]

When I simulate the noise performance of an amplifier using Cadence Spectre, I can get the values of output noise voltage (Vn,out) and noise figure (NF). But I use the formula
NF=square(Vn,out/A)*1/(4kTRs) (A is the voltage gain.)
the result of NF is different with the simulation result.
Why?

 

[fanshuo]

I believe the Vn_out is in the unit of v/sqrt(Hz)
so
NF=10LOG10((Vn,out/A)^2/4kTRs)

 

[heritage]

Thanks.
It's just the difference of units, but the result is the same.