Relation between Current and Noise (Input or Output referred)

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Hello,
For a transistor the input refered noise decreases with current increase (noise- current trade - off)
But the output refered noise increases with current increase???!!!!!
So, I don't know which noise should I consider if I want to decrease the noise of the circuit???
 

The output thermal current noise increases with the current, but the transistor transconductance also. Then, you calculate the input noise dividing by gm^2, thus the input noise decrases.

Consider the MOS thermal noise: SIDout = 8/3 kT gm = 8/3 kT 2ID/(VGS-VTH) and SVin = SIDout/gm^2 = 8/3 kT / gm = 8/3 kT * (Vgs-VTH)/2ID. This is valid in strong inversion and saturation.

The same holds for the bjt with slightly different formulas and for MOS in weak inversion.
 

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