Thermal Noise Current Expression for the MOS

[aryajur]

I was trying to derive the Thermal Noise Current Expression for the MOS. Could anyone give me a reference as to where I can find it, or how to derive it? I guess it must be similar to the derivation of Cgs in Saturation.
I am talking about the expression

Idn² = 4KTγ gm where γ=2/3

 

[Vamsi Mocherla]

Re: MOS Noise Current

Like you have said, the thermal noise in a MOSFET is similar to the Cgs derivation. I mean, thermal noise in a MOSFET is due to the resistance of the channel between the drain and source. So, in saturation, you will see that the channel is pinched off. The effective resistance is 2/3 times the total resistance (1/gm) of the channel. Since it is noise current you are measuring, it will be multiplied by gm^2.

 

[aryajur]

Re: MOS Noise Current

1/gm is the small signal resistance. The noise occurs because of the actual resistance of the channel and has to be derived by finding the actual physical resistance of a differential element in the channel and then integrating it over the channel.
I found the derivation in the book by Yannis Tsividis. The book can be downloaded from


for anyone who is interested to look it up. My hunch was correct about the similarity with Cgs derivation. The book derives that also.