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Measurements >> Phase Noise and Jitter Measurements >> thermal noise of MOS in non-saturate area
https://designers-guide.org/forum/YaBB.pl?num=1183128485

Message started by boris on Jun 29^th, 2007, 7:48am

Title: thermal noise of MOS in non-saturate area
Post by boris on Jun 29^th, 2007, 7:48am

In "Design of Analog CMOS Integrated Circuits" by Behzad Razavi, the thermal noise of MOS is I2=4kTγgm
while in "The Design of CMOS Radio-Frequency Integrated Circuits" by Thomas H. Lee, the thermal noise of MOS is I2=4kTγgd0.
If the MOS work in saturate area, we can find that gm=gd0. So these two functions is the same. But if the MOS work in non-saturate area, the result is different. What is the thermal noise of MOS in non-saturate area?

Title: Re: thermal noise of MOS in non-saturate area
Post by didac on Jul 1^st, 2007, 7:59am

Hi,
If you look at footnote 7 in Razavi's book he states that in fact is not a gm it's gds at VDS=0, so in fact gds=gd0. In non-saturate area noise is equal to I2=4kTγgd0, with γ=1, while in saturation γ=2/3(long-channel devices) and γ=2..3(short-channel devices).
Hope it helps,

Title: Re: thermal noise of MOS in non-saturate area
Post by boris on Jul 10^th, 2007, 6:08am

Thanks to didac. I didn't see the footnote by carelessness.

There is another question. As you said, in non-saturate area noise is equal to I2=4kTγgd0. So the noise should be independent to Vds, which is not agree with the simulation result. (I use spectre to do noise simulation. The process is TSMC 0.18um CMOS)