(MOSFET) Why does Rds decreases when Ugs increase in saturation mode without channel lenght modulation?

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subatomic particle

Joined May 8, 2018
65
Hello guys,
here is gds in saturation mode and without considering Channgel length modulation
1655415129839.png

my Question is how does increasing Ugs makes Rds decrease??
here is a picture to illestrate what i mean.
The slop remain constant if we dont consider CLM so why does the formula still have Ugs??
1655415480127.png
 

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Papabravo

Joined Feb 24, 2006
18,806
any help??
I think your notation in the text and the graph is ambiguous. Capital U is the symbol for voltage in German documents that I have seen while in North America we use a capital V. Small g refers to conductance in North America which seems backwards for the equation you show. On the graph you have labeled the saturation regions as gDS=0, but in fact I think you mean the channel resistance approaches 0 in the saturation region and thus the equation is no longer valid. Along any of the characteristic curves the values of Ugs and Uth are constant and do not change. I'm not even sure what you are asking. We know from the device characteristics, that more Gate to Source voltage will reduce the channel resistance up to some limit beyond which the device will be destroyed or there will be no further reductions in channel resistance. That datasheet for a particular device will tell you where the measurement was made.

EDIT: This article may provide additional insight for you:
https://www.allaboutcircuits.com/te...g-mosfet-on-state-drain-to-source-resistance/
 
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