Relation betn Switching time of the Mos transistor and Gm

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aok_fine

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I know that increasing the Gm of the transistor, decreases the rise/fall time i.e increases the switching speed. However, I don't know exactly why? and what's the mathematical expression?

Plz, Help me!
ThanQ

AOK
 

Switching time t ~ RC , where R = output impedance (of a driver), C = load capacitance.
Consider the transconductance Gm as inverse resistance R, hence t ~ C/Gm .
 

Thnx
Yeah, I see... But this means we assume charging and discharging during switching occurs in the triode (linear) region. This not so accurate, right??
 

aok_fine said:
... charging and discharging during switching occurs in the triode (linear) region. This not so accurate, right??
Click to expand...

It's an approximation of course. But if the switch is well driven into the linear region, this will provide quite a good estimation.
 
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