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Modeling >> Semiconductor Devices >> Rout
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Message started by aaron_do on Feb 7^th, 2007, 6:21pm

Title: Rout
Post by aaron_do on Feb 7^th, 2007, 6:21pm

Hi all,

I was wondering how to calculate the MOSFET output impedance. I've come across two ways. Both seem correct.

1) based on channel length modulation, Rout ≈1/(lambda.IDS).

2) Based on reverse leakage through cgd, Gout ≈gm.Cgd/(Cgd+Cgs)=wT.Cgd. → Rout=1/(wT.Cgd).
- This one assumes that the gate is left in open circuit.

AS we can see neither of them are frequency dependent. Do I just add them in parallel? And which one tends to dominate (seems like the second one is quite a bit smaller for 0.18 um technology)?

thanks,
Aaron