Re: y pmos always have bigger size than nmos

[Lee Kar Leong]

Hi,

thank for your information . may I ask question

Why not NMOS to connect to Vdd, PMOS to Vss??

On 5 July 2012 18:19, Anbu Chozhan <anbu...@gmail.com> wrote:

pmos has low mobility than nmos. To compensate with nmos speed pmos
area is 2 to 3 times greater than nmos

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[Narveer Yadav]

Lee,
NMOS has electrons as majority charge carriers and PMOS has hole as majority charge carriers. Electrons has mobility ~2.7 times higher the holes. The main reason behind making PMOS larger is that  rise time and fall time of gate should be equal and for this the resistance of the NMOS and PMOS should be the same. This can be achieved only by sizing the PMOS ~ 3 times to the NMOS sizing. For your second question check below link.

https://groups.google.com/forum/?fromgroups&hl=en#!searchin/vlsi-design-forum/swap/vlsi-design-forum/HvmoYEtlf6A/Fn9hxN8sueYJ

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Regards,
Narveer Yadav