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need help !! pls answer my Question ..

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viggu007

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Hi all,

I am trying to understand the differences between pmos n nmos... i am unable to find the answer the below mentioned question ... can anybody help me out with that ?


Explain why PMOSFETS tend to be able to drive ½ the current of NMOSFETs with
similar dimensions?


thank you
 

safwatonline

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PMOS have holes as majority of carriers(i.e. current is due to holes), and since the holes are really electrons moving in the valnence band so they are heaviar "slower" , so holes have lower mobility and hence PMOS has lower gm "transconductance" and pass lower current for the same size of NMOS (i don't really remember the exact ratio but i think it was 2.4)
 

    viggu007

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mannnish

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In NMOS transistors, the silicon channel between the source and drain is of p-type silicon. When a positive voltage is placed on the gate electrode, it repulses the holes in the p-type material forming a conducting (pseudo n-type) channel and turning the transistor on. A negative voltage turns the transistor off. With a PMOS transistor, the opposite occurs. A positive voltage on the gate turns the transistor off, and a negative voltage turns it on. NMOS transistors switch faster than PMOS.
 

suhas kakade

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PMOS have holes as majority of carriers(i.e. current is due to holes), and since the mobility of holes is less than that of electrons hence PMOS has lower gm "transconductance" and pass lower current for the same size of NMOS.
 

    viggu007

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El-Hadidy

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I also support the first and the last answer. The second answer I can't understand well yet.

Thanks

El-Hadidy
 

viggu007

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thank you all for your responses.... I never thought in terms of mobility of holes and electrons for this question ... now i am convinced with the answers provided...
 

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