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Help !! Body effect in NMOS

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sbhalerao

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body effect nmos

Hi to all,
I am currently working on a circuit design that requires me to consider the body effect in NMOS.. could anyone clarify what this effect is exactly??
Also, what steps can be taken to avoid this effect ?? I want to tackle body effect as it is reducing the output voltage value in our design..
 

body effect

The threshold voltage of a MOSFET is affected by the voltage which is applied to the back contact. The voltage difference between the source and the bulk, VBS changes the width of the depletion layer and therefore also the voltage across the oxide due to the change of the charge in the depletion region. This results in a difference in threshold voltage which equals the difference in charge in the depletion region divided by the oxide capacitance, yielding:

dVth = ?2*?s*Na*q / Cox * ( ?2*?f-Vsb - ?2*?f )

The only way to avoid this is to use an "active well" process where you can connect the well to the source, forcing thus Vsb=0.

Hope this helps,

LucaS.
 

nmos body effect

I.sant explains well.
If anyone who answers the question will tell us his what is his jiob,it will be good.
 

body effect in nmos

you can refer to some book of semiconductor
 

what is body effect in ic design

what do you mean with active well ?
what happens with an N-well process, with sustrate-p. I've heard it also has body-effect in NMOS where vbs ≠ 0
 

cmos body effect

the textbook tells me when Vbs=0 there is no body effect...

is anything changed?
 

vsb for n-mos

strennor said:
the textbook tells me when Vbs=0 there is no body effect...

is anything changed?
Click to expand...

if Vbs=0 then we can ignore body effect
 

body effect reduce vt

put the source and substrate togathere then there will be no body effect since no vt variation will take place
 

nmos body effect parameter

manissri said:
put the source and substrate togathere then there will be no body effect since no vt variation will take place
Click to expand...

however not all process allow that. if i'm not mistaken, Nwell process, bulk must always connected to ground. however source might sometime not connect to ground esspecially in analog design
 

body effect in cmos

This is few pages in Razavi Book about Body effect
 

back body effect

get the expression for threshlod voltage for CMOS from any device physics book.

You will see that there is a term Vsb.

If this term is not made 0 then it can degrade the threshold voltagfe which in turn can degrade many parameters.
So to reduce body effect the substrate is connected to the source
 

hi.. anyone could please tell me if the body effect parameter changes with Vbs?? its the practical values do not match with the calculation using v=vth+gamma(...) and the gamma=sqrt(.....)/cox
 

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