Why the drain doesn't cause the body effect?

[MelZ]

In the layout,the source and the drain are indentical,why we don't consider the body effect caused by Vdb>0?

 

[BigBoss]

I think...
Vd-Vb region is reverse polarized pn junction deeper than pn junction between source and bulk.So, changings between these two is more effective than drain and bulk.
There may be some other explanations but it should be first order cause..

 

[crutschow]

The body effect changes the Vgs threshold so it effects that voltage for whichever terminal is used as the source. What type of effect do you think it could have on the drain?

 

[MelZ]

The body effect changes the Vgs threshold so it effects that voltage for whichever terminal is used as the source. What type of effect do you think it could have on the drain?

such as when we calculate the vdsat,Vth should be larger than Vth(source) due to the body effect,namely Vdsat<Vgs-Vth(Source),why neglect the variation？

 

[crutschow]

such as when we calculate the vdsat,Vth should be larger than Vth(source) due to the body effect,namely Vdsat<Vgs-Vth(Source),why neglect the variation？

Sorry I don't understand what effect you are talking about. :???:

 

[MelZ]

When we calculate the current,we neglect the Vth variations in the channel,why?

 

[arunkumarshanti]

In the layout,the source and the drain are indentical,why we don't consider the body effect caused by Vdb>0?

Hi,

w.r.t NMOS, the drain will always be at higher potential than the source & body. Recollect that in CMOS IC, NMOS body is always connected to least potential.

In the figure, you can witness the drain-body diode is readily reverse biased.

Hence we are not bothered about the body effect w.r.t the drain. To correct, Vdb will be >0 always.

For more info **broken link removed**