body effect is used when
vs=vd=o and vg less than vth
or when any other case

 

Is there a question in there? More details will get you a better answer.

 

vs=vd=o and vg less than vth

If you mean that o = ohm then what you said is the Vds of mosfet in a saturation status, during that time the vg should be great than Vth, as a normal mosfet will greater or equal to 10V for an N type, and the logic level mosfet will greater or equal to 4.5V for an N type.

 

If you mean that o = ohm then what you said is the Vds of mosfet in a saturation status, during that time the vg should be great than Vth, as a normal mosfet will greater or equal to 10V for an N type, and the logic level mosfet will greater or equal to 4.5V for an N type.

If there's a question in the OP's post - it probably has to do with the body diode.

 

If there's a question there, is right!

My devining rod has me thinking that the OP is asking about when it is important to take body (i.e., bulk-bias) effects into account versus when they can be ignored. That, or asking when body effects can be used to help achieve design goals, such as intentionally employing bulk bias modulation.

 

If there's a question in the OP's post - it probably has to do with the body diode.

Yes, but because the infos from op was too less about that, the true is I'm not sure what he asked for?

So I just talking something about Vd=Vs=0 Ohm and also I'm not sure the meaning is the same with op.

 

Yes, but because the infos from op was too less about that, the true is I'm not sure what he asked for?

None of us are, which is why we are throwing out sheet anchors hoping that the OP will come back and clarify their question (or at least actually pose one). Perhaps the thoughts we are throwing out will help the OP formulate a question that gets at the point they are interested in.

So I just talking something about Vd=Vs=0 Ohm and also I'm not sure the meaning is the same with op.

I have no idea what "Vd=Vs=0 Ohm" means. Vd and Vs are voltages, not resistances or impedances or reactances or anything else that can have the unit of ohms.

 

I have no idea what "Vd=Vs=0 Ohm" means. Vd and Vs are voltages, not resistances or impedances or reactances or anything else that can have the unit of ohms.

The original is vs=vd=o, so I thought that maybe the op tried to said the one is when Vds is On(sat), so the Vd=Vs, and Vds = 0V, the other one is Rds=0 Ohm.

Whatever which one that they are incorrect, because the Vds can't be 0V and the Rds can't be 0 Ohm either, so what I expressed Vd=Vs=0 Ohm that just following the op's described, it can't be a really formular.

 

oh sorry sir.
just i have read in the text book about body effect. in that he have given only this statement about body effect in razavi
body effect is used when
vs=vd=o and vg less than vth
so i want to know the total concept for body effect
so kindly help me.

 

oh sorry sir.
just i have read in the text book about body effect. in that he have given only this statement about body effect in razavi
body effect is used when
vs=vd=o and vg less than vth
so i want to know the total concept for body effect
so kindly help me.

Then go out and look at other sources of information about body effect. There are options for research beyond one text by one author. You might start with a google search on "FET body effect" and see what you find. Another term to look for would be "FET back gate".