# mosfet /// body effect

Discussion in 'General Electronics Chat' started by vidiyala, Oct 11, 2013.

1. ### vidiyala Thread Starter New Member

Oct 11, 2013
2
0
body effect is used when
vs=vd=o and vg less than vth
or when any other case

2. ### wayneh Expert

Sep 9, 2010
15,560
5,764
Is there a question in there? More details will get you a better answer.

3. ### ScottWang Moderator

Aug 23, 2012
6,482
1,001
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.

4. ### ian field AAC Fanatic!

Oct 27, 2012
6,379
1,157
If there's a question in the OP's post - it probably has to do with the body diode.

5. ### WBahn Moderator

Mar 31, 2012
23,587
7,216
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.

6. ### ScottWang Moderator

Aug 23, 2012
6,482
1,001
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.

7. ### WBahn Moderator

Mar 31, 2012
23,587
7,216
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.

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.

8. ### ScottWang Moderator

Aug 23, 2012
6,482
1,001
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.

9. ### vidiyala Thread Starter New Member

Oct 11, 2013
2
0
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.

10. ### WBahn Moderator

Mar 31, 2012
23,587
7,216
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".