Positive condition of body w.r.t source with body effect

Q.  Which condition is applicable for a body to be more positive than source in a small signal equivalent circuit of N-type MOSFET inclusive of body effect?
- Published on 24 Sep 15

a. Vbs > 0
b. Vbs < 0
c. Vbs = 0
d. None of the above

ANSWER: Vbs > 0
 

    Discussion

  • Satyawati Patil   -Posted on 07 Oct 15
    According to the body effect in MOSFET, there is no connection of a body or substrate to the source. The small signal equivalent circuit of MOSFET also includes an additional dependent current source,which is expressed as gmVbs .

    The direction of current dependent source is also considered to be similar as that of the main current source (gmVGS).
    If the body is found to be more positive than source, then it implies that the small signal body to source voltage is greater than zero.

    Due to this, source to body voltage (VSB) as well as threshold voltage (VT) decreases by increasing the value of drain current. Therefore, the value can be positive only when body to source voltage is greater than zero.

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