n-channel MOSFET - Inverse relation of transconductance & source resistance

Q.  The value of transconductance decreases in simplified low frequency equivalent circuit of n-channel MOSFET due to increase in the value of _______
- Published on 24 Sep 15

a. Source resistance
b. Load resistance
c. Both a and b
d. None of the above

ANSWER: Source resistance

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    Discussion

  • Satyawati Patil   -Posted on 07 Oct 15
    The simplified low frequency equivalent circuit of n-channel MOSFET assists in the clarification of the consequences of source resistance by neglecting 'ro'. In addition to this, all the inter-electrode capacitances are replaced by open circuits because they have a tendency to offer very high reactance at low frequency.

    By evaluation of an entire circuit, the drain current is given by,

    ID = g'm x Vgs -------------- (I)

    where, g'm represents the transconductance value & hence, can be expressed as,


    g'm = gm / ( 1+ gm rs) ---------- (II)

    From equation (II), it can be concluded that the value of transconductance (g'm) exhibits inverse relationship with the value of source resistance.

    Hence, it is quite obvious that the transconductance (g'm) decreases due to an increase in the source resistance in simplified low frequency equivalent circuit of n-channel MOSFET.

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