Question

An n-channel MOSFET has overdrive voltage of 1 V to get the drain current of 1 mA. If the drain current required to be 2 mA, then new overdrive voltage will be

(Assume MOSFET to be in saturation region)

Answer 1

The overdrive voltage of MOSFET is given by
$V_{ov}=V_{GS}-V_T=1V\text{(given)}$
In the saturation region of MOSFET,
$\text{The drain current,}{I}_D=K(V_{GS}-V_T{)}^2$
$\therefore 1\text{mA}=K(1{)}^2$
$\therefore K=1{\text{mA/V}}^2$
The new drain current,
$I_{DN}=2\text{mA (given)}$
$\text{For new overdrive voltage, drain current}{I}_{D2}\text{is}$
$\therefore I_{D2}=K(V_{GS}-V_T{)}_{\text{New}}^2$
$2\text{mA}=1\times {10}^{-3}(V_{GS}-V_T{)}_{\text{New}}^2(\because I_{D2}=2\text{mA) Given}$
$\therefore V_{ov}=(V_{GS}-V_T{)}_{\text{New}}=\sqrt{2}=1.414V$