Given ID = 14 mA and VGS = 1 V, determine VP if IDSS = 9.5 mA for a depletion-type MOSFET.
$$ \begin{aligned} &\text { Write the expression for pinch off voltage. }\\ &V_{P}=\frac{V_{G S}}{1-\sqrt{\frac{I_{D}}{I_{D S S}}}} \cdots \cdots(1) \end{aligned} $$
Determine the value of pinch off voltage for a depletion-type MOSFET.
Recall equation (1).
$$ V_{P}=\frac{V_{G S}}{1-\sqrt{\frac{I_{D}}{I_{D S S}}}} $$
Substitute \(14 \mathrm{~mA}\) for \(I_{D}, 1 \mathrm{~V}\) for \(V_{G S}\) and \(9.5 \mathrm{~mA}\) for \(I_{D S S}\) in the equation.
$$ \begin{aligned} V_{P} &=\frac{1 \mathrm{~V}}{1-\sqrt{\frac{14 \times 10^{-3} \mathrm{~A}}{9.5 \times 10^{-3} \mathrm{~A}}}} \\ &=\frac{1}{1-\sqrt{1.4737}} \mathrm{~V} \\ &=-4.67 \mathrm{~V} \end{aligned} $$
Thus, the value of pinch off voltage, \(V_{P}\) is \(-4.67 \mathrm{~V}\).