Question 4.SP.13: A p-channel MOSFET operating in the enhancement mode is char......
A p-channel MOSFET operating in the enhancement mode is characterized by V_T = -3 \text{V} and I_{DQ} = -8 \text{mA} when V_{GSQ} = -4.5 \text{V}. Find (a) V_{GSQ} if I_{DQ} = -16 \text{mA} and (b) I_{DQ} if V_{GSQ} = -5 \text{V}.
(a) Using the given data in (4.6) leads to
i_D = I_{\text{Don}} \left( 1 – \frac{v_{GS}}{V_{T}} \right)^2 (4.6)
I_{\text{Don}} = \frac{I_{DQ}}{(1 – V_{GSQ}/V_T)^2} = \frac{-8 × 10^{-3}}{(1 – (-4.5) – 2)^2} = -32 \text{mA}
Rearrangement of (4.6) now allows solution for V_{GSQ}:
V_{GSQ} = V_T \left[1 – \left(\frac{I_{DQ}}{I_{\text{Don}}} \right)^{1/2} \right] = (-3) \left[1 – \left(\frac{-16}{-32} \right)^{1/2} \right] = -0.88 \text{V}
(b) By (4.6),
I_{DQ} = I_{\text{Don}} \left(1 – \frac{V_{GSQ}}{V_T} \right)^2 = -32 × 10^{-3} \left(1 – \frac{-5}{-3} \right)^2 = -14.22 \text{mA}