In the MOSFET circuit shown in Fig. 7.36, calculate the drain current and the drain voltage for (a) [latex]V_{GS}[/latex] = 0.5 V, [latex]R_{D}[/latex]= 1 kΩ and (b) [latex]V_{GS}[/latex]=3 V, [latex]R_{D}[/latex]=1 Kω. The threshold voltage is 2 V and value of k = 1.5 mA/V² .

(a) [latex]V_{GS} = 0.5 V, V_{T}[/latex] = 2 V Since [latex]V_{GS}[/latex] is less than [latex]V_{T}[/latex], the transistor is in cutoff region and hence, [latex]I_{D}[/latex] = 0. (b) Let us assume at this point that the transistor is in the saturation region, then [latex]I_{D} = K(V_{GS} – V_{T}) ^{2} =1.5 × (3–2)^{2} = 1.5[/latex] mA [latex]V_{DS} = V_{CC} – I _{D} R_{D} = 4– (1.5 × 10^{-3} × 1× 10^{3} )[/latex] = 2.5 V To check that the transistor is in saturation, we use the reduction [latex]V_{DS} ≥ (V_{GS} – V_{T})[/latex] i.e. [latex](V_{GS} – V_{T}) ≤ V_{DS}[/latex] or (3–2) ≤ 2.5. So, our assumption is correct and the transistor is in the saturation region.

Question 7.12: In the MOSFET circuit shown in Fig. 7.36, calculate the drai...

Basic Electrical and Electronics Engineering-II

In the MOSFET circuit shown in Fig. 7.36, calculate the drain current and the drain voltage for (a) $V_{GS}$ = 0.5 V, $R_{D}$ = 1 kΩ and (b) $V_{GS}$ =3 V, $R_{D}$ =1 Kω. The threshold voltage is 2 V and value of k = 1.5 mA/V²
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(a) $V_{GS} = 0.5 V, V_{T}$ = 2 V
Since $V_{GS}$ is less than $V_{T}$ , the transistor is in cutoff region and hence, $I_{D}$ = 0.
(b) Let us assume at this point that the transistor is in the saturation region, then

$I_{D} = K(V_{GS} – V_{T}) ^{2} =1.5 × (3–2)^{2} = 1.5$ mA

V_{DS} = V_{CC} – I _{D} R_{D} = 4– (1.5 × 10^{-3} × 1× 10^{3} )

= 2.5 V
To check that the transistor is in saturation, we use the reduction $V_{DS} ≥ (V_{GS} – V_{T})$ i.e. $(V_{GS} – V_{T}) ≤ V_{DS}$ or (3–2) ≤ 2.5. So, our assumption is correct and the transistor is in the saturation region.