Fixed bias can also be utilized for the enhancement-mode MOSFET, as is illustrated by the circuit of Fig. 4-25. The MOSFET is described by the drain characteristic of Fig. 4-9. Let R1 = 60 kΩ, R2 = 40 kΩ, RD = 3 kΩ, RL = 1 kΩ, VDD = 15 V, and CC → ∞. (a) Find VGSQ. (b) Graphically determine VDSQ

Question

Fixed bias can also be utilized for the enhancement-mode MOSFET, as is illustrated by the circuit of Fig. 4-25. The MOSFET is described by the drain characteristic of Fig. 4-9. Let [latex]R_1 = 60 kΩ, R_2 = 40 kΩ, R_D = 3 kΩ, R_L = 1 kΩ, V_{DD} = 15 ext {V, and} C_C → ∞[/latex]. (a) Find [latex]V_{GSQ}[/latex]. (b) Graphically determine [latex]V_{DSQ}[/latex] and [latex]I_{DQ}[/latex].

Accepted Answer

(a) Assume [latex]i_G = 0[/latex]. Then, by (4.3),
[latex]R_G = \frac{R_1R_2}{R_1 + R_2} \quad ext{and} \quad V_{GG} = \frac{R_1}{R_1 + R_2} V_{DD}[/latex] (4.3)

[latex]V_{G S Q} = V_{G G} = \frac{R_2}{R_2 + R_1} V_{D D} = \frac{40 imes 10^3}{40 imes 10^3 + 60 imes 10^3} 15 = 6 ext{V}[/latex]

(b) The dc load line is constructed on Fig. 4-9 with [latex]v_{DS}[/latex] intercept [latex]V_{DD} = 15 ext{V}[/latex] and [latex]i_D[/latex] intercept [latex]V_{DD}/R_L = 5 ext{mA}[/latex]. The Q-point quantities can be read directly from projections back to the [latex]i_D[/latex] and [latex]v_{DS}[/latex] axes; they are [latex]V_{D S Q} \approx 11.3 ext{V}[/latex] and [latex]I_{D Q} \approx 1.4 ext{mA}[/latex].

Question 4.SP.20: Fixed bias can also be utilized for the enhancement-mode MOS......

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