The D-MOSFET amplifier shown in Fig. 32-19 has VGS(off) = -2 V, IDSS = 4 mA, and gmo = 2000 μS. What is the circuit’s output voltage?

Question

The D-MOSFET amplifier shown in Fig. 32-19 has [latex]V_{GS(off)} = -2 V, I_{DSS} = 4 mA, and g_{mo} = 2000 \mu S[/latex]. What is the circuit’s output voltage?

Accepted Answer

With the source grounded, [latex]V_{GS} = 0 V and I_D = 4 mA.[/latex]

[latex]V_{DS} = 15 V – (4 mA)(2 k\Omega ) =7 V[/latex]

Since [latex]V_{GS} = 0 V, gm = g_{mo} = 2000 \mu S.[/latex]

The amplifier’s voltage gain is found by

[latex]A_V = g_m r_d[/latex]

The ac drain resistance is equal to

[latex]r_d = R_D \parallel R_L = 2 K \parallel 10 K = 1.76 k\Omega[/latex]

and [latex]A_V [/latex]is

[latex]A_V = (2000 \mu S)(1.67 k\Omega) = 3.34[/latex]

Therefore,

[latex]V_{out} = (V_{in})(A_V) = (20 mV)(3.34) = 66.8 mV[/latex]

Question 32.3: The D-MOSFET amplifier shown in Fig. 32-19 has VGS(off) = -2...

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