Question

In the circuit shown below, the transistor operates at $I_D=0.4mA$ and $V_D=0.5V.$ The NMOS transistor has $V_t=0.7V,{\mu }_n{C}_{\propto }=100\mu A/V^2,L=1\mu m$ and $\omega =32\mu m.$ Assume $\lambda =0.$ The value of $R_{s}is$

• A. $4.75k\Omega$
• B. $4.25k\Omega$
• C. $3.75k\Omega$
• D. $3.25k\Omega$

Answer 1

The correct option is D $3.25k\Omega$

(d)
$\because V_{DG}>V_t$
$\therefore$ It the saturation mode of operation,
$I_D=\frac{1}{2}{\mu }_{\propto }\frac{W}{L}(V_{GS}-V_f{)}^2$
$400=\frac{1}{2}\times 100\times \frac{32}{1}(V_{GS}-0.7{)}^2$
$V_{GS}=0.5+07=1.2V$
$R_S=\frac{V_S-V_{SS}}{I_D}=\frac{-1.2-(-2.5)}{0.4}=3.25k\Omega$