Question $4$: $(20$ pts$)$

For the circuit shown on the right, both of the NMOS transistors have $V_l=0\mathrm{.}9V$ and $k_n=1\mathrm{.}5m\frac{A}{V^2}.$

Calculate the voltage $V_B$;

$($hint $I_{D1}=I_{D2},I_1=I_2,$ use system equations to solve$)$

Calculate the voltages $V_A$ and $V_c$;

$($hint $l_1=l_{D1},l_2=l_{D2},$ use system equation to solve$)$

Prove both NMOS are in the saturation mode; $($hint: $V_{Ds}{V}_{ov})$