(Solved): All transistors in the current-source circuit shown below have parameters VTP=0.4V,kp ...

All transistors in the current-source circuit shown below have parameters $V_{TP}=?0.4\mathrm{V},k_p^{?}=50?\mathrm{A}/{\mathrm{V}}^2$, and $?=0$. The bias sources are $V^{+}=5\mathrm{V}$ and $V^{?}=?5\mathrm{V}$. The currents are to be $I_{Q2}=200?\mathrm{A}$ and $I_{REF2}=125?\mathrm{A}$. For $M_B$, we require $V_{SDB}(sat)=0.8\mathrm{V}$, and for $M_A$, we require $V_{SDA}=4\mathrm{V}$. Transistors $M_A$ and $M_B$ are matched. (a) Find the $W/L$ ratios of the transistors. (b) Find the value of $R_D$.