For the circuits below use the following parameters:

R$1=$ R$2=200$k$,$ Rd $=10$k$,$ Vth $=0\mathrm{.}6$V$,$ and kW$/$L $=3$mA$/$V$^2,$ neglect the channel length modulation effect.

Find:

a$)$ The region of operation of the MOS transistor M$1$ if VDD $=5$V

b$)$ the drain current ID if VDD $=5$V

c$)$ The drain current ID if VDD $=1\mathrm{.}8($Hint: check the region of operation$)$

d$)$ the maximum allowable value of VDD to such that M$1$ is in the cit$-$off region