Problem $1(25$ points$)$ For the circuits below use the following parameters: Account R$1$R$2200,$ RD $=10,$ VTH $=0\mathrm{.}6$V$,$ and kW effect. k$3$mA$/$V$2,$ neglect the channel length modulation L

a$)$ The region of operation of the MOS transistor M$1$ if VDD $5$V $[5$ pts$]$ b$)$ The drain current ID if VDD $=5$V $[10$ pts$]$ c$)$ The drain current ID if VDD $=1\mathrm{.}8$V $($Hint: check the region of operation$)[5$ pts$]$ Discussions d$)$ The maximum allowable value of VDD to such that M$1$ is in the cut$-$off region. $[5$ pts$]$