Question $5$

$($a$)$ A source follower amplifier is shown in Fig. $5-1.$ Use an AC equivalent circuit model that

includes R$\_($g$)$ to derive an expression for the voltage gain. Calculate the gain if the JFET. use the pi model

transconductance is $3$ mS $.$

Fig. $5-1.$ Source follower amplifier.

$($b$)$ The drain current of a JFET operating in the Ohmic region is given by$,$

I$\_($D$)=($I$\_($DSS$))/($V$\_($p$)^(2))[2($V$\_($GS$)+$V$\_($P$))$V$\_($DS$)-$V$\_($DS$)^(2)]$

i$.$ Derive an expression for the JFET small$-$signal channel resistance.

ii$.$ In the circuit of Fig. $5-2,$ the JFET V$\_($DS$)=0$V$.$ Determine the output voltage.