written 6.9 years ago by |
Step 1: Circuit Diagram
Step 2: Finding $I_{DSQ} and V_{GSQ}$
Since mid-point biasing is mentioned then,
$I_{DSQ}=\frac{1}{2}I_{DSS}=\frac{1}{2}\times8mA$
$I_{DSQ}=4mA$
We know that,
$I_{DSQ}=I_{DSS}(1-\frac {V_{GSQ}}{V_P})^2$
$4mA=8mA(1+\frac{V_{GSQ}}{3})^2$
$V_{GSQ}=-0.87V$
Step 3: Finding Rs
$V_{GS}=-I_{DSQ}\times R_s$
$-0.87=-4mA\times R_s$
$R_s=217.5\Omega$
Step 4: Finding Rd
Apply KVL from $V_{DD}$ to Ground,
$V_{DD}-I_{DSQ}(Rd+Rs)-V_{DSQ}=0$
Since mid point biasing is mentioned,$V_{DSQ}=\frac{1}{2}V_{DD}$
$V_{DD}-V_{DSQ}=I_{DSQ}(Rd+Rs)$
$V_{DD}-\frac{1}{2}V_{DD}=I_{DSQ}(Rd+Rs)$
$\frac{1}{2}V_{DD}=I_{DSQ}(Rd+Rs)$
$\frac{1}{2}V_{DD}=4mA(Rd+217.5)$
Assume, $V_{DD}= 20V$
10=4mA(Rd+217.5)
$Rd=2.28K\Omega$
Step 5: Finding$ R_G$
As JFET Gate and Source is reverse bias it offers very high input impedance in $M\Omega$
Hence,
$R_G=1M\Omega$
Step 6: Designed Circuit Diagram