## Q. 4.3

For the amplifier of Example 4.2, let $v_i = \sin t(ω = 1 rad/s)$ and $C_S → ∞$.   Graphically determine $v_{ds}$ and $i_d$.

## Verified Solution

Since $C_S$ appears as a short to ac signals, an ac load line must be added to Fig. 4-6(b), passing through the $Q$ point and intersecting the $v_{DS}$ axis at
$V_{DSQ} + I_{DQ} R_{ac} = 12.5 + (1.5)(3) = 17 \text{V}$

We next construct an auxiliary time axis through $Q$, perpendicular to the ac load line, for the purpose of showing, on additional auxiliary axes as constructed in Fig. 4-6(b), the excursions of $i_d$ and $v_{ds}$ as $v_{gs} = v_i$ swings $±1 \text{V}$ along the ac load line.   Note the distortion in both signals, introduced by the square-law behavior of the JFET characteristics.