The ac equivalent circuit of a common-source amplifier is shown in Figure P4.18. The small-signal parameters of

Question:

The ac equivalent circuit of a common-source amplifier is shown in Figure P4.18. The small-signal parameters of the transistor are $g_{m}=2 \mathrm{~mA} / \mathrm{V}$ and $r_{o}=\infty$.

(a) The voltage gain is found to be $A_{v}=V_{o} / V_{i}=-15$ with $R_{S}=0$. What is the value of $R_{D}$ ?

(b) A source resistor $R_{S}$ is inserted. Assuming the transistor parameters do not change, what is the value of $R_{S}$ if the voltage gain is reduced to $A_{v}=-5$.

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