Single Stage Amplifiers

Ideal amplifier

• Linear
• Infinite input resistance
• Infinite driving capability

\[ v_{out}= A_v v_{in} \]

Common source amplifier

A single-transistor amplifier with the source connected to AC ground.

CS-stage with resistive load

• \(V_{in} < V_{TH}\): cut off, \(V_{out} = V_{DD}\)

• \(V_{in} - V_{TH} < V_{out}\), saturation, \(V_{out} = V_{DD} - I_dR_D\)

• \(V_{in} - V_{TH} > V_{out}\), linear

\[ A_v=\frac{\partial V_{o u t}}{\partial V_{i n}}=-\mu_n C_{o x} \frac{W}{L}\left(V_{i n}-V_{T H}\right) \cdot R_D \]

\[ A_v = -g_m R_D \]