Q6Analog Electronics

Question

(B) Compare the common source, common drain & common gate amplifiers with its input and output characteristics.

Answer 1

Common Source (CS): Input at Gate, Output at Drain, Source is common. Voltage gain $A_{v} = - g_{m} R_{D}$ (inverting, high gain). High input impedance, moderate output impedance. Analogous to BJT Common Emitter.
Common Drain (CD) / Source Follower: Input at Gate, Output at Source, Drain is common. Voltage gain $A_{v} \approx + 1$ (non-inverting). Very high input impedance, very low output impedance. Used as a buffer. Analogous to BJT Common Collector (emitter follower).
Common Gate (CG): Input at Source, Output at Drain, Gate is common. Voltage gain $A_{v} = g_{m} R_{D}$ (non-inverting, high gain). Very low input impedance ( $\approx 1/ g_{m}$ ), high output impedance. Good for high-frequency applications. Analogous to BJT Common Base.

Summary Table: CS â€” high $A_{v}$ , high $R_{in}$ , medium $R_{o u t}$ , 180Â° phase shift. CD â€” $A_{v} \approx 1$ , very high $R_{in}$ , very low $R_{o u t}$ , 0Â° phase shift. CG â€” high $A_{v}$ , low $R_{in}$ , high $R_{o u t}$ , 0Â° phase shift.

Q6Analog Electronics

Question

Answer