Common-Base Amplifier

The common-base (CB) amplifier is a BJT configuration where the base is AC-grounded. It offers low input impedance and high voltage gain, commonly used for high-frequency applications.

Key Relations

• Voltage gain ≈ g_m R_C
• Input impedance ≈ 1 / g_m
• Transconductance: g_m ≈ I_C / V_T

Example

For I_C=2 mA, g_m ≈ 0.002 / 0.0257 ≈ 0.078 S. With R_C=4 kΩ, A_v ≈ 0.078 × 4000 ≈ 312.

FAQs

Why low input impedance?
The emitter sees a small-signal resistance ~1/g_m.

Use cases?
RF stages and impedance-level shifting.