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Common-emitter amplifier

Op-amps and analog ICs · Advanced · about 20 minutes · part of Zen’s Electronics Design Mastery

The classic one-transistor amplifier. R1–R2 bias the base, R_E sets the emitter current and stabilises it, and a small signal on the base swings the collector current, so the collector voltage swings by −(R_C ∥ R_L)/(R_E + r_e) times as much, inverted.

Common-emitter amplifier: the circuit on the simulator's bench

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How it works

VB ≈ VCC · R2/(R1+R2) = 2.105 V; IE ≈ (VB − 0.65)/RE = 1.38 mA; VC = 5.557 V

re = 26 mV / IE = 18.7 Ω

Av = −(RC ∥ RL) / (RE + re) = −4.41

Try it on the bench

  1. Raise V_in to 1 V: the collector swing hits the rails and the output clips.
  2. Set R_E to 470 Ω: more gain, but the bias point moves too.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Transistors”.

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