Multi-stage Amplification

In order to have an amplification gain, multi-stage amplification circuits are needed. Such a circuit is typically composed of two or more cascaded transistor amplifiers, coupled in one of three possible ways:

• Capacitor coupling:
  • Independent DC operating point;
  • AC amplification of high gain if coupling capacitors are larger enough;
  • Cannot amplify DC and low frequency signals;
  • Difficult implementation on IC.

• Transformer coupling:
  • Independent DC operating point;
  • Can achieve maximal power by impedance match;
  • Cannot amplify DC and low frequency signals;
  • Difficult implementation on IC.

• Direct coupling:
  • DC operating point not independent;
  • Can amplify both DC and AC signals;
  • Easy implementation on IC.