Whitepaper

Amplifier Classification A vs. AB

Exodus Advanced Communications

This application note from Exodus Advanced Communications details the differences between Class A, B, and AB amplifier designs. The paper focuses on bias characteristics affecting performance metrics like efficiency and linearity in RF & Microwave amplifiers utilizing devices such as LDMOS, MOSFETs, GaN, or GaAs. Class A amplifiers offer the best linearity (360° conduction angle) at 25-30% efficiency, while Class B achieves 70-80% efficiency but suffers from crossover distortion with a 180° conduction angle. The preferred compromise is Class AB, providing 50-70% efficiency and improved linearity by overlapping the conduction angles of paired devices in a push-pull configuration to minimize distortion. The document also clarifies that amplifier robustness isn't inherent to class but dependent on overall engineering design including heat dissipation and power supply sizing.