Class A, B, AB, C, D Amplifiers: The Trade-off Between Efficiency and Linearity
Time：2026-04-07 Views：4
The class of a power amplifier is determined by its conduction angle, and each class makes a different trade-off between linearity and efficiency. From classic Class A to switching Class D, each has its best-suited applications.
Class A has a 360° conduction angle; the transistor is always on. It offers the best linearity and lowest distortion, but its theoretical maximum efficiency is only 50% (typically below 35% in practice). Class A is used in high-fidelity audio and ultra-low-distortion test & measurement front-ends.
Class B (180° conduction) raises efficiency to about 78.5% but introduces crossover distortion. Class AB lies between A and B (180°-360° conduction) and is the most widely used class today, offering a good balance for base stations, walkie-talkies, and radar. Class AB efficiency ranges from 50% to 60% with acceptable linearity.
Class C (conduction angle <180°) can achieve >80% efficiency but has poor linearity, making it unsuitable for amplitude-modulated signals. It is used in FM broadcast transmitters, resonant wireless charging, and other constant-envelope or switching applications.
Class D uses transistors as switches, with theoretical efficiency of 100% (over 90% in practice). It is mainly used in audio amplification and some RF power sources (e.g., Class E, Class F). However, the output requires a low-pass filter to recover the waveform, and switching frequency is limited.
How to Choose?
For modern wideband modulated signals (5G, WiFi 6), Class AB remains the mainstream foundation, but combined with Doherty or envelope tracking, effective efficiency is greatly improved. Ampbuc offers multiple classes of amplifier modules and recommends the optimal architecture for each customer’s signal characteristics.
Class A has a 360° conduction angle; the transistor is always on. It offers the best linearity and lowest distortion, but its theoretical maximum efficiency is only 50% (typically below 35% in practice). Class A is used in high-fidelity audio and ultra-low-distortion test & measurement front-ends.
Class B (180° conduction) raises efficiency to about 78.5% but introduces crossover distortion. Class AB lies between A and B (180°-360° conduction) and is the most widely used class today, offering a good balance for base stations, walkie-talkies, and radar. Class AB efficiency ranges from 50% to 60% with acceptable linearity.
Class C (conduction angle <180°) can achieve >80% efficiency but has poor linearity, making it unsuitable for amplitude-modulated signals. It is used in FM broadcast transmitters, resonant wireless charging, and other constant-envelope or switching applications.
Class D uses transistors as switches, with theoretical efficiency of 100% (over 90% in practice). It is mainly used in audio amplification and some RF power sources (e.g., Class E, Class F). However, the output requires a low-pass filter to recover the waveform, and switching frequency is limited.
How to Choose?
For modern wideband modulated signals (5G, WiFi 6), Class AB remains the mainstream foundation, but combined with Doherty or envelope tracking, effective efficiency is greatly improved. Ampbuc offers multiple classes of amplifier modules and recommends the optimal architecture for each customer’s signal characteristics.
