Amplifiers have many classifications, and each class has its advantages and disadvantages. The different classes of amplifiers are A, B, AB, C, D, E, F, T, and even more “alphabet soup.” Designers typically work with classes A, B, AB, and C.
The class A amplifier has high linearity with high gain ability. It has a 360-degree conduction angle that leads to the amplifier remaining in the active state at all times, and it’s able to use the entire input signal. The class A amp has good high frequency and feedback-loop stability. A drawback is that it only has 25% to 30% efficiency.
Class B amplifiers use two active devices that are biased one-by-one, each in half of the actual full cycle, meaning that every device will only be biased during 180 degrees of the cycle. Two transistors provide the combined current drive to the load. This improves the efficiency as compared to the 25% to 30% efficiency of the class A amp.