Push-Pull Pair - Class B, Class AB and Class A operation

In this video Gregory will explain the working principle behind push-pull pairs or complementary emitter follower stages. The differences between Class B, Class AB and Class A of operation is discussed and a practical circuit is explained and develop for demonstration on the bench.

00:22 - Working principles
08:03 - Biasing for Class B operation
10:54 - Improvements by Class AB
14:26 - Current waveforms
15:55 - Condition for Class A operation
16:41 - Output impedance discontinuity in Class AB
20:38 - Bench circuit description
27:42 - Waveforms on the scope
33:09 - Ending

Push-pull stages are fundamental building blocks of electronics design and are present in all kinds of circuits, from high power, high fidelity and digtal high speed.

Many operational amplifier use push-pull stages on the output to provide low impedance to drive real world loads. Many analog or digital signal need to be transmitted with matched impedance lines and this kind of output stage provides the power gain necessary for signal transmission even between different signal domains.