Transistor Amplifiers: NPN Configuration and Characteristics

This lecture covers the principles of bipolar junction transistors, focusing on NPN transistors as voltage amplifiers. It begins with a reflection exercise on the band diagram of a PNP transistor and the concepts of gain in common base and common emitter configurations. The instructor explains how to optimize gain and defines transconductance in the context of an NPN transistor. The lecture details the process of setting the operating point and introducing an AC signal, along with the calculation of gain. The characteristics of input and output are discussed, including the relationship between base current and collector current. The importance of coupling capacitors for AC signals is emphasized, as well as the stability of the operating point. The lecture concludes with typical values for silicon BJTs, including current gain and transconductance, providing practical insights into the performance of NPN amplifiers in real-world applications.