Transistor Configurations: Common Base and Common Emitter

This lecture covers the configurations of bipolar transistors, focusing on the common base and common emitter setups. It begins with an introduction to the common base configuration, where the base is grounded, and discusses the input and output circuits. The instructor explains the current gain in this mode, represented by alpha, which typically approaches 0.99 due to the high beta value of the transistor. The lecture then transitions to the common emitter configuration, detailing how the emitter is grounded and the relationships between input and output currents. The instructor emphasizes the importance of optimizing the transistor's structure to achieve a high beta value, which is influenced by the doping levels of the emitter and base. The concept of Early voltage is introduced, explaining how it affects the transistor's performance. The lecture concludes with a discussion on the ideal structure for bipolar transistors and how to estimate Early voltage, highlighting the relationship between collector current and the width of the depletion region.