This document describes the common collector (CC) amplifier circuit, also known as an emitter follower. It provides the key equations for analyzing the CC amplifier, including expressions for output voltage, current, gain, input and output impedances. It also discusses the Darlington amplifier and series regulator circuits. The key points are: - The CC amplifier has a voltage gain approximately equal to 1 and a high input impedance and low output impedance. - Gain, input and output impedances depend on factors like the transistor's beta and the resistor values. - The Darlington amplifier has an extremely high input impedance due to its double beta gain stage. - A series regulator provides a stable output