# What is the significance of Input Resistance and Output Resistance in CE,CC,CB amplifiers?

Common Emitter, Common Collector and Common Base amplifiers have their specific purpose with differing voltage/current gains. For example, I know for a common collector has a voltage gain of approximately one, lagging behind 0.7 volts and has a high current gain.

But each amplifier configurations also have differing Rin and Rout characteristics, namely

CE Amplifier - Rin ~ moderate, Rout ~ moderate
CC Amplifier - Rin ~ large, Rout ~ small
CB Amplifier - Rin ~ small, Rout ~ moderate


Why is this information regarding input and output resistance important in these amplifiers? What purpose do they serve?

• 'What purpose do they serve?' To place proper loads on their inputs and outputs. – EM Fields Jan 26 '16 at 0:31
• So, if you know that circuit analysis is required, why don't you just do the circuit analysis with variable input and output impedance loads, see what happens, and answer the question for yourself? – EM Fields Jan 26 '16 at 0:51