@Alex For the common emitter, the collector is treated as infinite impedance (current sink) unless the Early Effect is also added in (which it appears it is not in your example.) Because of that, the output impedance is RC (without RL included.) For the common collector, keep in mind that the emitter looks like a voltage source, not a current source. So little-re is there. The rest comes from the source impedance divided by beta+1. The main thing is to recognize that for CE, the collector acts like a current source, but for CC the emitter acts like a voltage source.
↧