Electrical – What determines input /output impedance of a transistor configuration


I cannot intuitively get any answer about how CE CB CC have different output/input impedance

Best Answer

When the AC voltage is the same but AC current is buffered by hFE then the Emitter Follower or CC transforms impedance on the other side of base or Emitter by hFE in each direction looking in. Thus Zin at Base is hFE larger than Emitter load and Zout of Emitter is hfe smaller than Rb (equiv) or Zbase (equiv)

A transistor circuit design can amplify voltage, or current or lower impedance or increase both V*I at same impedance.

It's like gears and torque or force or impedance from either side is transformed by gear ratio.