I'd like to calculate the gain of a common emitter transistor circuit I'm looking at that has a a constant current source as the emitter load. Now I know the gain is going to be -gm(Re||RL) but how do I calculate what the effective resistance of the current source is? The current source I'm using is one that uses a Zener diode to keep a constant voltage across base to emitter junction, and thus a constant current through the collector of and the emitter to collector of the input transistor.(adsbygoogle = window.adsbygoogle || []).push({});

A tangentially related question is, if I were using a Darlington pair as the device connected to the constant current source instead of a transistor, how would I go about calculating the transconductance of the Darlington? Thanks for any assistance!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Calculating the effective impedance of a current source

**Physics Forums | Science Articles, Homework Help, Discussion**