BJT diff amp question

Thread Starter


Joined Nov 13, 2011
You are not making any sense
In post #19 you tell me not to use the diagram i drew

Then you tell me to use it?

Please clarify?

Thanks for your help


Joined Feb 17, 2009
I think that the answer to your question is symmetry. Because this circuit is all about symmetry we can split 250 in half.
Additional notice that from small-signal AC analysis the current source are open circuit. So, the resistance between two emitters dose not change. And the differential amplifier is a cascade connection of the two "basic" BJT amplifiers. The first one is CE (Common emitter) and the second stage is CB (Common base) stage.
Also notice that Vdi = Vbe1 + Veb2 (from KVL loop). And this means that as Vbe1 increase Vbe2 must decrease by the same amount.
For example if Vbe1 changes from 0.60V to 0.61V the Vbe2 will drop by 0.01V from 0.6V to 0.59V.
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