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Problem with bootstrapped emitter follower!



Jan 1, 1970
Hi, I'm studing the bootstrapped emitter follower amplifier, but I don't
understand how Zi is given by Zi = Rboot/( 1 - A ), where A is the gain.

In my book the explanation of this formula is this:

An input wiggle of vin result in an emitter wiggle ve +-= vi ( sorry for
the +-= I don't know how to write that the two quantity aren't perfectly
equal :) ).

So i = (vin - ve )/Rboot +-= 0, i.e Zin = vin/Iin = infinity.

Why in this analysis ib ( the current that through the transistor ) is

Thank for your help!