Emitter follower for bandgap reference

Thread Starter

user123random

Joined Feb 28, 2016
2
Can anyone show me how to prove the following circuits in picture are equivalent ?
I suppose, for PNP (Q2) emitter follower, V(base) is almost equal to V(Emitter). Am I missing something ?

 

Thread Starter

user123random

Joined Feb 28, 2016
2
I think both transistors are biased by PMOS with the same Vb



how to prove both circuits topologies (series diode and emitter follower) are equivalent ?
 

jaydnul

Joined Apr 2, 2015
175
Well if that is true, then think of the FETs as current sources with current = I.

Q1 biases itself, so for simplicity lets say Veb = 1V for our transistors to have a current = I. Q2's base is now raised to 1V, but in order for it to also have current = I, it's Veb must be 1V.

1V = Ve - 1V >>> Ve = 2V which is where you get the 2Vbe value in your schematic.
 
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