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Z(out) for small signal analysis with BJT for unbypassed emitter and r0 in place

Electrical Engineering Asked by user7058377 on December 24, 2021

from

enter image description here

this BJT small signal I try to solve Z(out) but I find

RC || (ro + RE)

because Z(out) is calculated with ib = 0 => beta ib = 0

from this link too V(in) was calculated

But the expression for Zo given in the book by Boylestad and Nashelsky is

Zo = RC || [ro + β (ro + re) / (1 + β re / RE)]

Can You explain how to retrieve this ?

2 Answers

If you put the equations correctly:

point C :   io vo ve ib
point E :      vo ve ib
ib def  :         ve ib

3 unknowns : (vo OR io) AND ve AND ib

to get vo = function(io) OR io = function(vo)

enter image description here

Answered by user7058377 on December 24, 2021

Solution : Vi = 0 not => ib = 0 enter image description here

Answered by user7058377 on December 24, 2021

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