# Homework Help: Two stage amp (BJT) homework

1. May 30, 2017

### Alkozy

1. The problem statement, all variables and given/known data
see pic in the attachment
beta = 100
2. Relevant equations
Rinput=Rth
Vinput=VTH
iB= ic/beta
IE=ic /alpha
iB=iE/(beta+1)
gm=IC/VT
Avo=-gmRC
Av=-gm(RC||RL)
Gv=-Beta[(RC||RL)/Rsig+(beta+1)re
re=alpha/gm

3. The attempt at a solution
solving each stage separately. First DC analysis. open all Capacitors.
V thevinin can be obtained by voltage divider = 2.88 v
R input = 31.97 K ohm
loop between the base and emitter
2.88-iB (31.97k)-0.7-iB(beta+1)(3.9k)=0
I have attached a pic of my attempt to solve it. please see attachment 2

i couldn't complete the solution

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Last edited by a moderator: Jun 1, 2017
2. Jun 1, 2017

### Staff: Mentor

There is an important "+" sign missing from your first handwritten equation, iB = 2.88 (31.97k .....

This is something you would have readily discovered by repeating your analysis from scratch. Often that is the most expedient course, when trying to identify ones mistake.