Two-Stage BJT Amplifier Homework: Solving for Input Resistance and Voltage Gain

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SUMMARY

The forum discussion focuses on solving for the input resistance and voltage gain of a Two-Stage BJT Amplifier with a beta value of 100. Key equations utilized include Rinput = Rth, Vinput = VTH, and the voltage gain formula Gv = -Beta[(RC||RL)/Rsig + (beta + 1)re]. The user successfully calculated the Thevenin voltage (VTH) as 2.88V and the input resistance (Rinput) as 31.97K ohms. However, they encountered difficulties in completing the solution due to a missing "+" sign in their handwritten equation, which highlights the importance of thorough analysis and verification of each step.

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Homework Statement


see pic in the attachment
beta = 100

Homework 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

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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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.
 

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