Understanding why R_E is in parallel with g_m in a BJT

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R_E is in parallel with 1/g_m1 in a BJT small signal model due to the relationship between emitter resistance and transconductance. The discussion highlights confusion around the role of parameters like V_A and r23, indicating a need for clearer definitions. The analysis assumes β approaches infinity to simplify the circuit, suggesting that circuits dependent on β are less desirable. Participants express uncertainty about the implications of this assumption on the overall analysis. Understanding these relationships is crucial for accurately modeling BJT behavior in small signal applications.
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Homework Statement


Why is R_E in parallel with 1/g_m1?
I drew the small signal model but it does not make sense to me


Homework Equations


70-2a8fc58e7f.jpg



The Attempt at a Solution

 
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I get that V_A is given by a voltage divider, but why is R_E in parallel with 1/g_m1?
 
Q3 is just a diode so gm3 can't play a role.

What is r23? What is VA? You need to define some of these parameters. I assume gm = β but am not sure ...

I analyzed the circuit assuming β → ∞. Why? Because any circuit that is β-dependent is not a good circuit.

So I got what looks like your expression if gm → ∞. I know that's not what you are trying to find out - sorry.
 

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