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ce in such a small signal model of CE circuit. Why "re" ( the small signal resistor of the emitter = VT/IE ) is not represented? However, I've noticed that it is shown in CE amplifier with emitter degeneration and also in CB, but not in CE without emitter degeneration nor CC amplifier circuits!

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Why "re" ( the small signal resistor of the emitter = VT/IE ) is not represented?

because it is internal to the device -> that's why it is in that shaded box.

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  • \$\begingroup\$ In the shaded box I see r(pi) and ro. Not re,? \$\endgroup\$ – utdlegend Mar 31 '17 at 18:44
  • \$\begingroup\$ @utdlegend Because this time \$re\$ is hiding inside \$r_{\pi}\$. As we all know \$r_{\pi} = \frac{v_{be}}{i_b} = \frac{\beta}{gm} = (\beta+1)*re \$ and \$gm = V_T/I_C = \frac{\beta}{(\beta+1)*re}\$ \$\endgroup\$ – G36 Mar 31 '17 at 19:18

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