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I am trying to calculate the Input Resistance and Mid-band Gain of a CE-CE stage.

Here's what I got so far:

enter image description here

I am having some doubts regarding my calculations though. Mainly with the input resistance. Can we really ignore the second transistor when calculating Rin?

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What I've learned, the input resistance in emitter circuit \$ r_e \approx r_{BE} = \beta U_T / I_C \$, the \$ U_T \$ is the temperature voltage of about 26 mV at room temperature. More precisely: $$ U_T = kT/e_0 = \frac{1.38\cdot10^{-23} \text{ J/K} \cdot 296 \text{ K}}{1.60\cdot 10^{-19}\text{ C}} = 25.5 \text{ mV}$$ The output doesn't influence the input resistance so much and can be neglected in that emitter circuit.

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  • \$\begingroup\$ Sorry for the late response. What about the gain though? Is it really just double the gain of a single CE? \$\endgroup\$ – user3601507 Dec 20 '18 at 17:38

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