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Homework Statement
Find the voltage gain [itex]A_{v}[/itex]
http://imageshack.com/a/img692/3117/qkwp.png
Homework Equations
The Attempt at a Solution
Is this the correct small signal equivalent?
http://imageshack.com/a/img203/5812/1yfe.png
I'm trying to find the output impedance [itex]Z_{O}[/itex] but can't seem to derive the correct output voltage?
Apparently
[itex]i_{O} = i_{D}(1 + g_{m}R_{S} + \frac{R_{D} + R_{S}}{r_{d}})[/itex]
I'm trying to solve for the output voltage using
[itex]A_{v} = \frac{v_{O}}{i_{O}} = \frac{i_{D}R_{D}}{i_{O}}[/itex]
I'm trying to find a expression in which [itex]i_{O}[/itex] is a function of [itex]i_{D}[/itex] and the resistors etc and try to get [itex]i_{D}[/itex] to cancel out so that way I can calculate the output impedance.
I have a feeling that my small signal circuit is incorrect.
Thanks for any help.
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