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Homework Statement
Calculate ##R_S## given the expression:
$$A_v = - \frac{g_m (R_L || R_D)}{1 + g_m R_S}$$
The parameters ##g_m = 1.292 \frac{mA}{V}##, ##R_L = 180 k \Omega##, ##R_D = 18 k \Omega##, ##A_v = 5 \frac{V}{V}##.
Homework Equations
The Attempt at a Solution
My question is about the negative sign. When I go to compute ##R_S##, do I pretend the negative sign isn't there or something? If I leave the negative sign in the calculation I get:
##R_S = - 4.05 k \Omega##
Resistances must be positive, so the above does not make physical sense.
If I pretend the negative sign isn't there then I get:
##R_S = 2.5 k \Omega##
What is the proper way to compute the resistance?
EDIT: I believe the gain should be ##A_v = -5 V/V## even though it was given as 5, so the resistance ##R_S = 2.5 k \Omega## should be correct.
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