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Homework Statement:
 Find the gain for this VGA
Relevant Equations:

I(sat) = k(V_gs  V_t)^2
M1 = M2 = M3
I need to find A_v, I want to relate Vin to Vout. To do this I did KVL on the major loop:
$$V_{DD} = I_D*R_D + V_{SD1}  V_{SD2}  I_D*R_D$$
Since M1 = M2 then everything would cancel out and I would just get V_dd = 0 which is probably wrong. This is assuming V_sd1 = V_sd2, is that correct?