inductor source degenareted LNA

hello,

I'm trying to desing a inductor source degenareted LNA which its topology can be found in Tom lee 's book.
I was wondering why we should tuned out the output. I know the reason actually , to increase the gain. But how does Ldrain do this? With CL of the next stage it should be resonate to achieve the maximum gain . At resonance frequency output is thus pure ohmic .. what it is the purpose of doing this?

thanks for the answer..

o/p capacitance usedto represent the load next stage is(or load is MOSFET) that oxide layer produce capacitance effect. so output represented by a capacitor. inductor is used for band width enhancement

Hello,
Also I would like to know what Zout shoul be of my LNA . If its off chip most probably its 50 Ohm but if it on chip it is not necessary to be 50 ohm but how can I know the exact value?