Now I am studying about the behavior of the Q-factor in the resonant circuit because the Q-factor of the circuit directly determine the performance as the EOM driver.
Here I summarize the fundamental which explains why Q-factor is important.
The EOM driver circuit can be approximately described as shown in figure below
Z represents the impedance of a resonant circuit.
In an ideal case, the transformer just raise the voltage level n-times larger. Rin is the output impedance of the signal source and usually has 50[Ohm].
The transformer also makes the impedance Z 1/n^2 smaller. Therefore this configuration gives a following relation between Vin and Vout.
Where G is the gain for the voltage. And G goes to a maximum value when Rin=Z/n2. This relation is shown clearly in the following plot.
Note that I put Rin=50 [Ohm] for calculating the plot.
Under the condition Rin=Z/n2( generally referred as impedance matching ), the maximum gain can be expressed as;
It means that larger Z makes more efficient gain. In our case, interested Z is considered as the impedance at a resonance.