What are you trying to achieve with your modulated signal? OOK? Non-suppressed carrier? Suppressed carrier? You need to be clear about your goals. 555 timers are normally suited for anything but basic modulation schemes.

@Andy aka: it would be OOK (I just learned the term now).

How do you intend to connect it to the MOSFET? If you mean to have the 555 timer on the gate, then you'll have to be very careful with which part to pick, since most MOSFET aren't fast enough to live up to your realtime spec. What 555 timer are you using? In case it's a single chip IC, there should be parts with built-in BJT for the output.

@Lundin: I would connect the slow signal at the gate, and the fast signal (from 555) at the source. I would use the NE555 (TI). That should work, right?

@mrwavelets‭ So the MOSFET is not there to give a higher voltage needed for the amplitude? In that case it isn't necessary, since your particular part can drive a relatively high current directly.