How to multiply the frequency of a clock?

Is this an existing board or are you still designing. Your best bet is to use an external clock generator that you can "genlock" to your 50kHz clock. The external clock can either be a VCO or a digitally synthesized clock (AD9954 as an example). The important thing is you have to be able to control the frequency of it.

Then you have to write a phase detector and control the external clock to keep it locked to your 50kHz clock. How closely your generated clock tracks the 50kHz clock in phase and frequency will depend on the bandwidth of your loop filter. If you use a digital synthesis clock, I recommend using a PID controller.

I don't know that you can get to a high enough frequency inside a Cyclone II to allow you to do a digital PLL. Depends on your design requirements I suppose.

Jake