Hi
As MSSN asked, What kind of circuit do you need the high frequency clock for?
You can't say only “300Mhz”.
At less, you need to know the following characteristics:
Jitter
Output Level
Duty Cycle
Tolerance (%)
Output Power
Max Consumption
Usually for this frequencies, you can use a based crystal oscillator (reference), VCO (oscillator), Comparator and a divider (prescaler). That is PLL.
Don’t forget the temperature range, it is very important. (Temperature compensated)
Regards
Pont de Pedra