Q:

Do I have match impedance while routing PAL video tracks? 

I am designing a PCB with PAL video output.  PCB contains 50ohm and 100 ohm traces.  The connection between RF coax connector is very close.  So 75 ohm traces are 80 micron for my stack-up.  I am confused whether to route them so thin track or not.  Signal bandwith is 15MHz.  Any suggestions? 

A:

A golden rule for deciding on whether matching impedances are required is that if the highest signal frequency (including relevant harmonics) has a wavelength of X then, the longest un-terminated signal track is X/10. 
15 MHz has a wavelength of 20 metres so, you should consider using matching impedances and correct balanced routing (where applicable) if the connection length is longer than 2 metres.  
However, taking into account that the velocity of propagation along PCB tracks is about two-thirds of the speed of light means that the original 20 metre wavelength for 15 MHz (the maximum frequency) is reduced to 13.3 metres.  Hence the golden rule suggests un-terminated tracks no longer than 1.33 metres.