Questions about High Speed PCB impedance
When designing a high speed digital design including an FPGA and GSPS A/D interfaced with multi-gigabit/s serial ports. I have some questions like following:
1.When I use tools to calculate the impedance of a trace on a PCB. The impedance is irrelevant to the length of a trace in these tools. But as I know the impedance of a trace should depend on its length.So I am confusing about it.
2.In a serial port, is the impedance matched by using series termination resistors or by tuning the traces themselves to suitable width or distance?
3.Led light on what situation in general we should use resistors and on what situations the traces make the desired impedance?