robertferanec , 03-07-2019, 02:07 AM
I guess, you are asking about PCB impedance. In this case, impedance are some characteristics / parameters of tracks which you route on PCB. For example wider track have different parameters than thinner tracks. Also, if you route tracks closer to GND plane, these tracks will have different parameters as if you route them far away from GND plane.
Now, when you are routing important tracks (for example high speed), you need to use tracks with specific parameters (so signal quality is kept the best) - this means, you need to follow recommended impedance (e.g. general recommended impedance for digital signals is 50 OHMs) .... this means, that for example you have to use specific track width on your PCB when you are routing these important signals.
Impedance in PCB depends on your stackup (e.g. what materials you use or how thick the layers are) and on your track geometry. The best is to play with an impedance calculator - you can for example download free tool called Saturn PCB. But real impedance you only can get from PCB manufacturer - they will for example tell you exactly what track width you need to use for specific stackup to get specific impedance.
I am not sure what you mean by the second question.