Because circuit design becomes increasingly complex and high-speed, how you can ensure the integrity of various signals (especially high-speed signals), that is, to make sure signal quality, has gets a problem.
At this stage, will certainly take advantage of tranny line theory to analyze. Control signal characteristic impedance matching becomes the important point. Non-strict impedance manage will cause considerable transmission reflections and signal effects, leading to design problems.
Common signals such since PCI bus, PCI-E tour bus, USB, Ethernet, DDR memory space, LVDS signals, etc., just about all require impedance control. Impedance control ultimately needs to be realized through PCB design, and higher needs for PCB board technological innovation.
To make sure typically the quality of signal inside complex design, we need to control the opposition and reactance of a great electrical circuit.
Like single-ended impedance 50 ohm ±10%， differential impedance 100ohm ±10%.
The impedance of a PCB is largely determined by these parameters:
Distance regarding signal layer and potential