As circuit design becomes increasingly complex and high-speed, how to ensure the integrity of various signals (especially high-speed signals), that is, to ensure signal quality,has becomes a problem.
At this point,will take advantage of transmission line theory to analyze. Control signal characteristic impedance matching becomes the key point. Non-strict impedance control will cause considerable signal reflections and signal distortions,leading to design failures.
Common signals such as PCI bus, PCI-E bus, USB, Ethernet, DDR memory, LVDS signals, etc., all require impedance control. Impedance control ultimately needs to be realized through PCB design, and higher requirements for PCB boardtechnology.
To make sure the quality of signal in complex design, we need to control the resistance and reactance of an electrical circuit.
Such assingle-ended impedance 50 ohm ±10%， differential impedance 100ohm ±10%.
The impedance of a PCB is largely determined by the following parameters:
Distance of signal
layer and potential