With the increasingly complex and high-speed circuit design, how to ensure the integrity of various signals (especially high-speed signals), that is, to ensure the signal quality, has become a difficult problem. At this time, it is necessary to analyze with the help of transmission line theory, and control the characteristic impedance matching of the signal line becomes the key. If the impedance control is not strict, it will cause considerable signal reflection and signal distortion, resulting in design failure. 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 achieved through PCB design