The CPU needs an external lvds interface screen. The solution is to first use the chip to convert parallel RGB data into lvds differential pairs, and then connect to the LCD. See the typical application schematic diagram in the manual of the conversion chip:
This made me wonder, because I saw it on the Internet: In PCB design, LVDS differential pairs need to be controlled by 100ohm impedance.
1. In the above figure, the 100ohm resistor connected in parallel between the differential pair refers to the actual resistance? Or just a reminder that 100ohm impedance control should be done here?
2. If it is the former, then the 100ohm resistor should be used for another purpose, which is different from the impedance control during PCB manufacturing. Therefore, when designing the PCB, it is still necessary to control the impedance, just like the DDR clock. Is that correct?
Minerva Posted on December 11, 2020
1. This 100 ohm is the actual resistance, which is used for impedance matching, because pure PCB impedance control is sometimes difficult to achieve complete matching
2. PCB impedance control is still to be done. If you have learned signal integrity, you will know that if impedance matching is not done, the signal will be reflected and the signal integrity cannot be guaranteed. This is fatal in high-speed signal transmission
Sora Posted on December 11, 2020
This kind of differential line needs strict impedance matching, and equal length and distance are necessary.
Nicklas Posted on December 11, 2020
This 100 ohm impedance is the internal impedance of the chip GM8285 pairwise differential signal pin, so there is no need to add another 100 ohm impedance during design.
