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Forum Index : Microcontroller and PC projects : RGBHV taces on PCB...width requirement?
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| Decoy Senior Member  Joined: 02/08/2019 Location: DenmarkPosts: 109 |
Hi guys I am wondering if there are any requirements for thickness of traces for video on PCBs? Also, should R, G, B be a different thickness than horizontal and vertical sync traces - or can it all be as thin as possible? They will run for no more than 10 cm on the PCB. Thanks! Nicholas |
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| Volhout Guru  Joined: 05/03/2018 Location: NetherlandsPosts: 3476 |
Hi Decoy, The short story: no, on this board you can route them any width you like. With 10cm length you have no problems at all. If you want the best video, you should however provide isolation between the 5 signals r,g,b,vsync,hsync Industry standard is to provide 3x trace width clearance. Meaning that with 0.2 mm trace width, the traces should be kept 0.6mm appart. (Btw that is also good practise for sensitice digital signals like I2C) Technical The 10cm is soo much shorter than the wavelength of the highest frequency of the signals on rgb, that controlled impedance traces is not needed. The copper losse will cause attenuation of the video. But the resistance of 10cm copper traces, even at 0.12 mm trace width can be ignored, and otherwise compensated in the serial termination resitance of the video dricer. So...route anyway you like, but keep traces away from eachother and the other signals on the board. Succes, Volhout P.s. For the best video it is essential that there is a continuous ground between video chip and connector. No gaps in ground plane, an ground preferably under the r,g,b,hsyn,vsync signals. Edited 2020-02-02 21:30 by Volhout PicomiteVGA PETSCII ROBOTS |
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| Decoy Senior Member Joined: 02/08/2019 Location: DenmarkPosts: 109 |
Volhout, thank you very much for your answer! That was a very nice explanation! |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
A very good explanation. Noise is absolutely critical, even millivolts of ground noise from adjacent digital circuitry will become very obvious on the screen in plain background areas such as the light grey areas on the display you are looking at right now. Solid unbroken ground plane goes a long way to achieving that. Impedance matching comes in as a very close second requirement. Both the source and the destination need to be correctly terminated, the source being the most important. Usually its 75 ohms, but not always. Track widths and board thickness are important at microwave frequencies, but seem to have no noticeable effects at much lower video frequencies. Looking at rgb video on a spectrum analyser there is very little energy over about 200 Mhz. So just use normal track widths and spacings any you won't have any problems. Cheers, Tony. |
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