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  • Advice in proper grounding

    hello all,

    iam new to this forum and need some hints in properly routing ground of a mixed signal pcb. sorry for my englisch skills

    I have a 4 layer board design with 4 identical channels of a analog circuit which gets controlled by dac´s and digital Potentiometers.

    At the top layer i have my components and traces, then on
    the upper inner layer i will use power lines and what i thought is to surround them with poured Ground.
    At the third layer i was thinking About Routing a complete groundplane accross the whole board
    At the Bottom layer i also thought About surrounding the NF Signal traces with poured Ground.

    But anyhow it doesnt feel Right and iam anyhow lost after reading and watching everything About Grounding multilayerboards. So i want to ask you how it would be more good.

    The power rails for the big top orientated analog sections are +9V and -9V, the Bottom section of the board onle handles digital spi stuff, cuz i Need fast update of the dac´s and on that side all runs at 3.3V

    Here is a Picture of the whole except for the unfinished power source connector. the red circle shows the 3 devices of each channel, the spi bus is routed too
    Also i tried to route the digital fast Signals on the two inner pcb layers and protect them via Ground on the outer layers.

    in the picture, ground is not visible. i use eagle cad.

    thanks to all



    Click image for larger version

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  • #2
    - I do not know much details about your design, but normally I try to have a solid GND as the second layer under components.
    - when I have analogue on one side and digital on the opposite site, I always try to have separate solid GND planes for them (means at least two solid GND planes in my stackup directly under outer layers, one for digital, one for analogue)

    But I do not do much mixed boards, I may not be the best to help.

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    • #3
      Does this video https://www.youtube.com/watch?v=52fxuRGifLU talk about a better 4 layer stack-up? Sig - Gnd - Gnd - Pwr/Sig. Otherwise there are more Rick Hartley video's that show it.
      Route the power, I doubt you need many amps of current.
      Both analog and high(er) speed digital need good return paths.

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