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Lesson 9 - LENGTH MATCHING

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  • Lesson 9 - LENGTH MATCHING

    Hello.
    Is the first time I do memory layout, so excuse me if I ask stupid questions. I am trying to do the length matching to complete lesson 9 of the SCHEMATIC & PCB DESIGN course. I have been looking at the spreadsheet to know what should be the final length of the tracks. For example, for the line DRAM_D0, the total length should be 783. When I measure it in Altium, the length is ridiculous small compared to the length it should have. Take a look at the images, I am pretty sure I have not understand something...

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    Click image for larger version

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    What I do not understand? Thank you in advance.

  • #2
    I believe you are confused by the units. In the table you have the lengths in mills (1 thousandth of an inch or 0.0254 mm). In Altium you currently have the units in mm (it can be seen in the PCB panel). You can switch between units by pressing Q.

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  • #3
    Yes, I also think you may need to change units. The Excel is in "mils" and your PCB looks like "mm". Let us know if it helped.

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    • #4
      Yes. The problem seems to be the units. I was a little bit tired when I tried to do the activities...Sorry for the stupid question.

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      • #5
        Don't worry Problem solved, that is important

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        • #6
          In your training videos, yo are referring to POLAR spreadsheet to set line width and spacing, is this POLAR tool part of Altium? or it is some third part tools?
          To the best of my knowledge there is no stack up setup and simulation tool inside Altium, where we should get this information? Can we ask it from PCB manufacturer before start routing?

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          • #7
            You can use the Saturn PCB toolkit which is free and is probably good enough [1]. Some manufacturers can determine your stack up (with third party software that they have purchased) if you specify the trace width, trace impedance and the gap width for differential pairs for each layer. Have a look at the iMX6 Rex Module and highlight the manufacturing notes layer.

            [1] http://www.saturnpcb.com/pcb_toolkit.htm

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            • #8
              IMR, answer is perfect. Thank you

              - I would like to add, that POLAR is a separate software used by many PCB manufacturers
              - This may help you: How to design PCB stackup. I have created several posts about stackup design and how to get it. Try to search at my blog: http://www.fedevel.com/welldoneblog/?s=stackup

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