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MicroZed Hardware Design MicroZed signal propagation speed
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MicroZed signal propagation speed

apacker@biosonicsinc.com
apacker@biosonicsinc.com over 3 years ago

Hello,

I am using MicroZed 7020, industrial temp version, with a custom carrier board developed in-house.  I am trying to calculate some signal propagation times to enter into Vivado as "set_input_delay" and "set_output_delay" constraints.  I am new to this so I may be misunderstanding something very basic or simply not know where to look in the docs for the info I need.  But my understanding so far is that to calculate the propagation time between a Zynq IO port and the corresponding pin on the MicroZed JX1/JX2 connector, I need to know the length of the net in the MicroZed PCB itself, as well as the propagation speed in that net.  I found the list of net lengths for the MicroZed.  So for example, if I am using Zynq pin T14, which is connected to JX1.23 by the net JX1_LVDS_4_P, I can look up and see that the length of JX1_LVDS_4_P in rev G of the MicroZed is 2163.282mils.  But how do I figure out the propagation speed?  My understanding is that it depends on the materials used in the MicroZed PCB.  Is that info in the documentation somewhere?  Thanks very much!

-Asa

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  • jafoste4
    jafoste4 over 3 years ago +1 verified
    Hi Asa Please refer to the Carrier Design Guide for MicroZed and the MicroZed Net Length report for the SOM you are using. This is all available in the technical documents section located here /products…
  • jafoste4
    +1 jafoste4 over 3 years ago

    Hi Asa

    Please refer to the Carrier Design Guide for MicroZed and the MicroZed Net Length report for the SOM you are using. This is all available in the technical documents section located here

    /products/devtools/avnetboardscommunity/w/boards/23075/microzed

    For reference you should be able to get away with matching the lengths based on the Carrier Design guide using the net length reports.

    But if you want to dig into propogation delays here are the metrics associated with the SOM PCB

    mm to inch conversion 25.40 mm/in
    mil to inch conversion 1000.00 mil/in
    mm to mil conversion 0.0254 mm/mil
    mil to mm conversion 39.37 mil/mm
    PCB Trace Constant (interior layer) 170.00 ps/in
    6.69 ps/mm
    0.17 ps/mil
    PCB Trace Constant (exterior layer) 136.00 ps/in
    5.35 ps/mm
    0.14 ps/mil

    -Josh

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  • apacker@biosonicsinc.com
    0 apacker@biosonicsinc.com over 3 years ago in reply to jafoste4

    Hi Josh,

    Thanks very much for this info!  I think this is exactly what I need.  I don't think matching net lengths applies to my issue because I am talking to a serial ADC, sending it an SCLK signal from the Zynq, and then reading the data back at the Zynq.  So I have to take account of the time SCLK takes to get to the ADC, and the time the data takes getting back to the ADC, to know when to sample it.

    Is the table you sent available in the documentation somewhere?  Would the same values apply to all flavors of MicroZed?  I mean 7010 v 7020, commerical temp v industrial.  What about PicoZed?  We are likely going to migrate at some point to the PicoZed 7020 industrial-temp board.  Thanks!

    Asa

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  • jafoste4
    0 jafoste4 over 3 years ago in reply to apacker@biosonicsinc.com

    Hello Asa,

    Yes this would apply to all MicroZeds and PicoZeds. They have similiar PCB maufacturing characteristics. The table I shared was taken from our validation efforts with MicroZed in ensuring proper length matching when taking the propogation delays of the Zynq device into consideration. This is not a public document.

    -Josh

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  • apacker@biosonicsinc.com
    0 apacker@biosonicsinc.com over 3 years ago in reply to jafoste4

    Great, thank you.  One last question: your table refers to speeds for "interior layer" and "exterior layer", while the net lengths document refers to "Signal Layers Only".  Does "signal layer" equal "interior layer"?  Sorry, this is probably a dumb question, but I'm a little out of my depth here.

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  • jafoste4
    0 jafoste4 over 3 years ago in reply to apacker@biosonicsinc.com

    Hi Asa,

    No worries. Technically the net length report is the interior and exterior length combined. For the sake of your use case, you don't need to take the exterior length metric into consideration because the length is neglidible. We are talking about maybe 1-2 mil per signal. So a difference of 0.03ps.

    Just use the interior layer metric.

    -Josh

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