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DS90UH948-Q1: RC Filter on LVDS CLK signals

Alix
Prodigy 40 points
Part Number: DS90UH948-Q1

Tool/software:

For strict EMC concern, added below small RC filter on CLK1+/1- and CLK2+/2- in order to decrease the slew-rate of edg. How about the risks? 

  • 0
    TI__Genius 16660 points

    Hi Alix,

    There is a concern about having this CLK pulse be out of sync with the data signals with any added skew, the recommendation is to route OLDI inter-pair skew under 60 ps. Please make sure the routing meets this recommendation.

    Hope this helps!

    Best,

    Miguel

  • 0 in reply to Miguel Bolante
    Prodigy 40 points

    Hi, Miguel,

    Currently we follow below guideline:

    Inter-Pair(P/N): 1.27mm

    Inter-Pair(CLK to Data): 7.62mm

    Based on below pre-condition, we made a fast calculation:

    1) Frequency: 90MHz

    2) 1 UI: 1.5873ns

    For worst case consideration, the skew should be 50ps if inter-pair(CLK to Data) length difference is 7.62mm.

  • 0 in reply to Alix
    TI__Genius 16660 points

    Hi Alix,

    With 90 MHz being the approximate frequency planned for the output and inter-pair skew of OLDI pairs (CLK and Data) being under 60 ps, this should be within recommendations for OLDI output from the layout perspective.

    Be sure to minimize intra-pair skew (P/N) as much as possible. If planning to use higher frequencies, please run this test again to check the inter-pair skew results against recommendations.

    Best,

    Miguel

  • 0 in reply to Miguel Bolante
    Prodigy 40 points

    HI, Miguel,

    OK, thanks!