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DS90CR288A - RSKM at f=20MHz

Guru 19775 points
Other Parts Discussed in Thread: DS90CR288A

Hi Team,

Please allow me to ask you the specification for RSKM for DS90CR288A, using at low clock frequency like 20MHz.

What would be the minimum value for f=20MHz or minimum value that could satisfy all data rate ?
Please advise us how customer should design for RSKM.
Actually, customer will use the device at f=37.125MHz.

I found the following post which had been answered about RSKM, however, I could not make myself clear.

e2e.ti.com/.../388874

Thanks in advance.

Best Regards,
Kawai

  • Hi Team,

    I apologize for rushing you but we would appreciate it if we could have your advice by 7/1 Wednesday US time.

    Best Regards,
    Kawai
  • Hi Kawai-San,

    DS90CR288A has been characterized at 85MHz pixel clock and RSKM was found to be 295ps. At 20MHz or 37.125MHz pixel clock we have not characterized the device but if the customer can meet worst case 295ps we should be fine and with big margin.

    Given we have 295ps RSKM @85MHz pixel clock, we can estimate RSKM at 20MHz or 37.125MHz. Based on our calculation at 20MHz we could have about 1nS of RSKM. Or at 37.125MHz it would be about 560ps. Please note these are just estimate and we have not characterized the device at 20MHz or 37.125MHz.

    Also, please note RSKM should be greater than: (Transmit clock skew + Inter symbol interference + cable skew). During product development the customer can check to make sure RSKM meets this requirement with margin.

    Regards,,nasser
  • Hello Nasser-san,

    Thank you very much for your cooperation.

    I understood that the specification RSKM = 295ps is applicable to all range of PCLK. I will just ask them to design "(Transmit clock skew + Inter symbol interference + cable skew)" to be smaller than the RSKM value 290ps defined in the datasheet.

    Best Regards,
    Kawai
  • Hi Kawai-San,

    Sure please go ahead and ask the customer to design their system such that (Clock Jitter + ISI + cable skew) to be less than 295ps.

    Regards,,nasser

  • Hello Nasser-san,

    Is it possible to providing us the calculation how you had estimated the RSKM value for each PCLK frequency ?
    It would be helpful if you could share us the information.

    Best Regards,
    Kawai
  • Greetings Kawai-San,

    At 85MHz, maximum pixel clock:

    Bit time = (1/(85E6*7)) = ~2ns

    Minimum RSKM = 295ps

    295ps/2000ps = .1475 or we need about 14.75% of bit time for RSKM on each side of the ideal strobe position(please note figure 21 of the data sheet).

    At 20MHz pixel clock:

    Bit time = (1/(20E6*7)) = ~ 7ns

    7ns * .1475 = ~ 1ns

    So this means we should have 1nS of RSKM on left hand side of the ideal strobe position and another 1ns on right hand side of the strobe position(please note figure 21 of the data sheet).

    Regards,,nasser