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DS90UB935-Q1: if there is any difference when CLK_OUT is the same, Frequency error is 0

Hazel Sun
Expert 6535 points
Part Number: DS90UB935-Q1
Other Parts Discussed in Thread: DS90UB953-Q1EVM

Hi  team,

my customer use Non-Sync-external clock mode.

they want CLK_OUT=24MHz， and CLKIN is integer.  you can see the following can meet this:

according to our DS, it seems the Frequency error is 0. so i want to check if there are any differences among CLK_IN=32Mhz,36Mhz,48Mhz, which one do you prefer? thanks 

  • 0
    TI__Expert 8030 points

    Hi Hazel,

    Thanks for reaching out. 

    You are correct in that each of the solutions chosen by the customer will result in a frequency error of zero. Since this is the case, the preferred solution should be the one that results in the least amount of expected jitter. For each of the chosen CLK_IN frequencies, here is an estimation of the expected jitter:

    CLK_IN = 48 MHz, Expected Jitter = 1.041666667 ns

    CLK_IN = 36 MHz, Expected Jitter = 1.388888889 ns

    CLK_IN = 32 MHz, Expected Jitter = 1.5625 ns

    As shown by the calculations above, a CLK_IN value of 48 MHz will result in the least amount of expected jitter. Therefore, the customer should prefer this solution. 

    Regards,

    Kenneth

  • 0
    Prodigy 50 points

    Hi Kenneth，

    Thanks for replying! 

    If I choose a crystal with a CLKIN input of 32MHz±ppm, does it meet the input requirements of the 935 itself?  Does it affect the output CLKOUT frequency deviation? 

    Also, For CLKIN clock input square wave or sine wave?  Which is better?

    thanks!

    qingzhi.li

  • 0 in reply to user6283026
    TI__Expert 8030 points

    Hello,

    user6283026 said:
    If I choose a crystal with a CLKIN input of 32MHz±ppm, does it meet the input requirements of the 935 itself?  Does it affect the output CLKOUT frequency deviation? 

    Any oscillator with a ppm that is less than or equal to +/-50 should be okay to use with this device for the CLKIN connection.

    Additionally, the external oscillator connected to the CLKIN pin also needs to meet the jitter and frequency range requirements that are specified by Section 6.3 of the DS90UB935-Q1 datasheet.

    If the oscillator that you have chosen has a ppm less than or equal to +/- 50, and meets the reference clock frequency and input clock jitter specifications shown by the table above, it should be okay to use as an input to CLKIN for the DS90UB935-Q1.

    user6283026 said:
    Also, For CLKIN clock input square wave or sine wave?  Which is better?

    I'll discuss this specific topic with other members of the team and provide a response within the next 24 hours.

    Regards,

    Kenneth

  • 0 in reply to Kenneth Arnold
    TI__Expert 8030 points

    Hello,

    Thank you for your patience.

    user6283026 said:
    Also, For CLKIN clock input square wave or sine wave?  Which is better?

    For CLKIN, our preference is that you use a square wave oscillator that meets the specifications outlined in my previous post. For a specific oscillator recommendation, you can refer to the oscillator used on the DS90UB953-Q1EVM. Here is a link to the product folder for this evaluation module: https://www.ti.com/tool/DS90UB953-Q1EVM.

    Regards,

    Kenneth

  • 0 in reply to Kenneth Arnold
    Prodigy 50 points

    Hello,

    Thanks for the prompt and efficient reply!
    For the DS90UB935-Q1 serializer, can I read and identify CLK_IN input frequency value by querying the registers? THE REASON IS THAT THE ACTIVE CRYSTAL OSCILLATOR USED BEFORE WAS 49.152MHZ, NOW IT IS CHANGED TO 32MHZ, I WANT TO CONFIGURE DIFFERENT SOFTWARE BY CLK_IN RECOGNITION, IS THIS FEASIBLE? If not, is there another way?
    Thank you!

    qingzhi.li

  • 0 in reply to user6283026
    TI__Expert 8030 points

    Hello,

    There is no register in the DS90UB935-Q1 that can provide the frequency value of any signal that is connected to the CLKIN pin of the device. Any frequency changes to the CLKIN signal will have to be measured using a method separate from the DS90UB935-Q1.

    Regards,

    Kenneth