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LMH0397: lmh0397 cable equilazer index

Serif Yilmaz
Prodigy 20 points
Part Number: LMH0397

Tool/software:

Hello, 

In lmh0397 user guide, it states that default cable equalizer index lower limit is 9 and upper limit is 11, but I see that ithis value can be between 0-55.

During cold and hot test, we seen flickers in sdi hd mode. I suggest that this issue can be sourced from this cable equilazer index limit. 

So, what should be these limits and where can i find useful references to understand this index. 

Thank you.

  • 0
    TI__Expert 7380 points

    Hi Serif,

    I hope you don't mind if we ask a couple of questions to understand your application better.

    • How long are the cables in your setup?
    • What is your input? Are you using SDI_IO or IN0?

    Best,

    Nick

  • 0 in reply to Nick Peabody
    Prodigy 20 points

    Hi Nick,

    I have approximetely 2 meter cable and my input is SDI_IO.

    Thanks.

  • 0 in reply to Serif Yilmaz
    TI__Expert 7380 points

    Hi Serif, 

    See datasheet section 8.3.11.1

    "Cable EQ Index (CEI) The Cable EQ Index (CEI) indicates the cable EQ boost index used at SDI_IO+ in EQ Mode. CEI is accessible through ConfigIO Page Reg 0x25[5:0]. The 6-bit setting ranges in decimal value from 0 to 55 (000000'b to 110111'b in binary), with higher values corresponding to larger gain applied at the SDI_IO+ input."

    With a 2 meter cable I would not expect to see a very high EQ index value. It would likely stay at 0 or go to 1 at temperature. A possible test you could do is to read the CEI register in the ConfigIO page to determine if cable EQ is the issue.

    Best,

    Nick

  • 0 in reply to Nick Peabody
    Prodigy 20 points

    Thanks Nick, I will experiement this.

    You said it must be 0 or 1 but threshold value for cei is 9-11. So, it is out of range actually

  • 0 in reply to Serif Yilmaz
    TI__Expert 7380 points

    Hi Serif,

    No problem. I am wondering where you see that the threshold is from 9-11? I've seen CEI to be from 0-55 in decimal.

    Best,

    Nick

  • 0 in reply to Nick Peabody
    Prodigy 20 points

    0x2b and 0x2c registers specifies threshold, am i understand wrong?

  • 0 in reply to Serif Yilmaz
    TI__Expert 7380 points

    Hi Serif,

    I think I understand now.

    The EQ is bypassed when the EQ index falls below the bypass threshold lower limit, and the cable EQ is re-enabled when the EQ Index exceeds the bypass threshold upper limit.

    This screenshot explains it. The lower threshold can be any value in register 0x2B[0:5] meaning that at maximum it can be decimal 63 (0x3F). The higher threshold is 0x2C[0:5] and similarly can be a maximum of decimal 63. The CEI can be adjusted between 0-55, so if you were to set the higher threshold to hex value 37 (decimal 55) and the lower threshold to 00, the EQ would not be bypassed under any EQ setting.

    Does that explain the threshold?

    Best,

    Nick