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LMH1297: sdi_io_drv_pre_val

K.Yaita
Guru 29720 points
Part Number: LMH1297

Hi Team,

Is there any information about sdi_io_drv_pre_val of ConfigIO Register 0x62 [6:5]?
I couldn't catch if pre-emphasis is increased or decreased when the value is incremented.
I would also like to know the gain value for our reference.

Best Regards,
Yaita

  • +1
    TI__Guru* 93670 points

    Hi Yaita-San,

    Pre-emphasis is directly proportional. However, this has not been characterized.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Guru 29720 points

    Hi Nasser-san,

    Thank you always for your support.
    If we change sdi_io_drv_pre_val "10 (default)" to "00", does pre-emphasis weaken?
    I would like to know what case we should adjust the parameters.
    Is it recommended to adjust the parameter to meet long cable?

    Best Regards,
    Yaita

  • +1 in reply to K.Yaita
    TI__Guru* 93670 points

    Hi Yaita-San,

    If you change this parameter to oo it weakens the pre-emphasis.

    Also, please do not recommend to change this parameter to meet long cable reach. This parameter affects over/under shoot of the waveform. Changing this parameter may cause violation of the SMPTE +/-10% over/under shoot requirement.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Guru 29720 points

    Hi Nasser-san,

    Thank you for your answer.
    Is it not recommended even weakens the pre-emphasis from default?
    The background of the question is I heard my customer saw CRC error when sdi_io_drv_pre_val =10 (default) with CANARE L-5.5CUHD 70m cable.
    He set sdi_io_drv_pre_val =00 then he saw no CRC error. 

    Best Regards,
    Yaita

  • +1 in reply to K.Yaita
    TI__Guru* 93670 points

    Hi Yaita-San,

    With present settings we meet SMPTE requirements. Perhaps customer layout could be different. You can use LMH1297EVM to re-produce the error condition noted by the customer. This is the first time we hear pre-emphasis setting causing error under certain condition. Please note after 70m cable attenuation the high frequency content of the pre-emphasis is gone.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Guru 29720 points

    Hi Nasser-san,

    Thank you always for your support.
    I would like to ask the following for my reference.

    I believe the only requirement for SDI cable driver is to meet SMPTE specification.
    On the other hand, how long can we extend cable length depends on SDI equalizer.
    Is my understanding correct?

    Best Regards,
    Yaita

  • +1 in reply to K.Yaita
    TI__Guru* 93670 points

    Hi Yaita-San,Your understanding is correct. The only requirement for SDI cable driver is meeting SMPTE output electrical parameter using a short cable -1m. There is nothing related to the cable reach. As you noted cable length is solely depends on the equalizer.

    Regards,, Nasser