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SDI Interface- Single ended and differential

Madhu Sharma
Expert 2915 points
Other Parts Discussed in Thread: LMH0303, LMH0302

Hi,

I'm using SDI driver with part number LMH0302SQE. In the Typical application circuit, differential mode is
selected(both SDO and SDO# are connected to different BNC connectors and taken out). But in some other
datasheets of similar components ( say for ex. LMH0303), only SDO is used and SDO# is grounded( single
ended).

- Please let me know exactly at what conditions, single ended/ differential options are used.
- When differential mode is selected, Please let me know how the cabling is done, since connecting
different cables to SDO and SDO# may cause loss of signal at the receiver if cable lenghts are different.

Thanks & Regards,
Madhu Sharma K

  • 0
    TI__Mastermind 29655 points
    Hi Madhu,

    For SDI applications, the signal is sent through a 75-ohm coax cable. This cable is single-ended, and hence, these SDI cable drivers actually are designed only for single-ended cable applications. This true for the LMH0302 as well as the LMH0303. Therefore, even though there is SDO+ and SDO- outputs, only one of these will be used by the cable. The unused polarity is usually terminated to GND with a similar RL network applied in order to maintain continuity between the two polarities. There is not an application I am aware of where BOTH SDO+ and SDO- are used in a differential BNC cable application. You can only pick one polarity or the other.

    Are you trying to create a design where both SDO+ and SDO- are used differentially?

    Thanks,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Expert 2915 points

    Hi Michael,

    SDI output from my design will be connected either to a SDI display or to a SDI to HDMI converter. Since I could not get any information about the SDI displays and SDI to other standard converters which operate with differential SDI, Im planning to design single ended sDI. I request you to mention if you are aware of any differential SDI dispaly or converters.

    Also, Our customer suggests us LM0302 sDI cable driver. Since the IC datasheet doesn't have much information about design and layout guidelines(Though LM0302 datasheet tells about SD302 evaluation board, I could not get any information about this board in TI webiste), Please let me know whether i can refer the datasheet ( and EVB) of similar part LM0303 for these guidelines.

    Regards
    Madhu Sharma K

  • 0 in reply to Madhu Sharma
    TI__Guru* 93670 points

    SD302_schematic.pdfSD302_gerber.zipSD302_BOM.xlsHi Madhu,

    Please attached note LMH0302 gerber, schematic and BOM.

    Regards,,nasser

  • 0 in reply to Madhu Sharma
    TI__Mastermind 29655 points
    Hi Madhu,

    I am not aware of a differential SDI display or converter. In my experience, I have only seen single-ended transmission of SDI signals over 75-ohm coax.

    I wonder if you may have an older version of the LMH0302 datasheet. This datasheet was recently updated this month and includes new information about layout guidelines and examples.

    Regards,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Expert 2915 points
    Hi Michael,

    In LMH0302, since I'm using only SDO+, How to terminate the unused SDO-?? RL circuit in series with 4.7uF to GND is OK??

    Regards
    Madhu Sharma K
  • 0 in reply to Madhu Sharma
    TI__Guru* 93670 points

    Hi Madhu,

    Un-used SDO- gets terminated with RL Circuit + 4.7uF + 75 Ohm to GND.

    Regards,,nasser