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Original question:

LMH0302SQE/NOPB - Differential output

LMH0302SQE/NOPB - Using single LMH0302 for two 3G-SDI output.

Praveen N1
Intellectual 430 points
Other Parts Discussed in Thread: LMH0302, LMH0307, LMH0397

Hi Team

We need a two 3G - SDI outputs (1080p and 60FPS)

In our previous reference design for each SDI output, they used a separate driver IC (LMH0302). Please find the snippet for a better understanding. 

In the new design, we planned to use a single LMH0302 driver IC for two SDI outputs. Basically, Connecting SDO(Bar) to another BNC connector. Please find the snippet for a better understanding. 

  1. I like to know if any issues will come while driving two SDI outputs from a single LMH0302SQE/NOPB?
  2. What do I need to consider while doing this change? (Layout wise) - It should be routed 150ohm differential pair output or each should be a 75 Ohm single-ended output. 

Regards 

Praveen 

 

  • 0
    TI__Guru* 93670 points

    Greetings,

    1). You can use two SDI outputs as you have noted in 2nd image. However, if one output is not terminated, this could affect signal quality on the other output that is in use. For best signal quality you can consider using LMH0397 and use both SDI_IO and SDI_OUT positive outputs. Otherwise, you can consider using LMH0307.. 

    2). Please note for DVB/ASI is polarity sensitive and you should use positive outputs. You can use single ended 75-ohm trace. Or use closely coupled 150-ohm trace but then you need to change to single ended 75-ohm output to connect to two BNCs.

    Regards,,Nasser

  • 0 in reply to Nasser Mohammadi
    Intellectual 430 points

    Hello Nasser

    Thanks for this explanation. 

    We are working on a medical application, So image quality is an important factor. 

    As you said we can also go with LMH0307, But it is not tested with our team. As of now, I think using two LMH0302 for 2xSDI output will be a safe option.  (Because we are already tested the LMH0302). 

    Will you please give your feedback on this? 

  • +1 in reply to Praveen N1
    TI__Guru* 93670 points

    Hi Praveen,

    Two LMH0302 should is a safe approach since customer has already used this part. From signal quality point of view, LMH0397 is the best since it has integrated SDI clock recovery circuitry.

    Regards,Nasser 

  • 0 in reply to Nasser Mohammadi
    Intellectual 430 points

    Hi Nasser 

    Thanks a lot for the clear explanation.