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LMH0307: LMH0307 two channel signal have no output

Sammi Shang
Expert 4450 points
Part Number: LMH0307

Dear team,

Would you kindly help check PCB and schematic of customer?

The two channel in the middle has normal output, but the two channel far away has no output. Customer wonder if the line is too long or the resistance influence. They have changed the inductor from 3.4nH to 12nH. The signals are normal when output HD-SDI and SD-SDI signal.

Thanks.

Best regards,

Sammi

  • 0
    TI__Guru 60870 points

    Hello,

    An engineer has been assigned but response may be delayed due to the holidays.

    Regards,

    JMMN

  • 0
    TI__Guru* 93670 points

    Hi Sammi,

    To maintain a balanced impedance on both positive and negative 75-ohm outputs, we maintain the same length on positive and negative outputs. I checked below schematic and don't see an issue. The fact, using 12nH the signals are normal for HD and SD this tells me this could be related to impedance/return loss. Please note the followings:

    1). I am assuming we are maintaining 75-ohm controlled impedance traces on this desSD307_gerber.zipLMH0303_LMH0307_Eye_Diagrams_First_EVK.pdfign. It would be a good to do return loss measurement to confirm this.

    2). Please attached note pcb layout/gerber for the LMH0307 evaluation board. Please make sure we follow this pcb layout as close as possible. I have also enclosed a report on output eye diagram at 3G SDI as well.

    3). Please pay close attention to the pcb layout the way positive and negative 75-ohm outputs are routed. This provides an optimum balanced impedance on these outputs.

    Regards,, Nasser