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LMH1297: LMH1297EVM cable length vs attenuation

Satoshi
Guru 19605 points
Part Number: LMH1297
Other Parts Discussed in Thread: , LMH0384, LMH0324

Customer is evaluating LMH1297EVM for ① and ② connection.

Is there way to amplitude signal from Transmitter side?

①Normal operation;

②Abnormal operation;

In the case of ①, Test result were normal operation.

 ⇒Both EVM’s LED are lighting (green), and SDI monitor is display.

But in the case of ②, Test result were abnormal operation.

 ⇒Receiver EVM’s LED are not lighting, and SDI monitor is not display.

I think that the reason is cable attenuation, I want to know the way to amplitude signal from Transmitter side.

BY the way, in the case of extended 100m+20m is normal operation.

Best regards,

Satoshi

  • 0
    TI__Mastermind 29655 points
    Hi Satoshi-san,

    If the receiver EVM's LED is not on, that means that the LMH1297EVM is unable to lock to the incoming signal. I believe that this is due to the insertion loss of the 200m cable being too much for the LMH1297EVM to equalize and achieve lock.

    The baseline amplitude of the SDI_OUT VOD is set to 800 mVpp. This VOD can be increased Reg 0x68[6:0]. Please reference Section 3.15.2 in the LMH1297 Programming Guide for more information.

    Even if you increase SDI_OUT VOD, you will still reach a cable length beyond which you cannot equalize the signal. Can you provide some more details about the setup?

    1. Are you running 12G-SDI?
    2. Is the camera sending any particular test pattern, or is it just a live image?
    3. What cable are you using? Is it Canare L5.5-CUHD?

    Regards,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Guru 19605 points
    Michael-san

    Thank you for quick reply,

    I answer the your question, please see below.

    --------------------------------------------
    1. Are you running 12G-SDI?
    ⇒Customer is running HD-SDI.

    2. Is the camera sending any particular test pattern, or is it just a live image?
    ⇒Live image.

    3. What cable are you using? Is it Canare L5.5-CUHD?
    ⇒Cable is Canare L-5C2VS.
    www.canare.com/ProductItemDisplay.aspx
    --------------------------------------------

    Additional question;
    ・About increase SDI_OUT VOD, is the case of EQ mode also increase SDI_OUT VOD?
    　Or, CD mode only?
    ・Is there the other recommended device for Tx side?

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Mastermind 29655 points
    Hi Satoshi-san,

    Thanks for the information! The Canare product page you sent me only shows Attenuation (dB/100m) at 10 MHz, which is significantly less than 750 MHz. I would like to compare the loss profile of this Canare cable with the Belden 1694A, for which we have tested extensively and seen that we can accomplish a reach of 300m.

    Since they are running HD-SDI (1.5G), can the customer provide the attenuation at the Nyquist frequency (750 MHz)?

    Regarding your additional questions:

    1.SDI_OUT VOD control is applicable in EQ Mode and CD Mode. The only difference in these modes is whether SDI_IO is an input or output. Please increase SDI_OUT VOD for the first LMH1297 to increase the drive strength of the first device's SDI_OUT.

    2. On the Tx side, what happens if you remove the first LMH1297? When the first LMH1297 is removed, how much Canare cable can you support between camera and LMH1297 receiver?

    Thanks,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Guru 19605 points
    Michael-san

    Thank you for advice,

    I answer question 2 below;
    I think that additional equalizer connect for between LMH1297EVM(Tx) to LMH1297EVM(Rx), cable range will be extended.
    【Camera ⇒ LMH1297EVM ⇒ Cable ⇒ Equalizer ⇒LMH1297EVM ⇒ SDI monitor】
    Is above image correct?

    If correct, my considering Equalizer is LMH0384.
    Is there better device than LMH0384?

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Mastermind 29655 points

    Hi Satoshi-san,

    I was actually thinking the same thing as you.

    When the LMH1297 is used in EQ Mode and SDI_OUT is enabled, there may be cross-talk from SDI_OUT that interferes with the input on SDI_IO at maximum cable reach. To test whether this is the case, you should use a stand-alone EQ, then place the second LMH1297EVM in CD Mode, just as you suggested.

    Instead of the LMH0384, I recommend using the LMH0324, which enables even longer cable reach than the LMH0384. The connections would therefore be:

    [Camera => LMH1297EVM (EQ Mode) => Cable => LMH0324 => LMH1297EVM (CD Mode) => SDI Monitor]

    An easy way to test with the LMH0324 is with the LMH0324-18EVM.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Guru 19605 points
    Michael-san

    Thank you for detailed information.

    Sorry for additional question, can LMH0324 equalize more than 4dB～5dB on this cable condition?
    I was going to confirm the detailed datasheet, but requesting "more information" is still not accept.

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Mastermind 29655 points

    Hi Satoshi-san,

    Sorry for the delay in response.

    Yes, the LMH0324 is capable of compensating more than 4-5 dB attenuation loss, since the maximum Belden 1694A cable it can equalize is about 200m at 3G and 280m at 1.5G. Please enter a request for more information on the LMH0324 product landing page, and we can grant you access to the design documentation if you require more information.

    Thanks,

    Michael