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LMH1297: how to increase HEO/VEO read from LMH1297?

jack.xu
Prodigy 40 points
Part Number: LMH1297
Other Parts Discussed in Thread: , SIGCONARCHITECT

Hi, team:

    We develop a 12G-UHD converter product using  LMH1297. We use PHABRIX QX12G to generate 12G color bar signal to our board. The cable is belden  4694R+Amphenol 31-70548-12G plug. BNC socket  on the PCB is samtec BNC7T.  Lock status from LMH1297 is locked when cable length is 1m , but  the HEO/VEO read from LMH1297 is 0.59UI/178mV. This value is very low. When we use 30m cable, the signal is unlock frequently.

    Lmh1297 datasheet said it can suport up to 65m , how can I increase the HEO/VEO by setting register? Our customer need to run at 30m.

I think our PCB layout has no problem, we use SAMTEC's  recommended design, and we have passed high speed SI simulation and final PCB TDR test.

Thanks a lot.

e 

  • 0
    TI__Guru* 93670 points

    Hi Jack,

    At very short cable, HEO/VEO that you have indicated should be fine and we should run error free. Device is expected or rated to operate error free at up to 75m B1694A cable. B4694R is the new Belden cable rated for UHD data rates and we should be able to operate error free at 30m cable length.

    1). You noted there is intermittent lock at 30m. Could you verify level on OUT_CTRL pin? I am expecting this pin to be floating.

    2). Secondly, is it possible for you to get LMH1297EVM ? This way we can compare LMH1297EVM versus your board. Also, this would enable us to use SigconArchitect GUI to control LMH1297EVM AND OR your own device(as long as you are using SMBus interface).

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 40 points

    Hi,Nasser,

        1) OUT_CTRL pin is float, the pull up resistor and pull down resistor are not mounted on PCB. 

    2)  I don't have LMH1297EVM, but our customer has. He will send to me next week.

    3)  Moreover, we configure the LMH1297 through SMBUS by FPGA, and the register setting is common EQ mode same as LMH1297 programing guide 

    Are there any register related to improve HEO/VEO quality?

    What cause LMH1297 unlock the input signal at 30m cable? 

    Why is the HEO read from LMH1297 less than 200mV at 1m cable? The 12g signal generator is OK, selfloop eye and jitter meet SMPTE standard

    to

    Kind regards, Jack

  • 0 in reply to jack.xu
    TI__Guru* 93670 points

    Hi Jack,

    1). Are there any register to improve HEO/VEO:

    LMH1297 is an adaptive equalizer and should be able to operate adptively up to 75m B1694A cable length. So if it works at 1m we should be able to operate at 30m as well.

    2). 30m Unlock:

    LMH1297 has EQ block followed by a CDR retimer block. If the output of the EQ block is closed or partially closed then CDR cannot recover clock to retime the signal. Therefor it would loses lock. Based on your description, EQ block does not seem to be operating normally and thus there is eye closure at 30m cable length.

    3). HEO Less than 200mV:

    HEO and VEO readings at taken from the output of the equalizer. Then CDR or retimer retimes this signal and cleans up eye closure. So this is why you see a clean eye diagram at the output even though HEO/VEO are low values.

    Some ideas to check:

    1). Do you have signal on IN0(pins 18 and 19) when you are running these test? Do you see a difference if there is no signal on IN0?

    2). Can you check input return loss or do a TDR on SDI_IO pin?

    3). SDI_OUT_SEL is floating since Resistors are NC. Please confirm.

    4). Please go ahead and test LMH1297EVM so we can correlate with your own board measurement. This EVM comes with a GUI. After checking LMH1297EVM at 30m, you can assign a different SMBus address to your own device and then wire SMBus interface from this board to your own board. This way you can correlate with LMH1297EVM settings and etc.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 40 points

         I have got the LMH1297EVM now . I want to compare the HEO/VEO between the EVM board and our product.

    I install SigCon Architect 3.0. But there is no LMH1297 device. How to solve this problem?

    thanks.

  • 0 in reply to jack.xu
    TI__Guru* 93670 points

    Hi Jack,

    You have downloaded Sigconarchitect3. For LMH1297 support and other evaluation board, please install SigconArchitect V2.0.0.8 at the following link:

    http://www.ti.com/tool/SIGCONARCHITECT?keyMatch=SIGCONARCHITECT&tisearch=Search-EN-everything&usecase=part-number

    Also, LMH1297 profile is on a secure site. Please send me email - after registering at TI.COM - and we can get you access to these files. Here is email address: nasser.mohammadi@ti.com        Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 40 points

    Hi,Nasser:

        I have compared our product with LMH1297EVM from 10 meter to 60 meter cable. 

    1. In EQ mode, use PHABRIX QX12G as signal generator , our product can only support  20m maximum. But for LMH1297EVM, it can be up to 60m.

    2. Set our product as CD mode and send test colour bar SDI signal to LMH1297EVM, EVM board  work normally too at 60m.

    So, i guess, our transmit signal path is ok, but receive path is not ok. Maybe the retern loss is not very good.

    My question:

    Can you tell me how to setup the return loss test on our product for EQ and CD mode?

    Does the board need to be powered up when connect to VNA?

    Our VNA use  50ohm cable and SMA plug, how to connect to our 75ohm cable and bnc socket?

    Thanks.

  • 0 in reply to jack.xu
    TI__Guru* 93670 points

    Hi Jack,

    1). How to setup return loss test: Please just power up the device and setup the device for EQ mode. Then you should be able to run return loss measurement. Normally cable driver has more return loss margin so if you pass EQ return loss you should be fine with cable driver mode return loss.

    2). Please contact Keysight or Maury Microwave. These vendors have return loss kits and calibration kits for 12G SDI applications.

    Regards,, Nasser