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LMH0303: LMH0303 HD-SDI CABLE DRIVER

user5074302
Prodigy 50 points
Part Number: LMH0303

Hi,

We are using LMH0303 cable driver, the ouput of the driver is going to a 75ohm HF connector(Attaching the schematic).

The Output voltage swing is around 768mV and 270ps to 320ps, but the eye diagram shows lot of distorted. We are passing this signal over a 75ohm coaxial slipring, the output here is also distorted.

Please see Attached figure1, figure3, which shows the eye diagram at the output connector.

The input to the driver i.e figure2 looks clean.

Schematic:

We are using 6.8nH at the SDO output and SDO\ is terminated without a inductor.

figure:1

Figure:2

figure:3

  • 0
    TI__Guru* 93670 points

    Greetings,

    Please clarify:

    1). You are saying you are using SDO\ without inductor. Does it mean L9 in your schematic is not loaded?

    2). Your data rate is about 1.7Gbps?

    3). When you are running this test, what is the SD\HDbar tied to ? Is it high or low?

    Your eye diagram clearly shows a double eye on low or zero voltage level.

    Regards,,nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 50 points
    Hi Nasser,

    The issue has been resolved, but i would like to know why SDO\ needs a 75ohm pull up when we have single end configuration? Actually L9 and R85 wwhere made DNP , after mounting R85 it started working pefectly.
    The data rate is 1.4Gbps and the video resolution is 720p.

    Regards
  • 0 in reply to user5074302
    TI__Guru* 93670 points

    Greetings,

    LMH0303 75-ohm output is differential - not single ended - and requires balanced impedance on positive and negative outputs. Even though you are not using negative output, we still need to provide 75-ohm termination.

    Regards,,nasser