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LMH0303: LMH0303 Cable Length and Operation with the LMH0384 Equalizer

Richard Elmquist
Mastermind 45250 points
Part Number: LMH0303
Other Parts Discussed in Thread: LMH0384

My customer is asking the following questions regarding the LMH0303 (driver) and LMH0384 (equalizer). My questions and comments are in Black.

I am actually after the LMH0303 (Vsdo) spec versus various cable lengths. From the datasheet (LMH0303) on page 6 it is 720mVpp to 880mVpp (I think this is speced at 0 m only?) 

Is there any reason this is not specified at various cable lengths give the starnard Belden cabling? Do we have these numbers?

Let me give you some more context into what I am doing in the lab.

I am using the LMH0303 as my transmitter and sending signals at 300 ft. (via Belden 1694A) away to the LMH0384 (my receiver).

So far in my testing via a scope, I have characterized the Vsdo waveform of the LMH0303 at various cable lengths, namely 0 ft., 150 ft., and 300 ft. I can see significant attenuation and degradation at 300 ft away and the Vsdo waveforms seems to go as low as 300mVpp. With that said, I am afraid that the LMH0384 Vsdi spec is being violated (720 mVpp – 950mVpp) because I see only 300mVpp at the input of the LMH0384. However, the LMH0384 is still able to reconstruct the low input and I see a nice waveform at the output of the LMH0384, which is good. A bit confused to why it is failing spec but can still reconstruct. 

The LMH0384 seems to indicate that the input pp voltage should be much greater than 300 mV so I am a little confused as to what the Vsdi specification means. It seems that the customer just wants to understand what is happening. The specification seems to be violated and yet the interface works perfectly as stated above.

For this reason, do you have any data on the LMH0303 Vsdo at 300 ft. ? Also, how is it (it being LMH0384) able to buffer back the input with such a low 300mVpp input?

Can you help with these questions or explain what the customer is seeing?

Thanks for your help with this!

Richard Elmquist

  • 0
    TI__Mastermind 45250 points

    Here are some additional comments from the customer:

    I have not yet set any registers for both LMH0384 and LMH0303. I have configured both ICs similar to that of the eval board schematic with no I2C or SPI control yet.

    The data rate that I plan to send from TX (LMH0303) to RX (LMH0384) will be max 1.5 Gbps, i.e. 750MHz waveform at DDR.

    Thanks for your help!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Mastermind 45250 points

    Has anyone had a chance to look at the request above?

    Can you give a time frame as to when you might be able to provide the information?

    Thanks for your help with this!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Guru* 93670 points

    Hi Richard,

    1). Voltage output swing for LMH0303 device should be between 720mV to 880mV(According to the SMPTE standards). This is measure with 1m short B1694A cable and color bar video pattern. SMPTE does not specify output voltage swing after 90ft or other cable length(other than 1m short cable).

    2). Please note LMH0384 parametric table cable reach parameters(AC Electrical Parameters). Given 720mv to 880mV launch amplitude and various cable length as noted in this table, device can recover the signal with output jitter mentioned in the table.

    LMH0384 is a high gain equalizer with at least 40dB of gain. Therefore if launch signal is for example 720mV, it means even with 7.2mV of signal level - after 40dB attenuation or a long cable - it can recover the signal.

    Regards,,nasser 

  • 0 in reply to Nasser Mohammadi
    TI__Mastermind 45250 points

    Nasser,

    Thanks so much for your response!

    I will let you know if the customer has any additional questions.

    Thanks again.

    Richard Elmquist