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LMH0394: How does this compensate for a pathological pattern?

Tom Rogers
Prodigy 60 points
Part Number: LMH0394


I am working on a design that will accept  SMPTE ST 292-1.  The concern is its pathological patterns which I am told could have 40 consecutive zeros or ones.  I am told that most laser drivers will not accept these pathological patterns and I am told that your LMH0394 will compensate for this.  Assuming that this information is correct, how does the LHM0394 do it?  I have read through its data sheet and I see a Equalizer Filter block but that is for compensating for the coax cables.  Next is a DC Restoration/Level Control block.  I assume that this is for the pathological patterns but how does it help the laser driver that is connected to the outputs (DO/SDO(NOT))?  What I am looking for is a better understanding.

Thanks

  • 0
    TI__Guru* 93670 points

    Hi Tom,

    LMH0394 was built with internal circuitry to compensate for long string of one or zero.

    Embrionix and other vendors have optical modules and compensate for long string of ones or zeroes. Is it possible if you could please check to see what circuitry they between their laser driver and the laser.

    Regards,,,,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 60 points

    But can you explain how the LMH0394 compensates for long string of ones or zeroes?

  • 0 in reply to Tom Rogers
    TI__Guru* 93670 points

    Hi Tom,

    Pathological pattern has high low frequency or DC content. On the other hand, regular prbs or color bar pattern does not have a DC content because number of ones and zeros are the same within any video line. High DC or low frequency content in a data pattern generates a shift in DC voltage level -causing device to mis-sample incoming signal. DC restore circuitry restores or minimizez this DC level so the signal is samples at the same level of a PRBS or color bar level without causing any bit error.

    Regards,,nasser