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LMH0074: Behaviour in BYPASS mode

Merlebleu
Prodigy 20 points
Part Number: LMH0074
Other Parts Discussed in Thread: LMH0036, , LMH0384

I am designing a video module tasked with multiplexing 4 SD-SDI signals and return a digital indicating the presence of each signal. The application recommendation described in the LMH0036's datasheet fits my need perfectly, and I was planning to use the Carrier Detect CD pin of the LMH0074 for signal detection.

Does the LMH0074's CD output is still updated in BYPASS mode ? The datasheet mention briefly "CD has no function in BYPASS mode." but the block diagram and the Carrier Detect description then make no reference to this.

Also, does the LMH0074 apply some numerical operations to the signal (such as correction using CRC) or is its function purely analog ?

  • 0
    TI__Mastermind 29655 points

    Hi Merlebleu,

    Thanks for the post and apologies for the delay in response.

    The LMH0074 requires information from the Energy Detect block input to the AEC (Automatic Equalization Control) to assess whether a valid signal is present at the input.

    Since the BYPASS pin causes the input signal to bypass the EQ Filter and DC Restoration/Level Control, the Energy Detect portion of the input for the AEC is inactive, and therefore the CD pin may not output a signal that corresponds with whether a valid input signal is truly present at SDI/SDI#.

    Regarding the second question, there is no numerical operation applied to the signal. the Cable EQ function is purely analog.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 20 points

    Thank you for your awnser, that solved the points i was uncertain about.

    Ended up settling for the LMH0384 to get around the CD issue.