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Original question:

LMH0318: is not reclocking

LMH0318: is not reclocking

Simon Brown
Intellectual 340 points
Part Number: LMH0318
Other Parts Discussed in Thread: USB2ANY

I have an SDI signal at 1.483Gbps going through a cable equalizer and into the LMH0318.  The input signal, as measured on a Phabrix SX has 0.12UI jitter at 100kHz.  The output signal from the reclocker has 0.14UI jitter at 100kHz and the rise times and fall times are longer.  The status registers say it has locked onto the input, and that the CDR is working, but it doesn't seem to do it's job.  I have tried different EQ settings, different signal drive strength settings (these do change the overall amplitude of the waveform, so clearly we are controlling the LMH0318), but I cannot get a proper eye opening on the output or get any jitter removed - at the moment it seems to be adding to it.

Regards,

Simon

  • 0
    Intellectual 340 points

    Further information:

    I use this initialisation sequence:

    raw318 (0xff, 0x04, 0x07); // Select channel registers
    raw318 (0x16, 0x25, 0xff); // Enable full temperature range
    raw318 (0x3E, 0x00, 0x80); // Init CDR State machine control
    raw318 (0x55, 0x02, 0x02); // Init CDR state machine control
    raw318 (0x6A, 0x00, 0xff); // Init CDR state machine control
    raw318 (0x03, 0x00, 0xff); // Setup CTLE - this is for 10 inch FR-4
    raw318 (0x0A, 0x0C, 0x0C); // Reset the CDR
    raw318 (0x0A, 0x00, 0x0c); // Release CDR reset
    raw318 (0x31, 0x01, 0x03); // Enable IN0->OUT0, power down OUT1
    raw318 (0x2F, 0x00, 0xC0); // Enable SMPTE modes.
    raw318 (0x0A, 0x0C, 0x0C); // Reset the CDR
    raw318 (0x0A, 0x00, 0x0c); // Release CDR reset
    raw318 (0xff, 0x04, 0x07); // Select channel registers
    raw318 (0x80, 0x02, 0x03); // Enable OUT0

    I have also connected up the USB2ANY and controlled it that way.  If I just pass a signal through the relays and back out of the card, completely bypassing anything and the reclocker I get 0.05UI jitter at 100kHz.  If I then bypass my processing card and just pass the input signal through to the reclocker, in HD it struggles to lock onto the signal (too much degradation from the relays on our processing card), so I run the reclocker in "raw data" mode, and it's at 0.07UI.  If I then get my processing card to drive the signal and look at the raw data I get 0.12UI jitter, and finally if I then switch the reclocker to "retimed data" I get 0.14UI.  Whatever I do, if I look at the retimed data it ALWAYS has worse jitter performance than the raw data.  The driver is clearly doing its job, but the reclocker isn't.  I know that TI would not produce a chip that doesn't work, so it must be something I'm doing, but I've tried everything that I can think of and nothing improves the signal.  The datasheet says alignment jitter at 0.045UI or total jitter at 0.06UI.  Why am I getting more than twice that?

    We've got an order riding on this, and I need it resolved ASAP.  If a phone call would be useful, then let me know and I can email my phone number to you.

    Regards,

    Simon

  • 0 in reply to Simon Brown
    TI__Guru* 93570 points

    Hi Simon,

    Sure. Please send me your phone number(Nasser.mohammadi@ti.com) and let's discuss this.

    Regards,,, Nasser