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DS125BR401A detecting COMWAKE

Kuramochi Tadahiko
Guru 28715 points
Other Parts Discussed in Thread: DS80PCI810, DS125BR401A, DS125BR111, DS125BR820

Hi,

My customer is evaluating the DS80PCI810, and they got the information about DS125BR401A from the end customer.

The information is following;

The problem is occured that DS125BR401A can't detect the COMWAKE.

The cause supposed the problem amplitude( following waveform in the red circle).

There are 2 question.

1. Is this information correct ?

2. Does the DS125BR401A have same problem?

Thanks

Kuramochi

  • 0
    TI__Mastermind 43795 points

    Kuramochi,

    The DS125BR401A is designed to properly handle OOB signals.  This device uses a signal detect function to turn the output on/off quickly to minimize any distortion of the OOB signal.  For this reason the turn-on time and the turn-off time are designed to be equal.  By equalizing these two parameters some of the active OOB waveform is removed from the leading edge while an equal amount is appended to the trailing edge.  These two effects tend to cancel each other resulting in an OOB output with minimal timing distortion.

    The DS125BR401A includes configuration registers and pins to tune the device response to OOB signals like COMWAKE.  The DS125BR401A B-port must be set to non-limiting output mode and I also recommend that the DS125BR401A B-port outputs are set to < 1.0V VOD.  This combination will help to minimize the amplitude of the COMWAKE signal extension.

    Here are the registers bits to control this functionality (using Channel CH0 - CHB_0 as an example)

    Register 0x08[2] = 1'b  //* Use register to control output mode

    Register 0x10[6] = 0'b  //* Use non-limiting output style

    With Pin control  MODE_B = 1, DEMB1 = 0, and DEMB0 = 0 or R   (R = 20K to GND)

    Several devices recently introduced offer a more linear approach to signal conditioning.  The DS125BR820, DS125BR111, and DS80PCI810 no longer depend on the signal detect functionality to reproduce the OOB waveform.  These devices are less sensitive to system noise and virtually eliminate OOB distortion.

    Best Regards,

    Lee 

  • 0 in reply to Lee Sledjeski
    Prodigy 10 points
    Lee,

    What explains the +/- asymmetry in the signal out of the DS125BR401A? Obviously the positive amplitude of the differential signal is higher than the negative one. Also, if you look carefully, the positive signal waveform shows a de-emphasis effect (transition bits higher than the subsequent bits on the low frequency sections of the pattern) while the negative half of the signal waveform does not show this effect.

    Finally, is the output impedance of the DS125BR401A transmit driver maintained at 100ohm differential while the driver is in IDLE mode during the OOB gap?

    Thanks,
    Bernhard
  • 0 in reply to bernhard laschinsky
    TI__Mastermind 29655 points
    Hi Bernhard,

    The OOB signal is a burst signal provided by the source generator, and it could be possible that due to any impedance discontinuities in the connectors, non-idealities in the board routing, or mismatches in probe length when measuring the differential signals that you are seeing what appears to be assymetry and de-emphasis. It is also possible that the characteristics in the waveform were already present from the source generator before the DS125BR401A. Either way, we have noticed that the critical factor in order for the DS125BR401A to inter-operate with the OOB signal is the redriver's idle-to-active and active-to-idle response time and how minimal it is.

    Yes, the output impedance of the DS125BR401A is maintained at 100-ohm differential, even while IDLE. I have confirmed with design that this is the behavior for both the A-channel and B-channel directions.

    Thanks,

    Michael