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DS110DF111: Eye monitor - more details?

Prodigy 25 points

Replies: 3

Views: 57

Part Number: DS110DF111

Hi,

We are currently using the DS110DF111 re-timer in our application, and reading the output of the eye monitor. As you can see in the attachment provided, it looks like there is no crossing in the eye, and so I was wondering whether I could obtain more information about what this represents to help us understand why we are getting this.

- Is the obtained eye the differential result from both signals at the input? i.e. INA_P less INA_N
- or is it a representation of one of them only, i.e. this is the signal INA_P?

Any information you can provide will be appreciated!

Also, the settings being used to capture this eye are as follows:
- 0x3E, 0x00
- 0x11, 0x00
- 0x11, 0x80
- 0x24, 0x83
- read eye from register, 64x64 reads x2 (to ensure a full eye)
- 0x3E, 0x01
- 0x11, 0x01
- 0x24, 0x01

Thank you in advance.

Best regards,
Andrea

EYE_25.xlsx

  • Hi Andrea,

    The eye is based on both P/N signals - it is fully differential.

    The eye opening is not always centered in the 64x64 matrix.  In your case the crossing goes from column "AN" to "BU" and the opening is a combination of the remaining columns before and after this segment.

    The eye crossing looks quite wide.  The filename suggests that you are running at ~ 2.5Gbps?  For datarates less than 5 Gbps the CTLE function does not automatically adapt.  By default it is set to a relatively high value.  Changing this value in channel register 0x3A may improve your eye opening.

    Channel Register 0x3A = 0xA5  (Default)

    Channel Register 0x3A = 0x00  (new value)

    Regards,

    Lee

  • In reply to Lee Sledjeski:

    Hi Lee,

    Thank you for your reply. 

    Regarding the crossing, I agree with you that it is between column “AN” to “BU”. However wouldn’t the absolute values be higher @ 0V (green part) if it was a crossing? In the spreadsheet you can see that the values are much lower than the start of the crossing (yellow part).

    Also thank you for the tips regarding the CTLE. 

    Regards,

    Andrea

  • In reply to Andrea Mifsud1:

    Hi Andrea,

    The way that the device detects the edge results in less "hits" or lower numbers in the middle of the crossing.  This is normal behavior.

    If we can improve the jitter by adjusting the CTLE value the numbers should go up as a crossing becomes more well defined.

    Regards,

    Lee

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