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DS125DF1610: How to interpret EOM Full Eye Capture with different EOM_SEL_VRANGE from SigCon

Frank Wu
Prodigy 80 points
Part Number: DS125DF1610

Tool/software:

In the datasheet https://www.ti.com/lit/gpn/ds125df1610 page 21. It mentioned:
A full eye diagram capture can be performed when the CDR is locked. The eye diagram is constructed within a
64 x 64 array, where each cell in the matrix consists of an 16-bit word. Users can manually adjust the vertical
scaling of the EOM or allow the state machine to control the scaling which is the default option. The horizontal
scaling controlled by the state machine and is always directly proportional to the data rate.
When a full eye diagram plot is captured, the retimer will shift out 4 16-bit words of junk data that should be
discarded followed by 4096 16-bit words that make up the 64 x 64 eye plot. The first actual word of the eye plot
from the retimer is for (X, Y) position (0,0). Each time the eye plot data is read out the voltage position is
incremented. Once the voltage position has incremented to position 63, the next read will cause the voltage
position to reset to 0 and the phase position to increment.

In SigCon, I see negative voltage in the plot, and I change EOM_SEL_VRANGE, and find the eye shows on the very negative side. Please find the same signal with different setting below.

EOM_SEL_VRANGE = 100mV

EOM_SEL_VRANGE = 200mV

EOM_SEL_VRANGE = 300mV

EOM_SEL_VRANGE = 400mV

  • 0
    Prodigy 80 points

    The input data rate should be 5.6376Gbps. I am expecting the Datarate shows over here is 5.6376Gbps or 11.2752Gbps. How is the 10.3125Gpbs on SigCon so far away from it?

  • 0 in reply to Frank Wu
    TI__Mastermind 28050 points

    Hi Frank,

    These eye plots are definitely unexpected. I also would have expected the Data Rate box to show 5.6376 Gbps or 11.2752 Gbps. Allow me to test this in a bench experiment and see if I get the same result. I'll get back to you with some feedback by COB tomorrow, 9/24.

    Best,

    Lucas

  • 0 in reply to Lucas Wolter
    TI__Mastermind 28050 points

    Hi Frank,

    I transmitted a 5.6376 Gbps PRBS31 signal to a DS125DF1610EVM. I configured the device with the register settings I previous shared with you to obtain CDR lock at this data rate. Although the Datarate box incorrectly shows 10.3125 Gbps, I see a typical eye monitor capture. I expect this box is populated with 10.3125 Gbps by default and this does not have any actual effect on the eye capture.

    I have some questions to better understand your setup.

    1. Are you using an EVM or a custom board?
    2. Are you using the DS125DF1610 SigCon profile?
    3. What reference clock frequency are you using? Is this selected correctly on SigCon Architect?
    4. Do you have external AC coupling caps on the Rx and Tx channels?
    5. Are you using any register settings in addition to what I used?
    6. Is there anything else about your setup that is different from mine?

    Best,

    Lucas