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AFE7799: Why does the number of SerDes pins need 8 pairs instead of 4 pairs?

Part Number: AFE7799
Other Parts Discussed in Thread: AFE7769

1.Why is the SerDes interface of the chip? 8 pairs of TX lanes and 8 pairs of Rx LANs, instead of 4 pairs of TX lanes and 4 pairs of Rx lanes. What are the benefits of adding so many pins?

2.What is the difference between afe7799 and afe7769? How should I choose one of them?

  • Hi,

    1. having more lanes can allow 1) reduction of serdes rate 2) aggregate of wider bandwidth. There are different JESD204 modes calls for 8 lanes for 4T4R2F

    2. it is the number of LOs for different use case. AFE7769 has 4 PLL, while AFE7799 has 1 PLL. You can request more information for detail on the TI webpage. Someone will review your business opportunity and approve the access.

    -Kang

  •  2) aggregate of wider bandwidth. There are different JESD204 modes calls for 8 lanes for 4T4R2F

    ---------------------------------What does this mean? Is different jesd204 modes defined in the protocol?

    3.In addition, can you use 450MHz orx bandwidth to observe 200MHz transmit signal bandwidth? To achieve DPD function

  • Hi,

    2) I meant that you do not need to use all 8 lanes at all time. If you bandwidth requirement is low or your serdes rate is high enough, two lanes or 4 lanes are enough

    3) yes, this is assuming your DPD requires only 450MHz to perform 200MHz IBW correction. 

    -kang

  • With regard to the SerDes configuration of jesd204, we hope to use 4 pairs of lanes to realize the DPD scheme of 600MHz observation bandwidth, and the lane rates of transmitter and receiver are the same.

    Is the following configuration OK?

    JESD204B, C Frame Format for TX Chain: L-M-F-S-Hd = 48410 (One Link)

    JESD204B, C Frame Format for RX Chain: L-M-F-S-Hd = 28810 (One Link)

    JESD204B, C Frame Format for FB Chain: L-M-F-S-Hd = 22210

    The second question is about "sysref input level" in Datasheet Page23:

    Is 350mVpp a differential signal level or a single ended signal level? Is this a bug? In my understanding, the single ended signal level of LVDS signal is 350mV, while the differential signal level of LVDS signal is 700mV.

  • Hello,

    Could you please go to the AFE7769 website and request more information? The official datasheet will have guidance on the BW for 600MHz (i.e. 737.28MSPS for TX and FB) and the associated LMFS settings. Please request more information and we can send over more details through email.

    All the clocks are differential peak to peak. We can accept lower swing clock as a minimum, but recommends higher swing level for best noise performance.

    -Kang