Intel® Cyclone® 10 GX Core Fabric and General Purpose I/Os Handbook

ID 683775
Date 10/31/2022
Document Table of Contents Receiver Skew Margin for Non-DPA Mode

Different modes of LVDS receivers use different specifications, which can help in deciding the ability to sample the received serial data correctly.
  • In DPA mode, use DPA jitter tolerance instead of the receiver skew margin (RSKM).
  • In non-DPA mode, use RSKM, TCCS, and sampling window (SW) specifications for high-speed source-synchronous differential signals in the receiver data path.

RSKM Equation

The RSKM equation expresses the relationship between RSKM, TCCS, and SW.
Figure 111. RSKM Equation

Conventions used for the equation:

  • RSKM—the timing margin between the clock input of the receiver and the data input sampling window, and the jitter induced from core noise and I/O switching noise.
  • Time unit interval (TUI)—time period of the serial data.
  • SW—the period of time that the input data must be stable to ensure that the LVDS receiver samples the data successfully. The SW is a device property and varies according to device speed grade.
  • TCCS—the timing difference between the fastest and the slowest output edges across channels driven by the same PLL. The TCCS measurement includes the tCO variation, clock, and clock skew.
Note: If there is additional board channel-to-channel skew, consider the total receiver channel-to-channel skew (RCCS) instead of TCCS. .

You must calculate the RSKM value, based on the data rate and device, to determine if the LVDS receiver can sample the data:

  • A positive RSKM value, after deducting transmitter jitter, indicates that the LVDS receiver can sample the data properly.
  • A negative RSKM value, after deducting transmitter jitter, indicates that the LVDS receiver cannot sample the data properly.
Figure 112. Differential High-Speed Timing Diagram and Timing Budget This figure shows the relationship between the RSKM, TCCS, and the SW of the receiver.

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