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

ID 683461
Date 10/25/2023
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 122. 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 123. Differential High-Speed Timing Diagram and Timing Budget for Non-DPA Mode This figure shows the relationship between the RSKM, TCCS, and the SW of the receiver.

Example: RSKM Calculation

This example shows the RSKM calculation for FPGA devices at 1 Gbps data rate with a 200 ps board channel-to-channel skew.
  • TCCS = 150 ps
  • SW = 300 ps
  • TUI = 1000 ps
  • Total RCCS = TCCS + Board channel-to-channel skew = 150 ps + 200 ps = 350 ps
  • RSKM = (TUI – SW – RCCS) / 2 = (1000 ps – 300 ps – 350 ps) / 2 = 175 ps

If the RSKM is greater than 0 ps after deducting transmitter jitter, the non-DPA receiver will work correctly.