Intel® Agilex™ F-Series and I-Series LVDS SERDES User Guide

ID 721819
Date 11/30/2022
Public
Document Table of Contents

6.2.2. Receiver Skew Margin

Different modes of SERDES receivers use different specifications, which determine the ability to sample the received serial data correctly.
  • In the non-DPA mode, use RSKM, TCCS, and sampling window (SW) specifications for high-speed source-synchronous differential signals in the receiver data path.
  • In the DPA and Soft-CDR modes, use DPA jitter tolerance instead of the receiver skew margin (RSKM).
Equation 2. RSKM EquationThis equation expresses the relationship between RSKM, TCCS, and SW.

Table 36.  RSKM Equation Conventions
Symbol Description
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) The 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 SERDES receiver can sample the data:

  • A positive RSKM value, after deducting transmitter jitter, indicates that the LVDS SERDES receiver can sample the data properly.
  • A negative RSKM value, after deducting transmitter jitter, indicates that the LVDS SERDES receiver cannot sample the data properly.
Figure 30. Differential High-Speed Timing Diagram and Timing Budget

RSKM Calculation Example

This example shows the RSKM calculation for Intel® Agilex™ devices at 1 Gbps data rate with a 200 ps board channel-to-channel skew.

Equation 3. RSKM Calculation

The non-DPA receiver works correctly if the RSKM is greater than 0 ps after deducting transmitter jitter.

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