External Memory Interfaces Agilex™ 7 F-Series and I-Series FPGA IP User Guide

ID 683216
Date 9/19/2024
Public
Document Table of Contents

7.4.3.2. Skew Matching Guidelines for QDR-IV Configurations

The guidelines in this topic apply to QDR-IV memory configurations.

Board designers must observe the following guidelines for QDR-IV skew matching:

  • Perform skew matching in time (picoseconds) rather than in actual trace length, to better account for via delays when signals are routed on different layers.
  • Include both package per-pin skew and PCB delay when performing skew matching.
  • Skew (length) matching for the alert signal is not required.

The following table provides skew matching guidelines for QDR-IV topologies.

Table 149.  QDR-IV Skew Matching Guidelines
QDR-IV Length Matching Rules Length Matching in Time (ps)
Length Matching between DK/QK and CLK -50 < CLK - DK/QK < 50ps
Length Matching between DQ and DK/QK within byte -5ps < DQ - DK/QK < 5ps
Length matching between DK/QK and DK/QK# < 1 ps
Length matching between DK and QK pairs < 5 ps
Length matching between CLK and CLK# < 1 ps
Length Matching between CMD and CTRL and Clock -20 ps < CLK - CMD < 20 ps
Length matching among CMD and CTRL within each channel < 20 ps
Include package length in skew matching for FPGA device with no migration Required
Include package length in skew matching for FPGA device with migration when all package net length are available It is recommended to use the final migrated package net length
Include package length in skew matching for FPGA device with migration when all package net length are not available Not recommended