What is the Right Controlled Impedance for Your DDR5 Traces?
应用文章
Identify Controlled Impedance for DDR5 Designs
As articulated in [1], finding impedance values corresponding to signal groups within DDR4 modules is challenging. This sentiment remains true when it comes to starting DDR5 designs. There are no explicit recommendations for controlled impedance in the JESD 79-5 document, the standard for DDR5.
This document examines the controlled impedance recommendations by DDR device vendors, compares the recommendations to impedance on fabricated boards, and provides design suggestions. Given the lack of available DDR5 designs, this case study focuses instead on the impedances of existing opensource DDR4 designs.
The vendor-suggested maximum and minimum impedance range and the impedances in fabricated DDR designs were compared. The fabricated open-source boards all have DDR controlled impedances within the range suggested.