DDR3内存的PCB仿真与设计

经典DDR3PCB设计指导DDR3 PCB（Printed Circuit Board）设计是一项关键性任务，它直接影响到DDR3内存模块性能和稳定性。

下面是一些经典的DDR3 PCB设计指导。

1.布局设计首先，要确保PCB布局以尽量减小信号传输长度和最小化信号路径的交叉。

为此，可以采用层叠设计，将电源和地线平面放在内层，并尽量将数据和时钟线路与其他信号线路分开。

同时，还要保持清晰的电源和地线分布，以减少电磁干扰。

2.阻抗匹配DDR3接口要求较低的阻抗匹配，一般为50欧姆。

因此，在设计DDR3PCB时，需要使用特殊的阻抗控制技术，包括差分阻抗控制和单端阻抗控制。

通过正确选择PCB板材和线宽/线间距来控制阻抗，确保数据线和时钟线的阻抗匹配。

3.时钟信号时钟信号对DDR3接口的性能和稳定性至关重要。

在PCB设计中，时钟信号应该尽量与其他信号线隔离，并保持尽可能短的信号路径。

此外，要确保时钟信号的最大和最小延迟在规格范围内，并且要避免信号树中出现反向或环形延迟。

4.功耗分析和管理DDR3内存模块在运行时会产生较大的功耗，因此在PCB设计中需要进行功耗分析和管理。

这包括考虑供电线路的宽度和连接方式，设计足够的电源滤波电容，并确保电源线路的稳定性和低噪声。

5.地线规划合理的地线规划对于DDR3PCB设计至关重要。

正确规划地线可以减少信号的噪声干扰和串扰。

建议使用实特性阻抗为0的地线平面，以减少反跳和电磁干扰。

6.差分信号DDR3接口主要使用差分信号传输，如数据线和时钟线。

在PCB设计时，差分信号应该尽可能保持信号的匹配性，并采取差分对的布线方式，减少差分信号之间的串扰。

以上是经典的DDR3PCB设计指导，注意这只是指导性的建议，具体设计仍应根据具体的应用场景和产品要求进行调整。

此外，使用专业的PCB 设计软件进行仿真和分析也是十分重要的，以确保DDR3PCB设计的性能和稳定性。

DDR3内存的PCB仿真与设计
一、DDR3内存的PCB仿真
PCB（Printed Circuit Board，印制电路板）的设计是DDR3内存中非常重要的一步。

在进行实际制作之前，通过仿真来验证设计的正确性，可以帮助找出潜在的问题并进行优化。

1.电源噪声仿真
2.信号完整性仿真
3.时钟分布仿真
4.排布规则仿真
二、DDR3内存的PCB设计
在进行DDR3内存的PCB设计时，需要考虑以下几个方面。

1.布局设计
2.分层设计
3.时钟优化
4.信号完整性优化
5.地平面设计
良好的地平面设计可以提供稳定的地连接，减小噪声干扰。

需要合理规划地平面的宽度和连接方式，并与信号平面分层设计相结合。

总之，DDR3内存的PCB仿真和设计是提高DDR3内存性能和稳定性的重要手段。

通过仿真和设计的过程，可以找出潜在的问题并进行优化，提
高DDR3内存的性能和可靠性。

对DDR3内存的PCB设计要仔细考虑布局、分层、时钟优化、信号完整性优化和地平面设计等方面，以确保DDR3内存的正常运行。

DDR3硬件设计和Layout设计译自飞思卡尔官方文档Hardware and Layout DesignConsiderations for DDR3 SDRAMMemory InterfacesDocument revision historyDate Revision Changes 2015-03-29 1.0 第一次撰稿目录1 设计检查表 (3)2 终端匹配电阻功耗计算 (8)3 VREF (8)4 VTT电压轨 (8)5 DDR布线 (9)5.1 数据线— MDQ[0:63], MDQS[0:8], MDM[0:8], MECC[0:7] (9)5.2 Layout建议 (10)6 仿真 (12)7 扩展阅读 (13)8 历史版本 (13)9 声明 (13)这是一篇关于DDR3 SDRAM IP core的设计向导，出自飞思卡尔，为了实现PCB的灵活设计，我们可以采用合适的拓扑结构简化设计时的板级关联性。

飞思卡尔强烈推荐系统/板级工程师在PCB制板前进行设计验证，包括信号完整性、时序等等。

1 设计检查表如表1，罗列了DDR设计检查清单，推荐逐一检查，并在最右侧作出决策。

表1 DDR3检查清单序号描述是/否仿真1 是否最优化了①终端匹配电阻值、②信号线拓扑、③走线长度等？这些项目最好通过仿真进行优化！假如在DDR和控制器间应用了ODT（on-die termination）技术，那么在数据总线上就不需要额外的终端匹配电阻了。

DDR分组要求如下：■数据组：MDQS(8:0)，(8:0)，MDM(8:0)，MDQ(63:0)，MECC(7:0)■地址/命令组：MBA(2:0)，MA(15:0)，，，■控制组：(3:0)，MCKE(3:0)，MODT(3:0)■时钟组：MCK(5:0)，(5:0)数据组走线共计72位（64bit + 8bit ECC<ECC是Error Checking and Correcting的简写，即是错误检查和纠正，这种技术多用在服务器中>）。

目录DDR的PCB设计 (I)The PCB design of DDR.............................................. I I 第1章绪论.. (1)1.1 DDR的叙述 (1)1.2 DDR-DDR与SDRAM的区别 (1)1.3 DDR存储器电气特性验证 (4)第2章噪声来源及分析 (8)2.1 反射噪声分析和端接技术 (8)2.1.1 反射形成原因 (8)2.1.2 主抗匹配与端接方案 (9)2.1.3 端接方案的仿真结果 (12)2.2串扰噪声分析 (13)2.2.1 高速PCB板上的串扰分析模型 (13)2.2.2 高速PCB板上的串扰仿真结果 (13)2.2.3 减少高速PCB板上的串扰噪声的措施 (14)第3章完整性分析 (16)3.1电源完整性 (16)3.2 时序分析 (17)3.2.1公共时钟同步的时序分析 (17)3.2.2 源同步的时序分析 (22)3.3 案例 (24)第4章布局与布线 (29)4.1 PCB的叠层（stackup）和阻抗 (29)4.2 互联通路拓扑 (30)4.3 SDRAM的布局布线 (32)4.4 DDR的布局布线 (33)4.4.1 布局时应注意 (35)4.4.2布线时应注意 (35)4.4.3 布线要点 (37)4.6 供电 (38)结束语 (40)参考文献 (41)致谢 (42)附录数据线同组同层 (43)DDR的PCB设计摘要：随着微电子技术和计算机技术的不断发展，DDR双通道同步动态随机存储器在通信系统中的应用越来越显得重要，而随着电子产品的集成化，对DDR在PCB中的设计要求也越来越高。

为了更好的能理解DDR，本文还与SDRAM一并做了介绍与设计。

本设计为基于DDR双通道同步动态随机存储器的PCB设计。

本文主要介绍了在对DDR的PCB设计时，所面临的信号完整性。

详尽的阐述了影响信号完整性的反射、串扰和信号完整性中的时序分析的相关理论并提出了减小反射和串扰得有效措施。

ddr3 电路设计
DDR3是一种双数据速率（Double Data Rate）的SDRAM（同步
动态随机存取存储器），它具有高速、高密度和低功耗的特点。

在
进行DDR3电路设计时，需要考虑以下几个方面：
1. 时序设计，DDR3内部时序非常严格，需要精确的时钟控制
和信号同步。

在电路设计中，需要确保时钟信号的准确性和稳定性，同时要考虑数据和控制信号的延迟和对齐。

2. 信号完整性，DDR3的高速传输需要考虑信号完整性，包括
信号的传输线路设计、阻抗匹配、信号串扰和噪声抑制等方面。

在
电路设计中需要合理布局PCB，减小信号传输路径的长度，采用差
分信号传输等方法来提高信号完整性。

3. 电源和接地设计，DDR3需要提供稳定的电源和接地，以确
保芯片的正常工作。

在电路设计中需要考虑电源线和接地线的布局
和连接方式，减小电源噪声和提高电源供电的稳定性。

4. 自校准和时序校准，DDR3内部具有自校准和时序校准的功能，可以校正时钟和数据信号的偏移和延迟。

在电路设计中需要考
虑这些校准功能的实现和控制。

5. 热管理，DDR3在高速运行时会产生较多的热量，需要考虑散热设计，包括散热片的设计和散热风扇等。

总之，DDR3电路设计需要全面考虑时序、信号完整性、电源和接地、自校准和时序校准、热管理等多个方面，以确保DDR3芯片的正常工作和高速稳定传输。

想做个DDR设计不？想还是不想？你要知道FPGA这种东西，片内存储资源终究有限，实在谈不上海量存储。

万一哪天你想要海量存储数据了咋办？你是不是得用DRAM条子啊？什么？你还想用SRAM？今年已经2013年了童鞋~关于DRAM，或许是SDRAM，或许是DDR1（再次提醒你，2013年了已经），或许是DDR2或者DDR3。

这些条子都有一套控制协议，这套协议对不同的条子大同小异，但是里面又有各种细节的区别，这些你都搞懂了吗？没搞懂？其实，你不需要搞懂。

现在的EDA设计不需要你从基础知识开始研究。

这个时代，你要生存要发展，最佳的办法是站在巨人的肩膀上，而不是亲自长成个巨人。

DDR设计太常用了，只要你在搞FPGA，自然有人给你搞定一套IP，免费的给你用。

你不会还想自己从底层写起吧？多花些时间在没有免费IP用的协议合算法上吧。

现在进入正题：我刚刚讲的免费IP，在哪里？怎么用的？（小白问题，IP是什么，IP地址吗？）这里的IP就是Intelligence Property说白了就是xilinx里的core gen（对应于altera里面的mega wizard）这个文档就举一个例子来讲，选哪家呢?本人是xilinx和altera都来一个？条子选啥？SDR?DDR1? 各种条子全都写一套？（你以为写这个文档容易吗，是不是要连chipscope怎么用也一起出个文档啊？全部都写一套可以，先往我账户上打五千块钱，然后我再考虑考虑。

记住这个世界上没有白吃的午餐，你要看白痴都能看会的DDR教程，你就得听我在这里唠叨）本教程选择一个例子来讲，那就是xilinx平台下用DDR3（常见的笔记本内存条）接下来是你玩转这个教程所必须要准备的工具：xilinx ISE 14.1或者更高版本（不好意思，比14.1还低的版本我没试过。

vivado当然也可以，不过我是用的ISE）modelsim SE 6.6a或者更高版本（更低版本我负责的告诉你不可以，因为无法正常生成编译库，所以，6.5版本或者更低的你干脆就别装了）有鉴于这个文档的面相对象设定为连chiscope都不太会用的人，就是那种刚毕业不到一两年甚至还在校的，我必须郑重的告诉你一下这两个工具上哪里去下载：网上下载，百度股沟搜索会不会？什么？你告诉我搜不到？我给你跪了，菜鸟兄XILINX ISE 14.4这里下载http://simplecd.me/entry/L1a0enD2/破解文件：/f/62469961.htmlmodelsim 6.6这里下载（要注册和花积分的）：/viewthread.php?tid=232457破解文件：/f/34760037.html（注意，时间长了以后这几个链接是可能失效的，比如你可能在2015年看到这个2013年11月写的文档，到时候可能只能自己找下载了）PPT翻了一页了，工具都装完了吗亲？已经装完了啊？很好哦，那我们就开始吧！你知道用ISE做DDR设计的第一步是啥吗？当然是打开工具了——我估计这你肯定知道打开工具之后做啥？当然是生成一个IP，对xilinx来说也就是core gen了我估计你即便是新手上路，这个也是知道的——因为我前面刚刚讲过了嘛那么core gen生成完了之后呢？是不是要仿真啊？仿真需要什么？当然是modelsim了——我还是刚刚讲过，哈哈那你知道用modelsim仿真DDR的core gen，是需要xilinx仿真库的吗？什么？你不知道啥叫仿真库？乖乖隆地洞，我还是给你讲讲啥叫仿真库吧先关于FPGA的仿真库本人不是学校里的学究，本人是工程师所以用工程师的语言告诉你啥叫仿真库FPGA本身是一种特定的芯片，这个芯片里有很多特定的基本电路单元。

最新DDR3-硬件设计和-Layout-设计整理DDR3硬件设计和Layout设计译自飞思卡尔官方文档Hardware and Layout DesignConsiderations for DDR3 SDRAMMemory InterfacesDocument revision historyDate Revision Changes 2015-03-29 1.0 第一次撰稿目录1 设计检查表 (3)2 终端匹配电阻功耗计算 (8)3 VREF (8)4 VTT电压轨 (8)5 DDR布线 (9)5.1 数据线— MDQ[0:63], MDQS[0:8], MDM[0:8], MECC[0:7] (9)5.2 Layout建议 (10)6 仿真 (12)7 扩展阅读 (13)8 历史版本 (13)9 声明 (13)这是一篇关于DDR3 SDRAM IP core的设计向导，出自飞思卡尔，为了实现PCB的灵活设计，我们可以采用合适的拓扑结构简化设计时的板级关联性。

飞思卡尔强烈推荐系统/板级工程师在PCB制板前进行设计验证，包括信号完整性、时序等等。

1 设计检查表如表1，罗列了DDR设计检查清单，推荐逐一检查，并在最右侧作出决策。

表1 DDR3检查清单序号描述是/否仿真1 是否最优化了①终端匹配电阻值、②信号线拓扑、③走线长度等？这些项目最好通过仿真进行优化！假如在DDR和控制器间应用了ODT（on-die termination）技术，那么在数据总线上就不需要额外的终端匹配电阻了。

DDR分组要求如下：■数据组：MDQS(8:0)，(8:0)，MDM(8:0)，MDQ(63:0)，MECC(7:0)■地址/命令组：MBA(2:0)，MA(15:0)，，，■控制组：(3:0)，MCKE(3:0)，MODT(3:0)■时钟组：MCK(5:0)，(5:0)数据组走线共计72位（64bit + 8bit ECC<="" p="">的简写，即是错误检查和纠正，这种技术多用在服务器中>）。

想做个DDR设计不？想还是不想？你要知道FPGA这种东西，片内存储资源终究有限，实在谈不上海量存储。

万一哪天你想要海量存储数据了咋办？你是不是得用DRAM条子啊？什么？你还想用SRAM？今年已经2013年了童鞋~关于DRAM，或许是SDRAM，或许是DDR1（再次提醒你，2013年了已经），或许是DDR2或者DDR3。

这些条子都有一套控制协议，这套协议对不同的条子大同小异，但是里面又有各种细节的区别，这些你都搞懂了吗？没搞懂？其实，你不需要搞懂。

现在的EDA设计不需要你从基础知识开始研究。

这个时代，你要生存要发展，最佳的办法是站在巨人的肩膀上，而不是亲自长成个巨人。

DDR设计太常用了，只要你在搞FPGA，自然有人给你搞定一套IP，免费的给你用。

你不会还想自己从底层写起吧？多花些时间在没有免费IP用的协议合算法上吧。

现在进入正题：我刚刚讲的免费IP，在哪里？怎么用的？（小白问题，IP是什么，IP地址吗？）这里的IP就是Intelligence Property说白了就是xilinx里的core gen（对应于altera里面的mega wizard）这个文档就举一个例子来讲，选哪家呢?本人是xilinx和altera都来一个？条子选啥？SDR?DDR1? 各种条子全都写一套？（你以为写这个文档容易吗，是不是要连chipscope怎么用也一起出个文档啊？全部都写一套可以，先往我账户上打五千块钱，然后我再考虑考虑。

记住这个世界上没有白吃的午餐，你要看白痴都能看会的DDR教程，你就得听我在这里唠叨）本教程选择一个例子来讲，那就是xilinx平台下用DDR3（常见的笔记本内存条）接下来是你玩转这个教程所必须要准备的工具：xilinx ISE 14.1或者更高版本（不好意思，比14.1还低的版本我没试过。

vivado当然也可以，不过我是用的ISE）modelsim SE 6.6a或者更高版本（更低版本我负责的告诉你不可以，因为无法正常生成编译库，所以，6.5版本或者更低的你干脆就别装了）有鉴于这个文档的面相对象设定为连chiscope都不太会用的人，就是那种刚毕业不到一两年甚至还在校的，我必须郑重的告诉你一下这两个工具上哪里去下载：网上下载，百度股沟搜索会不会？什么？你告诉我搜不到？我给你跪了，菜鸟兄XILINX ISE 14.4这里下载http://simplecd.me/entry/L1a0enD2/破解文件：/f/62469961.htmlmodelsim 6.6这里下载（要注册和花积分的）：/viewthread.php?tid=232457破解文件：/f/34760037.html（注意，时间长了以后这几个链接是可能失效的，比如你可能在2015年看到这个2013年11月写的文档，到时候可能只能自己找下载了）PPT翻了一页了，工具都装完了吗亲？已经装完了啊？很好哦，那我们就开始吧！你知道用ISE做DDR设计的第一步是啥吗？当然是打开工具了——我估计这你肯定知道打开工具之后做啥？当然是生成一个IP，对xilinx来说也就是core gen了我估计你即便是新手上路，这个也是知道的——因为我前面刚刚讲过了嘛那么core gen生成完了之后呢？是不是要仿真啊？仿真需要什么？当然是modelsim了——我还是刚刚讲过，哈哈那你知道用modelsim仿真DDR的core gen，是需要xilinx仿真库的吗？什么？你不知道啥叫仿真库？乖乖隆地洞，我还是给你讲讲啥叫仿真库吧先关于FPGA的仿真库本人不是学校里的学究，本人是工程师所以用工程师的语言告诉你啥叫仿真库FPGA本身是一种特定的芯片，这个芯片里有很多特定的基本电路单元。

1、使用systemSI进行仿真的流程为：获取芯片IBIS模型》加载芯片IBIS模型》分配仿真bus》提取PCB S参数》配置仿真模型及参数》仿真其中提取PCB S参数的步骤为：将brd文件转化为spd文件》配置平面参数》设置电源net》选择需要仿真的net并自动生成port》设置port阻抗》仿真2、system SI IBIS模型加载步骤：其中点击1选择需要加载的IBIS模型，一个IBIS模型中可能包括多个器件型号，需要在右上方的“component”中选择对应的器件型号，然后点击bus definition定义总线（定义总线的主要作用是区分哪些信号需要仿真，并将需要仿真的信号分类为data、ctrl、addcmd三种类型），点击add添加新总线，在“Bus Type”中选择总线的类型，在“Bus Group”中设置Bus name，在“Timing Ref”中选择各个信号的参考时钟，“Edge Type”用于选择信号的触发方式，data触发方式为“BothEdges”，ctrl和addcmd的触发方式为“RiseEdge”，在“Signal Names”中选择该group中包括的信号，如果是data信号，还可以添加“Clock”即ctrl和addcmd的参考时钟，可以用于分析数据时钟与控制时钟的对应关系。

修改完成后点击OK，退出后点击“确定”分别对controller和memory进行配置，注意memory的配置需要与controller相对应，如下图3、提取PCB的S参数在开始菜单输入“SPDLinks”，打开Allegro Sigrity SPDLinks在步骤1的“Browse”中选择需要转换的.brd文件，点击“settings”进行参数设置，一般保持默认设置即可，如对参数有特殊需求，可参考help》translators》SPDLinks对相应的参数进行设置，设置完成后点击“Translate”即可生成.spd文件后，打开powerSI软件，导入.spd文件，先对层叠结构进行设置，点击“Model Extraction”中的“Check Stackup”，一般如果.brd文件中设置好了以后层叠结构会自动导入，如未导入，根据.brd文件中cross section的设置对powerSI的层叠结构进行相同的设置即可层叠结构设置完成后需设置电源网络，点击“select Nets”》“Skip setup P/G nets”进入net manager界面根据实际设计，分别选择电源网络和地网络，右键选择“classify”》“As PowerNets”或“As GroundNets”电源网络分配完成后选择需要分析的port，方法为：将所有net前方框中的对勾去掉，只保留需要仿真的网络。

Freescale SemiconductorApplication NoteThe design guidelines presented in this application note apply to products that leverage the DDR3 SDRAM IP core, and they are based on a compilation of internal platforms designed by Freescale Semiconductor, Inc. The purpose of these guidelines is to minimize board-related issues across multiple memory topologies while allowing maximum flexibility for the board designer.Freescale highly recommends that the system/board designer verify all design aspects (signal integrity, electrical timings, and so on) through simulation before PCB fabrication.Document Number:AN3940Rev. 1, 03/2010Contents1.Designer Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.Termination Dissipation . . . . . . . . . . . . . . . . . . . . . . . 73.V REF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.VTT Voltage Rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8yout Guidelines for the Signal Groups . . . . . . . . . . 86.Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.Further Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138.Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Hardware and Layout Design Considerations for DDR3 SDRAM Memory Interfacesby Networking and Multimedia GroupFreescale Semiconductor, Inc.Austin, TXDesigner Checklist1Designer ChecklistIn the following checklist, some of the items are phrased as question, others as requirements. In all cases, it is recommended to consider the line item and check it off in the rightmost column of Table1.Table1. DDR3 Designer’s ChecklistItem Description Yes/NoSimulation1.Have optimal termination values, signal topology, trace lengths been determined through simulation for eachsignal group in the memory implementation? If on-die termination is used at both the memories and the controller,no additional termination is required for the data group.The following unique groupings exist:1.Data Group: MDQS(8:0), MDQS(8:0), MDM(8:0), MDQ(63:0), MECC(7:0)2.Address/CMD Group: MBA(2:0), MA(15:0), MRAS, MCAS, MWE.3.Control Group: MCS(3:0), MCKE(3:0), MODT(3:0)4.Clock Group: MCK(5:0) and MCK(5:0)These groupings assume a full 72-bit data implementation (64-bit + 8 bits of ECC). Some products may onlyimplement 32-bit data and may choose to have fewer MCS, MCKE, and MODT signals. Some products supportthe optional MAP AR_OUT and MAP AR_ERR for registered DIMMs. In such cases, MAP AR_OUT should betreated as part of the ADDR/CMD group and MAPAR_ERR can be treated as an asynchronous signal.2.Does the selected termination scheme meet the AC signaling parameters (voltage levels, slew rate, andovershoot/undershoot) across all memory chips in the design?Termination SchemeIt is assumed that the designer is using the mainstream termination approach as found in commodity PC motherboards. Specifically, it is assumed that on-die termination is used for the data groups and that external parallel resistors tied to VTT are used for the Address/CMD and the control groups. Consequently, differing termination techniques may also prove valid and useful. However, they are left to the designer to validate through simulation.3.Is the worst case power dissipation for the termination resistors within the manufacturer’s rating for the selecteddevices? See Section2, “Termination Dissipation.”4.If resistor packs are used, have data lanes been isolated from the other DDR3 signal groups?Note: Because on-die termination is the preferred method for DDR3 data signals, external resistors for the datagroup should not be required. This item would only apply if the ODT feature is not used.5.Have V TT resistors been properly placed? The R T terminators should directly tie into the V TT island at the end ofthe memory bus.6.Is the differential terminator present on the clock lines for discrete memory populations? (DIMM modules containthis terminator.) Nominal range => 100–120 Ω.7.Recommend that an optional 5pF cap be placed across each clock diff pair. If DIMM modules are used, the capshould be placed as closely as possible to the DIMM connector. If discrete devices are used, the cap should beplaced as closely as possible to the discrete devices.V TT Related Items8.Has the worst case current for the V TT plane been calculated based on the design termination scheme? SeeSection2, “T ermination Dissipation.”9.Can the V TT regulator support the steady state and transient current needs of the design?Designer ChecklistTable1. DDR3 Designer’s Checklist (continued)Item Description Yes/No 10.Has the V TT island been properly decoupled with high frequency decoupling? At least one low ESL cap, or twostandard decoupling caps for each four-pack resistor network (or every four discrete resistors) should be used. Inaddition, at least one 4.7-μF cap should be at each end of the V TT island.Note: This recommendation is based on a top-layer V TT surface island (lower inductance). If an internal split isused, more capacitors may be needed to handle the transient current demands.11.Has the V TT island been properly decoupled with bulk decoupling? At least one bulk cap (100–220μF) capacitorshould be at each end of the island.12.Has the V TT island been placed at the end of the memory channel and as closely as possible to the last memorybank? Is the V TT regulator placed in close proximity to the island?13.Is a wide surface trace (~150 mils) used for the V TT island trace?14.If a sense pin is present on the V TT regulator, is it attached in the middle of the island?V REF15.Is V REF routed with a wide trace? (Minimum of 20–25 mil recommended.)16.Is V REF isolated from noisy aggressors? In addition, maintain at least a 20–25 mil clearance from V REF to othertraces. If possible, isolate V REF with adjacent ground traces.17.Is V REF properly decoupled? Specifically, decouple the source and each destination pin with 0.1uf caps.18.Does the V REF source track variations in V DDQ, temperature, and noise as required by the JEDEC specification?19.Does the V REF source supply the minimal current required by the system (memories + processor)?20.If a resistor divider network is used to generate V REF, are both resistors the same value and 1% tolerance?Routing21.The suggested routing order within the DDR3 interface is as follows:1.Data address/command2.Control3.Clocks4.PowerThis order allows the clocks to be tuned easily to the other signal groups. It also assumes an open critical layeron which clocks are freely routed.22.Global items are as follows:•Do not route any DDR3 signals overs splits or voids.•T races routed near the edge of a reference plane should maintain at least 30–40 mil gap to the edge of the reference plane.•Allow no more than 1/2 of a trace width to be routed over via antipad.23.When routing the data lanes, route the outermost (that is, longest lane first) because this determines the amountof trace length to add on the inner data lanes.24.The max lead-in trace length for data/address/command signals, are not longer than 7 inches?25.Are the clock pair assignments optimized to allow break-out of all pairs on a single critical layer?Designer ChecklistTable1. DDR3 Designer’s Checklist (continued)Item Description Yes/No 26.The DDR3 data bus consists of 9 data byte lanes (assuming ECC is used). All signals within a given byte laneshould be routed on the same critical layer with the same via count.Note: Some product implementations may only implement a 32-bit wide interface.Byte Lane 0—MDQ(7:0), MDM(0), MDQS(0), MDQS(0)Byte Lane 1—MDQ(15:8), MDM(1), MDQS(1), MDQS(1)Byte Lane 2—MDQ(23:16), MDM(2), MDQS(2), MDQS(2)Byte Lane 3—MDQ(31:24), MDM(3), MDQS(3), MDQS(3)Byte Lane 4—MDQ(39:32), MDM(4), MDQS(4), MDQS(4)Byte Lane 5—MDQ(47:40), MDM(5), MDQS(5), MDQS(5)Byte Lane 6—MDQ(55:48), MDM(6), MDQS(6), MDQS(6)Byte Lane 7—MDQ(63:56), MDM(7), MDQS(7), MDQS(7)Byte Lane 8—MECC(7:0), MDM(8), MDQS(8), MDQS(8)T o facilitate fan-out of the DDR3 data lanes (if needed), alternate adjacent data lanes onto different critical layers.See Figure1 and Figure2.Note: If the device supports ECC, Freescale highly recommends that the user implement ECC on the initialhardware prototypes.27.DDR3 data group—impedance range and spacingOption #1 (wider traces—lower trace impedance)•Single-ended impedance = 40 Ω. The lower impedance allows traces to be slightly closer with less cross-talk.•Utilize wider traces if stackup allows (7–8mils)•Spacing to other data signals = 1.5x to 2.0x•Spacing to all other non-DDR signals = 4xOption #2 (smaller traces—higher trace impedance)•Single-ended impedance = 50 Ω.•Smaller trace widths (5–6mil) can be used.•Spacing between like signals should increase to 3x (for 5mil) or 2.5x (for 6mil) respectively28.Check the following across all DDR3 data lanes:•For MPC8572 and MPC8536, are all the data lanes matched to within 0.1 inch?•For all other devices, are all the data lanes matched to within 2.0 inch?29.Is each data lane properly trace matched to within 20 mils of its respective differential data strobe? (Assumeshighest frequency operation.)30.When adding trace lengths to any of the DDR3 signal groups, ensure that there is at least 25 mils betweenserpentine loops that are in parallel.Designer ChecklistTable1. DDR3 Designer’s Checklist (continued)Item Description Yes/No 31.MDQS/MDQS differential strobe routingNote: Some product implementations may support only the single-ended version of the strobe.•Match all segment lengths between differential pairs along the entire length of the pair. T race match the MDQS/ MDQS pair to be within 10 mils.•Maintain constant line impedance along the routing path by maintaining the required line width and trace separation for the given stackup.•Avoid routing differential pairs adjacent to noisy signal lines or high speed switching devices such as clock chips.•Differential 75–95 Ω•Diff Gap = 4–5 mils (as DQS signals are not true differential...aka pseudo differentialOption #1 (wider traces—lower trace impedance)•Single-ended impedance 40 Ω. The lower impedance allows traces to be slightly closer with less cross-talk.•Utilize wider traces if stackup allows (7–8mils)•Spacing to other data signals = 2x.•If not routed on the same layer as its associated data, then 4x spacingOption #2 (smaller traces—higher trace impedance)•Single-ended impedance = 50 Ω.•Smaller trace widths (5–6mil) can be used.•Spacing between like signals (other data) should increase to 3x (for 5mil) or 2.5x (for 6mil) respectively.•Do not divide the two halves of the diff pair between layers. Route MDQS/MDQS pair on the same critical layer as its associated data lane.32.DDR3 address/command/control group—impedance range and spacing•Daisy chain from chip to chip. The routing should go from chip 0 to chip n, where chip 0 is the one that has the lower data bits DQ[0:7]… and chip n has the upper data bits. The daisy chain should end at the terminationresistors that are after chip n.•With regards to physical/spacing propertiesOption #1 (wider traces—lower trace impedance)•Single-ended impedance = 40 Ω. The lower impedance allows traces to be slightly closer with less cross-talk.•Utilize wider traces if stackup allows (7–8mils)•Spacing to other like signals = 1.5x to 2.0x•Spacing to all other non-DDR signals =3–4xOption #2 (smaller traces—higher trace impedance)•Single-ended impedance = 50 Ω.•Smaller trace widths (5–6mil) can be used.•Spacing between like signals should increase to 3x (for 5mil) or 2.5x (for 6mil) respectively•Spacing to all other non-DDR signals =3–4x•With regards to tuning•T une signals to 20 mil of the clock at each device.33.DDR3 differential clocksRoute as diff pair. With regards to diff properties, recommendations are as follows:•P-to-N tuning = 10 mils•T arget single-ended impedance 40–50 Ω. The lower impedance reduces cross-talk.•Differential 75–95 Ω•Diff Gap = set per stackupOption #1 (wider traces—lower trace impedance)•Attempt to utilize wider traces if stackup allows (7–8mils)•Spacing to other signals = 4x.Option #2 (smaller traces—higher trace impedance)•Single-ended impedance = 50 Ω.•Smaller trace widths (5–6mil) can be used.•Spacing to other signals = 4x.Designer ChecklistTable1. DDR3 Designer’s Checklist (continued)Item Description Yes/No34.Are all clock pairs routed on the same critical layer (one referenced to a solid ground plane)?35.Are all clock pairs properly trace matched to within 25 mils of each other?36.The space from one differential pair to any other trace (this includes other differential pairs) should be at least 25mils.37.If unbuffered DIMM modules are used, are all required clock pairs per DIMM slot connected?Note: Single ranked DIMM requires 1 clock pair and dual ranked DIMM requires 2 clock pairsMODT/MDIC Related Items38.Are the MODT signals connected correctly?•MODT(0), MCS(0), MCKE(0) should all go to the same physical memory bank.•MODT(1), MCS(1), MCKE(1) should all go to the same physical memory bank.•MODT(2), MCS(2), MCKE(2) should all go to the same physical memory bank.•MODT(3), MCS(3), MCKE(3) should all go to the same physical memory bank.39.Is MDIC0 connected to ground via an 40-Ω precision 1% resistor? Is MDIC1 connected to DDR power via an 40-Ωprecision 1% resistor?Miscellaneous Items40.Are the power-on reset config pins properly set for the correct DDR type?Note: Not all Freescale products support external power-on reset configuration pins for selecting the DDR type.Therefore, this item does not apply to all Freescale products.Registered DIMM Topologies (All items above still apply)41.For memory implementations that use registered DIMM modules, the board designer should attach a reset signalto the DIMM sockets. This reset signal should be derived from a ‘power good’ monitor status circuit.Note: The reset pin to the DRAM is 1.5V LVCMOS.42.Though registered DIMMs require only a single clock per bank, all DDR3 clock pairs at the DIMM connectorshould be attached (analogous to unbuffered DIMMs) so the design can also support unbuffered DIMMs withminimal changes.43.If the controller supports the optional MAPAR_OUT and MAPAR_ERR signals, ensure that they are hooked upas follows:•MAP AR_OUT (from the controller) => P AR_IN (at the RDIMM)•ERR_OUT (from the RDIMM) => MAPAR_ERR (at the controller)44.MAP AR_ERR is an open drain output from registered DIMMs. Ensure that a 4.7K pull-up to 1.5 V is present onthis signal.Discrete Memory Topologies (All items above still apply with exception of registered DIMM items)45.Construct the signal routing topologies for the groups like those found on unbuffered DIMM modules (that is,proven JEDEC topologies).46.When placing components, optimize placement of the discretes to favor the data bus (analogous to DIMMtopologies).Optional: Pin-swap within a given byte lane to optimize the data bus routes further.Caution: Do not swap individual data bits across different byte lanes.Termination Dissipation2Termination DissipationSink and source currents flow through the parallel R T resistors on the address and control groups. The worst case power dissipation for these resistors is as follows:Power =I 2×R T =(13mA)2×(47Ω)=7.9mW.Small resistors that provide dissipation of up to 1/16 W are ideal. See Section 4, “VTT V oltage Rail ,” for assumptions made for current calculations.3V REFThe current requirements for V REF are relatively small, at less than 3 mA. This reference provides a DC bias of 0.75V (V DD /2) for the differential receivers at both the controller interface and the DDR devices. Noise or deviation in the V REF voltage can lead to potential timing errors, unwanted jitter, and erratic behavior on the memory bus. To avoid these problems, V REF noise must be kept within the JEDEC specification. As such, V REF and the V TT cannot be the same plane because of the DRAM V REF buffer sensitivity to the termination plane noise. However, both V REF and V TT must share a common source supply to ensure that both are derived from the same voltage plane. Proper decoupling at each V REF pin (at the controller, at each DIMM/discrete, and at the V REF source) along with adhering to the simple layout considerations enumerated in the checklist in Table 1 prevents potential problems .Numerous off-the-shelf power IC solutions are available that provide both the V REF and V TT from acommon source. Regardless of the generation technique, V REF must track variations in V DDQ over voltage, temperature, and noise margins as required by the JEDEC specifications.47.If a single bank of x16 devices is used, let the DDR3 clocks be point-to-point. Place the series damping resistor (R S ) close to the source and the differential terminator (R DIFF ) at the input pins of the discretes.If more than five discretes are used, construct the clocks like those on unbuffered DIMM modules. Alternatively, place an external PLL between the controller and the memory to generate the additional clocks.48.If multiple physical banks are needed, double stack (top and bottom) the banks to prevent lengthy and undesirable address/cmd topologies.49.Properly decouple the DDR3 chips per manufacturer recommendations. T ypically, five low ESL capacitors per device are sufficient. For further information, see article entitled Decoupling Capacitor Calculation for a DDR Memory Channel, located on Micron’s web site.50.T o support expandability into larger devices, ensure that extra NC pins (future address pins) are connected.51.Ensure access/test points are available for signal integrity probing. This is especially critical if using blind and buried vias within the memory channel. If through-hole vias are used under the BGA devices, then generally these sites can be used for probing.52.Ensure R T , resistors on the address and control groups are located after the last DRAM chip in the-fly-by topology.53.Ensure the reset pin has been considered and connected to the proper reset logic. Note: The reset pin to the DRAM is 1.5V LVCMOS.Table 1. DDR3 Designer’s Checklist (continued)Item DescriptionYes/NoVTT Voltage Rail4V TT Voltage RailFor a given topology, the worst case V TT current should be derived. Assuming the use of a typical R T parallel termination resistor and the worst case parameters given in Table 2, sink and source currents can be calculated.The driver sources (V TT plane would sink) the following based on this termination scheme:(V DD_max –V TT_min )/(R T + R DRVR )=(1.575–0.702 V)/(47+20)=13 mA The driver sinks (V TT plane would source) the following based on this termination scheme:(V TT_max – V OL / (R T + R S + R DRVR )=(0.798–0 V)/(47+20)=12 mAA bus with balanced number of high and low signals places no real demand on the V TT supply. However, a bus with all DDR address/command/control signals low (~ 28 signals) causes a transient current demand of approximately 350 mA on the V TT rail. The V TT regulator must provide a relatively tight voltage regulation of the rail per the JEDEC specification. Besides a tight tolerance, the regulator must also allow V TT along with V REF (if driven from a common IC), to track variations in V DDQ over voltage, temperature, and noise margins.5Layout Guidelines for the Signal GroupsTo help ensure the DDR interface is properly optimized, Freescale recommends the following sequence for routing the DDR memory channel:1.Route data2.Route address/command/control3.Route clocks The data group is listed before the command, address, and control group because it operates at twice the clock speed, and its signal integrity is of higher concern. In addition, the data group constitutes the largest portion of the memory bus and comprises most of the trace matching requirements (those of the data lanes). The address/command, control, and data groups all have a relationship to the routed clock.Therefore, the effective clock lengths used in the system must satisfy multiple relationships. The designer should perform simulation and construct system timing budgets to ensure that these relationships are properly satisfied.Table 2. Worst Case Parameters for V TT Current Calculation ParameterValuesCommentV DDQ (max) 1.575 V From JEDEC spec V TT(max)0.798 V From JEDEC spec V TT(min)0.702 V From JEDEC specR DRVR 20 ΩNominally, full strength is ~ 20Ωs R T 47 ΩCan vary. T ypically 25–47Ωs.V OL0 VAssumes driver reaches 0V in the low state.Layout Guidelines for the Signal Groups 5.1Data—MDQ[0:63], MDQS[0:8], MDM[0:8], MECC[0:7]The data signals of the DDR interface are source-synchronous signals by which memory and the controller capture the data using the data strobe rather than the clock itself. When transferring data, both edges of the strobe are used to achieve the 2x data rate.An associated data strobe (DQS and DQS) and data mask (DM) comprise each data byte lane. This 11-bit signal lane relationship is crucial for routing, and Table3 depicts this relationship. When length matching, the critical item is the variance of the signal lengths within a given byte lane to its strobe. Length matching across all bytes lanes is also important and must meet the t DQSS parameter as specified by JEDEC. This is also commonly referred to as the write data delay window. Typically, this timing is considerably more relaxed than the timing of the individual byte lanes themselves.Table3. Byte Lane to Data Strobe and Data Mask MappingData Data Strobe Data Mask Lane NumberMDQ[0:7]MDQS0, MDQS0MDM0Lane 0MDQ[8:15]MDQS1, MDQS1MDM1Lane 1MDQ[16:23]MDQS2, MDQS2MDM2Lane 2MDQ[24:31]MDQS3, MDQS3MDM3Lane 3MDQ[32:39]MDQS4, MDQS4MDM4Lane 4MDQ[40:47]MDQS5, MDQS5MDM5Lane 5MDQ[48:55]MDQS6, MDQS6MDM6Lane 6MDQ[56:63]MDQS7, MDQS7MDM7Lane 7MECC[0:7]MDQS8, MDQS8MDM8Lane 8NOTEWhen routing, each row (that is, the 11-bit signal group) must be treated asa trace-matched group.5.2Layout RecommendationsFreescale strongly recommends routing each data lane adjacent to a solid ground reference for the entire route to provide the lowest inductance for the return currents, thereby providing the optimal signal integrity of the data interface. This concern is especially critical in designs that target the top-end interface speed, because the data switches at 2x the applied clock. When the byte lanes are routed, signals within a byte lane should be routed on the same critical layer as they traverse the PCB motherboard to the memories. This consideration helps minimize the number of vias per trace and provides uniform signal characteristics for each signal within the data group.To facilitate ease of break-out from the controller perspective, and to keep the signals within the byte group together, the board designer should alternate the byte lanes on different critical layers (see Figure1 and Figure2).Layout Guidelines for the Signal GroupsFigure 1. Alternating Data Byte Lanes on Different Critical Layers —Part 1Data Lane 7Data Lane 5Data Lane 3Data Lane 1Layout Guidelines for the Signal GroupsFigure 2. Alternating Data Byte Lanes on Different Critical Layers—Part 2Data Group 6Data Group 4Data Group 8Data Group 2Data Group 0Simulation6SimulationThis application note provides general hardware and layout considerations for hardware engineers implementing a DDR3 memory subsystem.The rules and recommendations in this document can serve as an initial baseline for board designers to begin their specific implementations. The fly-by memory topology and many interface frequencies are possible from the DDR3 interface, so it is highly recommended that the board designer verify that all aspects (signal integrity, electrical timings, and so on) are addressed through simulation before board fabrication.In tandem with memory vendors, Freescale provides IBIS models for simulation. The board designer can realize a key advantage in the form of extra noise and timing margins by taking the following actions:•Optimizing the clock to signal group relationships to maximize setup and hold times•Optimizing termination values. During board simulation, verify that all aspects of the signal eye are satisfied, which includes at a minimum the following:—A sufficient signal eye opening meeting both timing and AC input voltage levels—Vswing max not exceeded (or alternatively max overshoot/max undershoot)—Signal slew rate within specificationsFigure3 shows the SSTL signal waveform.Figure3. SSTL Signal WaveformFurther Reading 7Further ReadingFollowing is a list of documentation that may be useful:•DDR3 chapter of the corresponding PowerQUICC or QorIQ processor reference manual•Micron web site: . For example, Design Guide for DDR3-1066 UDIMM systems: TN_41_08•JEDEC web site: . For example, the DDR3 SDRAM specification8Revision HistoryTable4 provides a revision history for this application note.Table4. Document Revision HistoryRev.Date Substantive Change(s)Number103/2010In T able1, for item# 28, changed the second bulleted sentence as follows:For all other devices, are all the data lanes matched to within 2.0 inch?001/2010Initial public releaseDocument Number:AN3940 Rev. 103/2010Information in this document is provided solely to enable system and software implementers to use Freescale Semiconductor products. There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document.Freescale Semiconductor reserves the right to make changes without further notice to any products herein. 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DDR3设计规范总结PCB Layout在实际的PCB设计时，考虑到SI、EMC的要求，往往有很多的折中方案。

通常，需要优先考虑对于那些对信号的完整性要求比较高的。

设计PCB 时，当考虑一下的一些相关因素，那么对于设计PCB来说可靠性就会更高。

1. 首先，要在相关的EDA工具（Cadance-Allegro）里要设置好里设置好拓扑结构和相关约束。

2. 将BGA引脚突围，将ADDR/CMD/CNTRL引脚布置在DQ/DQS/DM字节组的中间，由于所有这些分组操作，为了尽可能少的信号交叉，一些独立的管脚也许会被交换到其它区域布线。

3. 由串扰仿真的结果可知，尽量减少短线（stubs）长度。

通常，短线（stubs)是可以被削减的，但不是所有的管脚都做得到的。

在BGA焊盘和存储器焊盘之间也许只需要两段的走线就可以实现了，但是此走线必须要很细，那么就提高了PCB的制作成本，而且，不是所有的走线都只需要两段的，除非使用微小的过孔和盘中孔的技术。

最终，考虑到信号完整性的容差和成本，可能选择折中的方案。

4. 将Vref的去耦电容靠近Vref管脚摆放；Vtt的去耦电容摆放在最远的一个SDRAM外端；VDD的去耦电容需要靠近器件摆放。

小电容值的去耦电容需要更靠近器件摆放。

正确的去耦设计中，并不是所有的去耦电容都是靠近器件摆放的。

所有的去耦电容的管脚都需要扇出后走线，这样可以减少阻抗，通常，两端段的扇出走线会垂直于电容布线。

5. 当切换平面层时，尽量做到长度匹配和加入一些地过孔，这些事先应该在EDA工具里进行很好的仿真。

通常，在时域分析来看，差分线里的两根线的要做到延时匹配，保证其误差在5mil，而其它的信号要做到10mil。

4、从上所知，当频率越来越高，则对DDR信号处理要求越来越严格，所以我们统一按最严格的要求规则处理DDR信号：现阶段所面对的DDR目前大都属于DDR3类型，也有少许DDR4类型的，将来会面对更多 DDR4、 DDR5的产品我们目前比较常见的是 UDIMM 和 SODIMM ，因市场定位不一样，所以会有形状大小的区别。

DDR3DDR4DDR5设计和仿真流程这个功能是ADS2019 update1里面才具有的功能。

小编非常喜欢这个功能，因为这个功能把仿真软件和测试设备的优势结合在了一起。

通过仿真发现和避免一些设计的问题。

Keysight发布了ADS2019U1版本的新功能memory designer。

新功能使开发人员能够轻松地完成DDR仿真所需的设置，并将仿真数据进行一致性测试分析, 从而减少了完成产品开发工作所需的时间。

1.DDR的设计挑战我们通过以下案例来看一个常规的DDR 仿真需要完成哪些设置：这是一款Xilinx的FPGAdemo板设计。

在本案例中, 所有4颗DRAM 都直接焊接在 PCB 上。

假定我们需要仿真每个DRAM上两字节通道 (dq0-dq15 和 dqs0-dqs1) 的写入周期。

仿真中还包括两条地址线 (a0 和 a1) 和一个时钟信号 (ck0)。

地址和时钟信号连接所有四个DRAM。

要完成这样的仿真，按照常规的流程，我们需要通过电磁场仿真器抽取PCB上以上所有网络的频域模型。

如果考虑电源分配网络对信号质量的影响，那在抽取时也应包含电源与地平面的频域模型。

这样，需要抽取的PCB网络端口数超过170个。

抽取完成后，设计者需要设置主控芯片和DRAM 芯片模型参数。

这些芯片模型一般来自芯片厂家的IBIS文件。

仿真中用到的每个芯片管脚都需要从模型文件中选出并进行相应配置。

这些必要的配置包括封装参数，子模型选择，发送端数据速率及码型，IBIS corner等。

在很多设计中，设计者还需要对芯片参数进行优化扫描，以获取最优的参数组合。

芯片模型设置完成后，下一步是将芯片管脚与抽取的PCB 模型端口进行连接。

在端口数目非常多时，逐个连接每个端口会是一个非常繁琐的过程，并且容易出错。

连接完成的仿真电路图如下图所示：电路连接完成后，还需设置需要的测量项。

DDR3包括之前的规范要求的测量项主要是电平和时序相关的测量。

经典DDR3PCB设计指导DDR3（Double Data Rate 3）是一种高速、大容量的随机存取存储器（RAM）技术，被广泛应用于各种计算机系统中。

在设计DDR3 PCB时，需要考虑信号完整性、EMI、布局、电源管理等因素，以确保系统的稳定性和性能优化。

以下是经典的DDR3PCB设计指导：1.保持信号完整性：-使用合适的信号走线宽度和间距，根据DDR3规范进行引脚布局和布线。

-控制信号的线长匹配，特别是对于时钟和命令/控制信号，通过控制线长来减小延迟。

-使用差分对来传输数据和时钟信号，并保持差分对长度相等，以最小化信号的失真和串扰。

2.使用层次布局：-使用多层PCB设计，将信号和电源/地线分开布局在不同的层次上，以减少干扰和串扰。

-高速信号层应该位于内层或表层以提高信号完整性，电源/地线可以位于内层。

3.地线规划：-根据信号引脚布局的特性，在有需要的地方增加避雷阻抗到地线。

-在信号回流点上使用地孔，以确保地线的连续性和稳定性。

-用足够的地区域保持良好的接地电流路径，以防止信号引脚之间的环形回流。

4.电源管理：-确保DDR3模块的电源电压稳定性，以避免信号和时序问题。

-确保电源管脚的降压滤波电容足够，以提供稳定的电源。

-使用布线良好的电源平面，以减少噪声和电流环路。

5.EMI控制：-在高速信号线周围添加地层和电源层，以提供屏蔽和隔离。

-使用过滤电容和磁珠来抑制电磁干扰。

-使用有源和被动的EMI抑制技术，如电磁屏蔽罩和衰减器。

6.综合考虑布局：-在布局时考虑信号走线和连接器的位置，以便在PCB上布线并连接到其他组件。

-将信号线走向控制在最短的长度，以最小化时延和损耗。

-尽量避免信号线的交叉和平行布线，以减小串扰和信号失真。

-对于高速和敏感信号，使用较短的连接线和更紧密的布局。

综上所述，经典的DDR3PCB设计指导涵盖了信号完整性、EMI控制、布局和电源管理等方面的要点。

通过遵循这些指导原则，可以最大程度地提高DDR3系统的稳定性和性能优化。