CADENCE仿真步骤

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cadenceic基础仿真经典实用

•cadence ic 基础仿真
• 选择分析模式：
•cadence ic 基础仿真
• 电路中有两个电压源，一个用作VDD,另一个用作信号输入 Vin
V in
•cadence ic 基础仿真
• 输出的选择
•cadence ic 基础仿真
• 分析一阶共源放大器获得的波形图 • 波形图显示了当Vin 从0->2V 时输出的变化
•cadence ic 基础仿真
• 下图为以温度为变量进行直流分析时候的波形图
•cadence ic 基础仿真
带隙基准的温度参考
•cadence ic 基础仿真
•cadence ic 基础仿真
•cadence ic 基础仿真
•cadence ic 基础仿真
实例5 一阶放大器
共源的一阶放大器
• 下图显示了为仿真产生的输出日志文件 •
•cadence ic 基础仿真
• 产生的波形如下所示：
•cadence ic 基础仿真
• 可以通过设定坐标轴来获得电流—电压曲线 • 按以下方式进行： Axis-> X Axis
•cadence ic 基础仿真
• 按下图所示，将X轴设定为二极管上的电压降
•cadence ic 基础仿真
• 在改变了X轴之后，波形应如下图所示：
•cadence ic 基础仿真
• 由于我们只对二极管的伏安特性曲线感兴趣，因此我们可以只选择流经二极管的电流与其两端压降。新的曲线如下图所示：
•cadence ic 基础仿真
实例2 双极型晶体管的伏安特性曲线
• 首先为双极型晶体管电路新建一个cell view • 利用原理图编辑所需要的仿真电路
然后单击ESC。 • 可以得到如下图所示的一族伏安特性曲线

cadenceic教程schematic及其仿真

cadenceic教程schematic及其仿真第一章． Cadence cdsSPICE的使用说明Cadence cdsSPICE 也是众多使用SPICE内核的电路模拟软件之一。

因此他在使用上会有部分同我们平时所用到的PSPICE相同。

这里我将侧重讲一下它的一些特殊用法。

§ 1－1 进入Cadence软件包一．在工作站上使用在命令行中（提示符后，如：ZUEDA22>）键入以下命令icfb&↙(回车键)，其中& 表示后台工作。

Icfb调出Cadence软件。

出现的主窗口如图1-1-1所示：图 1-1-1Candence主窗口二．在PC机上使用1）将PC机的颜色属性改为256色（这一步必须）；2）打开Exceed软件，一般选用xstart软件，以下是使用步骤：start method选择REXEC（TCP-IP）,Programm选择Xwindow。

Host选择10.13.71.32 或10.13.71.33。

host type选择sun。

并点击后面的按钮，在弹出菜单中选择command tool。

确认选择完毕后，点击run！3）在提示符ZDASIC22> 下键入:setenv DISPLAY 本机ip:0.0(回车)4）在命令行中（提示符后，如：ZUEDA22>）键入以下命令icfb&↙(回车键)即进入cadence中。

出现的主窗口如图1-1-1所示。

以上是使用xstart登陆cadance的方法。

在使用其他软件登陆cadance时，可能在登录前要修改文件.cshrc，方法如下：在提示符下输入如下命令：vi .cshrc↙ （进入全屏幕编辑程序vi）将光标移至setevn DISPLAY ZDASIC22:0.0 处，将“ZDASIC22”改为PC机的IP，其它不变（重新回到服务器上运行时，还需按原样改回）。

改完后存盘退出。

然后输入如下命令：source .cshrc↙ （重新载入该文件）以下介绍一下全屏幕编辑程序vi的一些使用方法：vi使用了两种状态，一是指令态（Command Mode），另一是插入态（Insert Mode）。

CAdence16.6PSpice1，使用自带例程进行第一个仿真

CAdence16.6PSpice1，使⽤⾃带例程进⾏第⼀个仿真1、建⽴原理图选择如下
2、新建⼀个⼯程，如下：
3、上图点击OK，进⼊界⾯，界⾯有下拉框，以放⼤器为例
4
5、发现⼯程⾥边⾃带如下：
6、点击1处，弹出2的参数会话框
7、点击第⼀张图，开始运⾏
8、弹出新的，运⾏结果如下：
在7界⾯更改了参数以后，只需要在8的界⾯点击运⾏就能看到新的波形了
9、可以在红圈位置直接删除不想看到的，点击选中，delete
10、点击1，在2位置添加想看到的曲线
例如看功率如下
11、如何看功率最⼤值，打击1，2处选择函数，3处选中要看的
得到结果如下
12、点击如下按钮，让此界⾯永远处于最上，之后让界⾯像第⼆张图这样
13、我们此时可以移动原理图的探针，我们会发现，波形跟着实时改变
14、⽣成报告。

window--copy to clipboard，之后在word⾥边可以直接粘贴。

15、通过点击如下按钮，能看到直流静态⼯作点、直流静态电流，功耗。

CADENCE仿真流程

CADENCE仿真流程1.设计准备在进行仿真之前，需要准备好设计的原理图和布局图。

原理图是电路的逻辑结构图，布局图是电路的物理结构图。

此外，还需要准备好电路的模型、方程和参数等。

2.确定仿真类型根据设计需求，确定仿真类型，包括DC仿真、AC仿真、时域仿真和优化仿真等。

DC仿真用于分析直流电路参数，AC仿真用于分析交流电路参数，而时域仿真则用于分析电路的时间响应。

3.设置仿真参数根据仿真类型，设置仿真参数。

例如，在DC仿真中，需要设置电压和电流源的数值；在AC仿真中，需要设置信号源的频率和幅度；在时域仿真中，需要设置仿真的时间步长和仿真时间等。

4.模型库选择根据设计需求，选择合适的元件模型进行仿真。

CADENCE提供了大量的元件模型，如晶体管、二极管、电感、电容等。

5.确定分析类型根据仿真目标，确定分析类型，例如传输功能分析、噪声分析、频率响应分析等。

6.仿真运行在仿真运行之前，需要对电路进行布局和连线。

使用CADENCE提供的工具对电路进行布局和连线，并生成物理设计。

7.仿真结果分析仿真运行后，CADENCE会生成仿真结果。

利用CADENCE提供的分析工具对仿真结果进行分析，观察电路的性能指标。

8.优化和修改根据仿真结果，对电路进行优化和修改。

根据需要，可以调整电路的拓扑结构、参数和模型等，以改进电路的性能。

9.再次仿真和验证根据修改后的电路，再次进行仿真和验证，以确认电路的性能指标是否得到改善。

最后需要注意的是，CADENCE仿真流程并不是一成不变的，根据具体的设计需求和仿真目标，流程可能会有所调整和修改。

此外，CADENCE还提供了许多其他的工具和功能，如电路板设计、封装设计、时序分析等，可以根据需要进行使用。

CADENCE仿真步骤

CADENCE仿真步骤
Cadence是一款电路仿真软件，它可以帮助设计师创建、分析和仿真
电子电路。

本文将介绍Cadence仿真的步骤。

1.准备仿真结构：第一步是准备仿真结构。

我们需要编写表示电路的Verilog或VHDL代码，然后将它们编译到Cadence Integrated Circuit (IC) Design软件中。

这会生成许多文件，包括netlist和verilog等文件，这些文件将用于仿真。

2.定义仿真输入输出信号：接下来，我们需要定义仿真的输入信号和
输出信号。

输入信号可以是电压、电流、时间和其他可测量的变量。

我们
需要定义输入信号的模拟和数字值，以及输出信号的模拟和数字值。

3.定义参数：参数是仿真中用于定义仿真设计的变量，这些变量可以
是仿真中电路的物理参数，如电阻、电容、时延、输入电压等，也可以是
算法参数，如积分步长等。

4.运行仿真：在所有参数和信号都设置完成后，我们可以运行仿真。

在运行仿真之前，可以使用自动参数检查来检查参数是否正确。

然后，使
用“开始仿真”命令即可启动仿真进程。

5.结果分析：在仿真结束后，我们可以使用结果分析器来查看输出信
号的模拟和数字值，以及仿真中电路的其他特性，如暂态分析、稳态分析、功率分析等。

以上就是Cadence仿真步骤。

CadenceallegroPI仿真

CadenceallegroPI仿真PCB中导⼊⽹表后，设置层叠结构（电源层、地层），划分好电源层，接下来：a) 将allegro切换到Allegro PCB PI option XL版本，Analysis->Preference，点开电源完整性选项卡，其中的⼀些常见选项如Min.plane/board area的值（⼩于它的平⾯仿真时直接就忽略了）；b) Analysis->Power Integrity，（第⼀次建⽴会有警告，确定），接下来就是设置了，依次为：板⼦尺⼨->层叠结构->电源层的DC⽹络电压->添加电源层对(可以看到电源层对之间的内部电容)->选择仿真要⽤的的电容->选DCL(decap capacitou library,去耦电容器库)->勾选Board⽂件夹下的各电容（可以看到电容值、ESR、电感、谐振频率）->finish。

如图图1 PI设置向导完后的界⾯c) 选择需要仿真的电源层对，设置该层的纹波，最⼤的变化电流（可以看到该平⾯的⽬标阻抗）->点Single Node Simulation进⾏单节点仿真（不考虑元器件的摆放位置，验证电容的数⽬及型号是否满⾜），如图2：图2 单节点仿真图从图中可以看出，在200M频率内，⿊⾊的线为有电容之后的曲线，它位于⽬标阻抗（黄⾊）线下⾯，说明在200M的频率（⾃⼰理解为PCB 电源层给供电的IC芯⽚的频率）内，电源是完整的。

但实际情况并不⼀定是这样，如图3：图3 在单节点仿真中加实际情况如红⾊的曲线，则应为电源平⾯选⼀个电容的谐振频率为fa的电容，再次仿真之后，会得到有两个峰值的曲线，再加谐振频率等于，峰值对应的横坐标（谐振频率）的电容值即可，依次这样进⾏，直到整条曲线在要求的频率范围之内，位于⽬标谐振频率曲线下⾯。

（在调的时候，不⼀定是⾮得改原理图中电容的⼤⼩，也可适当增加原理图中滤波电容的数量）如蓝⾊曲线，相对于红⾊曲线，其谐振频率不到1M，⽅法同上，不过选这样的电容，电容值都⽐较⼤，如100uF。

cadence运放仿真-35页PPT文档资料

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其它有关的菜单项（1）
Tools/Parametric Analysis
它提供了一种很重要的分析方法——参量分析的方法，也即参量扫描。可以对温度，用户自定义的变量variables 进行扫描，从而找出最合适的值。
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其它有关的菜单项（2）
Outputs/To be plotted/selected on schematic
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Calculator的使用
Calculator是一个重要的数据处理工具，可以用来仿真电源抑制比，相位裕度，共
模抑制比
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其它有关的菜单项（3）
Results菜单
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模拟结果的显示以及处理
在模拟有了结果之后，如果设定的output有 plot属性的话，系统会自动调出waveform 窗口，并显示outputs 的波形，如左图
Sweep Variable： Frequency Sweep Range ：1 Hz~100M Hz 仿真完成后，点击 Result -> Direct Plot -> AC Gain&Phase 查看运放的幅频特性和相频特性
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仿真结果
该运放直流增益为80.9dB，单位增益带宽为82M Hz，相位裕度为67.32deg。
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Analog Design Simulation菜单介绍
Session菜单
Schematic Window Save State Load State Options Reset Quit
回到电路图
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Cadence仿真流程

Cadence仿真流程Cadence 仿真流程第⼀章在Allegro 中准备好进⾏SI 仿真的PCB 板图1）在Cadence 中进⾏SI 分析可以通过⼏种⽅式得到结果：Allegro 的PCB 画板界⾯，通过处理可以直接得到结果，或者直接以*.brd 存盘。

使⽤SpecctreQuest 打开*.brd，进⾏必要设置，通过处理直接得到结果。

这实际与上述⽅式类似，只不过是两个独⽴的模块，真正的仿真软件是下⾯的SigXplore 程序。

直接打开SigXplore 建⽴拓扑进⾏仿真。

2）从PowerPCB 转换到Allegro 格式在PowerPCb 中对已经完成的PCB 板，作如下操作：在⽂件菜单，选择Export 操作，出现File Export 窗⼝，选择ASCII 格式*.asc ⽂件格式，并指定⽂件名称和路径（图1.1）。

图1.1 在PowerPCB 中输出通⽤ASC 格式⽂件图1.2 PowerPCB 导出格式设置窗⼝点击图1.1 的保存按钮后出现图1.2 ASCII 输出定制窗⼝，在该窗⼝中，点击“Select All”项、在Expand Attributes 中选中Parts 和Nets 两项，尤其注意在Format 窗⼝只能选择PowerPCB V3.0 以下版本格式，否则Allegro 不能正确导⼊。

3）在Allegro 中导⼊*.ascPCB 板图在⽂件菜单，选择Import 操作，出现⼀个下拉菜单，在下拉菜单中选择PADS 项，出现PADS IN 设置窗⼝（图1.3），在该窗⼝中需要设置3 个必要参数：图1.3 转换阿三次⽂件参数设置窗⼝i. 在的⼀栏那填⼊源asc ⽂件的⽬录ii. 在第⼆栏指定转换必须的pads_in.ini ⽂件所在⽬录（也可将此⽂件拷⼊⼯作⽬录中，此例）iii. 指定转换后的⽂件存放⽬录然后运⾏“Run”，将在指定的⽬录中⽣成转换成功的.brd ⽂件。

cadence仿真步骤

CDNLive! Paper – Signal Integrity (SI) for Dual Data Rate (DDR) InterfacePrithi Ramakrishnan iDEN Subscriber Group Plantation, FlPresented atIntroductionThe need for Signal Integrity (SI) analysis for printed circuit board (PCB) design has become essential to ensure first time success of high-speed, high-density digital designs. This paper will cover the usage of Cadence’s Allegro PCB SI tool for the design of a dual data rate (DDR) memory interface in one of Motorola’s products. Specifically, this paper will describe the following key phases of the high-speed design process: Design set-up Pre-route SI analysis Constraint-driven routing Post-route SI analysisDDR interfaces, being source synchronous in nature, feature skew as the fundamental parameter to manage in order to meet setup and hold timing margins. A brief overview of source synchronous signaling and its challenges is also presented to provide context.Project BackgroundThis paper is based on the design of a DDR interface in an iDEN Subscriber Group phone that uses the mobile Linux Java platform. The phone is currently in the final stages of system and factory testing, and is due to be released in the market at the end of August 2007 for Nextel international customers. The phone has a dual-core custom processor with an application processor (ARM 11) and a baseband processor (StarCore) running at 400MHz and 208MHz respectively. The processor has a NAND and DDR controller, both supporting 16-bit interfaces. The memory device used is a multi-chip package (MCP) with stacked NAND (512Mb) and DDR (512Mb) parts. The NAND device is run at 22MHz and the DDR at 133MHz. The interface had to be supported over several memory vendors, and consequently had to account for the difference in timing margins, input capacitances, and buffer drive strengths between different dies and packages. As customer preference for smaller and thinner phones grows, the design and placement of critical components and modules has become more challenging. In addition to incorporating various sections such as Radio Frequency (RF), Power Management, DC, Audio, Digital ICs, and sub-circuits of these modules, design engineers must simultaneously satisfy the rigid placement requirements for components such as speakers, antennas, displays, and cameras. As such, there are very few options and little flexibility in terms of placement of the components. This problem was further accentuated by the fact that several layers of the 10 layer board (3-4-3 structure with one ground plane and no power planes) were reserved for power, audio, and other high frequency (RF) nets, leaving engineers with few layers to choose from for digital circuitry.Figure 1. Memory Interface routes With the DDR interface data switching at 266MHz, we had very tight margins — 600ps for data/DQS lines, 280ps for the address lines, and 180ps for control lines. However, with the NAND interface we had larger margins that were on the order of a few tens of nanoseconds. In these situations, choosing a higher drive strength and using terminators of appropriate values (to meet rise times and avoid overshoot/undershoot) has become a common practice in DDR designs. However, due to the lack of space on the board, we were not in a position to use terminators. Therefore, we used programmable buffers on our processor, and with the help of Cadence SI tools were able to fine-tune the design. Our group migrated from using Mentor Graphics to Cadence SI during this project. As one might expect, this made the task of designing a high speed DDR interface even more challenging. To help overcome this, we worked extensively with Cadence Services, where Ken Willis supported us on the SI portion of the design.The Source Synchronous Design ChallengeBefore discussing the specifics of the Motorola DDR interface, a brief overview of source synchronous signaling is provided here for context. Historically, digital interfaces have utilized “common clock” signaling, as shown in the figure below.Clock DriverTcoInterconnect Delay D0 D1 D2 D0 D1 D2DriveReceiveFigure 2. Common clock designWith common clock interfaces, the clock signal is provided to the driving and receiving components from an external component. The magnitude of the driver’s Tco (time from clock to output valid) and the interconnect delay between the driving and receiving components becomes a limiting factor in the timing of the interface. From a practical standpoint, it becomes increasingly challenging to implement interfaces of this type above several hundred megahertz. In order to accommodate requirements for faster data rates, source synchronous signaling emerged as the new paradigm. This is illustrated in the figure below.StrobeD 0 D 1D 0 D 1DriveReceiveFigure 3. Source synchronous design.In a source synchronous interface, the “clock” is provided locally by the driving component, and is generally called a “strobe” signal. The relationship between the strobe and its associated data bits is known as it leaves the driving component, with setup and hold margins pre-established as the signals are put onto the bus.TsetupTholdFigure 4. Timing diagram. This essentially takes the driver’s Tco as well as the magnitude of the interconnect delay between the driving and receiving chip out of the timing equation altogether. The timing challenge then becomes to manage the skew between the data and strobe signals such that the setup and hold requirements at the receiving end are still met.Technical ApproachThe general technical approach used in this project can be broken down into the following key phases of the high-speed design process: Design set-up Pre-route SI analysis Constraint-driven routing Post-route SI analysisFirst the PCB design database is set up to enable analysis with Allegro PCB SI. Before routing is performed, initial trade-offs are examined at the placement stage, and constraints are captured to facilitate constraint-driven routing. When routing is completed, detailed analysis is performed, interconnect delays extracted, and setup/hold margins are computed. Any adjustments required are fed back to the layout designer, and the postroute analysis is repeated. This basic process is diagrammed below.Design Setup SI Models Pre-Route AnalysisStartConstraints RoutingPost-Route AnalysisnoMargins OK?yes EndFigure 5. SI design process flow. Detail on the major design phases are provided in the subsequent sections. Design Setup By virtue of its direct integration with the Allegro PCB layout database, Allegro SI analysis requires that the design be set up to facilitate the automated extraction, circuit building, netlisting, simulation, and analysis that it performs. This essentially means adding the needed intelligence to the physical Allegro database that allows the tool to do its job. This setup involves the following: Cross section DC nets Device definitions SI models By definition, SI analysis involves the modeling of interconnect parasitics. In order to do this accurately, the tool needs to know the properties and characteristics of the materials used in the PCB stack-up. This information is defined in the Cross Section form, as shown below.It is crucial to get this data correct, as it will be fed to the 2D field solver to model interconnect parasitics during the extraction process. The best source for this detailed information is generally from the PCB fabricator. Layer thickness, dielectric constant, and loss tangent are all critical parameters for the cross section definition. In order for circuit extraction to be done properly, the tool needs to know about DC nets in the design, and what their associated voltage levels are. This accomplishes two main things in the setup; a) enables voltage sources to be injected properly in the extracted circuits, and b) avoids having the tool needlessly trying to extract extremely large DC nets, and hanging up the analysis process. Take the example of a parallel resistor termination. Allegro SI will encounter the resistor as it walks the signal net to be extracted. The tool will look up the SI model assigned to this resistor, splice in the resistor subcircuit, and continue extracting whatever is on the other side of the resistor. If this is a large DC net (ex. VTT), the desire is for the tool to put a voltage source at the 2nd resistor pin, complete the circuit, and simulate the signal. To do this properly, the tool relies on a VOLTAGE property to exist on the DC net, with a numeric value defined. In the absence of the VOLTAGE property, the tool will simply continue to extract, which in the case of a 2000 pin ground net, would be a large waste of computational time. To identify DC nets, clicking “Logic > Identify DC Nets” will spawn the following form.All DC nets in the design should be identified, to fully optimize SI analysis. These can be identified up front in the schematic, as well as in the physical layout as shown here. The next step in the design set-up process is to verify that the logical “CLASS” and “PINUSE” attributes for the devices in the design are defined appropriately. These attributes originate from the schematic symbol libraries and are passed into the Allegro physical layout environment. In an ideal methodology, these libraries would be defined properly and would require no edits. However, this is not always the case, and as these attributes have a bearing on the behavior of the SI analysis, it is worth mention here. The “CLASS” attribute is used to distinguish between different types of components in the PCB design. Legal values of “CLASS” are listed below: IC – This is used for digital integrated circuits, which contain drivers and/or receivers. These types of components are modeled with an SI model of the type “IbisDevice”. When the automated circuit building algorithms in Allegro PCB SI encounter a model of this type, it looks up the buffer model (driver, receiver, or bidirectional) assigned to the pin in question, and inserts it into the circuit along with its associated package parasitics. IO – A component with CLASS = IO is intended for components that connect off-card to other physical layout designs, such as connectors. These components can be associated with a “DesignLink”, which provides netlisting to other physical designs and enables multi-board SI analysis. So circuit building algorithms expect to jump from a device of CLASS=IO to a similar device on a different physical layout. DISCRETE – For devices of this class, circuit building algorithms expect to traverse “through” the component, from one pin to another, inserting a subcircuit in-between. A good example of this would be a series resistor.If CLASS attributes are not set up properly in the source schematic libraries, they can be edited in the physical layout database for analysis by using the form shown below, launched from the “Logic > Parts List” menu pick.The “PINUSE” attribute also impacts the behavior of the SI analysis, as the tool uses this information to determine if a pin is a driver, receiver, bidirectional, or passive pin. As with the “CLASS” attribute, in an ideal methodology this is defined properly in the schematic libraries, and no editing is required in physical layout. “PINUSE” can be modified in two main ways for SI purposes. The most straightforward way is to ensure that the IOCell models used in the IbisDevice models assigned to components have the appropriate Model Type for the signals they are associated to. When SI models are assigned to components, the tool will check for conflicts between the model and the PINUSE it finds for the component in the design, and will use the SI model to automatically override the PINUSE found in the drawing. So if the correct pin types are found in the SI models, the layout will automatically inherit those settings. For components not explicitly modeled, their PINUSE can be set using the form shown below, launched from the “Logic > Pin Type” menu pick.Signal Integrity (SI) models can be assigned using the “Signal Model Assignment” form, shown below.Upon clicking “OK” the selected models will be assigned to the components and saved directly in the layout database. As mentioned previously, “PINUSE” attributes will be synced up, with the SI models superseding attributes in the original layout drawing.Pre-Route SI AnalysisPerforming pre-route analysis is a key part of the high-speed design process. Once critical component placement has been done, Manhattan distances can be used to estimate trace lengths, and can provide a realistic picture of how routed interconnect will potentially perform.Before simulations are run for critical signals, the timing of the interface must be well understood. To accomplish this, we will first sketch timing diagrams for each signal group and then extract a representative signal for analysis. Next, we will explore Z0, layer assignments, drive strength, route lengths, spacing, and terminations for these nets.To sketch the timing diagrams, we first analyze the memory interface. The memory interface consists of both DDR and NAND signals and has around seventy nets. To simplify the analysis of the interface, we first divide these nets based on function and then simulate one net from each group. Accordingly, we select one signal from each of the following groups —clock_ddr, strobe_ddr , data_ddr, control_ddr, address_ddr, control_nand, and data_nand — for our pre-route simulations.To understand the timing relations in the interface, we should look at the following operations between the memory device and the processor — read, write, address write, and control operations. Next, we identify the nets involved and the clocking reference signal for each of these operations. We then calculate the worst case slack available from the setup and hold numbers available in the data sheets. In particular, we adopted the worst case numbers across four different memory vendors, to ensure robustness of the manfactured system in the field..1.ReadDuring the read operation, the memory drives the data and DQS lines. The processor has a delay line (a series of buffers which can be tapped at different points), which is used to delay the DQS signal so that it samples the data at quarter of the cycle. The processor also offers programming options that allow us to apply an offset to the quarter cycle, enabling us to meet our setup and hold times. Hence, the processor self-corrects forstrobe/data skew using this delay line. The granularity of this delay line is 30 ps; that is, each of the buffers of the delay line contributes 30 ps of delay. The data lines 0-7 are clocked with respect to the DQS0 strobe signal, and the data lines 8-15 are clocked with respect to DQS1. Data and strobe lines should be clustered, with the matching constraints determined by the write cycle.2.WriteFigure 7. Write operation at memory interface.During the write operation, both data and DQS are driven by the processor. Data is latched at both the positive and the negative edges of the DQS signals. Here again, data bits 0-7 are clocked by DQS0 and data bits 8-15 are clocked by DQS1. The setup and hold times available as these signals come out of the DDR controller are 1.58ns and 1.7ns respectively and the corresponding times required at the memory to ensure correct operation is 0.9ns. Hence, the slack available for routing is the lesser of 1.58ns – 0.9ns or 1.7ns – 0.9ns, which comes out to be 0.68ns. This amounts to an allowable ~85mm mismatch between the data lines. In addition, we need to make sure that length of the DQS lines is around the average of all the data lines. The data mask signals DQM0 and DQM1 also come into play during the write operation and we should group them along with the respective data lines.3.Address busFigure 8. Address bus operation at memory interface.Both address and clock lines are driven by the processor. The address bits 0-12 are clocked by the differential clock and latched at the positive edge of the clock. The setup and hold times available for these signals from the DDR controller are 1.78ns and 4.22ns respectively and the corresponding times required at the memory to ensure correct operation is 1.5ns for both. Hence the worst case slack for routing is 0.28ns and we have to try to match our signals to meet these numbers. The 0.28ns slack amounts to ~14mm mismatch between the address lines and the clock.4.Control linesFigure 9. Control lines at memory interface.The control signals are clocked by the differential clock and latched at the positive edge of the clock. The setup and hold times coming out of the DDR controller are 1.64ns and 4.04ns respectively. The setup and hold times required at the memory to ensure correct operation is 1.5ns. Hence, the worst case slack for routing is 0.14ns and we have to try and match our signals to meet these numbers. The 0.14 ns slack amounts to ~7mm mismatch between the control lines and the clock.In addition, CLK to DQS skew is around 600 ps. With regards to the NAND lines, setup and hold numbers are in the order of tens of ns and hence routing them as short as possible based on their Manhattan lengths would suffice.To complete pre-route analysis, SigXplorer must be setup for these tasks:a. Extract a topology file for single net analysis. To bring up the net in SigXplorer, it is essential that the models are assigned, as described in Section 2, to each of the drivers, receivers, and components in the signal path.b. Set up parameters for extraction and simulate using SigXplorer.c. Perform measurements using SigWaveThe following screenshots of SigXplorer show this process in detail.Figure 10. SigXplorer screenshots.Since at this point none of the nets in the design are routed we need to set the percent Manhattan section for unrouted interconnect models. We should then select the net, as shown in the next screenshot, for analysis.Analyze Æ SI/EMI Sim Æ PreferencesThe speed at which the signal travels in the trace, where C is 3 x 108 m/s and E reff is the effective dielectric constant seen in the interconnectSets the default lengthfor unrouted transmission linesAt this point, it is important to check if your driver and receiver pins are set correctly. The net chosen in the above example is a data net, it is bi-directional, hence it can be driven both by the memory device as well as the processor. The view topology icon can be clicked to export this net in SigXplorer.The tool extracts the net along with drivers, receivers and strip lines on various layers of the board. Before you start the simulation, you must set the stimulus frequency, pulse step offset, and cycle count. This can be set in the following GUI.Analyze Æ PreferencesBoth the memory device and the processor have programmable drive strengths. The buffer model can bechanged to pick up the various drive strengths that are available in the dml models of the devices till we observe satisfactory waveforms in SigWave.Analyze Æ SI/EMI Sim Æprobeinvokes SigXplorerMake sure you check you driver and load pinsSigXplorer allows you to sweep any of the parameters such as the thickness, length, drive strengths and displays corresponding settle/switch delays, monotonicity, and glitch tolerance for the corresponding simulation. It also allows adding components such as resistors and capacitors and let’s us sweep their values. We added a resistor in series with our clock in or to get rid of ringing in the rising edge. The tool let us determine what values were suitable for this resistor. As shown in the next figure the waveform corresponding to our simulation can bebrought up on SigWave.driverreceiverYou can observe the rise/fall times, look for noise margins, overshoot/undershoot of the receiver waveform. The constraints we develop in the pre-route simulation will be used by the routing tool to ensure correct first time results. This leads to our next section; Constraint-driven routing.Constraint-driven routingOnce pre-route analysis has been done, and trade-offs have been examined, signal wiring constraints need to be developed to drive the constraint-driven routing process. With the DDR interface being point-to-point between the processor and memory, we translated our timing requirements into length constraints to make the routing as straightforward as possible. We also assigned layer constraints for our DDR signals. Both the length and the layer constraints can be directly applied to the constraint manager before the routing process starts.For our particular design, we determined the following layer assignments from the results of the pre-route simulations, taking into account the layer’s characteristic impedance per our stack-up:Layer 6 Æ ground planeLayer 7 Æ clock, add, ctrlLayer 8 Æ data, strobeLayer 9 Æ NAND interfaceBefore we set up our design for auto-routing, we routed the differential clock lines manually on the layers closest to the ground plane. For the rest of the nets, the layer constraints can be created as shown in the following snapshots of the constraint manager.Electrical Constraint Set Æ WiringRight click on board Æ Create new constraintName the constraint (ex. ECSET1)We choose one layer with horizontal orientation and one with vertical for each of our layer sets. You can form groups from the available layer sets and create a new constraint. This constraint, which we define as ECSET1, can be easily read back in the constraint manager and applied to the relevant net group, as shown in the following snapshot.We determined from pre-route analysis the slack available for each of our net groups; however, before we translate these into length constraints it is important to get a report of the Manhattan lengths of each of these signals. To illustrate this, we will focus on the address signals. The Manhattan report of the address lines showed that the shortest lines were 6mm and the longest were 17mm. Accordingly, the minimum length constraint must be longer than 6mm and the maximum length constraint must be longer than 17mm. Additionally, from our timing diagrams, we determined that the maximum spread can be no more than 14mm. Following these restrictions, we set the minimum and maximum length limits for the address line are 11.99 mmto 18.99 mm (shown in the constraint editor window below). Based on the layout designer's recommendations, we were able to constrain a bit tighter (7mm margin) and produce better margins.To enter the length constraint, we open the Net Æ Routing ÆTotal etch length section of the constrain manager. We followed this procedure for all the other net groups. The snapshot that follows shows length constraints associated with the address lines. Here, the key is to not to over-constrain your design, but at the same time have enough constraints so the timing and signal integrity parameters are met. Over-constraining the design severely inhibits the auto-router and may leave large portions of the design (as much as 90%) un-routed.Post-Route SI AnalysisOnce the design is fully routed, detailed simulations can be run for post-route verification. The goal at this phase is to determine final margins over all corners, and find and correct any SI or timing-related issues before the board is released for fabrication. Before starting simulation, it is important to verify that the design is properly routed and that it meets the specifications/constraints. In particular, it is essential to verify that the design does not include dangling and partially-routed/un-routed nets. We must also verify that all the nets meet the length constraints assigned to them. The Constraint Manager window helps identify nets that are in violation (shown in red) and nets that are in compliance (in green). For convenience and clarity, the Constraint Manager also reports the actual route length and the Manhattan lengths for each net.The next step is to bring up the physical layout and visually inspect the nets to ensure that each net is routed in its appropriate layer, or run DRCs if the signals were explicitly limited to specific layers in Physical Constraint Sets. When test points are associated with a net, we must manually verify that the points are in line with the nets (and are not stubs hanging off the nets). Note that when using the simpler Total_Etch_Length constraint, the auto-router can meet routing length constraints for the net, even when there are stubs in the design. These stubs can produce undesirable effects such as reflections and hence this step is important. If there are too manycritical signals to check manually on larger designs, this check can be automated by using an explicit topology and stub length constraints. After manual inspection, we begin post–route simulation and generate reports to analyze the design. We then export the reports to an Excel spreadsheet to facilitate analysis.We generated both delay and reflection reports. The delay report provides information on timing parameters such as propagation delay, switch and settle rise and fall times. The reflection report presents data on signal integrity parameters such as overshoot, undershoot, noise margin, monotonicity, and glitch. Preparing the design for post-route simulation involves the selection of various options in the SI\EMI Sim preferences list. The following screen display describes this process.In the form above, we set up the frequency of the stimulus and the duty cycle. We also set up V meas as thereference for delay calculations. Choosing the reference as V meas , rather than V IH and V IL , makes analysis much easier and is in accordance with the memory datasheet. We chose V meas as 0.9V which is half of the peak-to-peak voltage swing (1.8V).Now that the design is routed, we need to set the parameters for routed interconnects. Here you can specify the minimum coupling distance for nets for the tool to recognize it as a differential pair. This can be done by invoking Analyze Æ SI ÆPref ÆInterconnect Models.Analyze Æ SI/EMI Sim Æ preferencesThe preceding screenshot shows the option that allows us to select the delay and reflection reports. In this form, we also choose all three simulation modes — fast, typical, and slow — to cover all corner cases. In our experience, running typical mode simulations were not enough to determine final timing margins over process, voltage, and temperature. So, we exported the reports to an Excel spread sheet and analyzed the results. Reflection and delay reports simulate only a primary net and none of its neighbors. As a result, these reports do not take into consideration the parasitics of the power and ground pins.Timing > Control typNote:All timings in ns unless labelled otherwise.Component Timingdriving to MemoryTsetup 1.64Tsetup 1.5Thold 4.04Thold 1.5Skew_max = 1.64 - 1.5 = 140ps between clock and controlSkew_max=0.14Clock/Strobe RelationshipsSdram_Ctrl<6:7> is differential clockInterconnect TimingXNet Drvr Rcvr PropDly SettleRise SettleFall AvgSettleSDRAM_CTRL<6>U800 V2_UU2164 C7_U2160.142029 1.13851 1.20538 1.172XNet Drvr Rcvr PropDly SettleRise SettleFall MinSettle MaxSettle MinSettleSkew MaxSettleSkew MaxSkew MarginSDRAM_CTRL<0>U800U21640.1118 1.191 1.235 1.104 1.2350.0680.0630.0680.072SDRAM_CTRL<10>U800U21640.1254 1.165 1.207SDRAM_CTRL<11>U800U21640.1114 1.141 1.187SDRAM_CTRL<12>U800U21640.1217 1.178 1.221SDRAM_CTRL<13>U800U21640.1067 1.114 1.153SDRAM_CTRL<14>U800U21640.09823 1.104 1.143SDRAM_CTRL<2>U800U21640.1274 1.163 1.205SDRAM_CTRL<3>U800U21640.09163 1.108 1.153SDRAM_CTRL<8>U800U21640.1081 1.137 1.182SDRAM_CTRL<4>U800U21640.06959 1.143 1.247SDRAM_CTRL<5>U800U21640.0862 1.169 1.285The preceding spreadsheet was created with data from delay reports and was used to analyze the control lines with respect to the clock. The clock signal in our design is called SDRAM_CTRL<6>. The sheet also lists the driver (U800, the processor), receiver (U2164, memory device), propagation delay (0.142029 ns), settle rise (1.13851 ns), and settle fall (1.20538 ns) values. The average settle delay (1.172 ns) is calculated by averaging the settle rise and settle fall numbers.The control nets SDRAM<0> to SDRAM_CTRL <14> are listed next to the corresponding drivers, receivers, propagation delays, settle rise and settle fall delays. We then look for the minimum and maximum delays of all the settle rise and settle fall delays. These are listed under maximum settle delay (1.235 ns) and minimum settle delay (1.104 ns) respectively. Using these numbers, we calculate the maximum settle skew (0.063 ns), which is the difference between the maximum settle delay (1.235ns) and the average settle time (1.172 ns) of the clock signal. We also calculate the minimum settle skew (0.063 ns), which is the difference between the minimum settle delay (1.104ns) and the average settle time (1.172 ns) of the clock signal. Subtracting the maximum of these two skews, which in our case is 0.068 ns, from the total skew available (0.140 ns) gives the margin (0.072 ns) for these nets.。

cadence原理图仿真

cadence原理图仿真
在进行Cadence原理图仿真时，我们需要注意以下几点，以确保仿真结果的准确性和可靠性：
1. 确认所使用的元件符合仿真要求，并正确地添加到原理图中。

这包括在仿真库中选择合适的元件模型，并将其与其他元件正确地连接起来。

2. 确认仿真的电源和接地连接正确无误。

确保电源和地线的连接不会导致任何不良影响，如电压下降或噪声干扰。

3. 设置仿真参数，如仿真时间、仿真步长等。

根据所需的仿真精度和仿真效率，选择适当的仿真参数。

4. 进行信号源的设置。

这包括选择合适的信号源类型（如AC
信号、脉冲信号等）、设置信号源的频率和振幅等参数。

5. 添加测量器件，以便在仿真过程中监测所需的电压或电流。

这些测量器件可以是电压表、电流表或示波器等。

6. 设置仿真分析类型。

根据需要进行直流分析、交流分析或者是时域分析等。

选择适当的仿真分析类型以获得所需的结果。

7. 运行仿真并分析结果。

运行仿真过程，等待仿真完成后，通过分析仿真结果来获取我们所需的电压、电流或其他信号参数。

通过遵循以上步骤，我们可以在Cadence中进行原理图仿真，并获取准确可靠的仿真结果，以验证电路设计的正确性和性能。

基于Cadence的信号完整性仿真步骤

目录1.仿真前的准备工作 (2)1.1找到需要仿真的芯片的IBIS模型 (2)1.2模型转换（IBIS→DML） (2)1.3添加模型到Cadence的模型库中 (5)2. 对电路板进行设置（Setup Advisor） (7)2.1准备好要仿真的电路板 (7)2.2调用参数设置向导 (7)2.3叠层设置 (8)2.4设置DC电压值 (9)2.5器件设置（Device Setup） (10)2.6 SI模型分配 (12)2.7 SI检查（SI Audit） (16)2.8完成参数设置 (18)3.进行信号完整性仿真（反射） (19)3.1开始仿真 (19)3.2选择所要仿真的网络 (19)3.3提取网络的拓扑结构 (20)3.4给驱动端U8添加激励信号 (21)3.5设置激励信号的参数 (22)3.6执行反射仿真 (22)3.7仿真结果 (22)1.仿真前的准备工作1.1找到需要仿真的芯片的IBIS模型一般可以从芯片制造商网站上找到，如果没有，可能要通过其它途径获得如从SPICE模型中提取。

1.2模型转换（IBIS→DML）将IBIS模型转换为DML模型，运用Cadence的Model Integrity工具将IBIS模型转化为Cadence能识别的DML模型，并验证仿真模型。

（1）单击“开始”按钮→“所有程序”→“Allegro SPB 15.5”→“Model Integrity”，如图1-1所示：图1-1 Model Integrity工具窗口（2）选择“File”→“Open”，打开一个IBIS模型如图1-2所示：图1-2 打开一个IBIS模型（3）在“Physical View”栏中，单击IBIS文件“sn74avca16245”→选择菜单栏里的“Options”→“Translation Options Editor”→弹出“Translation Options”窗口，如图1-3所示：图1-3 Translation Options窗口（4）默认选择“Make model names unique”，这个设置为每个IOCell模型名附加IBIS文件名。

基于Cadence的电源完整性仿真步骤

基于Cadence的电源完整性仿真步骤1、设置电路板的参数用PI模式打开要仿真的电路板，仿真其CPU_1.8V电源平面的完整性。

1.1调用设置向导在PI中选择“Analyze”—>“Power Integrity”出现提示对话框，点击“确定”后出现设置向导窗口。

1.2板框（Board Outline）点击“Next”进入设置向导里的“Board Outline”窗口PI需要一个板框来进行布局和电源平面提取。

如果板框不完整或不存在，则上图右上角会有信息提示。

1.3Stack-up设置点击“Next”进入设置向导里的“Stack-up”窗口。

PI需要叠层关系来计算电源对从而为平面建模。

如果叠层不存在或者不包含平面层，则屏幕右上角会有信息显示。

在这里可以调整叠层关系（Edit stack-up）或从另一个设计中导入（Import stack-up）。

屏幕右上角有相应的示意图，如图：当不勾选“Physical view”时，各层厚度平均显示；勾选后各层按比例显示。

1.4DC Net-Plane Association点击“Next”进入设置向导里的“DC Net-Plane Association”窗口，如图：PI 在估算去耦电容之前需要给每一个需要仿真的电源平面分配DC电压，在这里可以调整现有的电压分配。

同一层的分割平面会有不同的“shape”，因此每个“shape”都有一个不同的DC网络。

1.5DC Power Pair Setup点击“Next”进入设置向导里的“DC Power Pair Setup”窗口，如图：在进行PI 之前，电源和地平面必须成对。

一个地可以被多个平面共享，但一次只能分析一对平面。

在“Plane 1”栏中选择要分析的平面，在“Plane 2”栏中选择对应的平面，选中的平面对将在右边的叠层视图中高亮。

点击“Add”创建对应的平面对。

1.6选择去耦电容点击“Next”，如图：1.7选择电容模型点击“Next”，如图：选好所用的电容模型后，点击“Finish”完成对电路板参数的设置，弹出“Power Integrity Design&Analyze”窗口，如图：2、单节点仿真可以通过运行单节点仿真来验证选择的电容数量能否在频率范围内维持目标阻抗。

Cadence基础仿真分析与电路控制描述

Cadence基础仿真分析与电路控制描述Cadence是一款主要用于集成电路设计和仿真分析的软件工具。

本文档将介绍Cadence的基础仿真分析功能以及电路控制描述的方法。

Cadence基础仿真分析Cadence提供了多种仿真分析工具，包括电路级仿真、时钟级仿真和系统级仿真等。

这些工具可用于验证电路设计的正确性，并进行性能评估。

在进行仿真分析之前，需要进行以下步骤：1. 设计：使用Cadence的设计工具创建电路图和原理图，定义电路的结构和功能。

2. 参数设置：对电路器件进行参数设置，包括电阻、电容、电感等元件的数值设定。

3. 仿真配置：选择适当的仿真工具和仿真设置，如仿真类型、仿真时间和仿真模型等。

接下来，执行仿真分析：1. 电路级仿真：通过电路级仿真工具，如Spectre，对电路进行验证和性能评估。

参数设置和仿真配置完成后，运行仿真并分析仿真结果。

2. 时钟级仿真：通过时钟级仿真工具，如Virtuoso AMS Designer，对电路中时序相关的功能进行验证。

设置时钟源和时钟周期等参数，并运行仿真以验证电路的时序性能。

3. 系统级仿真：通过系统级仿真工具，如Virtuoso System Design Platform，对整个电路系统进行仿真。

设置系统级的参数和信号源，并进行仿真分析。

电路控制描述在Cadence中，可以使用Verilog-A或Verilog-AMS等硬件描述语言来描述电路的行为和控制。

1. Verilog-A：主要用于模拟连续时间的电路。

可以使用Verilog-A描述电路的行为和相互之间的连接关系。

通过编写Verilog-A代码，可以实现电路的仿真和性能分析。

2. Verilog-AMS：结合了连续时间和离散时间的特性，可用于描述混合信号电路。

除了模拟电路行为之外，还可以描述数字电路部分。

通过编写Verilog-AMS代码，可以实现电路的混合仿真和性能分析。

使用这些硬件描述语言时，需要了解其语法和规范，并根据实际需求编写相应的代码。

Cadence-SI-Simulation

Cadence仿真介绍第一部分：仿真流程第二部分：IBIS模型IBIS模型和SPICE模型比较：SPICE模型：（1）电压/电流/时间等关系从器件图形、材料特性得来，建立在低级数据的基础上（2）每个buffer中的器件分别描述/仿真（3）仿真速度很慢（4）包含芯片制造工艺信息IBIS模型：（1）电压/电流/时间关系建立在IV/VT数据曲线上（2）没有包括电路细节（3）仿真速度快，是SPICE模型的25倍以上（4）不包含芯片内部制造工艺信息基于上述原因，对于在系统级的设计，我们更倾向于使用IBIS模型。

目前IBIS主要使用的有V1.1，V2.1，V3.2及V4.0等版本。

模型结构如下图：C_pkg，R_pkg，L_pkg为封装参数；C_comp为晶片pad电容；Power_Clamp，GND_Clamp 为ESD结构的V/I曲线。

输出模型比输入模型多一个pull-up，pull-down的V/T曲线。

Cadence的model integrity工具负责对IBIS模型进行语法检查、编辑以及进行DML格式转换。

Cadence仿真不直接使用IBIS模型，而必须先把IBIS转换成DML。

<实例操作演示>第三部分：电路板设置电路板设置包括：（1）叠层设置；（2）DC电压设置；（3）器件设置；（4）模型分配；上述步骤可以通过setup advisor向导设置。

1，叠层设置2，DC电压设置3，器件设置4，模型分配电阻、电容、电感等无源器件的模型可以通过建立ESPICE模型来获得。

<实例操作演示>第四部分：设置仿真参数模型分配完成后，就可以进行仿真了。

在进行仿真之前，需要对仿真的参数进行设置。

Pulse cycle count：通过指定系统传输的脉冲数目来确定仿真的持续时间。

Pulse Clock Frequency：确定仿真中用来激励驱动器的脉冲电压源的频率。

Pulse Duty cycle：脉冲占空比。

Cadence板级仿真

Cadence板级仿真Cadence的SQ仿真用于单板网络的拓扑提取或者信号质量仿真非常方便，即板级的仿真。

但随着系统的复杂，板间的信号仿真越来越多，这就涉及到两块电路板的系统级仿真。

两块PCB之间必然是通过connector连接在一起的，如果近似地处理，可以把connector当作是一根短的传输线，连接connector的两个对应网络分布在两块PCB中，我们可以分开处理，对两个网络进行分别提取，然后利用SigXplorer的Append功能进行Top整合，中间connector采用传输线近似。

这是最简单的方法。

当然还有另一种比较正式一点的方法，SQ本身就支持两块电路板的同步仿真，其原理与Xnet 的网络拓扑结构提取相当。

比如，如果我们不指定Xnet时，进行网络提取只能提取单根网络，当指定了Xnet之后，Probe提取出的网络就是Xnet，这里Xnet的指定就是给对应的无源元件，比如电阻、电容、电感等，分配Espice模型。

当然这里这里也包括连接器，只不过这比他们要稍微复杂一些。

下面就以一个例子来说明板级仿真的网络提取。

准备工作：仿真文件：cpu.brdmainboard.brd仿真模型：8347_tbga_rev203.dmlpca9548a_3_3v.dml仿真原理图：cpu.dsnmainboard.dsn拓扑结构简易视图如下：CPU端：Mainboard端：Analyze----SI/EMI Sim----Library...在Brower界面Add existing library，把需要的IC model放进去进行IC模型分配，Analyze----SI/EMI Sim----Model...在弹出的Signal Model Assignment里进行模型分配，默认的分配环境是Devices在这里进行模型分配，选中状态时，pcb界面的对应元件会临时高亮选中需要分配模型的Devices后，点击下面的Find Model，在Model Type Filter中选择IbisDevice，Model Name Pattern中输入“*”，选择正确的Model Name后模型就自动分配给对应的IC了分配好model后的devices这里不仅要给IC分配好模型，还需要给拓扑结构中的无源元件建立模型，比如这里的上拉电阻。

CADENCE仿真步骤

CADENCE仿真步骤1.电路设计：首先，需要使用电路设计软件（例如OrCAD）绘制电路原理图。

在设计电路时，应该合理选择电路元件，确保其参数和规格满足设计要求。

2.创建电路网络：在CADENCE中创建电路网络是第一步。

通过将电路原理图导入到CADENCE中，可以建立电路的模型。

在建立电路网络时，应定义元件的参数值，并将其连接起来。

3.定义仿真设置：在进行仿真之前，需要设置仿真参数。

这些参数包括仿真类型（例如直流、交流、蒙特卡罗等）、仿真步长、仿真时间等。

此外，还可以设置其他参数，如故障分析、参数扫描等。

4. 运行仿真：设置好仿真参数后，可以开始运行仿真了。

CADENCE 提供了多种仿真工具，如PSpice、Spectre等，可以根据不同的需求选择适合的工具。

在仿真过程中，CADENCE会使用电路元件的模型计算电路参数，根据仿真设置提供的信息生成相应的结果。

5.分析仿真结果：一旦仿真完成，CADENCE会生成仿真结果文件。

通过分析仿真结果，可以评估电路设计的性能。

常见的仿真结果包括电流、电压、功耗、频率响应等。

可以将仿真结果与预期结果进行比较，找出设计中的问题并进行优化。

6.优化电路设计：根据仿真结果，可以对电路设计进行调整和优化。

优化可以包括选择不同的元件、调整元件参数、改变电路拓扑等。

通过不断迭代仿真和优化，可以逐步改进电路设计，使其达到预期的性能指标。

7.验证仿真结果：当设计经过一系列的优化后，需要验证仿真结果是否可靠。

一种常用的验证方法是进行物理验证，即将最终的电路设计制作出来并测量其实际性能。

通过比较实际测量结果与仿真结果，可以验证仿真的准确性，并进行必要的修正。

8. 导出设计文件：一旦电路设计完成并验证通过，就可以将设计文件导出，准备进一步的生产制造。

将设计文件导出为标准的格式（如Gerber文件），可以将其发送给制造商进行生产。

总结：CADENCE仿真步骤包括电路设计、创建电路网络、定义仿真设置、运行仿真、分析仿真结果、优化电路设计、验证仿真结果和导出设计文件。

CADENCE仿真步骤

Cadence SPECCTRAQuest 仿真步骤[摘要]本文介绍了Cadence SPECCTRAQuest在高速数字电路的PCB设计中采用的基于信号完整性分析的设计方法的全过程。

从信号完整性仿真前的环境参数的设置，到对所有的高速数字信号赋予PCB板级的信号传输模型，再到通过对信号完整性的计算分析找到设计的解空间，这就是高速数字电路PCB板级设计的基础。

[关键词]板级电路仿真 I/O Buffer Information Specification（IBIS）1 引言电路板级仿真对于今天大多数的PCB板级设计而言已不再是一种选择而是必然之路。

在相当长的一段时间，由于PCB仿真软件使用复杂、缺乏必需的仿真模型、PCB仿真软件成本偏高等原因导致仿真在电路板级设计中没有得到普及。

随着集成电路的工作速度不断提高，电路的复杂性不断增加之后，多层板和高密度电路板的出现等等都对PCB板级设计提出了更新更高的要求。

尤其是半导体技术的飞速发展，数字器件复杂度越来越高，门电路的规模达到成千上万甚至上百万，现在一个芯片可以完成过去整个电路板的功能，从而使相同的PCB 上可以容纳更多的功能。

PCB已不仅仅是支撑电子元器件的平台，而变成了一个高性能的系统结构。

这样，信号完整性在PCB板级设计中成为了一个必须考虑的一个问题。

传统的PCB板的设计依次经过电路设计、版图设计、PCB制作等工序，而PCB的性能只有通过一系列仪器测试电路板原型来评定。

如果不能满足性能的要求，上述的过程就需要经过多次的重复，尤其是有些问题往往很难将其量化，反复多次就不可避免。

这些在当前激烈的市场竞争面前，无论是设计时间、设计的成本还是设计的复杂程度上都无法满足要求。

在现在的PCB板级设计中采用电路板级仿真已经成为必然。

基于信号完整性的PCB仿真设计就是根据完整的仿真模型通过对信号完整性的计算分析得出设计的解空间，然后在此基础上完成PCB设计，最后对设计进行验证是否满足预计的信号完整性要求。

Cadence 电路仿真

晶体管特性仿真
Tools->Analog Environment
仿真环境设置界面
变量编辑
分析类型选择
仿真条件设置
1.新建工作目录
2.绘制原理图 3.仿真条件设置 4.仿真结果输出与保存
执行仿真
Simulation->Netlist and Run
选择输出结果
输出特性曲线
1.File->Save as Image
仿真结果输出与保存filenewcellview输入工作目录名称选择原理图编辑工具原理图绘制软件界面使用快捷键i添加元件选择mos管连线1
Cadence 电路仿真
1.新建工作目录
2.绘制原理图 3.仿真条件设置 4.仿真结果输出与保存
虚拟机与主机共享设置.
File->New->Library
建பைடு நூலகம்工作目录lab1
2.输入目录: /mnt/hgfs/C/filename,并保存
3.在windows xp系统下的C盘可以看到所存的文件.
选择smic18mmrf
1.新建工作目录
2.绘制原理图 3.仿真条件设置 4.仿真结果输出与保存
File->New->Cell view
输入工作目录名称
选择原理图编辑工具
原理图绘制软件界面
使用快捷键”i” ,添加元件
选择MOS管
连线
1.新建工作目录
2.绘制原理图 3.仿真条件设置 4.仿真结果输出与保存

CADENCE 仿真流程

第一章进行SI仿真得PCB板图得准备仿真前得准备工作主要包括以下几点:1、仿真板得准备●原理图设计;●PCB封装设计;●PCB板外型边框(Outline)设计,PCB板禁止布线区划分(Keepouts);●输出网表(如果就是用CADENCE得Concept HDL设计得原理图,可将网表直接Expot 到BRD文件中;如果就是用PowerPCB设计得板图,转换到allegro中得板图,其操作见附录一得说明);●器件预布局(Placement):将其中得关键器件进行合理得预布局,主要涉及相对距离、抗干扰、散热、高频电路与低频电路、数字电路与模拟电路等方面;●PCB板布线分区(Rooms):主要用来区分高频电路与低频电路、数字电路与模拟电路以及相对独立得电路。

元器件得布局以及电源与地线得处理将直接影响到电路性能与电磁兼容性能;2、器件模型得准备●收集器件得IBIS模型(网上下载、向代理申请、修改同类型器件得IBIS模型等)●收集器件得关键参数,如Tco、Tsetup、Tholdup等及系统有关得时间参数Tclock、Tskew、Tjitter●对IBIS模型进行整理、检查、纠错与验证。

3、确定需要仿真得电路部分,一般包括频率较高,负载较多,拓扑结构比较复杂(点到多点、多点到多点),时钟电路等关键信号线第二章IBIS模型得转化与加载CADENCE中得信号完整性仿真就是建立在IBIS模型得基础上得,但又不就是直接应用IBIS模型,CADECE得软件自带一个将IBIS模型转换为自己可用得DML(Device Model Library)模型得功能模块,本章主要就IBIS模型得转换及加载进行讲解。

1、IBIS模型到DML模型得转换在Allegro窗口中选择Analyse\SI/EMI SIM\Library,打开“signal analyze library browser”窗口,在该窗口得右下方点击“Translate →”按钮,在出现得下拉菜单中选择“ibis2signois”项,出现“Select IBIS Source File”窗口(图1),选择想要进行转换得源IBIS文件,按下“打开”按钮,出现转换后文件名及路径设置窗口(缺省设置为与源IBIS文件同名并同路径放置,但此处文件名后缀为dml),设置后按下“保存”按钮,出现保存确定窗口(图2),点击OK按钮即可,随后会出现一个“messages”窗口,该窗口中得报告文件说明在模型转换过程中出现得问题,对其中得“warning”可不用在意,但如果出现“error”则必须进行修改后重新进行模型格式转化直到没有“error”出现为止,此时转换得到得dml文件才就是有效得。

cadence对pcb进行后仿真

一、一般流程1、IBIS库转换层DML格式2、给器件加载模型并定义管脚3、定义电源、地网络等4、提取拓扑结构5、设置仿真参数6、仿真结果分析具体步骤请参见一些cadence后仿真的相关pdf文档。

二、补充说明在加载模型之后注意定义管脚，如果没有定义，仿真结果会有很大差异。

方法如下：1、在上图给器件加载模型的窗口中，点击fild model 为器件加载模型，然后点击edit model，出现下图：2、选择assign signal pins 然后在all pin中选择需要定义的管脚。

被选择的管脚会出现在selected pin方框中。

点击右侧的browse 出现下图：3、在dml model browser中选择需要的Iocell 关闭窗口、确定、完成。

4、如需对差分信号进行仿真的话，需要对差分pin进行设置。

三、pcb中FPGA与DDR2之间一根数据线的仿真。

1、提取的信号线为下图中白色高亮。

1、提取的拓扑结构包括走线和过孔的一些具体信息。

U17是DDR2，FPGA1是xilinx—c6v130tff784 2、层叠结构所仿真的信号线走的是S1层，为达到50 ohm 匹配，s1上下介质厚度为6mil。

3、仿真参数4、仿真结果Ddr2发送fpga接收时候的波形：浅绿色和浅蓝色分别是ddr2的pin和pad处的波形。

黑色和蓝色分别是fpga的pin和pad处的波形。

Fpga发送，ddr2接收时候的波形：5、以下是将走线拉直以后的仿真结果：Ddr2 发送，fpga接收：Fpga发送。

Ddr2接收：新手第一次做的仿真，希望与大家一起交流讨论。

可以加Q： 5.1.9.7.3.1.9.8.。

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Cadence SPECCTRAQuest 仿真步骤[摘要]本文介绍了Cadence SPECCTRAQuest在高速数字电路的PCB设计中采用的基于信号完整性分析的设计方法的全过程。

[关键词]板级电路仿真I/O Buffer Information Specification（IBIS）1 引言电路板级仿真对于今天大多数的PCB板级设计而言已不再是一种选择而是必然之路。

在相当长的一段时间，由于PCB仿真软件使用复杂、缺乏必需的仿真模型、PCB仿真软件成本偏高等原因导致仿真在电路板级设计中没有得到普及。

随着集成电路的工作速度不断提高，电路的复杂性不断增加之后，多层板和高密度电路板的出现等等都对PCB板级设计提出了更新更高的要求。

PCB已不仅仅是支撑电子元器件的平台，而变成了一个高性能的系统结构。

这样，信号完整性在PCB板级设计中成为了一个必须考虑的一个问题。

传统的PCB板的设计依次经过电路设计、版图设计、PCB制作等工序，而PCB的性能只有通过一系列仪器测试电路板原型来评定。

如果不能满足性能的要求，上述的过程就需要经过多次的重复，尤其是有些问题往往很难将其量化，反复多次就不可避免。

这些在当前激烈的市场竞争面前，无论是设计时间、设计的成本还是设计的复杂程度上都无法满足要求。

在现在的PCB板级设计中采用电路板级仿真已经成为必然。

如果不能满足要求就需要修改版图设计。

与传统的PCB板的设计比较既缩短了设计周期，又降低了设计成本。

同时，随着软件业的高速发展，涌现出了越来越多操作更简便、功能更多、成本更低的EDA软件。

越来越完备的仿真模型也得以提供。

所有这些都为PCB设计中广泛的采用电路设计板级仿真提供了充分条件。

下面就Cadence SPECCTRAQuest这一高速电路板级设计仿真工具采用IBIS模型详细介绍进行板级仿真设计的全过程。

2 仿真前环境设置使用Cadence SPECCTRAQuest进行高速电路设计的仿真，不同的设计者根据各自的需要可以灵活的利用这个EDA工具进行仿真设计。

当然，在进行一个完整的PCB板设计前仿真时，按照一定步骤规地完成仿真设计，将会为你的仿真工作带来极大的方便。

可以减少整个仿真工作的工作量、可以减少整个仿真工作中出现错误的可能性、可以留下一个完整的有价值的文档，同时也能养成良好的仿真工作习惯，为今后高效的完成高速电路的仿真设计打下基础。

首先，我们知道Cadence公司的EDA软件可以运行在WindowsNT环境下和UNIX环境下，除非特别说明，本文所述都是在WindowsNT环境下。

SPECCTRAQuest是Cadence EDA工具中有关高速电路设计的一个模块。

在进行网络拓扑结构提取和信号分析之前，一些前期的准备工作必须正确完成。

★PCB板外型边框（Outline）根据实际结构设置PCB板边框。

★PCB板叠层（Stackup）主要确定PCB板布线层数以及层叠(stack-up)方式，会直接影响到印制线的布线和阻抗。

根据芯片管脚数、芯片密度、网表密度等方面来考虑。

然后根据实际情况确定叠层参数，可以选用各个PCB制板公司推荐的叠层参数。

关键是要选取合适的布线阻抗。

在Cadence中打开Setup Advisor进入Edit Stack-up对话框，如图1，进行编辑。

★导入网表（Netlist）★器件预布局（Placement）将其中的关键器件进行合理的布局，主要涉及相对距离、抗干扰、散热、高频电路与低频电路、数字电路与模拟电路等方面。

★PCB板布线分区（Rooms）主要用来区分高频电路与低频电路、数字电路与模拟电路以及相对独立的电路。

元器件的布局以及电源和地线的处理将直接影响到电路性能和电磁兼容性能。

★PCB板禁止布线区划分（Keepouts）根据PCB制板工艺的要求确定禁止布线区。

图1 Stack-up编辑框在完成上述工作以后，还要对将要进行仿真设计的PCB板做如下设置：●设置PCB板直流电源网络对于含有多种电压值电源供电的PCB板，正确的设置尤显重要。

在Cadence中打开Setup Advisor进入Identify DC Nets对话框，如图2，进行编辑。

图2 设置直流电源网络●设置器件类型一般器件类型在原理图库中已经指定并带入PCB图中，但仍然需要对器件类型进行确认，以防不正确的设置。

电阻、电阻排、电容、电感、晶体管、保险丝、二极管等都要设置成DISCRETE。

●为所有IC和独立元器件附仿真模型所有在仿真设计中需要模型的器件的仿真模型在原理图库中都应该正确指定，对于电阻、电容这些独立元器件需要在原理图中正确指定VALUE属性，SPECCTRAQuest可以自动为它们分配ESpice模型。

首先，打开Signal Library Brower对话框，若已有规的完整DML模型库，我们可以直接将需要的模型库加入到工作库中。

若只有IBIS模型，则需要按Translate->后选择ibis2signoise将IBIS模型转换成DML模型。

如图3。

图3 仿真模型库设置框然后打开Signal Model Assignment对话框，Auto Setup将自动分配模型给每个已经指定模型的器件。

如图4。

也可以按Find Model为器件手工分配模型，或按Create Model 编辑生成一个模型，这需要有足够的建模经验。

模型分配好后运行Signal Audit会有一个详细的报告，需要仔细的检查。

图4 仿真模型分配窗设置正确的管脚类型和器件类型一样，所有器件管脚类型在原理图中已经指定，但仍需确认。

连接器、独立元器件的管脚类型应为UNSPEC。

在图4窗口中点击RefDesPins栏后可以检查每个器件的每个管脚类型。

3 仿真步骤1、拓扑的抽取在模型添加完成后，即可进入信号线的仿真阶段。

从Allegro或SPECCTRAQUEST中都可以进入Constraint Manager，Allegro的路径是Setup－》Electrical Constraint Spreadsheet，SPECCTRAQUEST中的进入路径是Constraints－》Electrical Constraint Spreadsheet。

Constrain Manager是Cadence的约束管理器，所有连线的拓扑抽取以及对网络赋拓扑都是在这儿进行的。

打开界面，如同图5所示：图5 Constraint Manager 界面从左边分类栏看，分成两类，Electrical Constraint Set类是中所有已经输入到该管理器的电气约束约定，Net类是电路中所有的网络。

第一次打开时，第一类是空的。

对Net类，打开下面的任何一分类，都可以抽取拓扑。

在Net栏点击Signal Integrity、Timing、Routing的任何一个，右边就会将本板的全部网络显示出来，如图6所示。

各个网络按字母排列，其中前面有“＋”号的表示是总线或Xnet。

右击所选网络选择SigXplorer，就将拓扑抽取出来并进入SQ signal explorer expert 界面图7，所有网络的前仿真是在这个界面中进行的。

图6 抽取网络拓扑图7 Signal Explorer 界面2、参数设定因为对各个器件及阻容器件的模型已经在全部指定，所以抽取出来的拓扑上面的各IO 都有相应的IO模型，对那些没有指定的模型，Cadence会赋给它缺省的模型。

Cadence抽出的拓扑结构是根据各元器件的相对位置并考虑到布线方便抽取的，其中互连线的距离是它计算的曼哈顿距离（即Δx+Δy）。

仿真的主要目的就是根据仿真的结果优化网络的拓扑结构，用来约束PCB布线，使布线按照最优结果方向进行。

SQ Signal Explorer Expert界面除了菜单与工具栏以外分为两个部分，即上面的拓扑示意图与下面的参数、测量选择以及结果、控制的标签窗口。

在下面的Parameters标签窗口中的白色区域是可以编辑的，而灰色区域是无法编辑的，CIRCUIT是整个参数的总标题，下面的tlineDelayMode栏可以选择是用时间还是用长度表示传输线的延时（若用长度表示，则缺省的单位是mm，若用时间表示，则缺省的单位是ns，其中传输线的缺省传输速度是140mm每ns）；userRevision表示目前的拓扑版本（第一次一般是1.0，以后修改拓扑时可以将此处的版本提高，这样以后在Constraint Manage里不用重新赋拓扑，只要升级拓扑即可）。

点击开单板名称后（本例中即ODTA），下面就列出本拓扑的各个元件（包括器件、阻容、电源、传输线），可以编辑各个元件的特性；对器件，可以选择对应管脚的IO BUFFER模型，但一般不推荐去更改它的模型，因为已经赋给器件整体模型了，相应的IO Buffer的模型也就确定了。

对阻容器件，可以更改它们的阻容值；对电源，可以更改电源值；对传输线，可以更改以下几项：impedance，即传输线的交流阻抗，可以根据叠层情况在适当围更改它；propDelay，即传输线的延时来表示的长度；traceGeometry，传输线的类型，即是微带线或带状线，由于在前仿真中传输线是用一个集中式的无损耗模型来表示的，所以这边选择微带线或带状线的关系并不大；velocity，传输线的信号传输速度，这边一般不去改变它，用它的缺省值，即5567.72mil/ns，约14cm/ns。

为了得到更大围的仿真结果，扩大参数的选择围，我们一般对阻容器件的阻值、传输线的阻抗、传输线的长度选择多个值进行扫描。

在各个元件的参数设定后，即可在拓扑上加激励进行仿真。

首先是加激励源，点击模型上面、位号下面的Tristate，出现如图8所示的窗口进行选择：图8 激励源设置框在Cadence中共有7种激励：Pulse：脉冲方波，就是时钟源性质的波形，如果选择Pulse，整个界面中的其他选项是灰的，不允许再选；Rise：表示一个上升沿；Fall：表示一个下降沿；Custom：表示一种可以自定义的波形激励，这是最常用的波形，在这种形式下，首先在Frequency中输入信号的频率，在Pattern中输入波形的形状。