Cadence Design System Tutorial


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CADENCE DESIGN SYSTEM TUTORIAL

Chapter 1:

Introduction to Cadence

Chapter 2:

Schematics

Chapter 3:

Symbols

Chapter 4:

Hspice

Chapter 5:

Spectre

Chapter 6:

Layout

Chapter 7:

Layout Verification

Chapter 8:

Verilog

Chapter 9:

VHDL

Chapter 10: Bipolar Current Mode Logic

Chapter 11:

Standard Cells

Chapter 12:

Routing and Placement

Appendix A:

Shortcut Keys

Appendix B:

Remote Connection

By Rashmi Y. Dinakar Bryan S. Goda, John Mayega Chao You, Young Yim
e-mail: [email protected] (for questions and comments)
ECSE 4220: VLSI Design Rensselaer Polytechnic Institute
September 2011

Cadence Tutorial

Revision: 9/4/2009

Chapter 1: Introduction to Cadence

1.1 Introduction
Cadence Design Systems provides tools for different design styles. In this tutorial you will learn to use three Cadence products: Composer Symbol, Composer Schematic and the Virtuoso Layout Editor. This tutorial will help you to get started with Cadence and successfully create symbol, schematic and layout views of an inverter. You will also learn how to simulate your design using Hspice. The final check will be seeing if your layout matches your schematic.
Figure 1.1 shows the normal design sequence from design specifications to final layout simulation. This tutorial will take you through all the steps (except the last). In addition, there are chapters on Verilog, VHDL, bipolar current mode logic (CML), standard cells, and auto placement and routing.

Figure 1.1: Design Process Flow Diagram.

1.2 Getting Started
On the login screen enter your USERID and PASSWORD. To set up your ECSE ECL account for Cadence, Verilog, VHDL, Hspice, and AvanWaves, first logon to an ECL Sun using your account name. Type ls -al and verify that the following seven files are in your home directory. Missing or corrupted files may be replaced by typing:

cp ~cadtest/CDS/IC5.141USR5/.cdsenv .cdsenv

cp ~cadtest/CDS/IC5.141USR5/.cdsinit .cdsinit

cp ~cadtest/CDS/IC5.141USR5/cds.lib cds.lib

cp ~cadtest/CDS/IC5.141USR5/display.drf display.drf

cp ~cadtest/verilog verilog

cp ~cadtest/bindkeyAMS.il bindkeyAMS.il

(May not need)

cp ~cadtest/models.inc models.inc

(May not need)

cp ~cadtest/skew.file skew.file

(May not need)

If the directory /IC5.141USR5/ is missing, ask your TA for an updated replacement. A preconfigured

.bashrc file should also be in your directory. If it is missing or if you have customized it for other

applications, you may have to rename it and replace it by typing:

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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mv .bashrc .bashrc-old cp ~cadtest/CDS/IC5.141USR5/.bashrc .bashrc
In general you should keep a backup of any files you change in the same directory you are working in by copying the original file (cp filename filename-old) each time before making changes to the file.
Close your terminal window by typing:
exit
and then open a new one by holding the right mouse button down on a blank part of the screen, dragging down to 'Applications' and then dragging down on the pop-up menu to 'Terminal'.
If you don't want to replace or change your existing .bashrc file, before running Cadence or Hspice you will need to type:
source /cad/rc_scripts/rc.cadence_ic+icc source /cad/rc_scripts/rc.hspice

1.3 Starting Cadence
Follow these steps to load the Cadence software.
• Move the pointer into a xterm/terminal/console window. The window borders change colors, which
means that the window is active and ready to accept your commands. • To load the Cadence software, type: icfb &. The ampersand (&) puts the command in the background,
so you can continue using the window for other commands. The software is loaded when a new window opens up on the screen and the message "END OF USER CUSTOMIZATION" appears on the screen. This new window is called the Command Interpreter Window or CIW and is described in the following section.
1.4 About the CIW
The Command Interpreter Window is the first window that opens up when you run Cadence. Figure 1.2 shows the CIW
and a brief description of its parts. In this tutorial you will learn how to create the symbol, schematic, layout views of a design and, how to simulate the design. In Chapter 2 and 3 you will learn how to create the symbol and schematic views of design while in Chapter 4 you will learn how to simulate your design. Chapter 5 shows you how to layout your design Chapter 6 checks your schematic against layout to see if it matches your design.
1.5 Getting On-line Help
Help for Cadence is available online. Cadence has an extremely friendly user interface. Every window that opens up when you run Cadence has a Help button on the menu bar. Clicking on this button will open up the help manual at the page containing the information relevant to the window. For example, clicking the Help button on the Copy form will open up the manual at the page containing information relevant to the Copy command.

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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Figure 1.2: The Command Interpreter Window.

1.6 Invoking Commands
Commands can be invoked in Cadence in three ways:

1. Using the items on the menu bar of each window: This is the easiest way to invoke commands in Cadence. As mentioned earlier, Cadence has an extremely friendly user interface. Most of the Cadence menus are pull-down menus. You click a menu title to pull down the menu and see the commands listed on it. Some commands have forms that must be filled up to supply the additional information that the command needs. Some commands have option forms that you do not always need. You can use the User Preferences command to set whether or not option forms appear when commands start. To do this, i. In the CIW, click Options. The dots after a menu item mean a form appears after you click the item. ii. To close the Options menu without starting a command, click anywhere outside the menu. If you accidentally choose a menu item, click Cancel to cancel the command. iii. Click User Preferences. The User Preferences form appears. This form contains settings that control how Cadence behaves. The form has two main sections, Window Controls and Command Controls. The items on the form are self-explanatory. In the command controls section, observe the "Options Displayed When Commands Start" option. This is the option, which determines whether or not a form opens up when you invoke a particular command. If this has not been selected, select it. Also, it is useful to set the 'Undo Limit' to its maximum value to 10. This has all ready been setup for you in the .cdsinit file startup file. If not, make the necessary changes. iv. If you have made changes that you would like to preserve, click OK. Otherwise click Cancel to avoid changing the settings in this form.

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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2. Using Bind Keys: Letters and symbols to the right of a command describe a "bindkey" or set of keyboard keystrokes that perform the same function. The caret (^) represents the Control key: press the control key at the same time that you press the letter. Bindkeys are case sensitive. Make sure you know when the command letter is capitalized. Appendix A contains the Quick Reference for bindkeys that are supplied with Cadence. Using bindkeys is the fastest way to work with Cadence but, it requires a degree of familiarity with Cadence design environment.

3. Typing the corresponding skill function at the prompt in the CIW: This is an advanced way of invoking commands in Cadence and requires familiarity with the Cadence Design System and with the skill functions. Hence it is recommended that you use either the items on the menu bar or, the bind keys. If a skill function must be used, it will be mentioned at the appropriate place.

1.7 Creating a New Library
Take a look at the existing libraries. Select Tools → Library Manager. You should see the following (among other libraries):

US_8ths

analog.Lib Cadence Library, has ideal sources for voltages (vdc, vpulse)

basic

cdsDefTechLib

sample

sbaLib

sige5am

IBM SiGe 5HP Design Library

VLSI_CLASS Class examples of inverter, NAND gate, etc.

In order to separate your files from those that already exist in the system, you must create a library of your own and place your files in that library. Library creation is a critical step. You must do this exactly as stated under IBM_PDK, not under any other pull-down menu. If this procedure is not followed, you will not be able to edit the circuit layouts. Everything in the diagram will be collapsed down to a single layer. To create a new library from the CIW, do the following: • Choose IBM_PDK → Library → Create from the CIW. The New Library form opens up. In the form:
• In the 'Name' field, specify the name of the library • ‘Technology File’ field: select Attach to an existing techfile • Select OK

The Attach Design Library to Technology File form opens. In this form:

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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• Select sige5am for the ‘Technology Library’ field
• Select OK
An Add AMS Library Properties form opens. In this form
• Select M5 for 5 layers of metal for 'Number of levels of metal' (this is important otherwise your
layouts will be wrong)
• Select OK

1.8 Opening a New Cell View
To open a new cell view from the CIW, do the following: 1. Choose File → New → Cellview… from the CIW. 2. The Create New File form appears.
• In the 'Library Name' field, specify the library in which you want the new cell view to be stored. (Pick the library just created.)
• In the 'Cell Name' field, type a new cell name. • Set the 'Tool' field to either Composer-Symbol / Composer-Schematic / Virtuoso depending on
the view type. (For the first time through, pick Composer-Schematic in preparation for Chapter 2 of this tutorial. Chapter 3 will use Composer-Symbol.) • In the 'View Name' field, a view name - symbol, schematic, or layout - depending on what you selected under 'Tool', will be given. • Click OK

1.9 Opening an Existing Cell View
To open an existing cell view from the CIW, do the following: 1. Choose File → Open... from the CIW. 2. The Open File form appears.
• In the 'Library Name' field, specify the library that contains the existing cell view. • In the 'Cell Name' field, specify a cell name by doing one of the following:
• Type the cell name • Click on a cell name in the ‘Cell Names’ list box • Click Browse to open the Library Browser. • In the 'View Name' field, choose a view name. • Click OK

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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Cadence Tutorial
Figure 1.3 shows what a typical design window looks like.

Revision: 9/4/2009

Figure 1.3: Design Window.

1.10 Capturing Screen Images with XV, Snapshot, Screenshot, or sdtimage
As you proceed through this tutorial as part of the VLSI Design class you are expected to keep a record of your results after finishing each section. A convenient way to do this is by capturing images off the screen after each point in the design. Suppose you have a nice plot you want to save. You can type: xv & to start the xv program. Right click on the box and select Grab. A box should appear. Put in 2 or 3 seconds for the delay, hit AutoGrab, and move to the display window you wish to capture. You can left click to get the window or draw a box with the middle mouse button to select a rectangle you wish to view. You should see a copy of the box appear if you grabbed it correctly.

If you want to play with the colors, select 8 bit mode, then color editor. You can click on a color box and change it to meet your tastes. If you want to flip black to white, slide the dials (all 3) to 255. You can also play with the saturation to bring out the contrasts. It is strongly suggested that you remove any black backgrounds since they don’t print well, waste a lot of ink, and make it difficult to see the important features in your drawings. Save the file as a full color .gif or .jpg and then later you can ftp it to your RCS account and port it into PowerPoint or Word.

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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Cadence Tutorial
For a step-by-step procedure to grab screen shots:
1. Create a directory for saving your screen capture pictures in the Unix window. mkdir pics
2. Start the screen capture software using command: xv &
This window will open on the terminal:

Revision: 9/4/2009

3. Right clicking on the XV window will show:

4. Left click on the Grab button and up pops the screen:

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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5. You can use AutoGrab or Grab to capture the window or picture you want. Here, the AutoGrab will be used. For this example, fill in 3 seconds for the delay.

6. The AutoGrab button is enabled by Left clicking on it. You must activate (move your mouse to that window’s title bar and left click) the window you want to capture within 3 seconds. E.g. we choose the inverter layout window. It will be captured as shown below.

7. After you have captured the window go to the XV control window, shown in step 3, and click Save to save the picture:

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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Note: don’t forget to choose the correct folder in which you want to put your picture. Use a JPEG, GIF, or TIFF file format. You should add a .jpg, .gif, or .tif suffix to the saved file name.

9. Repeat steps 4 through 8 to capture all windows in which you are interested.

10. Use the following command to transfer the pictures you captured to your RCS account so that you can print them out in the VCC or insert them into a Microsoft Word document.
scp -r pics [email protected]:
The username is your RCS account name. Don’t leave off the “:” at the end of this command.
Another way to create an image file of the plots is as follows. Right click on a blank part of the screen and select Programs → Snapshot. Select Hide Window During Capture and then Left click on Snap. Move the cursor to the desired plotting window and Left click. Wait several seconds until the control panel reappears with an Image Viewer window of the captured plot screen. Select File → Save As in the Image Viewer window, pick a 'File Format' (TIFF is probably best for PC and Macintosh files), enter a file name, and select OK. Note that this method will work for capturing an image of any window on the Sun workstation.
The Dell workstations provide an application under the menu at the top left: Applications → Accessories → Take Screenshot. The control panel that opens allows you to grab the whole desktop, grab the current window, or grab a selected area. Grabbing the current window ('Grab the current window') will probably work best. Make sure the preferred window was selected before clicking on Take Screenshot, set the 'Save in folder' to the desired folder, and select Save. The process is more reliable with a 1 second delay before grabbing the shot.

Authors: R. Y. Dinakar, B. S. Goda, J. Mayega, C. You, Y. Yim

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Cadence Design System Tutorial