Share This PostToday’s tip is from Bill Tkachuk in CSD. It’s a great way to speed the definition and rule assignment for differential pairs. Give it a try and add any comments for tips you may have for working with diff pairs.Defining Differential Pairs within PADS RouterUsing PADS Router, you can define your Diff Pairs and assign the same rule set to multiple Diff Pairs at once.
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Using a trick with the Project Explorer you can define the Diff Pairs much more quickly than is possible in PADS Layout. Please follow the steps below:.
Open PADS Router and load your design file. Make sure your Project Explorer window is open. Go to View Project Explorer to toggle it on/off.
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Right mouse click in the Project Explorer window and choose Vertical Split.
1.1 Begin by opening PADS Logic. Select Start Programs Mentor Graphics SDD PADS2005 SP2 System Design PADSLogic.1.2 Ensure that your user library is loaded by usingthe library manager - File Library.(Refer to section 3 of the New Part Tutorial for step-by-stepinstructions).1.3 Start a new design by selecting File New.Your PADS Logic window should look something like this.1.4 Use the Add Part window to add an LM2675 voltageregulator to your design.To add a part to your design, click on the button on thedesign toolbar. This will open the Add Part from Library windowas shown below.To locate the LM2675 part, you will need to select your custom libraryfrom the Library dropdown list in the filter.
Select H:Pads Libraryuser.Ensure that the Items field contains a single asterisk. and thenpress Apply.
This will filter the results, displaying only theparts in your user library. The window should look like the onebelow.Press the Add button.
An outline of the LM2675 part will appearbelow the mouse pointer while it is within the design window.Close the Add Part window and click somewhere near the center of thesheet to add an instance of the LM2675 part. Press escape to exitadd part mode. You schematic window should look similar to theone below.Note: You may wish to zoom in on the LM2675 before completing thefollowing steps. (Refer to the User Interface Tutorial ifnecessary).1.5 Add capacitors to your design.Open the add part window by clicking the button on thetoolbar. In the library dropdown list, choose the misc library(C:MentorGraphics2005PADSSDDHOMELibrariesmisc). In theItems menu, type CAP. andthen press Apply.
This will filter the results to display onlythe parts starting with 'CAP' that exist in the 'misc' library.Select the part named CAP7343 from the list and press Add. Movethe Add Part window so that most or all of the design area isvisible.
Your screen should look similar to the one below.Place the CAP7343 capacitor to the left of the LM2675 as shownabove. Place a second CAP7343 to the far right as shown in theschematic below.Now select CAP1206 from the Add Part window, press Add and close thewindow.
Before adding the capacitor to your design, press Ctrl + R torotate it 90 degrees. Place the capacitor to the right of theLM2675 as shown below.1.6 Add additional circuit components to your design.Add an inductor and diode to your design as shown in the imagebelow. Use the IND-MOLDED part for the inductor and the DIODEpart for the diode. Both of these parts are found in the 'misc'library.1.7 Assign values to your components.Ensure that part selection is enabled by right clicking in an emptyarea and selecting the Select Gatesoption. This can also be achieved by pressing the buttonon the filter toolbar.Double click on the left-most capacitor. This will open the PartProperties window as shown below.Click on the Attributes button to open the Part Attributes window.Scroll down to the Value field, double click and enter 100uF in the text box.Press OK to close the Part Attributes window and return to the PartProperties window.
By default, the CAP7343 part will not displayits value in the schematic. To change this, click the Visibilitybutton to open the Part Text Visibility window.Check the Value checkbox on the right side to enable display of thecapacitor's value. Press OK to close the Part Text Visibilitywindow and then press Close to close the Part Properties window.Your schematic should now look like the one below.Repeat this process for the other components, assigning the valueslisted below:. Right Capacitor - 100uF.
Middle Capacitor - 0.01uF. Inductor - 33uH1.8 Change the PCB footprints assigned to the inductor anddiode.The IND-MOLDED and DIODE parts both default to using through-holefootprints. We will change these parts to use surface mountfootprints.Double click the inductor to open the Part Properties window.Click on the PCB Decals button to open the PCB Decals Assignment window.Click Browse. The Get PCB Decal from Library window willappear. This window functions almost identically to the Add Partwindow.The footprint we will be using for the inductor is named IND7 and isfound in the 'common' library.Select this decal and press OK.
Then press OK in the PCB DecalAssignment window and close the Part Properties window.Repeat this process for the diode, selecting the DIODE2 footprint fromthe 'common' library.1.9 Adding Header Pins to your design.We will now add a pair of 2-pin headers to the schematic. One2-pin header will be used for the input voltage source (12V), and theother will be used for the 3.3V output.Open the Add Part window. Select the 'connect' library from thedropdown list and enter HEADER. in the Items filter. Press Applyand select HEADER02 from the list of parts.Note: PADS implements connectors as if they were multi-gate IC's.In this case, each pin is treated as a separate gate and must be addedindividually.Add two header pins to the left of the schematic, and two to the right(Use Ctrl+F tomirror a part horizontally). Your schematic should look similarto the one below.1.10 Connecting your parts.Press the button on thedesign toolbar.
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This will activate Add Connection Mode.Place the cursor on pin 7 of the LM2675 and click once to begin addinga connection. Move the cursor to the left until it ishorizontally aligned with the left capacitor. Click once.This will add a vertex / pivot point to your connection. Move thecursor down and click on the top terminal of the left capacitor tocomplete the connection. Your schematic should look like theimage below.Continue adding connections until your schematic is fully connected asshown below.Note: To remove a misplaced connection, ensure that the selectionfilter allows selecting connections. Then click on the connectionyou wish to remove and press delete. You can also activate DeleteMode by pressing the button on thedesign toolbar.
This will allow you to remove objects with asingle click.1.11 Adding Power and Ground ConnectionsTo add a ground connection to your design, enter Connection Mode.Begin by starting a new connection from the bottom-most net and movingdown 2 or 3 spaces. Then right click and select Ground from thecontext menu.Position the ground symbol at the desired location and click once toplace it.Adding a power connection is done in a similar manner. Begin bystarting a new connection from the net connected to pin 7 of the LM2675and moving up. Right click and select Power from the contextmenu. Position the power symbol and click once to place it.Repeat this process for the net connected to the top right headerpin. Your schematic should look like the one below.By default, all power connections are automatically connected to a netnamed +5V.
We will need to change this for our design.Double click on the left power symbol. This will open the NetProperties window shown below.Change the Net Name field to +12V and select the Net Name Label checkbox.
Press OK.Repeat this process for the right power symbol, setting the Net Name to+3.3V. The completed schematic should look similar to the imageshown below.1.12 Save your schematic.
Select File Saveand save the schematic to H:PADSTutorialTutorial.sch.2. Creating a PCB Designusing PADS Layout. 2.1 Linking PADS Logic toPADS LayoutBefore you can begin laying out your PCB, you must transfer theschematic netlist to PADS Logic. The recommended way of doingthis is to create an application link between PADS Logic and PADSLayout.
In addition to allowing automatic synchronization of theschematic and layout information, linking also enables a feature knownas cross-probing. This basically allows the selection of a partor net in PADS Logic to result in the selection of the correspondingPCB footprint or trace in PADS Layout, and vice versa.To connect PADS Logic to PADS Layout, select Tools PADSLayout. The Connect to PADS Layout dialog will appear.Since we have not yet created a PCB Design file, click the Newbutton. A new PADS Layout window should appear as shown below.Note: On subsequent connections to PADS Layout or PADS Router, you willclick Open and select your existing design file.Note: If you have the available screen real estate, it is recommendedthat you resize the PADS Logic and PADS Layout windows so that both arevisible simultaneously. A multi-monitor setup is especiallyuseful for this.2.2 Transferring the Netlist from PADS Logic to PADS LayoutNote: Before transferring the netlist, ensure that your custom userlibrary has be added to Layout's Library List. Refer to the NewPart Tutorial if necessary.While PADS Layout is still open, switch back to PADS Logic. ThePADS Layout Link window should be visible.Click on the Preferences Tab and select the Compare PCB DecalAssignments checkbox.
This will ensure that the modified inductorand diode footprints are properly sent to PADS Layout.Now click on the Design Tab. Press the Send Netlist button totransfer your design to PADS Layout.Switch back to the PADS Layout window. You should now see acluster of parts located at the origin (Location 0,0).2.3 Creating the board outline.After transferring the netlist, you will need to create a boardoutline. Press the button toenable the Drafting Toolbar.On the Drafting Toolbar, click on the button toenter board outline mode.Since our circuit is extremely simple, a 1.0 inch by 0.7 inch PCBshould be large enough.Note: For the following steps, refer to the location indicator at thebottom-right corner of the window.
3.2 View/Modify the Design PropertiesTo view the current design properties, right-click and selectProperties from the context menu. This will open the DesignProperties window shown below.From this window you can adjust a plethora of attributes that affectyour design. Select the various tabs to get an idea of all theoptions available.
Now select the Routing tab.From this tab you can control, among other things, the default width ofyour PCB's traces.Change the Recommended value to 15 and the Maximum value to 20.Then press OK to confirm your changes.3.3 Use the PADS AutoRouter to route your design.We will now use the built-in autorouter to route the pcb design.Select Tools Autoroute Start to begin the autoroute process.After a few seconds, the design should be fully routed as shown below.3.4 Verify your designYou should now run a design check to ensure there are no routing errorswith your design. Select Tools VerifyDesign. The results of the test will appear in the OutputWindow located at the bottom right corner of the screen.3.5 Save your design. Select File Saveand then close PADS Router, returning to PADS Logic. Close thePADS Router Link dialog if it is still open.4.
Finishing your designin PADS Layout. 4.1 Linking PADS Logic toPADS Layout.You will now connect to PADS Layout again and complete the final stepsin your design. Select Tools PADS Layout to open the Connectto PADS Layout window. Select Open.,browse to H:PADSTutorial and open Tutorial.pcb.PADS Layout should open, displaying your fully routed design.4.2 Adding Copper Pours to your PCBYou will now add a copper pour to each side of your PCB. Enablethe drafting toolbar by pressing the button.Now press the button toenter Copper Pour Mode.Move the cursor over the origin and click once to start drawing theoutline of the copper pour.Move the cursor to location 0,700 and click to draw the left edge.Move the cursor to location 1000,700 and click to draw the top edge.Move the cursor to location 1000, 0 and double click to complete thecopper pour outline.The Add Drafting should appear as shown below.Select Top from the Layerdropdown list and select GND from the Netdropdown list.
Press OK.Repeat this process using the same coordinates and choosing Bottom forthe Layer. Select GND for the Net.After the copper pours have been added, the design window should appearas shown below.Note: If you need to re-route your design, you will need toremove thecopper pours and save your file before opening it in PADS Router.Ifyou fail to do this, PADS Router may not correctly route your PCB. 4.3 Flooding your design.You will now flood your design, filling in the copper pours withcopper. Select Tools PourManager to open the Pour Manager window.Press Startto begin the flood process. If there were no errors, close thePour Manager.
Your design window should now look similar to theimage below.If there were any errors, press the Setup buttonto open the Options Thermals window.Any copper pour errors can often be corrected by changing the type orwidth of the thermal spokes. Changing the type to 'Flood Over'should always prevent the 'too few spokes generated' error. This,of course, changes the method used to connect the copper pour to viasand pads of the same net. Note: Not all copper pour errors arecritical, it may not be deemed necessary to modify the Thermalsparameters.4.4 Verify DesignYou should now check your completed design for errors. Select Tools VerifyDesign to open the Verify Design window.Select Clearance from the Check list and press start. If thereare no errors, the following dialog will be displayed.Press OK and select Connectivity from the Check list.
Press Startto run the check. If there were no errors, close the VerifyDesign window. If any errors were detected, you should locate theerror image on your design and correct the problem.Note: If you need to re-route your design, you will need toremove the copper pours and save your file before opening it in PADSRouter. If you fail to do this, PADS Router may not correctlyroute your PCB.4.5 Save your design. Select File Saveto save your completed PCB design.5.
Generating Gerber Files. The steps needed to generate theappropriate gerber files will vary depending on the number of layersused and the PCB service that will be creating the board. Thissection will show the steps needed to create gerber files for aPCBExpress E2 2-Layer Board.5.1 Select File CAMto open the Define CAM Documents window.5.2 Top LayerPress the Add.button to display the Add Document window.Type Topin the Document Name field.Select Routing/SplitPlane from the Document Type dropdown list and select Top from thepopup window.Press the Layersbutton to open the Select Items window.Check the BoardOutline checkbox and press OK. The Add Document windowshould look like the one below.Press the DeviceSetup button to display the Photo Plotter Setup window.Press the Regeneratebutton and click yes.