Check if your PCB is correct

Protel DXP provides a rule-driven environment for designing PCBs and allows you to define various design rules to ensure the integrity of your board. Typically, you set up the design rules at the beginning of the design process and then use them to verify the design at the end.

Early in the tutorial we examined the routing design rules and added a new width constraint rule.

We also noticed that many rules have been created by the PCB Board Wizard.

To verify that the routed board complies with the design rules, we will now run a Design Rule Check (DRC):

1. Select Design » Board Layers (shortcut L ) and make sure the Show button next to the DRC Error Markers option in the System Colors cell is checked so that the DRC error markers will be displayed.
2. Select Tools » Design Rule Check from the menu (shortcut T, D). The Design Rule Checker dialog box has an on-line and a set of DRC options. Click a class to view all of its original rules.
3. Leave all options at their default values ​​and click the Run Design Rule Check button. The DRC will run and its results will be displayed in the Messages panel. Of course, you will notice that the pads of the transistors are highlighted green, indicating a design rule violation.
4. Review the Error List. It lists all the rule violations that exist in the PCB design. Notice that there are four violations listed under the Clearance Constraint rule. The details indicate that the pads of transistors Q1 and Q2 violate the 13mil safe spacing rule.
5. Double-click an error in the Messages panel to jump to its location in the PCB.

Usually you set the safe spacing constraint rules before designing the board and paying attention to routing techniques and the physical properties of the device. Let’s analyze the error and then review the current safe spacing design rules and decide how to solve the problem.

Find the actual spacing between the transistor pads:

1. With the PCB document active, place the cursor in the middle of a transistor and press the PAGEUP key to zoom in.
2. Select Reports » Measure Primitives (shortcut R, P). The cursor changes to a crosshair.
3. Place the cursor in the middle of a pad in the middle of the transistor and left-click or press ENTER. Because the cursor is over the pad and the wire connected to it, a menu will pop up to let you select the required object. Select the pad for the transistor from the pop-up menu.
4. Place the cursor in the middle of one of the remaining pads for the transistor and left-click or press ENTER. Select Pad from the pop-up menu again. A message box will open showing that the minimum distance between the edges of the two pads is 10.63 mils.
5. Close the message box and right-click or press ESC to exit measurement mode and rescale the document using the V, F shortcut keys.

Let’s look at the current safe spacing design rules.

1. Select Design » Rules from the menu (shortcut D, R) to open the PCB Rules and Constraints Editor dialog. Double-click the Electrical category to display all electrical rules on the right side of the dialog. Double-click the Clearance type (listed on the right) and then click Clearance_1 to open it. The bottom area of ​​the dialog box will include a single rule indicating that the minimum safe spacing for the entire board is 13 mils. The spacing between the transistor pads is less than this value, which is why they are considered a violation when we select DRC.
2. Select the Clearance type in the Design Rules panel, right-click and select New Rule to add a new Clearance constraint rule.
3. Double-click the new Clearance rule and set the Minimum Clearance to 10mil in the Constraints cell.
4. Click Advanced (Query) and then Query Builder to build a query from Memberships Checks, or type HasFootprintPad(‘BCY-W3/D4.7’,’’) in the Query field. The “” represents “any pad” named BCY-W3/D4.7.
5. Click OK to close the dialog box.
6. You can now re-run the DRC from the Design Rules Checker dialog box (Tools » Design Rule Check) by clicking the Run Design Rule Check button. There should be no violations

Well done! You have completed the PCB design and are ready to generate output documents.

Setting up project outputs

Project outputs, such as printing and output files, are set up in the Outputs for Project dialog box.

1. Select Project » Output Jobs. The Project [project_name] dialog box appears.
2. Click the output you want to set up. If the Configure button is active (not grayed out), you can modify the settings for that output.
3. Click Close when you are finished.
4. If you want to send the output to separate folders based on the output type, select Project » Project Options, click the Options tab, click Use separate folder for each output type, and click OK.

Printing to a Windows Printing Device

Once the PCB design and routing are complete, you are ready to generate the output documentation. This documentation should include a production tracing that describes the manufacturing information and a collection tracing that describes the component location information and the load sequence (command).

To generate these tracings, Protel DXP includes a sophisticated print engine that gives you complete control over the printing process. You can precisely define the combination of PCB layers you want to print, preview the tracing (called the printout), and set the scale and position on the paper before printing.

Now we will create a print preview using the default output settings and then modify the settings.

1. Select File » Print Preview from the PCB menu. The PCB will be analyzed and displayed in the Print Preview window with the default output. Click Close.
2. To check the combination of PCB layers included in the output, select Project » Output Jobs. The Project [project_name] dialog box appears. Select Composite Drawing from the Documentation Outputs cell and click the Configure button. The PCB Printout Properties dialog box appears. You can add or remove layers from the right-click menu options. Click OK to close the dialog box.
3. While we are still in the Project [project_name] dialog box, we want to modify the layer parameters for the hole guide combination. Select Composite Drill Drawing from the Fabrication Outputs cell and click the Configure button. By default, this printout includes hole guides (a system layer with a small cross at each drill hole), and punch layers (a special symbol at each drill hole that uniquely represents each drill size).

The hole guide layer is not needed in a normal punch drawing, so delete it. Right-click the DrillGuide layer in the Printouts Layers column and select Delete from the menu. Click OK to close the dialog box.

4. Now click Print Preview to view the punch drawing. You can then click Print to display the printer settings, and finally click OK to send the drawing to the specified printer.
5. Click Close to close the print preview window.
6. To change the target printer, set the page position and scale, you can select Page Setup in the Project [project_name] dialog box (or select File » Page Setup from the menu). Select your preferred printer and set the printer page to Landscape.
7. When you are done, close all open dialog boxes.

Fabrication Output Files

The final stage of the PCB design process is to generate the fabrication files. The file combination used to manufacture and produce PCBs includes the film (Gerber) file, NC drill file, insert (pick and place) file, bill of materials, and test point file. Output files can be set in the Project [project_name] dialog box (Project » Output Jobs) or through a separate command in the File » Fabrication Outputs menu. The settings for the fabrication documents are saved as part of the project file.

Generate Film Files

Each film file corresponds to a layer of the physical board – component silk screen, top signal layer, bottom signal layer, solder mask layer, etc. Before generating the Gerber and NC drill files for manufacturing your design, it is wise to check with your PCB fabricator to confirm their requirements.

To create the manufacturing files for this tutorial’s PCB:

1. With the PCB document active, select File » Fabrication Outputs » Gerber files. The Gerber Setup dialog box appears.
2. Click OK to accept the defaults. The Gerber files are generated and CAMtastic! opens to display them. Gerber files are saved in a Project Outputs folder that is automatically created in the same folder as your project file. Each folder has a file extension that corresponds to the layer name, such as Multivibrator.GTO for the top layer screen.

Bill of Materials

1. To create your bill of materials, first set up your report. Select Project » Output Jobs, then select Bill of Materials in the Report Outputs section of the Project dialog box.
2. Click Create Report. In this dialog box, you can set up the information you need for your BOM by dragging the column headers in the Visible and Hidden Columns.
3. Click Report… to display a print preview of your BOM. This preview can be printed using the Print button or exported to a file format such as Microsoft Excel’s .xls using the Export button.
4. Close the dialog box.

Congratulations! You have completed the PCB design process.

Simulating the Design

Protel DXP allows you to run a large array of circuit simulations directly from the schematic. In the following part of this tutorial, we will simulate the output waveforms produced by our multivibrator circuit.

Setting Up the Simulation

Before we run the simulation, we need to add a few objects to our circuit: a voltage source for the oscillator; a reference ground for the simulation and some net labels for the points in the circuit where we want to view the waveforms.

1. Click Multivibrator.SchDoc at the top of the window to make the schematic the current document.
2. We must place another connector with a voltage source. To delete the connector, click once on the connector body to select it, then press the DELETE key on the keyboard.
3. There is not enough room to place the voltage source at this time, so we will move the free end of the wire. To move the vertical end of the 12V wire, click once on the wire selection. When the small edit point square appears, click once on the point at the free end of the wire and move the point upward as far as it will go to where the wire changes direction. Click again to drop the point.
4. Repeat this process for the vertical end of the GND wire, moving it to the bottom of the drawing.
5. Select View » Toolbars » Simulation Sources to display the Simulation Sources toolbar.
6. Click the +12V source button on the Simulation Sources toolbar. A power supply symbol will float above the cursor. Press the TAB key on your keyboard to edit its properties. In the dialog box that appears, click the Attributes tab to make it active, and set the Designator to V1. Click the OK button to close the dialog box, and then place the power supply between the vertical endpoints of the 12V and GND wires.
7. Using the same technique you used to move the vertical endpoints of the 12V and GND wire sections, move them to the two ends of the voltage source, as shown in Figure 9.

Our last task before running the simulation is to place net labels at the appropriate points in the circuit so that we can easily identify the signals we wish to view. In this tutorial circuit, good spots are the base and collector of the two transistors.

1. Select Place » Net Label from the menu (shortcut keys P, N). Press the TAB key to edit the properties of the net label. In the Net Label dialog box, set the Net column to Q1B, then close the dialog box.
2. Place the cursor over the wire connected to the base of Q1. Refer to Figure 9 for the placement of net labels. Left-click or press ENTER to place the net label on the wire.
3. Press the TAB key to change the Net column to Q1C.
4. Place the cursor over the wire connected to the collector of Q2, left-click or press ENTER to place the net label on the wire.
5. Similarly, place the Q2B and Q2C net labels on the base and collector wires of Q2.
6. When you are finished placing net labels, right-click or press ESC to exit placement mode.
7. Save the simulated circuit to a different file name than the original schematic. Select File » Save As. In the Save As dialog box, type Multivibrator simulation.SchDoc.

Running a transient analysis

Your schematic now has all the necessary conditions, so let’s set up a transient analysis of the circuit. In our tutorial circuit, the RC time constant is 100k x 20n = 2 ms. To see5 cycles of oscillation, we want to set up to see a 10ms portion of the waveform.

1. Select Design » Simulate » Mix Sim from the menu to display the Analyses Setup dialog box. All simulation options are set here.
2. First we need to set the center point in the circuit that you want to observe. In the Collect Data For column, select Node Voltage and Supply Current from the list. This option defines the type of data you want to calculate during the simulation run.
3. In the Available Signals column, double-click the Q1B, Q2B, Q1C, and Q2C signal names. As you double-click each name, it moves to the Active Signals column.
4. Check Operating Point Analysis and Transient/Fourier for this analysis. If the Transient/Fourier Analysis Setup does not automatically display, click the Transient/Fourier analysis name.
5. Disable the Use Transient Defaults option so that the transient characteristics analysis rules are available.
6. To specify a 10ms simulation window, set the Transient Stop Time column to 10m.
7. Now set the Transient Step Time column to 10u, which means that the simulation can display a point every 10us.
8. During the simulation, the actual time interval is a cluster of automatically randomly obtained time intervals. In the Maximum Step column, limit the randomness of the time interval size and set the Transient Max Step Time to 10u.

Now you are ready to run the transient characteristics analysis.

1. Click the OK button at the bottom of the Analyses Setup dialog box to run the simulation.
2. After the simulation is executed, you will see an output waveform similar to that shown in Figure 10.

Congratulations! You have completed the circuit simulation and displayed its output waveform.

If you like, you can change some of the component parameters in the schematic and run the simulation again to see the changes. Try changing the value of C1 to 47n (double-click C1 to edit its properties) and then run the transient characteristics analysis again. The output waveform will show an uneven duty cycle waveform.