Making the Inverter Symbol

This part of the tutorial deals with the layout of the symbolic representation of our inverter.  As in part three, we will create a new cell view for the symbol. You can make the new cell view though any of the methods we have previously discussed. We will also name this view inv, but it will be a symbol rather than a schematic.
Figure 10. Create New Symbol Window

Make sure symbol is the View Name and Composer-Symbol is the Tool. Press OK to continue and a familiar window will appear in which you will draw the symbol.

First, we need to draw a triangle on its side to represent the body of the inverter.  Draw a vertical line on the left of the center line and connect the ends at a point on the right of center. To access the tools needed to draw the shapes click Add->Shape->Polygon. Figure 11 shows this window and other required settings.

Figure 11. Add Shape Window

After adding the triangle, we need to add a circle at the right point to indicate negation.  Click Add->Shape->Circle and then on the diagram click where you want the center of the circle, move the mouse until the circle is the size you want, and click again to stop sizing the circle.

Next we need to add the pins to our inverter.  As before, click Add->Pin to bring up the Add Pin Window. We will again create pins vdd, vss, in, and out. As in the schematic make sure the pins are specified as inputOutput. The Add Pin Window can be seen in figure 12 below.

Figure 12. Add Pin Window

Now we need to place the pins. This is done in the same manner as in the schematic, but these pins are represented differently. On these pins, one end of the line has a small box. This box is the actual pin. Place this box away from the symbol. The shortcut of right click to rotate will save a great bit of time here. Because the pin names may be hard to read now, you can move them by clicking Edit->Move or using the shortcut ‘m’.

Now we want to label the symbol. We will add two labels here. Begin by clicking Add->Label, which will invoke the Add Label box.

Figure 13. Add Label Window

The first label is going to be the instance label. This is the default label as seen above. Place this label near the symbol of the inverter. The second label will be the name label. If the Add Label box disappeared after adding the instance label, bring it back up. Change label type to normalLabel and type the name of the device in the Label field. Place this label on or near the symbol. When we place the symbol in schematics, all of the symbols will have the same name, but different instances, e.g. U1, U2, etc.

The last task is to add the selection box to the symbol. Click Add->Selection Box and click on the choice of Automatic on the window that appears.

The symbol is now finished and should look similar to the symbol below in figure 14. If you are satisfied with the symbol, save it by clicking Design->Save.

Figure 14. The Finished Inverter Symbol

We are now ready to move on to the final phase of this tutorial, Schematic Simulation.

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