Chapter 1: Introduction
1-12: Schematics and Layout Tutorial
1-12-2: Schematic Entry

Your first task is to create a schematic for a 2-input NAND gate. Each design is kept in a cell; for example, your schematic will be in the "nand2{sch}" cell, while your layout will eventually go in the "nand2{lay}" cell and your AND gate will go in the "and2{sch}" cell. Use the New Cell command (in menu Cell), or just type Ctrl-N. Enter "nand2" as the cell name and select "schematic" as the view. The editing window will now have the title "mipscells:nand2{sch}" indicating the library, cell name, and view. It is useful to put a label inside a cell, in addition to assigning its given name. To label your cell, select the "Components" tab of the sidebar (on the left), click on "Misc.", and select "Annotation text". Move the cursor to the location where you want the label to appear, and click to create the text. Change the text by double-clicking on it and typing "nand2". When done typing, click away from the text to exit the in-place editing (the text is now selected with an "X" through it). Then bring up the full properties dialog for this text with the Object Properties command (in menu Edit / Properties), or just type Ctrl-I. Set the "Text Size" to 5 units and click OK. When your cell is finished, you can move this label to a sensible location.

Electric defines various technologies for schematics and layout. To draw transistor-level schematics, you can use the symbols in the Components tab of the side bar.

Your goal is to draw a gate like the one shown here. Turn on the grid to help you align objects. To do this, use the Toggle Grid command (in menu Window), or just type Ctrl-G. Click on an nMOS transistor symbol in the Components tab on the left side of the screen. Then click in your schematic window to place the transistor in the circuit (perform this as two separate clicks, not drag-and-drop). Repeat until you have two nMOS transistors, two pMOS transistors, the Power symbol, and the Ground symbol arranged on the page.
Figure 1.34

These symbols are nodes in Electric parlance. You may move the nodes around by clicking and dragging. The transistors default to a width/length value of 2/2. Double-click on the pMOS transistor and change its width to 12. Recall that nMOS transistors are roughly twice as strong as pMOS transistors. So a single nMOS transistor would only have to be 6 wide. However, because the nMOS transistors are in series, they should also be 12 wide.

Now, connect the nodes with wires (called arcs in Electric parlance). Notice that when you click on a node, the closest port is also selected. These ports are the sides of arc connections. Click on a port such as the gate, source, or drain of a transistor. Right-click, hold the mouse, and drag away from the node. When you release the mouse, an arc will be created from the original node to the location of the cursor. A new "pin" node will also be created at the cursor to hold the other end of the arc. If you right-click and drag over an existing node, then you will connect to it. If two objects to be connected are not lined up, Electric will create two arcs to join them. The location of the cursor determines the angle of the bend, so wiggle it to see how the two arcs will run before releasing the button and creating the connection. See Section 2-2-2 for more on arc creation.

When the schematic is wired, you will need to create exports which define inputs and outputs of the cell. From the Components tab, select the "Off-Page" symbol and place it in the circuit. Connect the tip of the arrow the proper place in the circuit. To make an export on the other side of the Off-Page, select that port and use the Create Export command (in menu Export), or just type Ctrl-E. Name the export "a" and define its characteristic as "input". Similarly, create Off-Page symbols and exports for "b" and "y".

Now is a good time to save your library. Use the Save Library command (in menu File), or just type Ctrl-S. Get into the habit of saving your library regularly. Also, learn the keyboard shortcuts for the commands you use frequently.

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