Cadence Tutorial
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Overview
In this module you will create a schematic for a CMOS inverter.Creating a New Cellview
Each cell will have several views. These include schematic, symbol, layout, extracted, and potentially some others. Each view contains information about a different aspect of the object or its behavior.In the Library Manager window, highlight your newly created library and select File->New->Cellview
A create file dialog box will appear. Enter "inv" in the Cell Name field. Make sure that the View Name reads "schematic" and the Tool drop-down reads "Schematic". Click OK
The Virtuoso Window will open. Virtuoso is the tool that is used for drawing schematics and layouts.
Selecting and Placing Components
In the virtuoso window, select Add->Instance. This will open the component browser. You can also just hit the 'i' key to call the instance command. Select "NCSU-Analog Parts" from the library drop-down. Browse through the available parts to find Pmos4. When you select it, the Add Instance window will open as shown below. The other way to set up gate parameters is to press 'q' when you select the transistor in the Virtuoso window.
The top portion of the window should already be set to point to the Pmos4 cell, since you selected it with the component browser but if you change your mind, you can type in a new component name or browse for a different component.
The pmos4 is an example of a parameterized cell. P-cells have a variety of parameters that can be set when they are instanced and can also be changed later. Right now, the only parameter we will worry about are length and width. These are the phyiscal gate length and gate width of the transistor. These values are constrained by the design rules that the MOSIS sets for each process. By default, they are set to the minimum allowable value right now, so this is the smallest transistor you can fabricate on your chip. We'll leave it that way for now.
Select the virtuoso window and you will see the highlighted outline of a transistor. Click once to place one instance of the pmos4. Now return to the add Instance window, select nmos4 and add one instance of nmos4 as well. The location is not important since we can move them around later. You can move an instance by clicking it to select it and then using the move icon on the left toolbar, or hitting the 'm' key.
Wiring it Up
Position the transistors so that the pmos is above the nmos (remember, the pmos form the pull-up network, and the nmos form the pull-down network.) Now you will add wire to connect the components. Select the wire tool from the left toolbar. Wire the two transistors together to form an inverter. Don't forget to connect the body terminals to the supplies. Your circuit should look something like this:
Adding Pins
Now we need to add pins so we can get signals into and out of our circuit. In the virtuoso window select Create->Pin. The add pin dialog will pop up. Name the pin 'in' and select type inputOutput. Now place the pin on the schematic. Repeat this for the other pins 'out' 'vss' and 'vdd.' Once you have the pins in place, wire them up with the wire tool. You should get something like this: