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Applied Microwave Engineering Laboratory
Procedure #1 ADS Basics
Contained in this procedure:
- Creating a project workspace
- Creating a circuit schematic using lumped components
- Simulating a circuit to determine its S-parameters
- Graphing the simulation results
Agilent ADS (Advanced Design System) Design Type Support
When you first execute Agilent ADS, or anytime thereafter, you have the option of setting the type of design that is supported. The options are Analog/RF, Digital Signal Processing, or both. The option you should choose is Both, with the Default set to Analog/RF.
1. Creating a New Workspace and a Circuit Schematic
- From the Windows START menu, go to Programs/Advanced Design System/Advanced Design System.
- If you do not have an existing “workspace” to work with (you will only need one for the entire semester, as each project can contain multiple circuit designs):
a) Select File/New Workspace
b) Click on the Browse button to find your home directory where you want the workspace to be stored (ask your Teaching Assistant for guidance). Type in your workspace name in the space following the directory reference. You must use alphanumeric characters and underscores (no periods, hyphens, etc.)
c) Select the Length Unit to be millimeters.
d) Click OK.
Note : A workspace is a special directory structure within ADS that is used to organize files associated with a particular design task. Each project workspace consists of several sub-directories that are created automatically to store different types of files. The workspace structure helps keep related design information grouped together.
Click on the Window -> New Schematic menu or simply the ‘New Schematic Window’ button near the middle of the main ADS menu. As long as you work in this project workspace, all of your circuit designs, circuit layouts, and test benches will be stored in various sub-directories of your project.
- If you do have an existing workspace : a) File/Open Workspace
b) Change to the appropriate drive location
c) Double click on your project workspace
d) Single click on your project workspace again and click OK
Click on the Window -> New Schematic menu or simply the ‘New Schematic Window’ button near the middle of the main ADS menu.
- Clicking on the New Schematic button triggers the creation of what ADS refers to as a “cell.” A cell can have different types of representations associated with it, including a schematic and a layout. For now we will be working with the schematic representation. Specify a name for the cell.
Note : In the following steps you will be placing several items into the schematic. Most of these items will have red dots on one or more sides that are ‘connection points’. When placing the items, leave ample space between any two adjacent items such that the red dots from one item do not come into contact with those of another. Eventually, we will use the ‘wire tool’ to manually connect appropriate items together.
- Now let’s layout a low-pass filter that consists of the following: a series inductor, a shunt capacitor and another series inductor. For convenience, you can obtain a menu of common commands by clicking the right mouse button inside the drawing window.
a) On the left side of the schematic window you should observe a collection of lumped elements (resistors, capacitors, inductors, etc.) If this is not the case, click on the pull-down menu near the upper left side of the screen that represents the Component Palette List , and select the Lumped Element list.
b) Now let’s add an inductor to the design. On the left-hand side of the window, the second button down on the far-left represents an inductor. Click on this button, and then drag the mouse onto the schematic area and click to place the inductor. After you place the inductor, you have to ‘end’ this inductor-placement command. You can either right-click and choose End Command, or click on the large white arrow near the top of the schematic window. (Or, you can simply hit the Escape key.)
c) Now double click on the inductor you just placed into the schematic. Click on the ‘L’ parameter at the top of the parameter list and set the value to 79.6 nH. The remaining parameters do not have to be modified for this exercise. Click on OK at the bottom of the pop-up menu.
d) Return to the list of icons on the left-hand side of the schematic window and select the capacitor button (the third button down on the left-hand side of the list). Place the capacitor to the right of the first inductor, end the capacitor-placement command, and then double click on the capacitor and change the ‘C’ parameter to 63.7 pF.
e) In order to make the layout more representative of an actual layout, let’s also rotate the capacitor 90 degrees: go to Edit -> Rotate; click on the capacitor and then use the mouse to turn it appropriately. When finished with the rotation, click the large Arrow button on the top row to turn off the rotation mode. After rotating, you can also click on the capacitor and drag it into a better position. Click anywhere on the screen to de-select the object.
f) Finally, add another inductor to the right of the capacitor. Set the ‘L’ parameter to 79.6 nH. [You can either repeat the previous steps to place the inductor, or click on the Copy Items button that is to the immediate left of the Rotate Items button, and then click on the first inductor and drag the copy into position.]
- The next step is to add a “Termination” to both sides of the circuit. The type of termination that is used varies with the type of simulation that will eventually be performed. In this exercise we will be calculating the S- parameters of the low-pass filter, and for this we connect 50 Ohm terminations on both sides of the circuit. Click on the Component Palette List pull-down menu and select the Simulation-S_Param list. Click on the ‘Term’ button on the left-hand side of the schematic window (third button down on the right-hand side---it looks like a resistor with a box around it). Place a Term on the left-hand side of the first inductor and on the right-hand side of the second inductor. (The term number is automatically incremented from 1 to 2 after you place the first termination.)
- Now we add a “ground” to the lower port of the shunt capacitor and on each termination. The ground button is located near the top of the schematic window, two buttons to the left of the Library. After clicking on the ground button, position the mouse beneath the terminations and capacitor and click once underneath each of them. Remember to turn off the ground-placement function when you are finished (if you didn’t do this, you could continue to click and place grounds all over the schematic window).
At this point, your design should look as follows:
- After analyzing the circuit, click on the New Data Display Window button, which is to the right of the Library (books) icon. This will cause a graphics window to pop up.
- You have several types of plots to choose from. For this exercise, choose the Rectangular Plot, which is represented by the first button below the large white arrow, on the left-hand side of the window. Click on this button and drag the rectangle into the window, and click.
- To generate plots of S11 and S21 versus frequency, click on these entries under the Data Sets and Equations list, and click the Add button in the middle of the window. Select the dB format for each parameter. Now click on OK to generate the graph.
- You have several options for changing the default appearance of the plot. If you double click on an individual trace, you can change things like line thickness and color. If you double click on the graph---but not on an individual trace---you can add traces to the graph, change the limits of the x- and y-axes, etc.
- You can also Print the graph, and/or copy the graph to the Windows clipboard. Your plot (using the default settings) should appear as shown below:
0.0 0.5 1.0 1.5 2.0 2.5 3.
freq, GHz
0
dB(S(2,1))dB(S(1,1))
