A Crash Course on Using Agilent Advanced Design System (ADS) By Chris Sanabria, sanabria@ece.ucsb.edu 2/9/02 If you are an engineer and have anything to do with circuit simulation, in particular high frequency circuit simulation, or layout, this is a tool you will probably encounter at some time in your career. Agilent (and before them, Hewlett-Packard) spent years expanding this software that has become a staple in industry. As with any advanced technical program, there is a steep learning curve. Help within the program on a Windows platform can be found at any time by pushing the F1 key, which will bring up all the manuals. Their web site http://contact.tm.agilent.com/tmo/eesof/ is another resource. The manuals for the program are a few thousand pages long. This paper will get a new user up and running quickly. This will be a step-by-step example to get a user familiar with the LineCalc tool, an S-parameter simulation and AC simulation. It is strongly encouraged to explore the many tools and different ways of doing similar commands. Let s get started. Launch the program. If you can t find a shortcut, the executable will probably be in ADS2001\bin\hpads.exe. This will bring up one small window. Fig. 1 The Main Window ADS has its own hierarchy when dealing with any file. You cannot just open a circuit or look at a set of data. Everything is associated with a project file. These files will always end in _prj. For example, in Fig. 1 there is a folder called untitled_prj. Expanding it shows five folders. Everything from circuits, new components, data from instruments, data from simulations, data displays, layouts, etc. will be stored in one of these folders. Create a new project by clicking File New Project. Use the current directory and add the name my_first_project and hit OK. ADS will automatically add the _prj. A quick note about any file name in ADS: never use spaces. The program has its origins in the
UNIX operating system, which is both case sensitive and treats spaces differently than in Windows. Save yourself some future headaches; use underscores instead. Fig. 2 A Schematic Window A new window like Fig. 2 should have appeared (If not, on the main window some of the icons that were grayed out before opening can now be clicked. Click on the icon that is a white background with a capacitor and inductor fore ground.). Fig. 2 is a schematic window where components can be placed and simulations setup. We will create an RC circuit and do an AC simulation. Let s place some components. Notice in the left side of the schematic window there are already some to choose from. Click on the top left one, a resistor (not the boxed resistor, that is a model and we will not deal with it here), and place it on the grid with a left click. Hit the escape key to stop placing the component and to cancel most commands. Now, click a capacitor and place it in the grid, too. For style, we need to change the orientation of the capacitor. Left click the capacitor so that it is highlighted. In Fig. 2, there is an icon that says 90 degrees circled with a black 3 by it. Click this once and the capacitor will be rotated. Connect the two parts with wire, which will be a purple color. In Fig. 2, this is the icon of a wire with two red dots at the end, circles with a green 4. Click this, and left click an end of the resistor to an end of the capacitor. They will now be connected and the red dots at the ends will change to blue ones, meaning a connection has been made (When placing components, if the component being added is placed with its unconnected end on another component s unconnected end, ADS automatically
connects them like a wire. This can be useful when placing components and an annoyance when moving them around). We need a source. The two components we used are in the Lumped-Components library. Click on the pull-down icon which is circled with a red 1 in Fig. 2 and select the Sources-Freq Domain. Click the component V_AC, place it in the circuit, and connect it with a wire (not directly) to the other end of the resistor. To complete the circuit, grounds are needed. In Fig. 2, this is the symbol that looks like a circuit ground and is circled with a blue 2. Add two grounds and connect to the signal and capacitor. Note that you can search all the component libraries by clicking on the books icon near the ground icon. Fig. 3 Finished RC Circuit It will become very useful to label nodes and wires. Click the icon that says NAME and is circled with an orange 5 if Fig. 2. A small window will appear. In the window, type Vin and click on the purple wire connected between the source and resistor. It should now be labeled Vin in purple. Go back to the window and type in Vout and label the wire between the capacitor and resistor. Hit escape to terminate the window and command. The circuit should look almost like Fig. 3. As a side note, if the text of a component is in the way, hit F5, left-click on the component of the text you want to move (not the text itself) and move the text to a better position and left-click again. A simulation must be setup in the circuit if anything else is to be done other than have a pretty circuit picture. ADS can do many simulations including DC, AC, S- parameter, Harmonic Balance, Transient, and much more. We want an AC simulation; pull down the library menu to Simulation-AC and add the icon AC, which looks like a gear, to the circuit. It does not connect to anything, it merely tells ADS what model you are using. Double Fig. 4 - AC Simulation Properties
clicking this or anything in the circuit schematic brings up all the properties. Double click the AC block. We need to adjust the frequency range of interest. Change the range to that of Fig. 4. Save the file. Hit Ctrl + S and save the file as rc_test1. Notice that ADS saves these files in the networks folder under the my_first_project_prj folder. One last thing is to setup where the simulation data will go and where to display it. At the top of the schematic window go to Simulate Simulation Setup Make sure the Dataset and Data Display are both rc_test1. If we needed to have two sets of data, and not overwrite the original, this is where you should change the file name to which the data is saved. This also applies for the display window. We are ready to simulate. Hit the simulate button (or from the schematic window hit F7 or the gear icon in the top right of the schematic window). A blank data display window will now open as in Fig. 5. On the left side are 6 icons that can do rectangular plots, polar plots, Smith Chart plots, multiple plots, tables, and equations respectively. We will want to do a standard plot. Left click the rectangular plot icon, go to the middle of the window and left click (note that you can hold down the left mouse button and draw the size of plot you want. Give it Fig. 5 Data Display Window a try later). Now a series of little windows will popup. Do the following: click Vout and then the >>Add >> button. Another window will pop up telling you that the data is complex and asking how to plot it. Click phase and hit OK. Now hit OK and a plot should appear as in Fig. 6. Notice that at higher frequencies, the phase approaches -90 degrees, as is expected for an RC circuit. Double click the graph and the properties for the graph that were just setup will open. Notice that the same five icons are near the top of this window. Click the dual Fig. 6 Phase and Magnitude of RC Circuit
graphs icon here, select Vout again, click >>Add>>, this time select magnitude, and hit both OK buttons again. Now two plots with phase and magnitude will appear as in Fig. 6. You have now gone through the basics of ADS. Lets go though an S-parameter simulation. Go back to the schematic window, click File New Design and give it the name quarter_wave_example. Notice that there are buttons to open the design in the current window or a new window and that there are design templates. Go ahead and hit OK. Our design will be a simple quarter-wavelength matching network. If the frequency = 5 GHz, Zin = 50 Ω and Zout = 100 Ω, then we will need a transmission line of impedance 73 Ω. Transmission lines can be found in the Tlines-Ideal library. Use the pull-down menu to find it about a quarter of the way down the list. The component needed is the first one in the library, TLIN. Place this in the schematic. Its initial resistance is Z = 50 Ohm, left click the 50 and edit it to 73 Ohm (Again, any component parameter can be edited by double left-clicking the component). It s operating Fig. 7 Quarter-Wavelength Circuit frequency is 1 GHz; change it to 5 GHz. Change libraries to the Simulation-S_Param library. Two of the components will be needed from here. The first is the SP block, which makes ADS aware this will be an S-parameter simulation. In the block, change the step size to.1 GHz. The other is the Term. This is much like the terminals on a network analyzer. Place two of these in the schematic and change the second term to an impedance Z = 100 Ohm. Connect with wires, add grounds to the terms, and the circuit should like the same as in Fig. 7. Save the circuit. We may now simulate, hit F7. A new data display window will open up. Click on the Smith Chart icon and click in the plot area. Again, a window will popup. Select S(1,1), click >>Add>>, and hit OK. A Smith Chart should plot as in Fig. 8. Now click the dual plot icon and add S(1,1) in db and S(2,1) in db. Again, should look the same as Fig. 8.
Fig. 8 Quarter-Wavelength Display ADS has many other tools built into it. A popular one is LineCalc. This tool calculates impedances and dimensions for the much different geometry of wave-guides and microstrip lines. To start the tool, there must already be a schematic open. Use the quarter-wave circuit just built. From the schematic at the top choose Tools LineCalc Start LineCalc. A window such as that below will appear. Fig. 9 LineCalc Window
At the top is the Type of structure to be analyzed. The program defaults to microstrip. Take a look at some of the other available such as COAX and CPW. The ID is the name of the defaults being viewed. This has initial parameter values and an initial Type. You can make your own ID if you wish. For the microstrip the parameters stand for: Er relative permitivity Mur relative permeability H height of the substrate Hu if the design was covered by a metal box, this would be its height T conductor thickness Cond conductivity of the conductor TanD dielectric loss tangent Rough RMS surface roughness of the dielectric W width of conductor L length of line Z0 characteristic impedance of line E_Eff effective electrical length K_Eff effective dielectric permitivity of the system A_DB total attenuation of the system Let s go through an example. Set all but the Physical parameters (W and L) to those as in Fig. 9. Notice there are two arrows. Clicking the arrow pointing up will calculate W and L of the microstrip while clicking the down arrow will calculate Z0 and E_Eff. Push the up arrow. The simulator will run and the W and L will be calculated as in Fig. 9. Let s go the other way. Set W = 50 mil and click the down arrow. Now Z0 = 17.806900 and E_Eff = 98.733400. A wider conductor gives lower impedance as would be expected. This concludes this tutorial. I hope it was helpful. There is so much more to learn about this program but if you sit down and experiment for an hour or two it will be well worth your time. If there are questions or corrections please email sanabria@ece.ucsb.edu.