lab 1: circuit simulation fundamentalsdl.edatop.com/mte/ads/edatop.com_1b_lab.pdf · 2014. 12....

ADS Fundamentals - 2001

LAB 1: Circuit Simulation Fundamentals

Overview - This lab covers user interface basics, ADS files, schematiccapture, simulation, and data display. In addition, tuning and ADSexample files are also covered.

OBJECTIVES

? Create a new project and schematic designs

? Setup and perform S-parameter simulation

? Display simulation data and save files

? Tune circuit parameters during simulation

? Use the Examples files and node names

? Perform a Harmonic Balance simulation

? Write an equation in the data display

Lab 1: Circuit Simulation Fundamentals

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Table of Contents

1. Start ADS on the computer..............................................................3

2. Create a new Project. ........................................................................4

3. Examine the files in your new project directory........................5

4. Create a low-pass filter design. .....................................................5

5. Setup the S-param Simulation.......................................................9

6. Launch the simulation and display the data............................9

7. Save the Data Display Window................................................... 11

8. Tune the filter circuit..................................................................... 12

9. Simulate an RFIC with Harmonic Balance.............................. 16

10. Add a wire label (node name) , simulate, plot data ............. 20


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PROCEDURE

1. Start ADS on the computer.

Typically, on a PC, you can use the Start button to run ADS or ashortcut icon on your desktop. For UNIX users, type the script/command at the therminal prompt (hpads or similar).

Main window: PC version (UNIX is similar)


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2. Create a new Project.

For this step you will use the icons on the Main window. Using icons toexecute commands usually fewer mouse clicks. You can identify what anicon does by placing the cursor on the icon to see what it does: this is calledballoon help.

a. In the Main window, click the icon: View Startup Directory.This will show you in the default starting directory for ADSprojects.

b. Click: File > New Project. When the dialog box appears, youwill see the default working directory. On your own computerit will be C:\users\default but in an ADS classroom it may bedifferent (C:\users\ads) so check with the instructor.

c. Insert the cursor at the end of the line and type the name lab1as shown here

Note on Length Unit - The length unit is a setting for items such asmicrostrip lines and also used for layout. For this lab use thedefault value (mil).

d. Click OK to continue.

Create a NewProject

View StartupDirectory


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3. Examine the files in your new project directory.

a. The Main window File Browser area should now show that youare in the lab1 project directory. Notice that the sub-directories (data, networks, etc.) were created automatically.Also, notice that the schematic icon is now activated (no longergray).

b. In the main window, double click on the networksdirectory. The file browser now shows you are inthat directory which is empty (no schematics exist).

c. To return, double click on the two dots (..) next to the arrowand you will go up one directory.

4. Create a low-pass filter design.

a. In the Main window, click the New SchematicWindow icon (shown here). This is the same asselecting the menu command: Window > New SchematicWindow. Immediately, the Schematic window will appear. Ifyour preferences are set to create an initial schematic, you willhave two schematics now opened – close one of them.

ComponentPalette and scrollbar

Messages, X-Ylocation or cursor,and otherinformation.


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b. Save the schematic. Notice the top window border of theschematic shows the schematic name as untitled1. Click theSave icon (shown here) and the Save As dialog will appear.Type in the name lpf and click Save. This will save it in thenetworks directory of lab1 project.

NOTE on saving designs - After naming the schematic, the Save icon willnot bring up the Save As dialog box. Instead, it will save the nameddesign. To save the design with a different name, use the command: File> Save Design As.

c. Examine the schematic window commands and icons. Click onthe small arrow on the Component Palette list to see the palettechoices. Also, move the Scroll Bar down and up to see how it

works.

d. In the Lumped Components palette, select (click) the capacitorC shown here (not the C model). Then click the rotate icon asneeded to get the correct orientation and then click to insertthe capacitor as shown on the schematic. Next, insert another

ComponentHistory List

Component Palette Listdetermines the itemsavailable on thepalette.

Cursor withcross hairs =command isactive.

NOTE: some boxed items (R, L andC) are models – not components.

Rotate Wire


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capacitor.


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e. Continue creating the low-pass filter as shown byinserting the inductor. Then insert grounds and wire(icons are shown here) the components together. This willgive you practice with schematic capture. You can tryusing the copy, move and other icons or commands.

f. After the filter is built, edit the value of C2 to be 3 pico-farads. To do this, double click the capacitor symbol orselect the capaictor and use the icon (shown here). When thedialog box appears – change the value: C=3.0 pF, clickApply and OK.

g. Next, select the Simulation- S_Param palette and insert the S-parameter simulation controller (gear icon). Use the ESC keyto end the command.

h. Then insert the port terminations: Term Num= 1 and Termnum=2 shown here.

i. Use Component History: After the circuit is built, deletecapacitor C2 and then reinsert it by typing or selecting thecapital letter C in the Component History field and press Enter.Next, edit the value directly on the schematic by highlightingthe value and typing over it with the value (3.0 pF). Verify thatit has changed by looking at the value in the edit dialog box.

NOTE: You caninsertcomponents bytyping in thecomponent label(C, L, R etc)instead of usingthe palette.

Simulation Controller

Term


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5. Setup the S-param Simulation.

a. To setup the simulation, doubleclick on the S-parametersimulation controller on theschematic. When the dialog boxappears, change the Step-size to0.5 GHz and click Apply. Noticehow it updates the value on thescreen. The OK button does thesame thing as Apply and alsodismisses the dialog box – do notclick OK yet.

b. Click the Display tab and youwill see that the Start, Stop andStep values have been checked(by default) to be displayed onthe schematic. Later in thiscourse, you will use the displaytab to check other parametersyou want displayed on theschematic.

c. Click the OK button to dismiss the dialog box. You are nowready to simulate.

6. Launch the simulation and display the data.

a. On the top of the schematic window, click theSimulate icon gear (shown here) to start thesimulation process.

b. Next, look for the Status window to appear and you should seea messages similar to the ones here, describing the results ofthe simulation, the writing of the dataset file, and the creationof a display window. If not, ask the instructor for help.

NOTE: If youscroll up, youwill see moresimulationinformation.


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c. If no simulaton errors occurred, close the Status window. Youcan always get the status window back using the schematicwindow command: Window > Simulation Status (try it).

d. The Data Display window will appear with the name lpf in thetop left corner – this is the same name as your schematic. Also,you are looking at page 1 which is blank at this time. Examinethe picture below - the next steps will show how to display thesimulation data.

e. To create the plot, click on the Rectangular Plot icon and movethe cursor (with outlined box) into the window and click. Whenthe next dialog box appears, select the S(2,1) data and click theAdd button. Then select dB as the format for the data. Click OKin both boxes.

NOTE: An asterisk next to a window name (lpf*) means it is notsaved.

The defaultDATASETname appears

This palette is where youchoose a plot type, listtable, or equation toinsert.

These buttons are usedto zoom or scroll thedata.

*

RectangularPlot


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f. The plot should show a reasonable low pass filter response.

g. Put a marker on the trace: Click the menu command: Marker >New. Select a point on the the trace and click to insert themarker. Select the marker or the marker text and move themarker using the cursor or the keyboard arrow keys. Also,move the marker text by selecting it and positioning it asdesired. Try deleting the marker or putting another marker on

the trace.

7. Save the Data Display Window.

a. Save this data display window: Use the File > Save Ascommand and use the next dialog box to save it with the defaultname lpf. This means that it will be saved as a .dds file (datadisplay server) in the project directory and it will have accessto all data (.ds files or datasets) in the data directory.


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b. Close the data display window by clicking the X in the windowcorner.

c. Reopen the saved data display by clicking the Data Displayicon (shown here) from the Schematic or Main window. Afterthe window opens, click the Open icon folder (shown here).Select lpf.dds in the dialog and click Open. It will reappearwith your S21 plot. Also, notice that the default dataset name(lpf) remains from your previous simulation. KEEP THISWINDOW OPENED for the next steps.

8. Tune the filter circuit.

This step introduces the ADS tuning feature that allows you to tuneparameter values of components and see the simulation results in the datadisplay. In this step, you first select the components and then select thetuning feature. If you select the tuning feature first, you must select thecomponent parameters and not the components.

a. First, position the Data Display and theSchematic windows so you can see them both onthe screen. If necessary, re-size the windows anduse View All.

b. Second, in the lpf schematic, select components C1 and L1using the SHIFT or Ctrl key to select both of them as shown

View All

OPENING A SAVEDDISPLAY WINDOW

Open anexistingdatadisplay

DataDisplay


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here.

c. Now, start the turer by clicking thecommand: Simulate > Tuning or click thetuning icon (shown here).

Immediately, the status (simulation) window will appear along withthe Tune Control dialog box (shown here). Go ahead and tune thefilter using the default settings and watch the updated traces appearin the Data Display.

TuneParameters

Move the slider or click onthe buttons to tune values.Notice how the new tracesappear on the s_data plotafter each change.

Each tuning createsanother trace. The markermoves to the most recentsimulated (tuned) trace,This trace is the s_datadataset which is changedeach time you tune(simulate).

Note on Markers: The marker will stay on themost recent trace when using tune mode.


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d. Change the tuning range: In the Tune Control dialog,click Details and watch the dialog change from brief todetailed. Type in a larger range such as 6 and thentune the filter again. You should be able to see a

greater range of responses.

e. Continue tuning until you are satisfied with the results - clickthe Update button to have the Cand L unit values updated onthe schematic. If you click the Component button you willnotice that it allows you to add other parameters to the tuning.The Brief button returns to the smaller (brief) Tune Controldialog.

f. When you are satisified withthe tuned response, simplyclick the Cancel button andthe plot will contain the finaltuned trace similar to the oneshown here. It is notimportant to achieve anyparticular goal in this labexercise but simply to learnhow to use the Tuner.

Change theranges here.


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g. Save the data display and the schematic using the Saveicon (in both windows) shown here. Then close bothwindows (click the X box in the corner) so that only theADS Main window remains.


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IMPORTANT NOTE: Using ADS Examples

All of the examples shipped with ADS can beexamined in the Examples directory. However, touse them for your design work, you must, copy thefiles into another directory. In general, theexamples directory is read–only and the files mustremain unchanged. The following steps will giveyou some experience leveraging examples for yourown use.

9. Simulate an RFIC with Harmonic Balance.

Go to the ADS Main window and click on the ViewExample Directory icon to see the list of example topicsbut do not go any further, simply look at the choices.

a. In the Main window, click File > CopyDesign.

b. Select the From Design: This is where youget the example design - When the dialogappears, select the Example Directory andBrowse. Then use the dialog boxes, doubleclicking on Rfic > Amplifier_prj > networks > HBtest .dsn.

c. Specify the To Path: Select Working Directory, which should bethe networks directory of the lab_1 project (shown here). Alsocheck the box: Copy Design Hierarchy. Click OK and a copyof the HBtest and its hierarchy (sub-circuits) will copied intoyour lab1_project network.


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d. After the copy is completed, open the schematic window andopen the HBtest.dsn. Shown here is the top-level hierarchy ofthe HBtest.dsn. This is where the Harmonic Balancesimulation is set up. To see the amplifier sub-circuit click onthe amplifier symbol (shown here) and then click the icon: Pushinto Hierarchy.

e. Notice that the sub-circuit has severalbiased devices withthe modeldescription(model card)shown. Click thePop Out ofHierarchy to goback to the top levelwhere thesimulation is set up.


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f. After you return to the upper level,examine the Harmonic Balancecontroller by double clicking on it or byselecting it and clicking the edit icon(shown here).

g. The Harmonic Balance controller hasmany tabs for setting up simulationparameters. The purpose of this step isto get you acquainted with thesimulation controller and not to use allthe settings. Look through the tabs, donot make any changes, and Cancelwhen you are done.

10. Add a wire label (node name), simulate, and plot the data.

a. Click on the Name icon (shownhere). When the dialogappears, type in the name Vinand click on the wire or nodeat the input to the amplifier.Click Close when finished. Theschematic now has a Vin and aVout wire label..

a. Click the Simulate button.When the simulation finishes,the node voltages at Vin and Vout will be availabe in the DataDisplay.

EditComponent

Simulator is set to calculate 960 MHz with 5 harmonics(order). Notice that the RF source (schematic) is also 960MHz.


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b. Plot the spectrum of Vout in dBm – When the data displaywindow opens, select the Rectangular Plot and insert it.Immediately, another dialog will appear where you select Voutand click Add. Next, the dialog will ask you for the format:Spectrum in dBm. Click OK and the plot will appear.

c. Put a marker on the first tone to verify that it is 960 MHz.

d. Insert an equation by selecting theEqn icon and inserting it on thedata display. Immediately,another dialog will appear.


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e. Write the equation in the field with a mistake in spelling thenode name. For example, write a voltage gain equation as:Gain = Vout/Vn. Click Apply and you will see how the error is

recognized.

f. Correct the spelling mistake and click Apply again and OK.The correct equation will appear (shown here).

NOTE on data display equations: If the equation appears red in color,then it is invalid.

g. To list the equation value of Gain, insert alist by selecting the List icon. When thedialog appears, click the arrow and scroll down to theEquations list. When it appears select the Gain equation and

Add it and clickOK.

You should see a list of gainat each of the frequencies.This is the complex value ofvoltage gain for each

Type Vn to see amistake.


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frequency calculated by Harmonic Balance. Note that this circuit really hasmore current gain than voltage gain.


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h. Close all the windows – do not save the files in this lab. You willnot need this lab or any of its files to continue.

EXTRA EXERCISES: do these only if you have additional time. Otherwise,you can do them for practice after completing the course.

1. Go back to the S-parameter simulations for the filter and open the datadisplay page. Try writing an equation for the phase of S21 and then plot

it:

2. Go back to the HBtest simulation and increase the Order in the HarmonicBalance simulator to 7. Simulate again and note what happens. Also,change the value of Freq to 940 and note what happens – you can learnabout simulation errors from this type of exercise.

3. Write another equation for the last simulation as follows:

Gain_fund = Vout[1] / Vin[1]

Determine what the bracked value of [1] is doing in the equation.

4. Copy another example file that is interesting to you and also copy thedata display file for that example. To do this, you can open the file andthen save it using the browsers and going to the example directory in thelocation where ADS is installed.

5. Try using the Tuner on the last simulation for Harmonic Balance.


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