getting started with hfss transient

Getting Started with HFSS TransientBall Grid Array IC Package

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Contents-1

Table of Contents

1. BGA PackageOpening the Model . . . . . . . . . . . . . . . . . . . . . . . 1-2Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3Excitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4Transient Network Analysis Setup . . . . . . . . . . . 1-6Simulate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11Matrix Post Processing . . . . . . . . . . . . . . . . . . . 1-13Fields Post Processing . . . . . . . . . . . . . . . . . . . 1-15Appendix: Setting up a distributed simulation . . 1-19

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Edition Date Software Version

1 Jan 2006 10.02 May 2007 11.03 February 2009 12.04 September 2010 13.0

Getting Started with HFSS: A Dielectric Resonator Antenna Problem

Conventions Used in this GuidePlease take a moment to review how instructions and other useful infor-mation are presented in this guide.

• Procedures are presented as numbered lists. A single bullet indicates that the procedure has only one step.

• Bold type is used for the following:- Keyboard entries that should be typed in their entirety exactly as shown. For example, “copy file1” means to type the word copy, to type a space, and then to type file1.

- On-screen prompts and messages, names of options and text boxes, and menu commands. Menu commands are often separated by car-ats. For example, click HFSS>Excitations>Assign>Wave Port.

- Labeled keys on the computer keyboard. For example, “Press Enter” means to press the key labeled Enter.

• Italic type is used for the following:- Emphasis.- The titles of publications. - Keyboard entries when a name or a variable must be typed in place of the words in italics. For example, “copy file name” means to type the word copy, to type a space, and then to type a file name.

• The plus sign (+) is used between keyboard keys to indicate that you should press the keys at the same time. For example, “Press Shift+F1” means to press the Shift key and the F1 key at the same time.

• Toolbar buttons serve as shortcuts for executing commands. Toolbar buttons are displayed after the command they execute. For example,

“On the Draw menu, click Line ” means that you can click the Draw Line toolbar button to execute the Line command.

Alternate methods or tips are listed in the left margin in blue italic text.

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Getting Started with HFSS: A Dielectric Resonator Antenna Problem

Getting Help

Ansys Technical SupportTo contact Ansys technical support staff in your geographical area, please log on to the Ansys corporate website, https://www1.ansys.com. You can also contact your Ansoft account manager in order to obtain this information.All Ansoft software files are ASCII text and can be sent conveniently by e-mail. When reporting difficulties, it is extremely helpful to include very specific information about what steps were taken or what stages the simulation reached, including software files as applicable. This allows more rapid and effective debugging.

Help MenuTo access online help from the HFSS menu bar, click Help and select from the menu:• Contents - click here to open the contents of the online help.• Seach - click here to open the search function of the online help.• Index - click here to open the index of the online help.

Context-Sensitive HelpTo access online help from the HFSS user interface, do one of the follow-ing:• To open a help topic about a specific HFSS menu command, press

Shift+F1, and then click the command or toolbar icon.• To open a help topic about a specific HFSS dialog box, open the dia-

log box, and then press F1.

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https://www1.ansys.com/customer/

BGA Package

Network analysis can be performed both in the frequency domain and in the time domain. You may choose to per-form the analysis in the time domain in order to visualize the propagation of a short pulse through the device, in addition to obtaining the familiar S-parameters.In this exercise we will analyze a BGA package. We will obtain S-parameters over a broad frequency range and visualize the propagation of a short pulse.This Getting Started Guide assumes you have some famil-iarity with HFSS for frequency-domain analysis, but are new to Transient analysis. Therefore, for certain opera-tions like selecting faces and assigning boundary condi-tions, not every detail will be spelled out.

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Getting Started with HFSS Transient Solver: BGA IC Package

Opening the ModelIn HFSS open the example project Alinks_BGA.hfss, located in the Help folder of the HFSS installation directory (rather than the Examples directory). It is located in the Help folder rather the Examples because it is deliberately incomplete. You will add excitations and a setup, before analyzing and generating reports.Click HFSS>Solution Type verify the type setting as Transient Network Analysis.

GeometryThe geometry corresponds to a part of a BGA-type chip pack-age. It has four signal lines as well as power and ground nets. The model was created by AnsoftLinks from a layout.The geometry is complete – no additions or modifications are needed.

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BoundariesTwo boundary conditions have already been assigned. Select them in the Project tree to see where they are.

ReferencePlanes provides references (“grounds”) to the ports. Since the power and ground nets are also connected to these planes, each signal current has a return path. This is necessary for a meaningful simulation.

RadiationBoundary is a radiation boundary condition around the air volume. The air volume is large enough for an accurate signal-integrity simulation. We will not be determining radi-ated fields.

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Take a few moments to see what other boundary conditions are available in HFSS Transient. Boundaries that are grayed out are sometimes frequency-dependent boundaries (layered impedance, screening impedance) and not straightforward to implement in the time domain.

Excitations1 Select the unassigned sheet objects in the History tree one

by one and assign lumped ports to them.

2 Under “Use as reference”, check the reference plane to

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make the other conductor the terminal.

3 Open the Properties dialog for a port, and look at the Transient tab. Each port shall be “active” (with all ports active they each get an excitation one at a time, and a full S-matrix will be produced)

Tip: If you wish to save simulation time, make only one or a few ports of interest “active”. The passive ports will act as terminations. You will get only a partial S-matrix.

4 Click on the Post Processing tab, and confirm the default

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selection as Do Not Renormalize.

5 For each port, right-click on the Exciation icon in the Proj-ect tree and use “Auto-Assign Terminals”.

Take a few moments to see what other excitations are avail-able in HFSS Transient. Note we are not targeting certain applications: unit cells of periodic structures (phased arrays, FSS) or models with magnetic bias (ferrite circulators, ferrite phase shifters). These applications are better handled in the frequency domain by HFSS.

Transient Network Analysis SetupFirst define a face list where fields are to be saved.1 Switch to Face-Selection mode and select simultaneously

the top surfaces of both the power and the ground plane.

2 Click Modeler>List>Create>Face List

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3 Select FaceList1 in the History tree, and in the Properties window, change the name from Facelist1 to PlotFields.

Then add a solution setup.1 Right-click Analysis>Add Solution Setup

2 On the General tab specify a maximum of six adaptive passes.

HFSS Transient automatically sets parameters for deter-mining the mesh, such as the use of mixed element orders and the iterative solver in the frequency domain. The fre-quency at which the mesh will be adapted will be based automatically on the time profile you select next.

3 Select the Input Signal tab

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4 Specify a Broadband Pulse from DC to 10 GHz and ask for S-parameters every 10 MHz. The result will resemble that of an interpolating frequency

Note You can create a time-domain profile by specifying minimum and maximum frequencies. If you specify zero for the lower bound, the pulse shape changes and will really include frequencies all the way down to DC. Also note that, in addition to the sweep, a TDR pulse can be defined. This pulse is the same as the sweep from DC to a certain maximum frequency, but, for your convenience, it is specified by rise time.Finally, note that you specify one time profile here for all active excitations. In the more general Transient (“non Network Analysis”) design, you can specify different time profiles for different excitations, and run one simulation with all active ones turned on simultaneously. In Transient Network Analysis, all active excitations get the same time profile one by one, and you get one simulation per active excitation. This is the proper way to characterize a network.

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sweep with those specifications.

5 Select the Duration tab.The simulation will run until transient fields have mostly died out, determined by the Target Residual. In addition, a maximum simulated time is determined by 20× (model size) / (speed of light).In this case, we will set an extra limitation on the dura-tion. Considering the length of the traces, in one nanosec-ond the signal can travel from source to termination and back several times. It is therefore reasonable to limit the simulated time toat most 1.25 nsbeing the aforementioned 1 ns plus the duration of the

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input signal.

6 Select the Saved Fields tabCheck the face list PlotFields. Save fields every 4 ps.The latter is somewhat arbitrary. In 4 ps, the signal travels 0.6 mm in dielectric, so this sampling rate should provide a smooth animation for this model.

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7 Click OK.

SimulateThe simulation will take about 400 MB per excitation. If you have all ports active and have the ability to distribute the simulation, please do so. In a distributed simulation with at least eight processors and with enough RAM, each one of eight excitations gets its own process and they will all solve simul-taneously. The Appendix has more detail on how to distribute a simulation.1 Save the project and run the simulation.

HFSS will first perform the frequency-domain adaptive passes.

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After this, it will do the eight transient simulations, one per excitation.

2 While the simulation is running, right-click Results>Create Terminal Solution Data Report>Rectangular Plot

You can keep track of input signals, outputs on the various ports and field residuals as the simulation is progressing. For instance, create a plot like the one shown below:

The Residual is a measure of the maximum field remaining anywhere in the model. It is used as a stopping criterion under the Duration tab: by default, when the peak field has fallen to 0.001 times its maximum, the simulation is consid-ered done. An example of a Residual plot with a logarithmic vertical scale is shown below. Monitoring a plot like this dur-ing the simulation gives an idea of how much longer the simu-lation might take. The progress bar gives complementary information; it is based on the maximum simulated time.

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Residual

The residual doesn’t go down to -60 dB since we stopped the simulation early.

Matrix Post Processing1 In the Report window, in the Context area, change the

Solution from Time to Spectral.

This enables you to plot frequency-domain S-parameters generated by the transient simulation. Even while the sim-ulation is still running, the transient solver will already give you frequency-domain S-parameters based on the transient information it has gathered thus far. The plot will get updated very frequently. This can slow down the overall simulation, since every update requires transfor-

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mations from time domain to frequency domain.

An example of an S-parameter plot during simulation is shown below. The S-parameters plotted here correspond

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to reflection and transmission for a particular signal line.

Fields Post ProcessingTo plot fields, do the following:

1 In the Model tree, select the face list PlotFields.

2 In the Project Manager, right-click Field Overlays>Plot Fields>E_t>Mag E_t

3 Select a time

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Done

An example field plot is shown below. This plot can be ani-

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mated.

You may also want to look at the field plot from below and animate the late-time plane resonances, e.g. an animation from 0.6 ns to 1.25 ns with an adjusted scale for the fields.

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This concludes this Transient-Network Analysis Getting-Started exercise.

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Appendix: Setting up a distributed simulationDistributed simulations require a High Performance Comput-ing (HPC) license. Distributed simulations are set up under Tools>Options>General Options, under the Analysis Options tab. For instance, in the window below the user has access to a computer with eight or more processors called \\large_many_proc_machine. He lists this machine eight times.

Suppose the machine has 16 processors. In that case, the setting shown below is appropriate. It can be defined under Tools>Options>HFSS Options, under the Solver tab.

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In this example, for a non-distributed simulation, the user requests the use of all 16 processors. HFSS Transient scales well with the number of processors. For a distributed sim-ulation, he requests two processors per excitation.

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getting started with hfss transient

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