Introduction to ANSYS HFSS

ELCT 361 Introduction to ANSYS HFSS

Brandon Gore 1st Edition Sam Wang 2nd Edition

Special Thanks Thanks to ANSYS Corporation for donation of HFSS licenses to University of South Carolina classrooms Content from HFSS 14.0 help files: \Ansoft\HFSS14.0\Help\HFSSinto.pdf where is typically C:\Program Files\

Agenda Introduction and Applications Microstrip Start to End Tutorial Extras as backup

What is HFSS? High Frequency Structure Simulator A full wave electromagnetic field simulator for 3D volumetric modeling of passive devices Finite Element Method (FEM) – – – – –

Structure is subdivided into finite elements One element is a tetrahedra (tet) Entire collection of tets called the mesh Electromagnetic fields are found within each tet Maxwell’s equations are satisfied across element boundaries

What is HFSS? (continued) Adaptive meshing: automatically tuned most accurate and efficient mesh possible Model arbitrary shapes Visualize in Windows based GUI – 3D Model – Field Results – S-matrix Results

What is HFSS? (continued)

Possible HFSS Modeling Package Modeling – BGA, QFP, flip-chip PCB Board Modeling – ground planes, vias Silicon/GaAs – spiral inductors, transformers EMC/EMI – coupling, near/far field radiation Antennas/Mobile Communications – patches, dipoles, horns, cell phone antennas Connectors – coax, backplanes, SFP/XFP, vias Waveguides – filters, resonators, couplers Filters – cavity filters, microstrip, dielectric

Signal Integrity Uses Typical server board

Signal Integrity Uses 2-D representation of PCIe link

PCIe Device

CPU DIE Package

CAP CAP

PCIe link between CPU and connector

PCIe Connector

SLOT

Socket

Signal Integrity Uses Red Dash: modeled in 3D simulator

PCIe Device

CPU DIE Package

CAP CAP

PCIe link between CPU and connector

PCIe Connector

SLOT

Socket

HFSS GUI Design tree

3D modeler

Project manager

properties

progress messages

Microstrip Example The purpose of this segment is to use a simple microstrip example as a walkthrough for discussion of basic concepts and terminology such as – boundaries and excitations – model creation (drawing) – analysis setup – data reporting

5 Step for HFSS

Microstrip

Wave ports

Air FR4

Trace

Ground

Microstrip Design Simple stack up – trace – dielectric – ground

These can be made variables to facilitate optimization or quick redraw

1.3 mil 5 mil 1.3 mil

Project Settings Open HFSS and click insert HFSS design icon from the toolbar File save as “Project Examples” Rename design “single microstrip” From menu HFSS > Solution Type > Driven Terminal – – – –

Driven Modal Driven Terminal Eigen mode Transient

Menu: Modeler > Units > mils

Draw Ground Plane Place a 200mil x 200mil x 1.3mil ground Select 3D box from toolbar Click once on the origin, and twice more at arbitrary points in space Right Click (on CreateBox) > Properties Can add as variable instead of static number

Ground Plane Properties Attribute Tab:

Set attributes: Name: ground Material: copper Transparent 0

Viewing and Rotating Mouse + Hot Keys Rotate – Hold ALT Zoom – Hold ALT+SHIFT Pan – Hold SHIFT Fit to screen (no mouse click) – Control + D

Predefined views – Hold ALT, and double click one of 9 regions

Dielectric Draw another box on top the ground plane Set properties To open attributes and properties again… – – – –

Position 0,0,0 X size 200 mil Y size 200 mil Z size 5 mil

Set attributes – Name Sub – Material fr4_eproxy – Transparency 0.5

Click for attributes Click for properties

Signal Trace Draw a 3D box at an arbitrary location What if these Set properties – – – –

were variables?

Position 0, 95, 6.3 (0,($y/2-$w/2),$vss+$die_h) X size 200 or Ground_x Y size 10 or Line_y Z size 1.3

Set attributes – – – –

Name trace_a Material copper Color orange Transparency 01

Draw Ports Select YZ from the drawing plane drop down Draw a 2D rectangle with the following Properties – Position 0, 50, 1.3 – Y size 100 – Z size 50

Attributes – Name port1 – Transparency 0.9

Create another 2D rectangle Properties – Position 200, 50, 1.3 – Y size 100 – Z size 50

Attributes – Name port2 – Transparency 0.9

Possible to make a copy of port1

5 Step for HFSS

Assign Port 1 Right click on port1 from design tree. Assign excitation, wave port To create name, next Select ground as

reference, OK Repeat for port2

Air Box Draw 3D box Properties – – – –

Position 0,0,0 X size 200 Y size 200 Z size 100

Attributes – Name Air BOX – Material air – Transparency 1

Removing Intersections Two 3D geometries cannot overlap or intersect within one another The signal trace is currently intersecting the air box!(In HFSS 14, this is not considered to be intersection) – But how do you know!? Press Validate Design

Use the design tree to select both the Air BOX and wire Right click in the design window and select edit > boolean > subtract or press

Removing Intersections(Not right in HFSS14 for this case) Trace is the tool part. It will tool a hole in AirBOX, the size of wire. To keep trace as part of the design, be sure to check “clone tool objects before subtracting”!(Just learn how to do it but do not Validate again! really do it in HFSS14) Default material override also available

Is the intersection fixed?

Assigning Boundaries Select Airbox from the Design Tree Right Click > Boundaries > Radiation

5 Step for HFSS

Analysis Settings In the project manager, right click Analysis to Add Solution Setup General Tab – Solution Freq 20 GHz – Max number of passes 25 – Maximum Delta S 0.01

Everything else is default

20Ghz

Analysis Sweep Right click setup1 to add Add Sweep Sweep type interpolating Freq Step – Linear Count – 50Mhz to 20Ghz – Step size: 0.01GHz

Analysis Sweep Interpolation Setup

New window in HFSS v14 New setting in HFSS v14

5 Step for HFSS

Solve Validate

– This is ok. The wave port boundary will override the radiation boundary – No such warnings for this case in HFSS 14

Right click setup1 … Solve

Check Convergence HFSS menu > Results > Solution Data Convergence Tab Did solution converge in less than the maximum number of passes, below my delta S target?

S-Parameters can be extracted from here. Make sure to select your sweep

S-Parameters Scattering parameter models are one of HFSS’s output capabilities – R,L,G,C, time delay, and impedance can be extracted from s-parameters – S-parameters can be used as equivalent circuits in simulation – Characteristics of s-parameters can be used to gain intuition about circuit behavior for signal integrity problems

For more on s-parameters, refer to Frequency Domain slides from ELCT 762 & 865

View S11, S21 Create Report by right clicking on results in project manager Report type is Terminal S Parameters on Rectangular Plot Click St(wire_T1,wire_T1) and hold Ctrl and then click St(wire_T2_T1)

Double click

Plot E-Fields Eye Candy Select trace Right click in drawing window. Select plot fields, E, magE. Press Done, notice you are plotting at at 20GHz You can animate

Extra

Frequency Sweeps Discrete: full solution at every freq. Fast: adaptive solver to extrapolate solution from center frequency. Good for high Q-devices; but not for devices that pass through a cut-off. Fields can be displayed at any frequency. Interpolating: solves at discrete points that are fit by interpolating. The field solution is available only at the last solved fequency.

Definitions of Excitation Boundaries Excitation – permits energy to flow into and out of a structure Perfect E/H – perfect electrical or magnetic conductor Radiation –The wave is absorbed, essentially modeling the boundary as an infinitely open space

Definitions of Excitation Boundaries Wave Port – assumed to be a semiinfinitely long waveguide to the solver. Each wave port is individually excited and contains one watt of time-averaged power. It is used to calculate impedance, complex propagation constant, and s-parameters

Solution Types HFSS > solution type Driven Modal – Modal based s-parameters where matrix solutions are expressed in terms of incident and reflected powers of waveguide modes

Driven Terminal – Terminal based s-parameters of multi-conductor transmission line ports that are expressed in terms of voltages and currents

Eigenmode – Calculates the Eigen modes – that is the resonant frequencies and fields of a structure

History Tree Organization by material Expand design tree to undo an operation The last operation on an object must be undone first Select multiple objects that are hard to select in design view, and properties of all selected objects

To Clone, Copy, or Paste You can copy and paste designs in a project – Warning (you will do this): when you copy a design, CLOSE the drawing window. For example, you think you are editing your new design but you are still using the original!

You can copy and paste in the design tree – Now there are two traces, but they are overlap, occupying the same space! You must move it!

An alternative to copy: duplicate (clone)

Clones To clone, select object: edit>duplicate Along Line option allows you to draw a vector on which to duplicate objects The image created here, by selecting a vector of two points and selecting 3 total number when prompted

The vector drawn…

Clones_1

Even though the clone operation has been completed, you edit it in the history tree. For example, edit the vector and increase the amount of space between the original and clone.

A copy is independent of it’s original For a clone, what happens to the original, happens to the clone! Notice the naming convention – John – John1 (copy of john) – John_1 (clone of john)

Miscellaneous Topics When drawing any 2D line or 3D box, you can enter the coordinates manually at the lower right corner of the screen by hitting tab You can control what vertices your mouse snaps to by opening menu Modeler > Snap Mode

Miscellaneous Topics Relative Coordinate Systems – One use is to ‘split’ or remove all objects on one side of an axis

If HFSS crashes, a .lock file is created that prevents you from opening the project. You may need to delete this file. Dembedding under wave port allows you to remove a length transmission line from the model Design List under HFSS menu is useful for operating on all objects with in the design Differential S21: (S(Port2,Port1)-S(Port4,Port1)-S(Port2,Port3)+S(Port4,Port3))/2

Visibility To select a hard-to-reach face of an object, hold the mouse above the desired face and press “b” until that face is selected Don’t forget the View menu has a handy render>wireframe option and a visibility menu to turn objects on and off in the drawing window

Uniting Intersecting Parts Touching conductors should be united to simplify design for solver – Unite trace_top, via1, and trace_top_2 – Repeat for the second trace

The vias are intersecting with all 3 dielectric layers and possibly the air box – Subtract