Sonnet Intermediate Training

1

Sonnet Intermediate

Training

Daniel Ferguson

Sonnet Software, Inc.

100 Elwood Davis Road

North Syracuse, NY 13212

315-453-3096

http://www.sonnetsoftware.com

2

Sonnet Intermediate Training Outline

Sonnet Method-of-Moments Overview

Sonnet Meshing: Staircase and Conformal

Vias

Sonnet Port Models

De-embedding & Co-calibrated Ports

Adaptive Band Synthesis (ABS)

SMD Components & Terminal Width

Metal Thickness and Current Modeling

Model Substrate Anisotropy and Conductor

Roughness 4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com

2

Do you need Help?

Sonnet Application/Technical Support:

– Phn: (315)453-3096

– Toll-free NA: 877-7SONNET

– Email: [email protected]

Fully Dedicated to 3D planar EM app

support

– FULL Support Staff Retention over 25 years

Include License ID when possible

– Sonnet Task Bar: Admin->License Id

Sonnet “5 Minute Rule”

– We’re serious about that!

© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 3

Students

Have you used Sonnet before?

Technologies represented today?

Sonnet Suite: A Quick Walkthrough of

Helpful Resources


3

METHOD OF MOMENTS

OVERVIEW

How does it work?


6

MoM Algorithm Summary

1. Divide circuit into N

subsections.

2. fill NxN matrix with

couplings between every

possible pair of subsections.

3. Calculate coupling between

each pair of subsections

(matrix fill).

4. Invert matrix (matrix solve)

for current distribution and

S-parameters.

Each rectangle represents a

subsection, one of the N

elements. A subsection may

be as small as one grid cell

but no smaller.

Sonnet’s shielded planar MoM creates a background grid

4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com

4

© 2012 Sonnet Software, Inc www.sonnetsoftware.com 7

Shielded MoM Coupling

Shielded Green’s function is weighted sum of sines and cosines.

Same 4D integration (over source and field subsections) must be done.

This integration is easy: sine goes to cosine and cosine goes to sine. No numerical integration.

Sum of sines and cosines is done by FFT. Very accurate and robust.

Sonnet’s ability to do these integrations without numerical integration

leads to Sonnet’s robustness, dynamic range, and accuracy.

4/19/2012

8

MoM Matrix Element Coupling

Each matrix element

is the coupling from

one subsection to

another.

In other words, the

total voltage over the

area of subsection j

due to current over

the total area of

subsection i. Each yellow rectangle

represents a subsection, which

may be made up of multiple

grid cells.


5

9

MoM 4D Integration

Each matrix element

requires a 4-D

integration:

– Integrate twice over (x,

y) of the source (current

carrying) subsection.

– Integrate twice again

over (x’, y’) of the field

(voltage) subsection.

This matrix 4D integration applies to both unshielded and shielded

planar MoM. Sonnet’s ability to do these integrations without

numerical integration leads to Sonnet’s robustness, dynamic range,

and accuracy.


Shielded vs. Unshielded MoM


MoM – Shielded Domain MoM – Unshielded Domain

Substrates go to infinity

in all directions

6

Shielded MoM

Advantages

Box walls provide perfect

ground reference for port

calibration

– Essential for reliable S-

parameter dynamic range

VERY efficient for processes

with many layers

Naturally accounts for cover

and package walls

Exhibits monotonic error

convergence as mesh is

refined

Disadvantages

Uniform background

sampling grid

– User choice required

– May experience resolution

issues with large grid size

May need to move box walls

away from circuitry to

minimize wall coupling

May experience phantom

package resonances for

unenclosed circuits

– Mitigated by setting open

boundary for top cover


MESHING IN SONNET

Where the magic happens…


7

© 2012 Sonnet Software, Inc www.sonnetsoftware.com 13 4/19/2012

Rooftop Expansion Function

Ix

In MoM, we “assume” a basis function

for current on our mesh

discretizations. The rooftop expansion

function is used for nearly all planar

MoM codes.

The rooftop:

• Varies Linearly in one direction (x)

• Is constant in the cross direction (y)

Individual connected rooftops

Composite Current Solution

(x direction)

Section of discretized

transmission line


Rooftop Covers Two Subsections

Each subsection has part of a two-subsection

rooftop basis function in each direction.

One

subsection

X-direction

basis function

Y-direction

basis function The current on a given subsection is not a

constant across the subsection. The varies or

slopes with the rooftop basis function in each

direction. The x and y components vector add

and the resulting current can point in any

direction.

8

15

Sonnet Speed Memory Slider

The Sonnet speed

memory slider is a

three position

adjustment to the

Sonnet mesh.

Notice how the

middle position

keeps an edge

mesh.


Mesh: Fine/Edge

Mesh: Coarse/Edge

Mesh: Coarse/No Edge


Sonnet Mesh and Accuracy

Typically the biggest source of error in a Sonnet simulation

is the size of the subsections. Sonnet rectangular (AKA

staircase) mesh can be adjusted by the “speed memory

slider”, by the choice of underlying cell size, and by the X-

min, X-max, Y-min, and Y-max adjustments.

93 MB RAM 45 MB RAM 22 MB RAM

Mesh: Fine/Edge Mesh: Coarse/Edge

Mesh: Coarse/No Edge

9

Polygon-Level Mesh Controls

Advanced Controls are

provided on a polygon-

level basis

– Fill Type (Mesh type)

• Staircase (default)

• Diagonal (used for coarse grids)

• Conformal (curved/diagonal

lines)

– Subsection Controls

• XMin/YMin: Sets the minimum

subsection size in the X/Y

direction

• XMax/YMax: Sets the maximum

subsection size in the X/Y

direction

• Keep Edge Mesh on for

Accuracy

© 2012 Sonnet Software, Inc www.sonnetsoftware.com

4/19/2012 17

Select 1 or more metallization polygons,

then select “Modify->Metal Properties…”

or double-click on a selected polygon

Polygon-Level Mesh Controls

Xmin, Ymin are measured in terms of grid cells

– Default is 1,1 with Edge Mesh ON

“Coarse” slider corresponds to Xmin/Ymin of 50

Can be useful in situations where you are forced

to use very small grids; using Xmin or Ymin of 2-5

can save memory without impacting accuracy

Std Subsectioning

XMIN, YMIN=1

Linewidth = 10

cells

Std Subsectioning

YMIN=10

Edge Mesh OFF

Edge Meshing

with YMIN=10


10

Exercise: Filtwall Mesh Slider

From the Sonnet taskbar select

Project -> Browse Examples…


The Sonnet Example

Browser will open The example browser provides a

catalog of pre-computed

examples that you load into the

Project Editor to view, edit,

change or simulate. A great

learning tool!

Exercise: Filtwall Mesh Slider

1. In the Search field, enter

“filtwall” and click the “Search”

button

2. Double-click the

“filtwall” image to

load it into the

Project Editor

3. The project loads for

you…

4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com 20

11


Simulate 3 Filtwall Mesh Settings

1. Simulate the “Filtwall” filter at all

three settings of the speed memory

slider. Save each version to a

different file name.

2. In emgraph use “File” ->

“Add File(s)->Browse…”

to load in all three

versions.

3. Overlay the three plots

to see the differences

4/19/2012


Conformal Meshing

Conformal Mesh

• Curved and diagonal transmission lines can require a large number of rectangular subsections to simulate.

• Conformal meshing is a technique which can dramatically reduce the memory and time required for analysis of a circuit with diagonal or curved polygon edges.

12

23

Conformal Mesh Basis Function

Simplified model

of current

density basis

function for CM Transmission Line

Conductor

KEY: Conformal Mesh “Assumes” that most current

flows on the edges of circuit conductors

Good example

for CM (MMIC) Bad Circuit for

CM (patch ant)

Published: Jan. 2004 IEEE MTT Transactions pp. 257-264


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Conformal Mesh Subsections

5905 subsections / 272 MB

44 sec/freq on dual-core

laptop

Conformal Mesh

(conformal fill)

Rectangular Mesh

(staircase fill)

2162 subsections / 42 MB

11 sec/freq on dual-core laptop

Note that each conformal

section shown represents

multiple subsections.


Cross-over

edges aligned!

13


Conformal Mesh Strings

Traditional Roof-top Expansion

Function used for rectangular

meshing

Current “strings” used in

Conformal Meshing modeling

Conformal Meshing takes planar

MoM modeling from an O(N3)

Operation to an O(N2)

Sonnet is currently researching

Techniques for further reduction

To O(N)

J.C. Rautio, “A Conformal Mesh for Efficient Planar

Electromagnetic Analysis,

IEEE Transactions on Microwave Theory and Techniques,

Vol. 52, No.1, January 2005

4/19/2012


Conformal Mesh Current

• Current distribution at 7 GHz nearly identical right/left.

• Conformal region (left curve) has slightly “crystalline” appearance.

• Critical edge singularity clearly present in both.

• How are S-parameters affected?

14

Conformal Mesh Benchmark

Ang(S11) and

Ang(S22)

almost

identical.

Mag = 1.0.

Eight freq.

ABS analysis.



Where to use Conformal Mesh?

Use conformal mesh for:

Transmission lines with diagonal or curved edges

Transmission lines where line width is small compared to

Don’t use conformal

mesh for:

Patch antennas

Ground strap/fence

areas

Vias or via

connections

Manhattan geometries

Wide ground plane

areas

15


Applying Conformal Mesh

1. Select a curved

transmission line or

lines in your circuit

2. Bring up the Metal

Properties Dialogue

Double-click a

selected polygon

Select

“Modify->Metal

Properties”

Select Conformal for

Fill Type

30 4/19/2012

Mesh Comparison: CM and RM

Both fill types (CM and RM) can be used in the same

problem. XMIN,YMIN are ignored for CM fill.

Rectangular

mesh fill

applied to

Manhattan

(rectangular)

geometries

Conformal mesh fill

applied to curved and

diagonal transmission

lines


16

31

Conformal & Rectangular Mesh

Curved Transmission

Lines

Wilkinson Divider

Circuit

Internal

ports



Merge Internal Boundaries

Sonnet (and other EM simulators) mesh to internal polygon

boundaries. Unintended or unneeded internal polygon

boundaries can cause excessive meshing with no extra

value.

Unintended or

unneeded

internal polygon

boundaries can

cause excessive

meshing with no

extra value.

Before After

17

Helpful Tool: Merge Polygons



Merging Multiple Polygons

Metal Loss: 1=3=4 < 2

• Same Loss: Simple Combine

• Unequal Loss: Cutaway the metal with the higher loss

(lower loss dominates the overlap region)

18


Exercise: Meshing Polygons

1. Open the filtwall.son example, and set

mesh controls to Fine/Edge

Estimate Memory on Filtwall


2. Estimate the Memory using “Estimate” (or “Analysis” ->

“Estimate Memory”),and View Subsections. It should be 11MB

of RAM and 949 subsections (v.13.56, Fine/Edge).

Notice the

larger sub-

sections

here.

19

37

Create Polygon Boundaries 3. Create polygon boundaries by making 3 horizontal cuts

across the whole structure. Exact locations are not that

important.

In xgeom use “Edit” -> “Divide Polygons” to subdivide the

polygons. Save this to a new file name.


Divide

Divide

Divide

4/19/2012 38

Meshing To Boundaries

Meshing to

polygon

boundaries

can increase

your RAM

usage with

no benefit.

Notice the

smaller sub-

sections

here.

In the Subdivided circuit you should see 29MB of RAM and 1818

subsections, >2x more than in the original circuit.


4. Estimate Memory and View Subsections again…

20

Optional Exercise: Conformal

Meshing

Load

“1nH_oct_inductor”

example into the

Project Editor

Save to local file

Analysis->Estimate

Memory

– 14 MB of RAM

– 1:35 on laptop

View Subsections


Conformal Meshing

Shown


Meshing

Select all the metal

polygons in the circuit

(Control-A)

Modify->Metal

Properties…

Change from

Conformal Fill to

Staircase Fill

Save as new file

Analysis->Estimate

Memory… and View

Subsections


21


Meshing

Rectangular Meshing

Requirements:

– 198 MB RAM

– 4:19 to solve on laptop

Results overlay one

another

Conformal Meshing

should be used for

octagonal, circular

inductors


Meshing – Final Thoughts

Use Conformal Meshing for curved, diagonal

transmission lines

Sonnet meshing always observes the

boundaries

Merging polygons can reduce memory

requirements by reducing meshing

boundaries

Keep Edge Meshing on for accuracy

Further refinements can be made on a

polygon-by-polygon basis (XMIN,YMIN)

Meshing controls can be configured through

EDA framework interfaces © 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012

42

22

MODELING VIAS IN SONNET

Getting current between the planar metal levels…


44 4/19/2012

Vias: Vertical Connections

Vias Conduct current from one layer to another.

Multiple stacked vias can connect through many layers.

Vias may conduct current from a layer to ground on either top or bottom of the analysis box. (The Sonnet analysis box is global ground.)


Box bottom forms ground plane

connection

23


Via Posts Make up Vias


Via Subsections Top & Bottom

1 X subsection

X-Y Current

flows on top and

bottom faces of

a via subsection;

may vary in X

and Y

Z (vertical) current

flows through the

via subsection body;

it is constant with

respect to height

(no variation in Z).

Upper metal level

Lower metal level

Background Grid

Cell Points

The top and bottom of a via post are regular Sonnet

subsections. A via post occupies one via subsection.

24

Via Model Limitations

Sonnet vias should not be used to model vertical

resonators with a single via (use multiple stacked

vias) because Sonnet vias assume that current is

invariant in the Z direction.

Vias should be kept under ~1/10 of a wavelength

(well within general practice for most microwave

circuit design).

Vias have constant cross-section as allowed by the

background Sonnet grid. Sonnet does not model

pyramidal or other shapes with a changing cross-

section with height.



Via Elements in Sonnet

Vias can be created

with polygon definitions

(polygon vias)

– Rectangles

– Circles (N-sided)

– Arbitrary outline

Flexibility is provided

for vias of any

(constant) cross-section

Via models provide DC

and RF loss: R, L, & C.

Edge Via

25


Via Arrows and 3D Triangles pointing “down”

indicate the via goes down from

present layer

Triangles pointing “up” indicate

the via goes up from present layer

Both upward and downward vias

indicate that there are stacked

vias; one goes up from present

layer, and another goes down

from present layer

Metallization layer viewed


Creating Vias Two Ways

Vias can be defined

using the “Tools->Add

Via” menu group

The Sonnet Toolbox also

has a Via button group

for quick access to “add

via” mode

26


Creating Rectangular Vias

Ex: Create a square via 25 x 25 mil

Select “Draw Via

Rectangle” button,

and draw out the

rectangular via

outline

Click to start

Click to place

Opposite corner


Creating Circularly Shaped Vias

Ex: Create a circular via with 25 mil diameter

Select “Draw

Circular Via”

button; parameter

screen appears

Click to place the circular via

Cross-hatch shows the actual analysis

discretization that will be used (best

approximation allowed by the

background grid)

(right-click)

27


Arbitrary Via Polygons

Any existing metal

polygon may be

converted to a via

polygon

Select polygon that will form the

outline, then select

“Modify-> Convert to Via Polygon”

New Feature: Via Mesh

Sonnet 12

Sonnet 13

In Sonnet 12, when via polygon is not on

grid:

• Via metal would could be outside

polygon metal

• Via metal did not track with polygon

metal

• Usually uses more subsections

• Could short with nearby metal

The following example shows 3 via polygons directly below identical

planar polygons:

In Sonnet 13, when via polygon is not on grid:

• Via metal is never outside polygon metal

• Via metal always matches polygon metal

• Usually uses less subsections

• No unexpected short circuits

• Note: Analysis results could change from Sonnet 12

© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012

28

Via subsections: example

•The meshing improvement

almost always results in a

reduction in subsections.

•For this particular circuit,

the total number of via

subsections was reduced

by 32%.

•Notice how much

“cleaner” Sonnet 13 is.

Sonnet 12

Sonnet 13


Via Meshing Controls

Via Fill: How a via is meshed and

simulated

– Affects the shape factor, subsectioning

and memory requirements for the via or

via array

– New Via Pad setting enables closing

sheet on top/bottom of via


29

Ring

(Default)

Vertices Center Full

Using either of these choices gives faster, but less accurate results


Double-click a via, you get this:

This section describes when to use

each choice.


30

Via Meshing

©2012 Sonnet Software, Inc. www.sonnetsoftware.com

Ring Mesh

Full Mesh

Vertices Mesh

Center Mesh

Mesh Type Comment

Ring Mesh Default; good for

nearly every case

Full Mesh Solid meshing;

most accurate, but

high memory

Vertices Mesh Faster than Ring

and Full;

reasonably

accurate for small

vias

Center Mesh For speed;

approximate – Use

with care!

!

Via pads

on

off

2D view 3D view • Via pads are off by default

• “on” is useful if the via is being used to model the top or

bottom plate of a thick metal capacitor, and there is no

separate polygon representing the top/bottom plates


31

Metal Types: Planar or Via

Planar and via

metal types are

indicated in the

list as separate

entities

Two separate

buttons:

•Add Planar:

brings up

window you are

familiar with

•Add Via: Brings

up new window

(See next slide)


New Via Metal Types

•These are the

three types of

via metal

types

•Volume is the

most intuitive

for most users

• Surface and

Array are most

commonly

found in

silicon IC

processing


32

New Via Metal Types (Loss)

Volume – Enter conductivity and either a wall thickness or

model as a solid via

Surface – Enter Rdc (in ohms/sq), Rrf, and Xdc. Similar to

planar model using the same input variables.

Array – Enter conductivity and fill factor based on cross-

sectional area

– This is what you get if you use via simplification

– Calculated from combining array of micro-vias

– Uses “Fill Factor” for micro-via array density

Note: Via metal types are used for Via Polygons. Edge Vias

use a planar metal type because they inherit the properties

of the polygon to which they are attached.


Common Via Scenarios

Hollow Via:

Solid Via:

The

“Volume”

model can

be used to

model both

hollow and

solid vias.


33

Volume model


Opening Old Project Files

If you open an

old project file,

you will get this

message. Sonnet

creates new via

metal types for

you


34

Via Loss vs Via Mesh

Some users may mix up via loss with via meshing

For example, if you have a solid via: – Loss: You should use the Volume metal type

and choose “Solid”.

– Mesh: You can chose any of the mesh settings: Ring, Vertices, Center, or Full, depending on the level of accuracy you need

– Thus, most IC users would use “Solid” loss and “Ring” mesh


Via modeling error is usually related to cell size and quality of fit of via shape to the background grid.

At coarse grids, discretization error will generally over-estimate via inductance.

Refining the grid will result in inductance convergence of vias.

When testing convergence of via inductance in any EM tool, (as long as port calibration is accurate) the lowest inductance will be closest to correct.


Error Convergence of Vias

35


Via Inductance Convergence

2 layers of Alumina

er = 9.9, 25 mil thick

each

100 mil of air

with top cover

We will test the inductance of

this 2-layer via (microstrip to

embedded microstrip

transition)

Grid sizes of 5 x 5, 2.5 x 2.5

and 1 x 1 mil will be used

Port and connecting

line de-embedded

from results (both

sides)


Exercise: Via Mesh

Build the via structure and simulate from one to 10 GHz

with cell sizes of 5 mils, 2.5 mils, and 1 mil.

The default box size of 160 mils square works fine. Shift

the reference planes from both sides to isolate the via.

Draw the inner polygon 25 mils square and then use

“Modify” - > “Convert to Via Polygon” to create the via.

View of bottom

layer in Project

Editor Class Lab file:

via_layer-to-layer.son

36


Convergence Testing for Via

5 x 5 mil grid

2.5 x 2.5 mil grid

1 x 1 mil grid

0.2 x 0.2 mil grid

A 0.2 x 0.2 mil case is

added to show final

converged value – we’ll call

this the “correct” value

• Lowest inductance seen in finest mesh

• Monotonic error convergence is exhibited with mesh

refinement (typical of shielded MoM analysis

• Most coarse mesh is within 2% of converged value

4/19/2012


Via Example

Single Circular Via Double Circular Via Slot Via

Materials and Data:

25-mil Rogers TMM10 (er = 9.2, tand = 0.0022)

120 mil air above with top cover

160 mil x 160 mil box (with symmetry)

Cell size: 2.5 x 2.5 mil

Freq. range: 1-15 GHz

Questions:

1. What is the inductance of the

single 15 mil circular via with

pad?

2. Does a double via cut the

effective inductance in half?

3. Does a slot via further reduce

the effective inductance?

37


How To

First, create a blank template file, with substrate, cell size, symmetry, and a 25 x 50 mil feed line with port and reference plane

Use the Create Via palette item on the Tool Box

Display Inductance vs. Freq. directly in the Sonnet Data Viewer; (Equation->Add Equation Curve…)

Display L vs. Freq. data for all three vias on the same curve (File->Add File…)


Results

Circular Via

Double Via

Slot Via

38


Current Density Results – 10 GHz

View 3D Current

Density at 10 GHz

and select time

animation

Observation:

Most current

flows down near

side of vias (with

respect to the

connecting line


Via Example Conclusions

The double-via example did not reduce inductance by

50%; the reduction is about 30% (data at 10 GHz)

The slot via reduces the effective inductance by

another 6% over the double via

Inductance is most directly affected by the distance

that the currents travel from the edges of the

connecting line down the edges of the via barrel(s)

Most of the current travels down the near side of the

via barrel; back side of each via is nearly cold (current

seeks the shortest path possible to ground

39

Simplify Vias

• Silicon RFIC

processes often use

a very high number

of micro-vias

• This can lead to very

high memory

requirements in the

Sonnet solver.

3D View

2D View


Dense Arrays of Finite Vias lead to inefficient meshing


40

Via Simplification

• Automatically combine micro via

arrays into super-via regions that

mesh and simulate efficiently

• Preserve electrical performance

of micro via arrays (assumes each

micro via is solid)

• Often called “via defeaturing”

• This feature is part of translation

from 3rd party software into

sonnet (includes Cadence and

GDSII files)


Example 1

Combine these

vias into a single

via

Interconnects on a differential spiral balun

implemented in a silicon RFIC process:


41

Example 2

Combine these

vias into a single

via (for example)

Micro via array used in a silicon RFIC process for multi-layer metal

stacking. Dotted lines show the metal track widths above and below

the via layer


Via Simplification

GDSII import example:

For more information:

- Click Help Button

- See “Via Array Simplification” chapter of Sonnet Translators Manual


42

Original circuit with thick metal,

staircase mesh for metal and ring

mesh for vias and many micro

vias

Simplified circuit with thick

metal, conformal mesh for metal

and center mesh for vias and

single polygons in place of micro

vias


Baseline: 2.46 GB

Conformal: 1.55 GB

Conf+Simp Vias: 1.08 GB


43

Vias in RFIC Processes

Use Array Vias (Via Simplification) for

micro via arrays

Vertices or even Center Meshing can

be used for Array Via entities to

speed EM sim with minor error

(stacked thick metal interconnects)

Keep mind that via loss and via

meshing are separate settings


PORTS FOR EM ANALYSIS

Nodal connections for EM models…


44


Ports in EM Sim Swanson Book

“Many problems that we would like to solve using numerical methods have

ports. Ports allow us to excite a circuit or antenna and measure the results.

Depending on the type of circuit analyzed, we may need several types of

ports. Typical port types are single ended, differential, waveguide,

microstrip, and CPW. To be really useful, ports must be calibrated. Field-

solvers have numerical port discontinuities just like network analyzers and

test fixtures have physical port discontinuities. The easier type of port to

implement is on the boundary of the problem space. Most solvers also allow

access to ports that are internal to the problem geometry. Internal ports are

generally more difficult to implement and calibrate”

- Daniel G. Swanson, Jr. and Wolfgang J.R. Hoefer “Microwave Circuit

Modeling Using Electromagnetic Field Simulation” copyright 2003 Artech

House, ISBN 1-58053-308-6, pp. 173.

Port types, port numbering, and adding and removing ports are covered in

the Sonnet User’s Guide chapter 5. De-embedding is covered in chapter 6.


Sonnet Ports Introduction

“Ports allow us to excite a circuit or

antenna and measure the results.” Daniel G. Swanson, Jr. and Wolfgang J.R. Hoefer “Microwave Circuit

Modeling Using Electromagnetic Field Simulation” copyright 2003

Artech House, ISBN 1-58053-308-6, pp. 173.

Port types, port numbering, and adding and

removing ports are covered in the Sonnet User’s

Guide.

Adding ports to a Sonnet circuit structure is one

of the standard setup steps in the Sonnet Quick

Start Guide.

45


Basic Definitions

Standard Box Wall Ports

Standard Internal Ports

Via Ports

Auto-Grounded (AGI) Ports (obsolete)

Co-Calibrated (CC) PortsTM

– Sonnet Components (CC Port group)

1 + -

• Each Port has Two Terminals

• Port type is determined by where the terminals are connected


The Port Model

The port model is shown above

The model is an ideal generator with a user-selectable internal impedance; we choose R=50 and leave all other elements at zero by convention

This model affects S-parameters only; Y- and Z-parameters are termination independent

Sonnet Netlist Projects or network simulators can provide more general normalizations and/or terminations if desired

V

R + jX L

C

+

-

+

-

46


Standard Box-wall Port

Box wall provides

perfect ground reference

1 + -

PEC Top

PEC Bottom


Ungrounded Internal Ports

- +

• Differential port

• No common ground

• Port can be de-embedded, but remember that

reference is the metal on the (-) terminal

• Use with care

1

47


Special Port Numbering

Ports are numbered by default as they are created in the Sonnet Project Editor

Port numbers may be easily changed

The polarity of the port may be changed by using a negative port number

Ports with identical port numbers are electrically connected (common mode, even mode)

Ports with opposite signs represent differential mode (or odd mode)


Even Mode Ports

+

-

Common-mode Excitation

48


Odd Mode Ports

+ -

Odd-mode (Differential) Excitation

CPW Ports – 2 ways


Case 1: Conductor-backed CPW

Backside metal and box walls are part of the

return current path

Case 2: Conductor-backed CPW

Backside metal and box walls are NOT part of

the return current path—they are just “some

equipotential metal surface

~

Bo

x

Wall

+

-

- ~

Bo

x

Wall

+

-

-

49


Arbitrary Port Assignment

Combine multiple ports for phase balance analysis

Multiple gate

fingers fed

“common mode”

for each separate

active device

Sonnet Via Ports Sonnet allows ports to be placed in conjunction with a via in an EM structure.

These are called via ports. Via ports cannot be de-embedded.

The port number will only appear

on the bottom layer.

Sonnet via ports are used for several reasons:

1) When you wish to attach a port between two different levels in your circuit.

2) When you wish to connect a port to the interior of a polygon (which is not

allowed for co-calibrated ports).

3) When you want a vertical port (for example, a probe-fed patch antenna).

bottom

layer

top

layer

50


Auto-Ground Port Clearance

An auto-ground port in

Sonnet’s xgeom project

editor.

An auto-ground port in

Sonnet has extension to

ground like a via port.

Sonnet is able to completely

and accurately de-embed

the effects of this extension

to ground. On an auto-ground port in Sonnet, this

extension does NOT appear in the 3D

view.

Auto-ground ports in Sonnet pre-date co-calibrated ports. AG ports

are still available, but use co-calibrated ports instead, even for

single ports.


Auto-Ground Port Coupling

Sonnet can completely de-embed the effects of each auto-grounded

port extension to ground.

Sonnet is NOT able to de-embed the effects of coupling

between two nearby auto-grounded ports.

51


Co-calibrated Internal Ports

Multiple Perfectly

Calibrated Internal Ports

make it possible to

simulate everything but

the transistor, capturing

all passive circuit cross-

coupling and other

physical effects


Co-calibrated™ Internal Ports

All ports introduce discontinuities

De-embedding removes port discontinuities from our simulation models (and measurements!)

Internal ports have traditionally been difficult to de-embed with high dynamic range

New Co-Calibrated Internal Port technology introduces >100 dB of dynamic range for internal ports—an industry first

Multiple Co-Calibrated Ports may be placed very close together and port cross-coupling is removed

Theory is fully published

Co-Cal Internal Ports for

Transistor or other

component Connections

52


Co-calibrated Ports De-embed

Sonnet can completely and accurately de-embed the coupling

between two nearby co-calibrated ports!

Sonnet can accurately simulate the coupling between two metal traces

on both sides of an embedded component by using co-calibrated ports

for the component!


Co-Calibrated Port Groups

Sonnet can accurately de-embed the coupling among a group of

ports situated on a rectangle.

1 A

Group label

53


Nearby CC Port Groups

Sonnet cannot de-

embed the coupling

among different co-

calibrated port de-

embedding groups

close to one another.

Group A

Group B

Port Grouping - Example


In this case, failure to group the closely-spaced ports

resulted in an apparently lower inductance…this is due

to coupling between the two ports that is not removed

during the co-calibration process.

54


Internal Ports De-embedding

Like box wall ports, Sonnet co-calibrated internal ports can shift

a reference plane.

Like box wall ports, Sonnet co-calibrated internal ports are fully

calibrated to remove port discontinuity!

– Only Sonnet brings you perfectly calibrated internal ports


CC Ports – Considerations At runtime, the software builds a via to

the bottom of the Sonnet box for ground access

Requires unobstructed downward (or upward) access in your circuit (under/over the port) for via access to bottom/top of analysis box

Via and coupling to the connected transmission line are de-embedded; reference plane on top layer

Warning: Via may cross-couple to non-adjacent metal in the primary structure

Multiple Co-calibrated™ ports that are closely spaced may exhibit coupling that can be de-embedded.

The model actually simulated in

the software includes a via

accessing ground for the port; this

via is calibrated out

55

Sonnet Components

Sonnet Components

provide automatically

grouped CC Ports with

user-selectable ground

definitions

They can be used to

insert SMD parts or

active device models

Sonnet Components will

be covered in detail

later in this

presentation


DE-EMBEDDING EM PORTS

Getting port discontinuities OUT of your EM DUT…


56


De-embedding Definitions

“Just like physical coaxial connectors, electromagnetic sources also

introduce a discontinuity into the result. The discontinuities are due to the

evanescent, reactive, fringing fields surrounding the source. The

contribution to the calculated input impedance must be removed if

accurate results are to be obtained. In many cases the reference plane

must also be shifted from the source to the device under test (DUT). The

process of doing this is called de-embedding.”

J. C. Rautio, “A De-Embedding Algorithm for Electromagnetics,” International Journal of Microwave & Millimeter-

Wave Computer-Aided Engineering, Vol.1, No. 3, July 1991, pp. 282-287.

“Sometimes when we measure an active or passive device in a fixture, we

would like to remove the effects of the fixture; this process is called de-

embedding.”

Daniel G. Swanson, Jr. and Wolfgang J.R. Hoefer “Microwave Circuit Modeling Using Electromagnetic Field

Simulation” copyright 2003 Artech House, ISBN 1-58053-308-6, pp. 173.


De-embedding Designs in Sonnet

Sonnet de-embedding includes:

Port

Metal

Box

Walls

Sonnet

Design

(DUT) Transmission Line

Port

Transmission

Line

Calculate port discontinuities

Remove the effects of the port discontinuities from the analysis results

Shift reference planes (removes effects of transmission lines from analysis results) if reference planes are defined

Calculate transmission line parameters (Zo and eeff)

57


De-embedding Ports in Sonnet

Box Wall

R

C

Device Under Test

S-parameters

from em

without de-

embedding

Box-wall port

discontinuity

Shunt Cap for Port

discontinuity; R used

if the line has loss

- The Port Discontinuity -


De-embedding Ports in Sonnet

2

1

N

.

.

.

Ports

Box Wall

N-coupledtransmission lines

- Coupled Transmission Lines -

58


Multiple Coupled Lines

Zero-Length Coupled Standard

– Use any planar transmission

line(s)

Perfect Calibration:

|S11|=|S31|=|S41|= 0 (-inf dB)

Anything other is ERROR

Checks both the software cal

noise floor and the ability to de-

embed cross-coupling of feed

lines

Test: How good is the calibration in your software?


Zero-Length Coupled Line

Sonnet Results

A well-known

competitor’s

results

59


Co-Calibrated Internal Ports

De-embedding error in |S11| and cross-terms for each line lower than < -200 dB

2 4 6 8 10 12 14 16 180 20

-270

-240

-210

-180

-150

-120

-90

-60

-30

-300

0

freq, GHz

dB

(S(1

,1))

dB

(S(3

,1))

dB

(S(4

,1))

2 4 6 8 10 12 14 16 180 20

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

-1.0

1.0

freq, GHz

phase(S

(2,1

))phase(S

(4,3

))

Co-Calibrated Internal Ports

Feed lines de-embedded from result


Invoking De-embedding

De-embedding is usually required, and is on by default in the solver

Adding reference planes to a circuit in the Project Editor is not required; reference plane is the substrate edge unless defined

Using a Calibration Reference Plane setting can provide time savings for analysis of the de-embedding standards

– Assumes reference plane at substrate edge

– Microstrip: Use ~4-5x substrate thicknesses

– CPW: Use ~4-5x center conductor width

60


De-embedding Ports in em

W

em uses the cross-

section at the box wall

to compute Zo and eeff

W

- Transmission Line Parameters -


Non-physical De-embedding

Discontinuity

begins here

L1

W1

Don’t shift a reference plane past a discontinuity. Sonnet just

removes a uniform transmission line to shift the reference plane.

61


Two Discontinuities

W2

W1

L1

W1

In this case the reference plane shifted from the left side sees two

different discontinuities. The reference plane on the right is OK.


Reference Plane No Removal

Shifting a reference plane in Sonnet is not the same as

removing the metal from the simulation.

Shifting a reference plane in Sonnet subtracts a uniform transmission

line, not the metal itself. Be careful not to think of shifting a

reference plane as somehow completely removing all effects of the

metal.

An EM Structure in Sonnet with

reference plane shifted all the

way through the feed line.

The same EM Structure

in Sonnet with no feed

line at all.

1 2 1 2

62


Ref Plane Transmission Line

A shifted reference plane in Sonnet subtracts a uniform transmission

line at circuit level after the simulation of the entire metal geometry.

A uniform

transmission

line

A Sonnet structure

simulation with a

shifted reference

plane

The entire

Sonnet

structure

simulation


Fringing Not Removed A shifted reference plane does not remove the fringing from the de-

embedded metal because it subtracts a uniform transmission line at

circuit level after the simulation of the entire metal geometry.

A Sonnet structure

simulation with a

shifted reference

plane

The Sonnet

structure with

fringing to de-

embedded

metal

63


Reference Plane Unequal Widths

Because....

Two same-

sized metal

blocks with

different

width feed

lines de-

embedded by

a shifted

reference

plane are not

equal

because the

fringing is

different in

each case.


Step Discontinuity Model The notion of the identifying or even isolating the step discontinuity

effects also appears commonly in RF & microwave circuit simulation,

using a closed form model for discontinuity effects.

A uniform

trans-

mission line

A Sonnet structure

EM simulation

automatically

includes the fringing

and discontinuity

effects.

A closed for

circuit model

(without

fringing )

A model of

just the

discontin-

uity effects

e.g.

“MSTEP”

64


SOC Technique

Cal 1: short port 3

Cal 2: open port 3

• The dimensions of the polygon(s) associated with the port are

duplicated in the calibration standard

• SOC requires an open and short calibration standard.

• To accomplish this in Sonnet, an internal port is placed in the center

• A single EM simulation is performed to obtain both open and short

calibrations.


SOC Technique

Arbitrary Angle

Through lines

Some Math

Single EM simulation

CAL Standard #1 CAL Standard #2

Short-Circuit Port 3 Open-Circuit Port 3

Port Discontinuity

R

C

65


SOC special case

For orthogonal box wall ports, two “half” standards are analyzed:

• One using a magnetic wall, and

• One using an electric wall

• This is more efficient than analyzing a single double-length

standard (analysis time increases with cube of the size of the

circuit).


1.Take the cross-section of what

touches the box wall

2.Extend as thru line

3.Cal #1: electric wall (short)

4.Cal #2: magnetic wall (open)

Cal Standard Example

Original

Circuit

Cal . #1

E-Wall

(Short)

Cal #2:

H-wall

(Open)

66


Cal Standard Examples

For cases showing a

reference plane, em

first analyzes the

structure without the

reference planes,

then simulates

additional standards

(not shown) to

remove the port

discontinuity and

shift the reference

plane, just as it

would if this were

your primary

structure.


De-embedding of Coupled Lines

All coupling between lines is considered

All coupling between lines and sidewalls is considered

All coupled lines must be either horizontal or vertical

The width of each coupled line must be constant

The spacing between coupled lines must be constant

Zo and eeff are not printed because of multiple modes which exist

67


De-embedding Codes

De-embedded 50 Ohm S-Params. Mag/Ang. Touchstone Format (S11 S21 S12 S22):

10.0000000 0.014095 -89.19 0.999901 0.8037 0.999901 0.8037 0.014095 -89.20

P1 F=10.000 Eeff=(undefined: sl) Z0=( undefined: sl ) R=0.00000 C=0.004252

P2 F=10.000 Eeff=(undefined: sl) Z0=( undefined: sl ) R=0.00000 C=0.004252

Code De-embedded

S-parameters

Description

nd

mp

sl

nl

mv

bd

N/A

Valid

Caution

Valid

Valid

Caution

Port was not de-embedded. No data is available.

Multiple ports on the same box wall.

Length of first de-embedding standard is too short

Length of first standard is multiple of half wavelength

Multiple values of Eeff or Zo for a single port number.

Bad Eeff or Zo data due to unknown reason.

Note that your de-embedded results are valid for most of the above cases


Avoid Short Reference Planes

All types of ports should be kept away from other discontinuities

The port above is too close to the step discontinuity

Reference plane limitation is for boxwall ports only

The calibration standards may be too short (de-embedding code “sl”)

Remember: Reference planes are not a requirement for de-embedding

DUT 1

1

Box Wall Electric or Magnetic Wall

Fringing fields from DUT

interact with fringing fields

from the port. Calibration standards are

too short. Port interacts

Electric and Magnetic Walls.

68


De-embedding Ports in em

Transmission line properties close to error frequency will also be in error

The port discontinuity (R,C) is consistent for all frequencies shown

S-parameters are all valid

Zo

FREQ

Region of de-embedding code

P1 F=10.000 Eeff=(8.0281 0.0000) Z0=(15.70388 0.000000) R=0.00000 C=0.062621 P1 F=10.100 Eeff=(8.0296 0.0000) Z0=(15.70205 0.000000) R=0.00000 C=0.062572 P1 F=10.200 Eeff=(8.0311 0.0000) Z0=(15.70019 0.000000) R=0.00000 C=0.062519 P1 F=10.300 Eeff=(8.0326 0.0000) Z0=(15.69827 0.000000) R=0.00000 C=0.062469 . . . P1 F=33.400 Eeff=(8.4504 0.0000) Z0=(20.33748 0.000000) R=0.00000 C=0.053547 P1 F=33.500 Eeff=(8.4543 0.0000) Z0=(22.23237 0.000000) R=0.00000 C=0.053562 P1 F=33.600 Eeff=(8.4606 0.0000) Z0=(26.61252 0.000000) R=0.00000 C=0.053577 P1 F=33.700 Eeff=(undefined: nl) Z0=( undefined: nl ) R=0.00000 C=0.053594 P1 F=33.800 Eeff=(undefined: nl) Z0=( undefined: nl ) R=0.00000 C=0.053611 P1 F=33.900 Eeff=(undefined: nl) Z0=( undefined: nl ) R=0.00000 C=0.053631 P1 F=34.000 Eeff=(undefined: nl) Z0=( undefined: nl ) R=0.00000 C=0.053652 P1 F=34.100 Eeff=(8.4336 0.0000) Z0=(9.168726 0.000000) R=0.00000 C=0.053663 P1 F=34.200 Eeff=(8.4395 0.0000) Z0=(10.75418 0.000000) R=0.00000 C=0.053684

- De-embedding Code “nl” -

ADAPTIVE BAND SYNTHESIS

(ABS)

Getting more data out of less simulation…


69

4/19/2012 138 © 2012 Sonnet Software, Inc www.sonnetsoftware.com

From the Sonnet taskbar select

Project -> Browse Examples…

The Sonnet Example

Browser will open

The example browser provides a catalog

of pre-computed examples that you load

into the Project Editor to view, edit,

change or simulate. A great learning

tool!

Loading the hairpin example


1. In the Search field, enter “filtwall”

and click the “Search” button

2. Double-click the

“filtwall” image to load

it into the Project Editor

3. The project loads for you…

70

Hairpin ABS Settings

ABS

3.95 – 4.2 GHz


ABS Interpolated Points

Sonnet’s Adapative Band

Synthesis (ABS)

interpolates data points

from only 4 simulated

data points (indicated by

circles on graph). To test

the validity of these

interpolated points, we

can run a separate linear

frequency sweep (all

simulated points – no

interpolated points).


71

Linear Sweep Settings

Save the hairpin filter

locally (hairpin.son) and

also save it again to a new

name like

hairpin_lin.son.

Change the ABS to “Linear

Frequency Sweep”, the

Start frequency to 4.0

GHz and the Stop

frequency to 4.15 GHz

with a Step of 0.005 GHz.

Also select Analysis -> Clean Data and

analyze (Project->Analyze).


Linear and ABS Together

If you don’t

select

Circuit -> Clean

Data

you’ll get the

new linear

sweep points

included in the

previous ABS

results.


72

Linear Sweep Points

The linear

sweep points

for |S11|


Overlay Linear and ABS

The overlay doesn’t “look perfect”.

But we’re interested in linear

points vs. the ABS curve. The

line between the linear points

doesn’t matter.


73

Turn Off the Connecting Lines

Turn off the connecting lines on the linear

sweep curve (hairpin_lin S11) by right-

clicking on the linear signal and choosing

“Properties”.

Then toggle the Line Style until you

get “None”.


Linear Points on ABS

Now we can

see how well

the ABS sweep

matches linear

sweep points…

…quite well!


74

ABS Example


Measured Data for Filter Filter Simulation based on Sonnet ABS

simulation using only 5 EM data

simulation points ABS provides incredible simulation

time savings with full accuracy

15 Pole Microstrip Bandpass Filter

ABS Advanced Settings

Ultra-efficient interpolation method

Interpolates in the Moment Matrix

domain, not the S-domain

If package modes or other

resonances exist, ABS will find them

– Extra simulation points may be used

For loss-sensitive applications, turn

on “Q Factor Accuracy” under

Advanced Analysis Setup menu

The number of interpolation

samples taken by ABS can also be

changed under Advanced Setup

menu (default is ~300)


Analysis->Setup…

“Advanced” button

75

SONNET COMPONENTS

Including SMDs and linear active devices in EM



Sonnet Components

Sonnet EM analysis can

include surface mount

devices—either ideal or

with vendor-supplied S-

parameter models in

Sonnet Components

Components may be left

as “Ports only” so that

SMD models may be

attached in another RF

circuit simulator

4-Port Amplifier model

embedded in EM

simulation (linear)

2-Port surface mount

resistors, capacitors,

inductors embedded

in EM simulation

4/19/2012

76


Adding a Sonnet Component

Ideal Components are

Available in all Sonnet

Suites; Sonnet Lite and

LitePlus allow up to 3 ideal

components; all other

Sonnet Suites allow

unlimited Ideal Components

Ideal Component

Data File Component

“Ports Only” Component

Data File Components are available in

Sonnet Level3 Gold and Sonnet Professional

“Ports Only” Components

are available only in Sonnet

Professional


Creating an Ideal SMD

Ideal Components are 2-terminal devices (R, L, C)

The connection width can be the entire line width, one cell (Sonnet grid), or a user-defined width

This should be sized for the SMD terminal contact width, if known

Physical size of the package may be specified, but is only important for visualization

77


An SMD with a Vendor Model

Data File Components may have any number of terminals

SMDs may be transistors or any other linear device with an S-parameter data model for the frequency band of interest

Ground Node Connection—depends on the way the vendor measured or extracted the part model


Data File Ground Options

Assumed grounding for ports may be floating (local), global (analysis box) or a reference polygon connection

The ground type you select depends on how the device was measured or modeled; see your vendor datasheets for information on calibration or measurements references

Sonnet Co-Calibrated Internal Ports are used; ports are simultaneously de-embedded to remove cross-coupling between the ports

78

Sonnet Box Ground

Preferred when you know that your

model has parasitic coupling to ground

(e.g., surface mount part model includes

capacitance to ground plane)

– Using a Floating Ground would leave those

parasitics unconnected—leads to modeling

errors!

Best to use for single-layer boards where

measurement ground and EM model

ground are at the same location

Probably the most common for most SMD

vendor models—best to use this definition

if there is doubt



Floating Ground

Can be used when you know that your Component model has insignificant coupling to ground

A good option to use for multi-layer boards (i.e., PCB or LTCC) when your local ground is an intermediate layer that is different from the overall Sonnet Box bottom or top

Ideal Components (L, R, C) use this definition automatically

79


Polygon Edge Ground

Preferred when your SMD model assumes a ground reference to one (or more) of your surface conductor pads

Many SMD amplifier packages use ground referenced to one or more surface pads

Your EM model can include parasitics from topside ground to your overall circuit ground reference if you include the associated lines and vias—very important for accurate amplifier and oscillator modeling


Help for Data File Components Sonnet Project Editor automatically

selects an appropriate ground node definition based on the Component data file

Upon browsing to the Component Data File, the Project Editor previews the data file for possible ground parasitics by performing an internal fit to a PI circuit model

If shunt elements are found in the fit, the Sonnet Box Ground definition is selected for default

If no shunt elements are found, a Floating Ground is selected for default

You may modify the selection based on prior knowledge of the required ground reference

Read Data File

Floating Ground

Sonnet Box

Ground

Perform Internal

Fit to PI-model

Shunt element

Present?

80


About SMD Models… Best way to get good SMD part models:

Mount and Measure the part on a test board

– Test board should be identical (type, thickness, etc.) to the board you will use for the final design.

Standardize your SMD pad sizes

Measure on test board with reference planes at the outside edges of your SMD mounting pads

Set Sonnet Component calibration planes to go all the way through your SMD pads; let your measurement model include pads and SMD device together

Such models are already available through Modelithics (www.modelithics.com); Sonnet highly recommends Modelithics models for successful SMD-based high frequency RF designs.

Make sure you account for the step discontinuity between transmission line and SMD pad only once—either in the Sonnet EM model or in your measurement model

Build and measure your SMD…

Measurement

Reference planes

Then use the model in a Sonnet

Component with Component

Reference Planes like this…

Application

SMD Pad

Step discontinuity will be

included in the Sonnet EM

model


Component Assistant

A Component Assistant automatically opens with helpful reference information and setup tips

Component Assistant is Context Sensitive for any item on the Component menus—just click

http://www.modelithics.com/

81


Ports-Only Component for External Use

Non-linear transistor models can be added in an RF simulator; use a Ports-Only Component in Sonnet to get an EM extraction of the planar circuitry and import the model to your RF simulator

Analyze all interstage networks in Sonnet, then add transistor model in your circuit theory simulator between the appropriate ports


What is Terminal Width?

Sonnet can model the discontinuity of the current as it flows into the contact of the element which will be connected to a co-calibrated port.

Setting the Terminal Width tells Sonnet the size of this discontinuity

82


Terminal Width Examples

For a simple case, the feed

line width is simply the width

of the line connected to the

port

The terminal width is the electrical contact width of the

Component. For this coplanar waveguide with a two port

component, you would want to define the terminal width.


Terminal Width - Feed Line Width

Setting the Terminal Width

to “Feed Line Width”

means there is no

discontinuity in the

current.

83


Example Terminal Width Problem

This circuit

has a problem.

Can you spot

it?


Terminal Width Error Message

Pre-Analysis:

Sonnet Error EG2420:

Illegal calibration group configuration.

Filename: subsections.son

Calibration group C and calibration group D overlap each other.

Calibration group C location: level 0 x=175.0 y=2075.0 to x=4000.0 y=2325.0 microns.

Calibration group D location: level 0 x=175.0 y=2075.0 to x=4000.0 y=2325.0 microns.

When user tries to simulate, or selects, Analysis -> Estimate Memory,

the following error message occurs:

84


Terminal Width is a Port Property Message:

Calibration group C and calibration group D overlap each other.

Calibration group C location: level 0 x=175.0 y=2075.0 to x=4000.0 y=2325.0 microns.

Calibration group D location: level 0 x=175.0 y=2075.0 to x=4000.0 y=2325.0 microns.

Double-click this port to see the properties of

calibration group C


Terminal Width

Click the Properties

button

Terminal Width is set to

“Feed Line Width”.

What does this mean?

85


Very large Feed Line Width

In this case, port 7 is located

on the edge of two polygons,

so Sonnet thinks the feed line

is very wide!

Feed Line Width is shown

by the red arrow.


Port 9’s Terminal Width

overlaps Port 7’s

Terminal Width Overlap

86


How to fix the problem

To fix the problem, set the

Terminal Width manually


Another way to fix the problem

Another way to fix the

problem is to move the

polygons so the Feed

Line Width is clearly

defined.

It is ok for the ports to be

really close… because

they are co-calibrated!

87


Feedline GLG Metal Problem

Pre-Analysis:

Sonnet Error EG2410:

Illegal component configuration.

Filename: subsections.son

A metal polygon interferes with

component R1 at the following location:

level 0 (x=3080.0 y=2890.0) mils to

(x=3090.0 y=2900.0) mils.

If the Terminal Width is set to

“Feed Line Width” for this

component, the error message

below appears when trying to

view subsections. The

problem is that the shape of

the metal causes a problem

with the GLG metal.


User Defined Terminal Width

The solution is to set

the Terminal Width is

set to “User Defined”

and pick a value about

equal to the width of

the incoming

transmission lines.

Notice how the subsection viewer can show the GLG metal if it is

checked under the “View” pull down. The GLG metal is in blue

between the two transmission lines and underneath the component.

88


Vendor SMD Models in EM Simulation

Most SMD vendors provide S-parameter models on their web sites or via data CDs

To use correctly, we must understand the vendor’s measurement setup; this is important to the Sonnet Component Ground definition we use

Look for vendor’s reference plane definition for component measurements; this may lead to the need to add reference plane shifts for the Sonnet Component ports so we don’t include SMD pad parasitics twice (once in vendor measurements and again from EM analysis)

Some vendors measure parts on a test board, others may measure over an open gap under the contacts. If your part was measured using an open gap, you might want to use “Floating Ground” setting in your Sonnet Component.

G

T

Ref Plane Ref Plane

PART

PAD AIR PAD GAP

Ref Plane Ref Plane


ATC Capacitor Measurements

ATC 600 Series Measurement Notes and Test Conditions

This describes the applicable test conditions and equipment

used in the measurement of scattering parameters for the

ATC 600 series capacitors.

Each capacitor, with the exception of 600B devices, was

horizontally mounted -- electrodes parallel to the plane of the

circuit board -- in a series configuration on microstrip. The

600B units were mounted vertically (electrodes perpendicular

to the plane of the circuit board). As shown below, each unit

under test (UUT) subtended a “G”-mil gap in a “W”-mil

wide trace on Rogers 4350 softboard, “T” mils thick. “G,”

“W,” and ”T” are given in Table 1 for various-size capacitors.

In general, “W” was kept at about the width of the capacitor,

with “T” selected to make the trace width a 50-ohm line.

All measurements were made using an Anritsu 3680K

Universal Test Fixture and an HP8722D Vector Network

Analyzer having a four-receiver architecture.

Measurements have been de-embedded to the

edges of the capacitor under test using a

standard TRL calibration procedure. (I.e., S-

parameters are referenced at the edges of each capacitor.)

W

All dimensions in mils

trace (1/2 oz. Cu)

G

T

Rogers 4350 softboard

reference

planes capacitor under test

Case

Size

G

(mils)

W

(mils

)

T

(mils)

0402 24 22 10

0603 36 29 13.3

0805 46 52 23.3

“A” 35 52 23.3

“B” 80 52 23.3

From ATC “Readme” file with S-parameter models:

Example: SMD Low-Pass Filter

89


Using the Vendor Capacitor Model

Set Component Type to “Data File” and browse to the vendor *.s2p model file

Set Terminal Width to 20 mil (0402 package)

Set ref. plane to edge of package, as measured by ATC

Sonnet’s de-embedding effectively removes the metal between the reference planes from the EM simulation results

Use Sonnet Box Ground Node Connection, consistent with ATC’s measurement method

40 m

ils



Vendor Models and Ground Nodes

If your Vendor model exhibits shunt parasitics (parasitics to ground) then you should use a Sonnet Box ground, or accommodate linkage of the shunt parasitic to ground in the model to ground in the EM model.

One way to look for shunt parasitics is to load the Vendor model into the Sonnet Data Viewer, and look at the Sonnet PI-model extraction for this

– Load in Sonnet Response Viewer

– Select Output…|PI Model File…

Look for PI elements between nodes and ground (node 0).


90


180 4/19/2012

PI-Model Equivalent for C and L Extracted Sonnet PI model for 2.2 nH

CoilCraft Inductor:

Extracted Sonnet PI model for 2.0 pF ATC

Capacitor:

CAPID=C1C=0.08 pF

CAPID=C2C=0.08 pF

CAPID=C3C=2.18 pF

PORTP=1Z=50 Ohm

PORTP=2Z=50 Ohm

CAPID=C3C=0.043 pF

INDID=L1L=2.2 nH

RESID=R1R=0.23 Ohm

PORTP=1Z=50 Ohm

PORTP=2Z=50 Ohm

No shunt elements-can use

floating ground

Shunt elements-

should use box

(global) ground


Component Conclusions

Ideal Components make it very easy to run initial prototype simulations that include all EM effects of the interconnects and vias

Vendor models (Data File Components) can be added for even more realistic circuit modeling

Data File Components can also incorporate transistor models and other multi-pin surface package models

Ports-Only Components let you build EM models for full layout and leave connection ports where you can add your devices in a circuit simulation framework

Current Density can be shown with the effects of the Components

Sonnet Components put EM simulation to the front-end of high frequency circuit design

91

MODELING METAL

THICKNESS

True thickness modeling for conductors



Thick Metal Modeling

Sonnet thick metal modeling uses multiple sheets of

infinitely thin metal to model thickness.

Automated setup of 3D metal thickness in Sonnet

menus.

Sonnet thick metal may be used in combination with

zero-thickness metals.

“Microstrip Conductor Loss Models for

Electromagnetic Analysis”

by

James C. Rautio, Fellow, IEEE, and Veysel Demir,

Student Member, IEEE,

IEEE TRANSACTIONS ON MICROWAVE

THEORY AND TECHNIQUES, VOL. 51,

NO. 3, MARCH 2003 915

Discusses this n-layer thickness model.

92


Introduction to Thick Metal

All serious commercial EM tools now have

dedicated models for thick metal.

Many different ways to model thick metal.

When is a thick metal model needed?

How do we know if a model is correct?

How can we quantify the analysis error?

What are the advantages and disadvantages of

each model?

©2010 Sonnet Software, Inc. www.sonnetsoftware.com 185

A 3D Model of a Microstrip Line

To study field penetration

and currents in lossy metal

we’ll first look at results

from a full 3D solver for a

simple microstrip line. The

line uses lossy metal (3e7

S/m) on a lossy dielectric (r

= 2.5, tan = 0.001). We

put a port at each end of the

line and then look at fields

and currents on a cutting

plane slicing across the

model.

port

substrate

Lossy

metal

Cutting

plane

93

Thick Metal – Current in Lossy

Lines


edge of

line

“current” penetration into

substrate due to 0.001 loss

tangent

Current density inside a

5 m thick, 80

microstrip line on lossy r

= 2.5 at 30 GHz. The

current penetrates into

the lossy metal. The

skin depth is ~ 1/10 the

line thickness.

•Strong current at sharp corners.

•Current penetrates conductor due to skin effect. [skin depth = (2/ws)1/2]

•Maximum current at edge but varies with many factors.

•Current determines inductance and I2R loss.

top of

line

©2012 Sonnet Software, Inc.

www.sonnetsoftware.com

187

Microstrip Line: Current Density at 30

GHz

At this frequency the skin depth is ~1/10 the line thickness

The current stays near the surfaces but notice that it is not uniform in depth at the vertical edges Modeling this with one uniform cell in thickness would introduce modeling error

94



188

Microstrip Line: Electric Field at 30

GHz

At this frequency the skin depth is ~1/10 the line thickness.

The field stays near the surfaces and is highest at the corners (edges) of the line.


Coupled Microstrip Lines

To examine the field and

current penetration in

coupled lines, we will

model a pair of lossy

microstrip lines with a

small gap separating

them. We use the same

materials as in the earlier

model and again we will

look at the currents and

fields on a plane slicing

across the model.

95


Coupled Lines: Current Density at 30

GHz At this frequency

the skin depth is ~1/10 the line thickness.

Coupling between the lines depends on the physical distribution of the current.

Notice the higher current at the “coupled” edge but also high current on the opposite edge.

Current higher on the lower surface than on the upper.

(Click on image to animate)



191

Current Density at 100 MHz

At this frequency the skin depth is ~1/2 the line thickness.

Notice current penetration through out the line thickness.

Assuming that the current was on a shell on the outside of the metal would be wrong.

See the paper referenced below for a discussion of loss when the line thickness is comparable to the skin depth.

http://www.sonnetsoftware.com/support/downloads/publications/MicCondLoss_Mar03.pdf

(Click on image to animate)

96


Effective Gap Distance and

Metal Thickness

Skin depth causes effective gap width to increase.

Skin depth causes effective line width to decrease.

These effects are not included when using zero thickness sheets for side current.

skin depth

effective

gap

lossy

conductor

effective

width skin depth


Single-Sheet Model

One-sheet model excludes fields between sides of

thick line.

Usually OK if gap and line width > 2 × thickness.

Split between top and bottom surface current

must be estimated (most EDA tools completely

ignore this).

If in doubt, compare with two-sheet model result.

Actual Geometry One-Sheet Model

97


Two-Sheet Model

Two-sheet model includes most of the fields in the

gap.

Good for gap thickness.

For narrower gap, more sheets are needed.

To be sure, try with 2-sheet, then 4-sheet model and

note difference.

Actual Geometry Two-Sheet Model


4/19/2012

Multi-Sheet Model

• In above figure, notice most current is on

bottom sheet.

• Highest current (red) on edges of all four

sheets.

• Almost no current on inside metal (middle

two sheets, dark blue).

• Z-axis magnified 8x and vias not shown for

clarity. WhatsNew10.0\ThickCMexamplet

Advantage: Change in

effective gap width and line

width due to skin effect

accurately modeled.

Advantage: Low frequency

loss accurately modeled (skin

depth > thickness, when solid

model used).

Advantage: Transverse

current flows around sharp

edges by volume current

through vias connecting

edges.

Disadvantage: Large number

of sheets needed if gap width

<< metal thickness.

98


Multi-Sheet Model (Sonnet)

Multiple sheets to represent thick metal.

Can be done in any surface mesher.

Automated in Sonnet (type in number of sheets desired).

Vias automatically connect edges.

Hollow (tube-like) or solid.

Vias connecting edges of sheets not

shown.

Currents

auto

distributed

between

layers.


When to Consider Thick Metal

1. Thickness of transmission line is significant compared to its height above the ground plane (t > H/10)

2. Separation between adjacent transmission lines is on the order of 5t or less

3. Transmission 2D thickness is about the same dimension as its width.

99


Is a Thick Metal Model Needed?

Step 1: Analyze a typical structure with infinitely thin metal. This might be a model reduced in size but it should have the critical geometries of a full model.

Step 2: Analyze the same structure using a thick metal model.

Step 3: If the two results are essentially the same (with respect to your design requirements), use thin metal. If the results are sufficiently different, use the thick metal model.


Quantifying Meshing Error

All models use a mesh.

Fine mesh: More accurate but slow analysis, more memory.

Coarse mesh: Less accurate but fast analysis and less memory.

Step 1: Select a simple typical structure.

Step 2: Analyze with coarse, fast mesh.

Step 3: Analyze with fine, slow mesh.

Step 4: If differences are small, use coarse mesh. If differences are large, try an even finer mesh to make sure you have convergence.

100


Multi-Sheet Model

Multi-sheet model completely described and investigated.


Metal Types

Normal: 2D model; conductivity, thickness, current ratio. NOT Perturbational, uses surface impedance

Resistor: 2D model; ohms/square

Rdc/Rrf: Same as Normal, but specified in terms of Rdc (DC loss) and Rrf (RF loss); historical model for Sonnet

General: 2D model; Rdc, Rrf, Xdc, Ls

Sense: 2D model; Xdc. Used for sensing tan E fields

Thick Metal Model: 3D model; conductivity, thickness, number of sheets

Rough Metal Model : Thick or Flat; models RMS Surface roughness effects (more later)

101


Conductor Loss with 2D Models

Accurately models transition from electrically thin to electrically

thick

Includes both low frequency and high frequency effects

Requires two numbers to properly model frequency dependence

Does not include process dependant effects such as metal

porosity, impurity, roughness, etc.

Includes both real and imaginary components for normal

conductors

Attenuation (dB/mm)

Thickness Conductor

* See Finlay and Jansen, MTT Transaction, June 1988

Sonnet predicts the transition from thin to thick conductors


Thick Metal Summary

Many models of thickness: volume mesh, surface current (tube-like), and multi-sheet.

All have advantages and disadvantages.

Designers should first test to make sure thickness models are needed. – Usually only a limited number of shapes in a model need thick

metal

– Use thin metal for “normal” feed lines and thick metal for coupled geometries

Then test to be certain mesh is fine enough for required accuracy.

Make sure current distribution is reasonable if I2R loss is important.

102

ANISOTROPY AND

CONDUCTOR ROUGHNESS

Modeling real-world materials and fabrication effects…



Effect of Anisotropy

Data courtesy of D. Bates, Dielectric Laboratories

4/19/2012 205

103


Anisotropy: So what?!

Property exists in common substrates

Dielectric constant changes with the direction of

the E-Field

Even and odd modes have different velocities

4/19/2012 206


Anisotropy Specification

Sonnet Professional’s Dielectric Layer

specification allows anisotropic

dielectric substrates where the

horizontal dielectric is different from

the vertical dielectric.

104

Measurements: RA Resonator


Q: Where can we get accurate anisotropic dielectric properties of real

materials to use in our simulations?

A: Jim Rautio has recently published a measurement and extraction

method using the resonator shown above. More information is

available.

4/19/2012

Anisotropy: Rogers RO3010

RA Resonator method

used to characterize

substrate

What happens to a 5

GHz microstrip

bandpass filter if we

consider the material

anisotropy?


Vertical (Z) and horizontal (X-Y)

dielectric constants measured from

Rogers RO3010 substrate using the RA

Resonator method

105

Anisotropy Effect on 5 GHz BPF


Isotropic Material

Modeling – EM data

AnIsotropic Material

Modeling – EM data

Anisotropy – Final Thoughts

Dielectric Anisotropy has a stronger

effect on structures that utilize both

vertical and horizontal field coupling

Most vendors do not spec the dielectric

constants for Uniaxial Anisotropy;

isotropic assumptions are made and

published


106

Conductor Roughness Modeling


Roughness increases surface resistance and surface inductance

Sonnet model developed with Rogers Corporation

• How to

enable

Sonnet for

rough metal

• Adding

roughness to

a filter

Roughness Increases Loss

Surface current

travels further

through lossy

metal

Surface

resistance

increases


107

Roughness Increases

Inductance

Surface current

forms a loop

E-field is voltage

across loop

This is an

inductor

Actual situation

is fractal


Loss Validation

Sonnet/Rogers

roughness model is

extensively

validated.

DON’T use

increased metal

resistivity to model

roughness!


108

Surface Inductance Validation

Surface inductance

increases the

apparent Eeff

DON’T use

increased metal

resistivity to model

roughness!


Rough Conductor Definition


Use Thick/Thin Metal, set Top

and Bottom RMS Roughness

109

Metal Roughness Example

Load the “hairpin”

example from the

Sonnet Example

Browser

We will study the

effect of conductor

roughness on loss,

passband and

center frequency


Metal Roughness comparisons

Case 1: Lossless metal

(example is set up for

this)

Case 2: 0.5 oz Copper

(0.7 mil), Thick Metal

Model (TMM)

Losses and thickness

effects contribute

additional loss, slight

frequency shift

Shift is due to modeling

true thickness


110

Metal Roughness Comparisons

Case 3: 0.5 oz Copper

TMM with Roughness:

– Bottom surface: 3.0um

RMS

– Top surface: 0.5um RMS

Use the Rough Model

with Thick cross

section for best results

Bottom roughness is

usually larger due to

PCB conductor foil

adhesion process


4/19/2012 220

Metal Roughness Comparisons


Metal Roughness clearly increases passband loss and shifts center frequency

111

Thank you!

Remember the Sonnet 5 minute rule!

Contact us with ANY questions:

– [email protected]



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– www.sonnetsoftware.com

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