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
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 4
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METHOD OF MOMENTS
OVERVIEW
How does it work?
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 5
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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
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© 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.
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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.
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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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.
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
Shielded vs. Unshielded MoM
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 10
MoM – Shielded Domain MoM – Unshielded Domain
Substrates go to infinity
in all directions
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 11
MESHING IN SONNET
Where the magic happens…
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 12
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© 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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 14 4/19/2012
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.
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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.
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
Mesh: Fine/Edge
Mesh: Coarse/Edge
Mesh: Coarse/No Edge
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 16
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
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 18
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Exercise: Filtwall Mesh Slider
From the Sonnet taskbar select
Project -> Browse Examples…
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 21
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 22 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.
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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
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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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.
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
Cross-over
edges aligned!
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 25
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 26 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?
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Conformal Mesh Benchmark
Ang(S11) and
Ang(S22)
almost
identical.
Mag = 1.0.
Eight freq.
ABS analysis.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 27
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 28 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 29 4/19/2012
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
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
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Conformal & Rectangular Mesh
Curved Transmission
Lines
Wilkinson Divider
Circuit
Internal
ports
5/22/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 32 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 33
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 34 4/19/2012
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)
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 35
Exercise: Meshing Polygons
1. Open the filtwall.son example, and set
mesh controls to Fine/Edge
Estimate Memory on Filtwall
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 36
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.
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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.
4/19/2012 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
4. Estimate Memory and View Subsections again…
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 39
Conformal Meshing
Shown
Optional Exercise: Conformal
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 40
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Optional Exercise: Conformal
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 41
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
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MODELING VIAS IN SONNET
Getting current between the planar metal levels…
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 43
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.)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
Box bottom forms ground plane
connection
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 45 4/19/2012
Via Posts Make up Vias
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 46 4/19/2012
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.
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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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 47
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 48 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 49 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 51 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 52 5/22/2012
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)
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 53 5/22/2012
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
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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Ring
(Default)
Vertices Center Full
Using either of these choices gives faster, but less accurate results
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Double-click a via, you get this:
This section describes when to use
each choice.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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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)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Common Via Scenarios
Hollow Via:
Solid Via:
The
“Volume”
model can
be used to
model both
hollow and
solid vias.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
33
Volume model
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Opening Old Project Files
If you open an
old project file,
you will get this
message. Sonnet
creates new via
metal types for
you
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 68 4/19/2012
Error Convergence of Vias
35
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 69 4/19/2012
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)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 70
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 71
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 72 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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 73 4/19/2012
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…)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 74 4/19/2012
Results
Circular Via
Double Via
Slot Via
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 75 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 76 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Dense Arrays of Finite Vias lead to inefficient meshing
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Example 1
Combine these
vias into a single
via
Interconnects on a differential spiral balun
implemented in a silicon RFIC process:
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Via Simplification
GDSII import example:
For more information:
- Click Help Button
- See “Via Array Simplification” chapter of Sonnet Translators Manual
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
Baseline: 2.46 GB
Conformal: 1.55 GB
Conf+Simp Vias: 1.08 GB
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 85
PORTS FOR EM ANALYSIS
Nodal connections for EM models…
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 86
44
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 87 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 88 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 89 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 90 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 91 4/19/2012
Standard Box-wall Port
Box wall provides
perfect ground reference
1 + -
PEC Top
PEC Bottom
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 92 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 93 5/22/2012
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)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 94 4/19/2012
Even Mode Ports
+
-
Common-mode Excitation
48
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 95 4/19/2012
Odd Mode Ports
+ -
Odd-mode (Differential) Excitation
CPW Ports – 2 ways
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 96
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 97 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 99 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 100 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 101 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 102 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 103 4/19/2012
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!
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 104 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 105 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 106
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 107 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 108 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 109
DE-EMBEDDING EM PORTS
Getting port discontinuities OUT of your EM DUT…
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 110
56
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 111 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 112 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 113 4/19/2012
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 -
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 114 4/19/2012
De-embedding Ports in Sonnet
2
1
N
.
.
.
Ports
Box Wall
N-coupledtransmission lines
- Coupled Transmission Lines -
58
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 115 4/19/2012
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?
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 116 4/19/2012
Zero-Length Coupled Line
Sonnet Results
A well-known
competitor’s
results
59
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 117 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 118 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 120 4/19/2012
De-embedding Ports in em
W
em uses the cross-
section at the box wall
to compute Zo and eeff
W
- Transmission Line Parameters -
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 121 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 122 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 123
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 124
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 125
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 126
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 127
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 128 5/22/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 129 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 130 5/22/2012
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).
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 131 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 132 5/22/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 133 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 134 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 135 5/22/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 136 5/22/2012
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…
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 137
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 139
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
4/19/2012 140 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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).
4/19/2012 141 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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).
4/19/2012 142 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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.
4/19/2012 143 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
72
Linear Sweep Points
The linear
sweep points
for |S11|
4/19/2012 144 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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.
4/19/2012 145 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
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”.
4/19/2012 146 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
Linear Points on ABS
Now we can
see how well
the ABS sweep
matches linear
sweep points…
…quite well!
4/19/2012 147 © 2012 Sonnet Software, Inc www.sonnetsoftware.com
74
ABS Example
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 148
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)
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 149
Analysis->Setup…
“Advanced” button
75
SONNET COMPONENTS
Including SMDs and linear active devices in EM
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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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 152 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 153 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 154 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 155 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 157 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 158 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 159 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 160 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 161 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 162 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 163 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 164 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 165 4/19/2012
Terminal Width - Feed Line Width
Setting the Terminal Width
to “Feed Line Width”
means there is no
discontinuity in the
current.
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 166 4/19/2012
Example Terminal Width Problem
This circuit
has a problem.
Can you spot
it?
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 167 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 168 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 169 4/19/2012
Terminal Width
Click the Properties
button
Terminal Width is set to
“Feed Line Width”.
What does this mean?
85
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 170 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 171 4/19/2012
Port 9’s Terminal Width
overlaps Port 7’s
Terminal Width Overlap
86
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 172 4/19/2012
How to fix the problem
To fix the problem, set the
Terminal Width manually
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 173 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 174 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 175 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 176 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 177 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 178 4/19/2012
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
Example: SMD Low-Pass Filter
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 179 4/19/2012
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).
Example: SMD Low-Pass Filter
90
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 181 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 183 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 184 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 186
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
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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.
©2012 Sonnet Software, Inc. www.sonnetsoftware.com 189
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
©2012 Sonnet Software, Inc. www.sonnetsoftware.com 190
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)
©2012 Sonnet Software, Inc.
www.sonnetsoftware.com
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
©2012 Sonnet Software, Inc. www.sonnetsoftware.com 192
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 193 4/19/2012
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 194 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 195
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 196 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 197 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 198 4/19/2012
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.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 199 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 200 4/19/2012
Multi-Sheet Model
Multi-sheet model completely described and investigated.
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 201 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 202 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 203 4/19/2012
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…
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com
Effect of Anisotropy
Data courtesy of D. Bates, Dielectric Laboratories
4/19/2012 205
103
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
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
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 207
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
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?
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 210
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 211
106
Conductor Roughness Modeling
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 213
107
Roughness Increases
Inductance
Surface current
forms a loop
E-field is voltage
across loop
This is an
inductor
Actual situation
is fractal
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 214
Loss Validation
Sonnet/Rogers
roughness model is
extensively
validated.
DON’T use
increased metal
resistivity to model
roughness!
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 215
108
Surface Inductance Validation
Surface inductance
increases the
apparent Eeff
DON’T use
increased metal
resistivity to model
roughness!
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 216
Rough Conductor Definition
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 217
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 218
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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 219
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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
© 2012 Sonnet Software, Inc www.sonnetsoftware.com
4/19/2012 220
Metal Roughness Comparisons
© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 221
Metal Roughness clearly increases passband loss and shifts center frequency
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© 2012 Sonnet Software, Inc www.sonnetsoftware.com 4/19/2012 222
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