USC Signal Integrity Lab Course 2
Ansoft High Frequency Structure Simulator (HFSS)
ELCT 762
USC
1
Driven Terminal Problem
• Analyze two micro strip lines that pass
through via. Analyze the impact of return
loss and insertion loss. (S11, S21 )
• Use the 4 layer PCB in the following stack
up.
• Analyze the PCB at a size of 2 x 2 inch
2
Stack up
1
Copper 1OZ
FR4
2
DK = 4.1
copper 1 OZ
total thickness ( mil )
5 mil / 10 mil space
GND
47
1.4
DK = 4.1
Sig
5
1.4
copper 1 OZ
FR4
4
DK = 4.1
copper 1 OZ
FR4
3
1.4
GND
5
1.4
Sig
5 mil / 10 mil space
62.6
1 mil = 0.001 inch,
Signal trace width = 5 mil
Signal to signal space = 20 mil
3
Configuration
•
•
•
•
•
Start HFSS
Save file
Insert HFSS design
Setup solution type: Driven Terminal
Setup grid to 0.1 inch
4
Structure Design
• Draw a BOX at: 0, 0, 0, size: 2, 2, 0.005 inch. Assign material:
FR4_epoxy. Set transparent: 0.7 Rename it: FR4_1
• Draw 2nd BOX at 0, 0, 0.005, size: 2, 2, 0.0014 inch. Assign material:
Copper. Set transparent: 0.7 Rename it: GND1
• Draw 3rd BOX at 0, 0, 0.0064, size: 2, 2, 0.047 inch. Assign material:
FR4_epoxy. Set transparent: 0.7 Rename it: FR4_2
• Select GND1 by clicking in command history window. Click: Edit->
copy, and Edit -> Paste. Now, GND2 is copied from GND1 and is
placed at the exact same location!
• Double Click GND2 (create box) at command history window. At
property window, put 0, 0, 0.0534 as new origin. This moves GND2
to upper layer
5
Stack up Design
• Do the same thing to
copy FR4_1 and
make it FR4_3. Put
new origin as: 0, 0,
0.0548
• Now the stack up is
ready. It has two
ground layers and 3
FR4 layers.
• Grey color is for FR4
and Blue is for GND
Side view of PCB stackup
6
Add signal trace
• Draw a BOX at: 0, 1, 0.0598, size: 1.005, 0.005, 0.0014
inch
• Rename it: Trace1, Assign Material: Copper. Change the
color to: RED
• Copy Trace1, and Paste it. Now you got trace2. Change
trace2’s original at 0.995, 1, 0 inch, size: 1.005, 0.005,
-0.0014 inch
• Now Trace1 and Trace2 are on two different sides of the
PCB. They are located at center and overlap each other
by 10mil.
• In order to see both traces, you need to set transparent
property of all drawing to be ~ 0.7
7
8
What is via and anti-via
• What is via & anti-via
– What does via do?
– What does anti-via do?
9
Add via and anti-via
• Click the cylinder icon, draw a cylinder between
two traces.
• Change the current position to: 1, 1.0025, 0 inch,
radius: 0.005 and height: 0.0598 inch. Assign
the material: copper. Change the color: RED
Rename it: via1
• Do another cylinder (10mil radius), assign
material: Fr4_epoxy, rename it: anti_via1
• Two cylinders overlap and center at same
location. -- this will cause a problem and
confuse the software! Why?
10
Bolean function
• The overlap of two different materials will
cause design error. This can be corrected
by using Boolean function – subtract.
• In command history window, hold: Ctrl key
and click: FR4_1, FR4_2, FR4_3, GND1,
GND2, anti_via1
• This selects the 6 items above to perform
a Boolean function
• Click: 3D Modeler -> Boolean -> Subtract..
11
Bolean Function - subtract
• Subtract window pops up.
• Move, FR4_1, FR4_2,
FR4_3, GND1, GND2 to
Blank Parts window
• Move anti_via1 to Tool
Parts window
• Select “Clone tool objects
before subtracting” Why?
• Click “OK”
12
View - Visibility
• After subtraction, graphic
verification is hard since
all the components
overlap each other.
(visibility setting can
solve this problem)
• Click: View -> visibility
• Visibility window pops up.
Turn off the visibility on
all FR4 and anti_via1
• It is verified that via
passed through two
layers of ground without
touching it
13
Question.
• The overlap issue between FR4, GND and
anti-via is solved.
• There’s another overlap error. Which one?
14
Overlap problem 2
• There’s overlap between
anti-via and via.
• Use Boolean subtraction
function, subtract via from
the anti-via. Don’t forgot
to “clone” the via
• Use the visibility
command to verify that
anti_via1 has a hole in
the center.
15
Bolean function - unite
• Hold Ctrl key and click: FR4_1, FR4_2, FR4_3, anti_via1
• Click: 3D modeler -> Boolean -> unite
• All of above items will be united into one item. Name:
FR4_1. ( the new name is the first item you selected )
• You can only unite the items that touch each other and
have same material
• Your field solution is more accurate and process is faster
after you unite the similar items
• If you want to un-do the “unite”, go to command history
window and delete the “unite” under FR4_1
• Do the same thing to unite: trace1, trace2, via
16
Create 2nd trace
• In command history window, click and select: trace1
• Click: edit -> copy, then click: paste
• Now, you have trace3 created at the exact same location
of trace1. (they overlap each other)
• Click and select: trace3
• Click: Edit –> arrange -> move
• Use the mouse, drag trace 3 in the positive Y direction
20mils. (note: DY = 0.02 indicator at bottom right)
• To verify the move, in the command history window,
double click the move command.
17
Create 2nd trace, cont.
• Now, the sub window
pops up.
• Make sure the move
vector is 0, 0.02, 0
• This makes the 2nd
trace 20mil away from
1st trace.
• What is the air gap
size between the
traces?
18
2nd Anti-via
• Create an anti-via for the 2nd trace. The center
location should be 0, 1.023, 0
• Review slide 10 for creating an anti-via
• Rename the new item: anti_via2
• There’s an overlap issue between anti_via2 and
FR4_1, GND1, GND2, trace3. Review slides 12
and 15 to solve the overlap error
• Unite the FR4_1 with anti_via2. keep the name:
FR4_1 for the united item.
19
Structure with 2 traces
20
Add Air Box
• Need to add “Air” boxes on top
& bottom of PCB. Why?
• Draw a box at 0,0, 0.598, size:
2, 2, 1, Material: air, rename it:
air1
• Draw a box at 0, 0, 0, size 2, 2,
-1, Material: air, rename it: air2
• Change the color of air to:
white with transparent setting
of 0.95
• Air boxes overlap with trace1
and trace3. Use the Boolean
function to do the subtraction
21
Structure Design is completed
22
View at different angle
• Click: View -> Modify
Attribute -> Orientation
• You can set the Top view,
front view or side view.
This helps a lot when you
design with 2D objects.
• Now, set the view as:
front view. See top picture
• Select the FR4_1 item,
make the transparent
property: 0
23
24
Port & Terminals Sample
25
Port & terminal
Terminals
1
2
3
4
10w, w  h
or
5w (3h to 4h), w < h
Port is a 2D rectangular area
Terminals are each end of traces
6h to
10h
Port contains terminals
w
h
26
Port Assignment
• Set the view at: Front view
• Draw a 2D rectangle by clicking: Draw>Rectangle ( Set in plane direction: YZ)
• Enter original: 2, 0.988, 0.005. Y size: 0.05, Z
size: -0.05
• Set transparency: 0.8
• Rename: Port1
• Do another 2D rectangle at: 0, 0.988, 0.0548. Y
size: 0.05, Z size: 0.05
• See picture next slide.
27
28
Terminals
• Set the view at: front view
• Select by clicking: Port1
• Click: HFSS -> Excitation ->
Assign -> Wave Port
• Click: Next , the Wave Port
terminal window pops up.
• Set: Number of Terminals = 2,
Click: update
• Change the name of 2nd
Terminal line to T3.
• At T1 Terminal Line cell, click &
select: New Line
• Use coordinate system to key
in terminal lines
29
Terminal Lines
• The terminal lines have to be
on the Port1 plane. It has to go
from GND1 to Trace1
• It is very hard to use the
mouse to set the terminal line
because it will snap to a point
somewhere outside of the
Port1 plane.
• It is highly recommended to
key in the coordinate system
below the progress windows (
lower right corner). See picture
30
Terminal lines, cont.
• At coordinate system,
enter: 2.0, 1.0025, 0.005
inch for xyz. Hit: Enter
• Enter: 0, 0, -0.005 for
Delta x, y, z, hit Enter
• Now you got a terminal
line T1 from GND1 points
to trace1. It is on the
Port1 plane.
• Note the point direction, It
is point from low voltage
(GND) to high voltage
(trace1)
31
Terminal lines, cont.
• Add a second terminal lines for T3
• Starting point is: 2, 1.0225, 0.005. Delta Z
= -0.005
• Hit: Enter, Enter, Finish.
• Now, the Port1 is defined with 2 terminal
lines named: T1, T3
• Do same thing to define Port2 with
terminal lines of T2 and T4. (Note, Port2 is
on plane location x=0 )
32
Assign Boundary
• Assign radiation boundary on
external surface of airbox.
• Click: Edit -> Select -> Face
• Hold down CTRL key, and
select the external face of air1.
Hold the ALT key to rotate the
object to select faces
• Click: HFSS -> Boundary ->
Assign -> Radiation. Hit Enter.
• In project window, click
boundary -> RAD1, the
radiation boundary shows on
drawing window
• Do the similar boundary
assignment for air2
33
Boundary Assignment, cont.
• Now assign a radiation
boundary on all external
faces of FR4 material
(faces on the outside)
• Don’t assign boundary on
any metal objects
• Don’t assign boundary on
internal faces
• Sometimes, it is easy to
click one face and assign
one boundary. ( Click
multiple faces and assign
one boundary is also OK)
34
Boundary overlap warning
message
• If you run the validation
check, there will be
warning messages
regarding the boundaries.
It is because waveport1
assignment overlaps with
radiation boundary. In this
case, the port always has
higher priority to overwrite
the boundary.
35
Solution setup
• Click: HFSS-> Analysis
Setup -> Add Solution
Setup
• The Solution setup
window will pop up.
• We want to solve at 1
Ghz. Change the number
of Passes: 5
• Change the Max Delta S:
0.01
• Click OK to accept default
for rest of the settings.
36
Setup another solution
• Now, setup a sweep
under first solution
• Click: HFSS -> Analysis
Setup -> Add Sweep.
Click OK to pick setup1
• Edit Sweep window
popup
• Change Sweep type: fast
• Change Sweep size: 0.5
Ghz
• Click OK
37
Simulation!
• Click: HFSS -> Analyze
• Wait 15 min for this small simulation.
38
Simulation Results
• What simulation results can be found?
– S, Y, Z parameters, impedance matrix
– Plotting of above matrix
– E, H fields inside the structure
– Current density of structure
– Near & Far field radiations
39
S parameter
• Click: HFSS -> Results ->
Solution Data
• Click on tab: Matrix Data
• Solution Data window
pops up. It shows the S
parameter matrix.
• To show data for all
frequencies, click: All
Freqs.
• This table gives you data
for point analysis. For a
general AC analysis, a
plot is a better way
40
Plot of S11
• Click: HFSS -> Results ->
Create Report
• Change display type:
Smith Chart
• Pick Report Type:
Terminal S parameters.
Press OK
• Pick Quantity: first entry,
this is S11.
• Double Click this entry
(trace appears at top)
• Click Done
41
S11 on Smith Chart
42
Plot S21
• Click: HFSS -> Results ->
Create Report
• Set Display Type: Rectangular
Plot
• Click: OK
• At Plot window, select quantity:
waveport T2, T1. This is the
S21
• At function sub-window, select:
dB. This will plot the magnitude
of S21 in dB
• Double Click (put entry at top)
• Click: Done
43
S21 Magnitude in dB
44
S21, Real & Image Part
45
Homework
• Plot S31 Magnitude in dB (near end of
cross talk)
• Find S31, S41 at 1Ghz.
• Plot Electric field that generated by via.
Hint: Use HFSS -> Field -> Plot Field -> E Mag. Plot the
E mag on the face of FR4_1 (center layer face)
• Do an animation for above E – field.
46
Project 1
• Compare the T-lines pass via with a typical
micro strip. ( no via )
• Do the same simulation to find the
difference on return loss, insertion loss
and cross talk
• Suggest what is the cause of those
differences
• How to improve it? Suggestions?
• Show the improved result on simulation
47
Project 2
• Do the same thing as project 1 for a strip line.
Copper 1 OZ
FR4
1
4
DK = 4.1
DK = 4.1
copper 1 OZ
FR4
Copper 1Oz
GND
GND
5
1.4
DK = 4.1
5 mil / 10 mil space
47
1.4
DK = 4.1
Sig
5
1.4
copper 1 OZ
FR4
5
1.4
copper 1 OZ
FR4
3
DK = 4.1
Copper 1OZ
FR4
2
1.4
Sig
5 mil / 10 mil space
5
1.4
48