Download - EMI Driven by PI
-
7/27/2019 EMI Driven by PI
1/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMI Driven by PI
-
7/27/2019 EMI Driven by PI
2/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Outline
SI + PI = EMI These disciplines are no longer independent of each other
Fundamentals of EMI
Where does it come from and how is it minimized Five Step EMC Design Flow
Power Integrity design methodology to reduce EMI
Fundamentals of Power Integrity Design Process to meet design specs in the Time and Frequency
domain
2nd Presentation on EMI Driven by SI
Fundamentals of Signal Integrity
Crosstalk is the main contributor to EMI
Case studies that show perils of crosstalk in real world designs
-
7/27/2019 EMI Driven by PI
3/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
SI/PI/EMI Design Overview
Driver IC
Control IC Memory
Power Supplies
Display Panel
Signal Integrity- Impedance
- Crosstalk
- Reflection
- Termination
- Dielectric Losses
Power Integrity- Switching Noise
- Impedance Profile
- Power/Gnd Plane Resonance- Decoupling Capacitors
EMI/EMC- Common mode radiation
- Differentialmoderadiation
PCB
Pwr Noise
Signal
Signal Integrity
Time DomainFrequency Domain
Power IntegrityElectromagnetic
Interference
-
7/27/2019 EMI Driven by PI
4/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Three Basic Elements of EMC
EMI source
EMI source
Capacitive Inductive RadiativeConductive
Space & FieldConduction
EMS
EMS
Low & Middle Frequency
LC Resonance
High FrequencyLow, Middle & High
Frequency
Coupling process
Immunity
Emission
Shields
ShieldsEMI Filters
EMI Filters
Shields
Shields Shields
Shields Shields
ShieldsEMI Filters
EMI Filters
-
7/27/2019 EMI Driven by PI
5/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Loop Mode & Common Mode Noise
A PC Board & Cables
A Driver & Receiver
A victim device
Loop mode
current
Common modecurrent
by AC Analysis ofQ3D Extractor
Differential mode current flows --- Loop
Common mode current flows --- Open
We can see Common mode current is
more serious than Normal mode.
-
7/27/2019 EMI Driven by PI
6/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Antenna theory
r
AI)(f.E
-
sin106131
216
=r
lIfE
sin)(1047
=
-A Differential mode current flow Loop antenna theory
-A Common mode current flow Dipole antenna theory
Illustration of a loop antenna Illustration of a dipole antenna
r : distance r
Length :l
A : area of the loop
FCC B level Mag. E limit :40dBuV/m @ 3m
Mag. E( Loop antenna) : 20mA
Mag. E( Dipole antenna) : 8uA
II
-
7/27/2019 EMI Driven by PI
7/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMC Design Flow
Planes deliver power to ICs and return
path for signal
Ensure that Plane impedance is smooth
and low over broad frequency range
Resonance Analysis
Emissions Analysis
Impedance Analysis
Signal Extraction
Enclosure Simulation
-
7/27/2019 EMI Driven by PI
8/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMC Design Flow
Resonance Analysis
Emissions Analysis
Impedance Analysis
Signal Extraction
Enclosure Simulation
Resonances indicate areas of high
impedance and EMI potential
Ensure power planes do not resonant incritical locations
-
7/27/2019 EMI Driven by PI
9/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMC Design Flow
If signal is not at the receiver, it went
somewhere else
Ensure clean signal transmission andgood return path for critical nets
Resonance Analysis
Emissions Analysis
Impedance Analysis
Signal Extraction
Enclosure Simulation
-
7/27/2019 EMI Driven by PI
10/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMC Design Flow
Non-ideal planes and tight routing can
lead to unintentional signals
Ensure there are no unintentional
radiators
Resonance Analysis
Emissions Analysis
Impedance Analysis
Signal Extraction
Enclosure Simulation
-
7/27/2019 EMI Driven by PI
11/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMC Design Flow
Real enclosures are non-ideal andcan pass radiation
Ensure minimal radiation from PCB
escapes the chassis holes
Resonance Analysis
Emissions Analysis
Impedance Analysis
Signal Extraction
Enclosure Simulation
-
7/27/2019 EMI Driven by PI
12/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Electromagnetic
InterferencePower Integrity
PI Methodology
Signal Integrity
-
7/27/2019 EMI Driven by PI
13/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Power Integrity A Case Study
Active devices require clean power to operatecorrectly
Power distribution system (PDS) design engineers
must ensure that all parts receive voltage betweencertain limits and that noise is kept sufficiently low
Todays designs with many separate power domainsof high current and low voltage devices complicate
power integrity analysis
-
7/27/2019 EMI Driven by PI
14/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Board Imported from Layout
Measuring
impedance at
the six VCCpins on U41
VRM
-
7/27/2019 EMI Driven by PI
15/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
PDS Design Flow
EM extractionof impedance
for criticaldevices
Determinefrequencies ofspecification
violations
Simulate intime domain to
check forcompliance
Choose capacitoror geometric
change to addressviolations
Alter design
according tofindings
Start Finish
No
Yes
-
7/27/2019 EMI Driven by PI
16/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
1MHz1KHz
Switching
Power
Supply
Electrolytic
Bulk
Capacitors
High
Frequency
CeramicCapacitors
Power/Ground
Planes
BuriedCapacitance
1 GHz
100MHz
f
|Z|
targetZ
Mag. of Z
( ) ( )Current
RippleAllowedVoltageSupplyPowerZ
___ =Target
Frequency Domain PDS Targets
-
7/27/2019 EMI Driven by PI
17/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Defining the Target Impedance
0
0
0
VRM
VRM
VRM
50
R5
V33
DC=VCC
V35
io
pullup
pulldown
logic_in
enableout_of_in
Cpkg
C58
Lpkg
L59
Rpkg
R60
AName=vrm
To define the targetimpedance we need to
consider two factors:
Peak current Determines maximum
impedance
Spectral power Determines cutoff
frequency
Package Model
Driver
VRM
-
7/27/2019 EMI Driven by PI
18/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Peak driver current37.87 mA
Example:
Six drivers and 0.18 V
maximum voltage swing:
Peak Current
0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00Time [ns]
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
mag(Ipositive(vrm))[mA]
Ansoft Corporation DriverDriver Current
Curv e Inf o max
mag(Ipositive(vrm))
Transient37.8706
( )= m800
mA87.376
V18.0
-
7/27/2019 EMI Driven by PI
19/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20.4
0.5
0.6
0.7
0.8
0.9
1
Frequency [GHz]
CDF
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00Spectrum [GHz]
1.00E-012
1.00E-011
1.00E-010
1.00E-009
1.00E-008
1.00E-007
1.00E-006
1.00E-005
1.00E-004
1.00E-003
mag(vrm_
power)
Ansoft Corporation DriverXY Plot 4Curve Info
mag(vrm_pow er)
Transient
Driver Spectrum
Choose a frequency below
which most of the signal
energy lies
667 MHz = 97% of Spectrum
667 MHz
CDF
-
7/27/2019 EMI Driven by PI
20/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Power Integrity Investigation
Added two bulk
47 uF capacitors
as specified by
VRMmanufacturer
-
7/27/2019 EMI Driven by PI
21/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Bare Board vs. Bulk Capacitors
Resonance @ 50 MHz Bare BoardBoard w/
Bulk Caps
Target
impedance 800
mOhm to 667
MHz
-
7/27/2019 EMI Driven by PI
22/72 2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
V33
DC=VCC0
J5_VCC
Time Domain Schematic
VCC_U41-21
VCC_U41-42
VCC_U41-44
VCC_U41-63
VCC_U41-84
J5_VCC
VCC_U41-2
J5_VCC
VCC_U41-2
VCC_U41-21
VCC_U41-42
VCC_U41-44
VCC_U41-63
VCC_U41-840
50
R5
VCC_U41-2
V35
io
pullup
pulldown
logic_in
enableout_of_in
VCC_U41-2
0
Cpkg
C58
Lpkg
L59
Rpkg
R60
x6
800 Mbps data rate
DDR2 IBIS driver into idealtermination used as load for PDS
Package decoupling modeled
using a capacitor w/ ESR, ESL
Driver
VRM
Board
-
7/27/2019 EMI Driven by PI
23/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Switching Power Noise
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Time [ns]
1.20
1.40
1.60
1.80
2.00
2.20
2.40
Y
1
[V]
Ansoft Corporation BulkU41 Power
Cur ve Inf o pk2pk
V(VCC_U41-2)
Transient0.6787
V(VCC_U41-21)
Transient0.6995
V(VCC_U41-42)
Transient0.8191
V(VCC_U41-44)
Transient0.7597
V(VCC_U41-63)
Transient0.7882
V(VCC_U41-84)Transient
0.6858
Shaded area represents time
domain violation of 1.8 V 10%
~11-12 ns
period
Bulk Only
3Meter FF
-
7/27/2019 EMI Driven by PI
24/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Choosing a Decoupling Capacitor
To reduce the effect of aresonance, choose a
capacitor with a low
impedance at theresonant frequency
Board w/
Bulk Caps
22 nF
Capacitor
-
7/27/2019 EMI Driven by PI
25/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Bulk vs. HF Capacitors 1
No Resonance @ 50 MHz
Board w/Bulk Caps
Board w/
HF Caps 1
Target
impedance 800
mOhm to 667
MHz
-
7/27/2019 EMI Driven by PI
26/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Time [ns]
1.20
1.40
1.60
1.80
2.00
2.20
2.40
Y1[V]
Ansoft Corporation HF1U41 Power
Curve Info pk2pk
V(VCC_U41-2)
Transient0.6481
V(VCC_U41-21)
Transient0.6979
V(VCC_U41-42)
Transient0.8802
V(VCC_U41-44)
Transient0.9182
V(VCC_U41-63)
Transient0.6925
V(VCC_U41-84)
Transient 0.7319
Switching Power Noise
Shaded area represents time
domain violation of 1.8 V 10%
Bulk Only
3Meter FF
-
7/27/2019 EMI Driven by PI
27/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Extending Low Impedance
10 1.2 nF capacitorswere added across the
board to extend
minimum high-frequencyimpedance
1.2 nF capacitor was
chosen due to low
impedance at 200 MHz
4 of these were locatednear U41
-
7/27/2019 EMI Driven by PI
28/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
HF 1 vs. HF 2
New resonance @ 80 MHz
Impedance exceeds
800 mOhm @ 350 MHz
Board w/HF Caps 1
Board w/
HF Caps 2
Target
impedance 800
mOhm to 667
MHz
-
7/27/2019 EMI Driven by PI
29/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Switching Power Noise
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Time [ns]
1.20
1.40
1.60
1.80
2.00
2.20
2.40
Y1[V]
Ansoft Corporation HF2U41 Power
Curve Inf o pk2pk
V(VCC_U41-2)
Transient0.2552
V(VCC_U41-21)Transient
0.2857
V(VCC_U41-42)
Transient0.2930
V(VCC_U41-44)
Transient0.4047
V(VCC_U41-63)
Transient0.3083
V(VCC_U41-84)
Transient0.3359
Shaded area represents time domain specification 1.8 V 10%
-
7/27/2019 EMI Driven by PI
30/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Removing a Resonance
Six 8 nF capacitors wereadded near U41 to
cancel resonance at 80
MHz
Added capacitors
U41
-
7/27/2019 EMI Driven by PI
31/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
HF 2 vs. HF 3
No resonance @ 80 MHz
Impedance crosses
800 mOhm @ 500
MHz
Board w/HF Caps 2
Board w/
HF Caps 3
Target
impedance 800
mOhm to 667
MHz
-
7/27/2019 EMI Driven by PI
32/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Time [ns]
1.20
1.40
1.60
1.80
2.00
2.20
2.40
Y1[V]
Ansoft Corporation FinalU41 Power
Curve Inf o pk2pk
V(VCC_U41-2)
Transient0.2416
V(VCC_U41-21)Transient
0.2685
V(VCC_U41-42)
Transient0.2660
V(VCC_U41-44)
Transient0.3264
V(VCC_U41-63)
Transient0.3709
V(VCC_U41-84)
Transient0.3142
Switching Power Noise
Shaded area represents time domain specification 1.8 V 10%
Maximum peak to peak noise of 371 mV
-
7/27/2019 EMI Driven by PI
33/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Buried Capacitance
Due to parasitic inductanceit is impossible to decouple
the board with capacitors atfrequencies greater than afew hundred MHz
Using a thinner dielectriclayer between power andground planes introducesadditional capacitance andreduces high frequencyimpedance
d
AC =
Capacitance of
parallel plates:
-
7/27/2019 EMI Driven by PI
34/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
HF 3 vs. Buried Capacitance
Impedance crosses
800 mOhm @ >667
MHz
Board w/HF Caps 3Board w/
Buried
Capacitance
Target
impedance 800
mOhm to 667
MHz
Target impedance specification met
-
7/27/2019 EMI Driven by PI
35/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Time [ns]
1.20
1.40
1.60
1.80
2.00
2.20
2.40
Y
1
[V
]
Ansoft Corporation BuriedU41 Power
Cur ve Inf o pk2pk
V(VCC_U41-2)
Transient0.2177
V(VCC_U41-21)Transient
0.2295
V(VCC_U41-42)
Transient0.2418
V(VCC_U41-44)
Transient0.2549
V(VCC_U41-63)
Transient0.2729
V(VCC_U41-84)
Transient0.2169
Switching Power Noise
Maximum peak to peak noise 273 mV
24% smaller than limit
Shaded area represents time domain
specification 1.8 V 10%
Time-domain noise specification met3Meter FF
SpecificationSpecification
Met!Met!
-
7/27/2019 EMI Driven by PI
36/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Conclusions
SI / PI / EMI are all based on the sameelectromagnetic fundamentals and cannot be
separated
Impedance and resonant mode simulations connectthe frequency domain to the spatial domain and allow
selection of capacitor value and placement
Frequency domain extractions are useful for quickly
optimizing PDS designs, but time domain simulations
are necessary to ensure compliance with device specs Using a single design environment can help reuse the
same models for SI/PI/EMI simulations
-
7/27/2019 EMI Driven by PI
37/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Questions
Any Questions?Any Questions?
-
7/27/2019 EMI Driven by PI
38/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
EMI Driven by Signal Integrity
Fundamentals of Coupled SI/PI/EMI
Part 2
Aaron Edwards
-
7/27/2019 EMI Driven by PI
39/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
SI + PI = EMI
Trend: Cost / Performance targets drive theintegration of ICs, SoCs, and SiPs onto low cost
printed circuit boards.
Chip/Package/Board Co-design is required
POWER INTEGRITY
SIGNAL INTEGRITY
EMC/EMI
Far Field - CPM2 - 1.27v Baseline
-20.00
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
0.00 0.50 1.00 1.50 2.00
GHz
dBuV/m_
Where is the problem?
-
7/27/2019 EMI Driven by PI
40/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Where is the problem?
Intentional Signals
Focus on Clock and High Speed Signals
Stripline not necessarily better than Microstrip
Examine Clock Harmonics filter if necessary
Differential signaling is a standard to improve signal-to-
noise ratios, however, its use always leads to Common
mode noise Common Mode Conversion
SCD11=0.5*(S(1,1)-S(1,3)+S(3,1)-S(3,3))
SCD21=0.5*(S(2,1)-S(2,3)+S(4,1)-S(4,3))
Where is the problem?
-
7/27/2019 EMI Driven by PI
41/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Where is the problem?
Unintentional Signaling
Common mode will always existCommon Mode noise is the main contributor to EMI
How? Through Crosstalk
Beware the low speed nets; use post-layout analysis to scan
for unintended coupling
Coupling may be direct, through intermediate metal or even
from plane cavities
This presentation focuses on crosstalk, the primary SI
contributor to EMI radiation
Crosstalk
-
7/27/2019 EMI Driven by PI
42/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Crosstalk
Definition and Sources
Signal integrity examines the quality of transmittedwaveforms through a physical interconnect; Traces,
connectors, vias, etc
Crosstalk is the coupling of energy from one currentcarrying conductor to another. It occurs when the
electromagnetic fields from one conductor interferes
with another conductor, thus changing its desired
characteristics
There are 2 main components to Crosstalk:Mutual Inductance and Mutual Capacitance
How to calculate crosstalk
-
7/27/2019 EMI Driven by PI
43/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
How to calculate crosstalk
Mutual Inductance
Mutual Inductance induces current from an aggressor line
onto a victim line by the magnetic field.
The noise voltage that is injected onto the victim line can becalculated by 2 methods
Method #1 Method #2
Analytical Calculation Field Solution
Vnoise,Lm = Lm di/dt
How to calculate crosstalk
-
7/27/2019 EMI Driven by PI
44/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
How to calculate crosstalk
Mutual Capacitance
Mutual Capacitance is the coupling between 2 conductors
via the electric field.
The induced noise that shows up on the victim net can becalculated by 2 methods
Method #1 Method #2
Analytical Calculation Field Solution
Inoise,Cm = Cm dv/dt
C li Di t t C t lk St th
-
7/27/2019 EMI Driven by PI
45/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Coupling Dictates Crosstalk Strength
Near and Far End Crosstalk The magnitude of the Mutual Capacitive and Inductive Coupling will determine the amountof current induced on the victim net. The summation of these currents determine near and
far end crosstalk
ICM
ICM
ILM
Inear= ICM + ILM
Ifar= ICM - ILM
A l ti l C t lk C l l ti
-
7/27/2019 EMI Driven by PI
46/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Analytical Crosstalk Calculations
Driven Line
Un-driven Linevictim
Driver
Zs
Zo
Zo
Zo
Near End
Far End LCXTD =
+=
C
C
L
LVA MM
input
4
=
C
C
L
L
T
LCXVB MM
r
input
2
Terminated Victim
C
LZO =
TD
Tr ~Tr Tr
AB
VaVb=[NEXT]CrosstalkEnd-Near
Va
Vb=[kb]tCoefficienCrosstalk
Back of the envelope calculations can beused as a quick check:
Source signal
Far End of Source SignalNear-end X-talk
Far-end X-talk
A l ti l C t lk C l l ti E l
-
7/27/2019 EMI Driven by PI
47/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Analytical Crosstalk Calculation Example
nspFnHinLCXTD 139.026.2*55.81 ===
mVpF
pF
nH
nHmv
C
C
L
LV
AMMinput
5626.2
389.0
55.8
39.2
4
500
4 =
+=
+=
mVpF
pF
nH
nH
ps
pFnHinmV
C
C
L
L
T
LCXV
BMM
r
input
3726.2
389.0
55.8
39.2
100*2
26.2*55.81*500
2 =
=
=
TD
Tr ~Tr Tr
A
B
Trace Width 13mil
Height 10mil
Trace
Separation
7mil
Thickness 2mil
Dk 3.55
Vsource 1V
Vinput 500mV
Trace Length 1in
Source Impedance 50ohms
Termination
Impedance
61.5ohm
s
Risetime 100ps
Delay Time 200ps
8.55nH 2.39nH
2.39nH 8.55nHL /inch=
2.26pF 0.389pF0.389pF 2.26pF
C/inch=
ohmpF
nH
C
LZO 5.61
26.2
55.8===
Field Sol tion Crosstalk E ample
-
7/27/2019 EMI Driven by PI
48/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Field Solution Crosstalk Example
m2(A) = 57.4mVm1 (B) = -37.2mV
m4-m3 (TD) = 0.1359ns
HFSS
2D ExtractorSIwave
Same example using Method #2 Field solutions
Parameterization Captures Trends
-
7/27/2019 EMI Driven by PI
49/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
p
Impact of Length and Spacing
Trace Length
= 1,2,3,10in
As Length
increases, Ifaraccumulates
As Trace
Spacing
increases,
Ifardecreases
As Trace
Spacing
increases,
Inear
decreases
Trace Spacing=
7, 12, 17, 22, 27mil
Parameterization Captures Trends
-
7/27/2019 EMI Driven by PI
50/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Parameterization Captures Trends
Crosstalk Increase DecreaseCm
Lm
Trace
Spacing
GND Plane
Distance
Dk
Trace Width
Under-etching
NE FE NE FE
Good Coupling, when Xtalk is desired
-
7/27/2019 EMI Driven by PI
51/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
p g,
Differential Signaling
Why Differential Signaling?
When lines are tightly coupled, noise affects bothlines. Thus at the receiver, the difference between the
two lines remains constant
Stray transient noise on the two conductors will self-
cancel, which leads to a reduction of noise from the
power supply
Because differential signaling creates a known return
path, signal quality will significantly improve in the
presence of non-ideal ground return paths, or other
discontinuities such as connectors, wirebonds, vias,
etc..
Good Coupling
-
7/27/2019 EMI Driven by PI
52/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
p g
Differential Signaling
Back of the envelope calculations of Differential and Common Mode Impedancecan be used as a quick check
Lodd = L11 L12 Leven = L11 + L12Codd = C11 + C12 Ceven = C11 - C12
Zdifferential = 2*Zodd Zcommon = ()*Zeven
1211
1211
CCLL
CLZ
even
eveneven
+==
1211
1211
CCLL
CLZ
odd
oddodd
+==
Electric Field
Magnetic Field
Electric Field
Magnetic Field
3D Crosstalk Needs Field Solution
-
7/27/2019 EMI Driven by PI
53/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
3D Crosstalk Needs Field Solution
2.2 inch total length
of trace.
88 mil via transition
Near-End
Probe
Far-End Probe
Peak Near-End Crosstalk: 25mV
Peak Far-End Crosstalk: -21.8mV
Bad Coupling
-
7/27/2019 EMI Driven by PI
54/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Via Transition
Peak Near-End Crosstalk: 13.1mV
Peak Far-End Crosstalk: -14mV
Total length of parallel viarouting is 4% of the total length.
Yet the Near-End Crosstalk only
reduces by 48%.
The Far-End Crosstalk only
reduces by 36%Near-End
Probe
Far-End Probe
2.2 inch total length of trace
88 mil via transition
Bad Coupling
-
7/27/2019 EMI Driven by PI
55/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Via Transition
Peak Near-End Crosstalk: 19mV
Peak Far-End Crosstalk: -20mV
Near-End ProbeFar-End Probe
Added Ground Vias
Peak Near-End Crosstalk: 10.3mV
Peak Far-End Crosstalk: -10.9mV
Total length of parallel viarouting is 4% of the total
length.
Yet the Near-End Crosstalk
only reduces by 24%.
The Far-End Crosstalk only
reduces by 8%
Chip/Package/Board Co-Design
-
7/27/2019 EMI Driven by PI
56/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Electromagnetic
InterferencePower Integrity
Case #1
Signal Integrity
Capturing the Complete System
-
7/27/2019 EMI Driven by PI
57/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Designer
Nexxim
Ansoft EMI Design Flow
Resonance Analysis
Impedance Analysis
Near field plots
Far field plots
S.O.C.
DatabaseCPM Package
Database
PCB
Database
SIwave
S-Parameters
Frequency-
Domain
Voltages
Package and Board Models
-
7/27/2019 EMI Driven by PI
58/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Case #1
Package has beenmerged onto board
Coupling between the
bondwires, leadframe,and board are
simulated
Apaches Chip Power Model
-
7/27/2019 EMI Driven by PI
59/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Apache s Chip Power Model
VDDVDD
VDDQVDDQ
CPM I/O Interface
Chip Power Model
VSSVSS
SIGSIG
SIwave Full-Wave
Package/PCB Model
Input
Buffer
Level
ShifterBuffer
PCBPackage
Designer & Nexxim
-
7/27/2019 EMI Driven by PI
60/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Designer & Nexxim
Drive VDDs with CPM
Capture coupled high-
frequency noise
Run Near/Far-Field
Simulations using
transient results
SIwave
Model
CPM
Model
Terminations
Time and Frequency Domain Results
-
7/27/2019 EMI Driven by PI
61/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Time and Frequency Domain Results
Far Field - 1.27V - No Decaps - Baseline
-20.00
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
0 0.5 1 1.5 2
GHz
dBuV/
m__
Transient Power Noise 3m Far Fields
Near Fields at 1GHz
-
7/27/2019 EMI Driven by PI
62/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC ProprietaryBaseline 1.27 V w/ Decap 1.1 V
Chip/Package/Board Co-Design
-
7/27/2019 EMI Driven by PI
63/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Electromagnetic
InterferencePower Integrity
Case #2
Signal Integrity
Ansoft Virtual Chamber
-
7/27/2019 EMI Driven by PI
64/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Ansoft Virtual Chamber
27
Driver settings
Solving the Field Solution
U i Ti D i I f ti
-
7/27/2019 EMI Driven by PI
65/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Using Time Domain Information
28
FFT of Transient Data Near/Far Fields
Computed in
SIwave and HFSS
Time Frequency Radiation
Agreement captured in simulation
-
7/27/2019 EMI Driven by PI
66/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
g p
ONLY PCB Spectrum
10 M Measurement
SIwave
Excessive Common Mode coming from
D i
-
7/27/2019 EMI Driven by PI
67/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Glitch seen in
falling
waveform;
this will
create
Common
Mode Noise
Driver
Ideal DriverOriginal Driver
Transient Waveform
Common Mode Spectrum
Intentional Signaling contributing to EMI
-
7/27/2019 EMI Driven by PI
68/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Intentional Signaling contributing to EMI
Ideal DriverOriginal Driver
Even
Harmonics are
now absentbut EMI is still
high
Problemis not just
common
mode
Adding a filter to reduce problematic
hi h h i
-
7/27/2019 EMI Driven by PI
69/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
higher harmonics
Pi Filter added to driver
output to squelch higher
harmonics of 13.56 MHz
clock
Component values
optimized in
Designer
Reduced Common Mode after filtering
-
7/27/2019 EMI Driven by PI
70/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
educed Co o ode a te te g
Ideal Driver
Transient Waveform
Common Mode Spectrum
Filtered Driver
Signal integrity still OK but
high frequency spectrum is
reduced
EMI from Intentional and Unintentional
Si li d
-
7/27/2019 EMI Driven by PI
71/72
2008 Ansoft, LLC All rights reserved. Ansoft, LLC Proprietary
Signaling suppressed
Filtered DriverOriginal Driver
EMI is now
sufficientlysuppressed
Conclusions
-
7/27/2019 EMI Driven by PI
72/72
Crosstalk is major concern for SI Need to examine all relevant coupling: vias, traces, etc.
Simulation can help determine acceptable levels of coupling
Target impedance helps ensure good PI
Target impedance is defined in Frequency domain
Need to verify ripple in time domain
EMC is comprised of good PI and SI Poor plane design can spread common mode noise
Unintentional coupling is a big source of radiated emissions