EMC Simulation
in the Design Flow of Modern Electronics
Andreas Barchanski
CST AG, Germany
Jens Kr?mer, Pietro Luzzi
Festo AG1, Germany
E M C compliance is a necessary condi-
tion for releasing products to market.
National and international standards bodies such as the IEC2 and the FCC3 de?ne limits on the emissions a device is allowed to produce, and automotive and aerospace manu-facturers can set even stricter standards for their OEM suppliers. If these standards are not met, the product cannot be sold.
EMC engineering has traditionally been the domain of measurement alone, with the result that EMC compliance was only considered late in the design process, since it required a work-ing prototype. Correcting EM C problems at this late stage can be cost-intensive, especially if multiple prototype iterations are required.
In addition, although measurement can help identify the symptoms of EMC issues, it is only of limited use for identifying the root causes of the problems. This means EMC troubleshoot-ing using measurement is often limited to ap-plying countermeasures such as ?lters and ad-ditional shielding, which can increase the size and the cost of the product, instead of tackling the problem at its source.
Simulation allows EM C compliance to be analyzed earlier in the design process, and in greater depth than is possible with measure-ment alone. Because simulation doesn’t re-quire a physical prototype, it can be used to investigate many different con?gurations and
Fig. 1 Manufactured demonstrator board (top) and
the equivalent simulation model (bottom).
Reprinted with permission of MICROWAVE JOURNAL? from the December 2014 issue.
?2015 Horizon House Publications, Inc.
domain solver needs to simulate each
port separately, but it can simulate a
broad band of frequencies at once,
and is more ef?cient than the fre-
quency domain technique for electri-
cally large simulations.
Regardless of which simulation
method is used, the results are the
same: the S-parameters of the model
and the ?eld distribution inside it.
These S-parameters can be used to
produce a circuit-level model of the
component, which can be incorpo-
rated into the schematic of the device.
Circuit solvers are much faster than
3D solvers and, for a simple circuit, a
spectrum can be calculated within
seconds. This means that the circuit
elements can be adjusted interactive-
ly, and optimization of the circuit can
be carried out in a reasonable length
of time. This is especially useful for
extracting equivalent circuits for ele-
ments and for helping simulation and
measurement agree more closely.
In order to match the simulation
and measurement, the parasitic val-
ues of the mounted elements must be
known. To allow the input ?lter to be
simulated accurately, an equivalent cir-
cuit is added to the simulation model
representing the parasitics inherent in
the test ?xtures. By using the ‘Tune’
function, the values of the parasitics
are varied until the simulation’s behav-
ior matches the measurement. These
values are then applied across multiple
simulations, while maintaining good
agreement between measurement and
results (see Figure 2).
CONDUCTED EMISSIONS
Two parts of the system are in-
volved in conducted emissions: the
input ?lter and the voltage regulator.
For the analysis presented here, a
constant load of 2.5 ? is placed on the
board. This load leads to a high cur-
rent, so the emission is also quite high.
This is, therefore, a worst case set-up.
The conducted emission will be
measured using ports at the connector
that are connected on the other side
to an electric boundary, acting as a vir-
tual reference. This electric boundary
creates a low-impedance path for the
return current. It is not an ideal exter-
nal ground, as this cannot exist in a 3D
model.
As already discussed, the frequen-
cy domain solver is a good choice for
most conducted emissions simulations
C performance just
C
the interactions between signal lines
and components. Only a 3D simula-
tion can reveal these effects.
This means that circuit-level simula-
tion methods coupled to full-wave 3D
EM simulation can complement each
other. These can be combined in a
number of different ways: for example,
a ‘Combine Results’ task, based on the
superposition principle, can be used to
calculate the ?eld distribution when a
circuit is attached to a 3D model with-
out having to resimulate the entire 3D
model, while true transient/EM co-
simulation can be used to integrate cir-
cuits, including nonlinear components,
into a full-wave 3D simulation.
The ?rst step is to de?ne the mod-
el geometry and import CAD and
EDA data for PCBs and enclosures.
Lumped elements, ports, probes and
?eld monitors are also de?ned at this
stage. The ports are what will later
provide the link between the full-wave
simulation and the circuit simulation.
Once these are set up, the simulation
can begin.
Full wave solvers can be broadly di-
vided into time domain and frequen-
cy domain methods. For conducted
emissions, where the frequency range
is narrow and the ?elds are con?ned
to the electrically small board, the fre-
quency domain solver is usually the
best choice. A frequency domain di-
rect solver only requires one pass to
simulate all the ports, which is useful
for densely populated boards.
For radiated emissions, a time do-
main method is a better ?t. The time
components within the device – are
usually dif?cult to change later on and
can be crucial for the EM C compli-
ance of a device.
Simulation is also helpful at the
troubleshooting stage, where it is
a complementary tool to measure-
ment. Current and ?eld visualization
can serve to highlight the locations of
EMC problems. They offer more in-
sight into the behavior of the device
than a blip on a spectrum analyzer
graph can provide, although the mea-
surement is still critical for the ?nal
decision as to whether the device
passes or fails the test.
This article considers how to test
and develop the EM C work?ow for
modern electronic devices. The dem-
onstrator board (see Figure 1) is
based on modern electronic designs,
and the principles outlined here are
applicable to a wide range of devices.
On this board, the power is routed
through an input ?lter to a voltage
regulator module (VRM) that drives a
power delivery network (PDN) on the
PCB. A number of single ended and
differential drivers are placed on the
board. Some of them are routed over
a connector and all of them are ?nally
terminated on the board.
The demonstrator board contains
two versions of the same system on a
common substrate – one designed to
offer good EMC performance (the up-
per half of the board in Figure 1, called
the “good” layout), and one designed
to offer poorer performance (the lower
half, called the “bad” layout).
30
10.15
10100806040200–20–40Frequency (MHz)3010.15
10Frequency (MHz)
Simulated Measured
100806040200–20–40
PCB and outputs them as a near-?eld
diated emissions (in this case, 30 MHz to 1 GHz). In this example, the emis-
–40–60–80n i t u d e i n d B )
s Fig. 6 Electric ?eld around the PCB at
100 (top), 350 (center) and 700 MHz (bottom).
source ?le. This near-?eld source is then imported into a second simulation of the anechoic chamber, using a much coarser mesh. According to Huygens’ Principle, the second simulation will create the same radiated emissions as the full 3D model, and it only requires a few minutes. The same approach can be used for modeling other structures which can affect emissions, such as the housing of a PCB.
CONCLUSION
Simulation is a useful tool for the EM C analysis of complex electronics and allows engineers to identify possi-ble EMC problems early in the design process. Simulation can identify trends which are subsequently con?rmed by the measurements. Broadband simulations, in particular, are fast and straightforward and can provide useful data even in cases where the complex-ity of the measurements makes a direct comparison between simulation and measurement dif?cult. ■References
1. Festo, https://www.doczj.com/doc/1a5909225.html,
2. IEC/TR EN 61000, Electromag-
netic Compatibility (EMC)
3. Code of Federal Regulations, Ti-
tle 47, Part 15 (47 CFR 15), Fed-
eral Communications Commission
(FCC)
4. CST STUDIO SUITE, https://
https://www.doczj.com/doc/1a5909225.html,
5. LT8610: 42 V, 2.5 A Synchronous
Step-Down Regulator with 2.5 μA
Quiescent Current, http://www.
https://www.doczj.com/doc/1a5909225.html,/product/LT8610
6. CISPR 16, Speci?cation for radio
disturbance and immunity mea-
suring apparatus and methods
Andreas Barchanski is the EMC
market development manager at
CST. He holds an M.Sc. degree in
physics and a Ph.D. in numerical
electromagnetics from the Technical
University Darmstadt. He joined CST
as an application engineer in 2007.
Besides EMC, his main interest lies
in the simulation of various electronic
systems ranging from high speed
digital to power electronics.
Jens Kr?mer is the EMC simulation
and testing manager at Festo, a
leading world-wide supplier of
automation technology and a leader
in industrial training and education
programs. He holds a diploma in
electronics from the University
Stuttgart. His main interest lies in
energy propagation on PCBs and
through connectors – both intentional
and unintentional.
Pietro Luzzi is an EMC consultant
at Festo. He holds a bachelor’s degree
in electrical engineering. In 2012 he
joined the EMC Simulation & Testing
department, where he plans circuit
boards and simulates a variety of
interactions between EMC and the
PCB.