APEMC 2015
Coupling Analysis and Equivalent Circuit Model of
the IC Stripline Method
JongTae Hwang1,2, WonJoo Jung1, SoYoung Kim1
1
College of Information and Communication Engineering, Sungkyunkwan University, Suwon, Korea
2
DRAM Solution Team, Memory Division, Samsung Electronics, Hwasung, Korea
E-mail: ksyoung@skku.edu
Abstract—As portable electronic devices are widely used in
wireless communication, analysis of RF interference becomes an
essential step for IC designers. In order to test electromagnetic
compatibility (EMC) of IC operating at high frequencies, IC
stripline method is proposed in IEC standard. This method can be
applied up to 3 GHz and covers the testing of ICs and small
component. This paper represents simulation results of the open
version of IC stripline in 3D EM solver. Also, the coupling effect of
IC stripline method is analyzed with S-parameter results. The
distributed lumped-element equivalent model is presented for
explaining coupling relation between IC stripline and package.
This model can be used for quick analysis for EMC of ICs.
Keywords—IC stripline, Electromagnetic compatibility (EMC),
Circuit model, 3D EM simulation
I.
INTRODUCTION
Recently a variety of ICs has been used in electronic
devices with the rapidly increased operating frequency. Also,
in wireless communications, stacked ICs and reduced PCB
dimension cause more electromagnetic coupling in electronic
systems. Because radiated electromagnetic emissions from ICs
cause malfunction of electronic systems, it is essential for IC
designers to get enough margins for EMC. Over the years,
many researchers have been working on EMC analysis of ICs
[1].
Until recently, the standard EMC test method is transverse
electromagnetic (TEM) cell method according to IEC 61967-2
[2]. This method can be used to measure emission and
immunity of PCB level. As the operating frequency of IC
increases rapidly, IC stripline method was proposed as a new
alternative for radiative emission and immunity test in IEC
standard [3], [4]. This method shows higher intensity of
electromagnetic emission up to 20 dB better than TEM cell
method [5]. The operating frequency of IC stripline is up to 3
GHz. The open-version of IC stripline structure is shown in
Figure 1. Active conductor is a source of radiated coupling to
device under test (DUT). Also it can be a receptor of radiated
noise from DUT. While the closed-version has its housing
structure, the open-version has smaller dimension without
housing and cheaper cost compared to the closed-version [4].
978-1-4799-6670-7/15/$31.00 Copyright 2015 IEEE
Fig. 1. Simplified open-version structure of IC stripline
Simulations and tests to compare the IC stripline method
and TEM cell method were done in [5], [6]. The optimization
technique for improving voltage standing wave ratio (VSWR)
is proposed in [7]. Equivalent circuit models of TEM cell are
presented in [8], [9]. Also, equivalent circuit models of IC
stripline are examined in [10], [11].
In this paper, the dimension of open-version IC stripline
meeting the IEC standard will be proposed with the Sparameter results of 3D EM solver. Also, the dominant
coupling factors will be presented by comparing the Sparameter simulation results among different DUTs. With this
3D model of the IC stripline and DUT, equivalent lumpedelement circuit for electromagnetic coupling will be proposed.
The paper is structured as follows. Section II presents the
structure of open-version IC stripline and DUT model used for
modeling. Also, S-parameter analysis results using 3D EM
solver are examined. Section III introduces equivalent
lumped-element circuit model and its accuracy compared to
3D simulation. Finally, the conclusion is given in Section IV.
II.
IC STRIPLINE SIMULATION WITH 3D EM SOLVER
A. IC stripline structure for simulation
According to IEC 62132-8 [4], the goal of IC stripline
design is to guarantee VSWR of active conductor less than
1.25 up to 3 GHz. Active conductor consists of upper plane and
tapered regions of each side. The tapered region is the main
part that causes reflection when increasing VSWR. Shape and
angle of tapered region are the parameters for impedance
matching. The material used for active conductor is copper.
The 0.55 mm FR4 and copper ground plane are used for PCB.
The height of the active conductor to ground (H1) is chosen
APEMC 2015
from [7], [11]. The structural parameters of IC stripline are
shown in Figure 2 and the dimensions are listed in Table I.
are designed to be lower than those of the package pins. All the
cases are simulated including the IC stripline structure using
3D EM solver.
Fig. 2. Structure parameters of IC stripline
Fig. 4. 5 types of signal path shapes to model the die inside the QFP package
TABLE I.
W1
35.20
W2
2.00
DIMENSIONS OF IC STRIPLINE
Dimension [mm]
L1
L2
58.32 48.00
H1
8.00
H2
7.45
The most critical parameter to meet VSWR target is the
thickness of active conductor by 3D EM simulation. The
relation between thickness and VSWR is described in Figure 3.
The simulation result shows that 1mm thick copper gives the
lowest VSWR up to 3 GHz.
C. S-parameter analysis using 3D EM solver
Longitudinal direction of IC package shows more coupling
than transverse direction in [11]. So, S-parameter simulations
of longitudinal direction were done with 3D EM solver. Figure
5 shows the port definition of S-parameter simulation. S31 and
S41 represent near-end coupling and far-end coupling of DUT.
The S31 result of five DUTs using 3D EM solver are shown in
Figure 6.
Fig. 5. Port definition of S-parameter simulation
Fig. 3. Simulation result of VSWR versus copper thickness
B. DUT structure for simulation
DUT type for simulation is a quad flat package (QFP)
which has a dimension of 10×10×2.1 mm. Figure 4 shows five
possible ICs or die models that can represent inductance or
capacitance dominant interconnects of ICs. Two inductive onchip interconnects, the 12-curved and 6-curved signal lines,
represent the inductance dominant on-chip interconnect lines.
Small-plate and large-plate cases are representing capacitive
interconnects. These two models are developed to better
capture the capacitance dominant on-chip interconnects
compared to the models developed in [11]. In addition to the
signal line, two ground lines are place on both sides to better
model the on-chip interconnect structure. The distance between
the signal and ground lines are 5 pitches (package pin pitch)
apart from signal path in both directions. They are connected to
the PCB ground plane through via. In order to minimize the
coupling of interconnects, the heights of on-chip interconnects
Fig. 6. S31 simulation result of DUTs using 3D EM solver
In Figure 6, large-plate line has the largest couplings
among five DUTs while 12-curved line shows the least.
Highly capacitive signal line tends to receive more radiated
noise at the near-end than the inductive one. Figure 7 shows
the relation between capacitance and S31 where S31 increase
is estimated by
| (S31 of each DUT) – (S31 of 12-curved line DUT) |
APEMC 2015
The coupling capacitance between the IC stripline and DUT is
extracted from 3D EM solver. The trend of the coupling
capacitance between stripline and DUT is highly correlated to
the S31 increase.
conductor and DUT is modeled by mutual inductance and
coupling capacitance. The main methodology of creating the
equivalent model in this paper follows the modeling concept of
[11]. Figure 9 shows the final simplified model of equivalent
circuit. A new parameter for the capacitance between middle
active conductor and ground, Csl, is added to the previous
model. Compared to single LC T-model of [11], distributed
lumped-element model can provide more precise results. When
using distributed lumped-element model, the number of
segments should be determined. Tr is set to 0.1 ns which is the
shortest signal rise time derived from the higher test frequency
range which is 3GHz. The lengths of coupling dominant region
and the side parts are 16 mm respectively. The number of
segments of distributed model is calculated as follows.
number of segments 
Fig. 7. Comparison between the S31 increase and the coupling capacitance
The S41 results of five DUTs are shown in Figure 8. The
straight line shows the highest coupling compared to others.
The12-curved line which has the highest inductive coupling
and the large-plate that has the highest capacitive coupling
shows the least S41 coupling result. The S31 results show
about 5~8 dB more coupling at 2 GHz than S41 result.
10  length
Tr velocity
(1)
If the DUT dimension changes, the number of segments for the
coupling dominant region needs to be changed.
Three DUTs selected for equivalent model are straight line,
12-curved line and large-plate line. The latter two lines
represent inductive line and capacitive line, respectively. All
parts of DUT including IC, wire and other interconnects are
modeled as a distributed lumped-element circuit for analyzing
the coupling dominant region. Because the S31 difference
between 48mm and 70mm of L2 is under 0.5dB, the effect of
tapered region is negligible same as in [11]. Each region
consists of 50-cascaded lumped LC elements based on T-model.
The LC parameters of Figure 9 are listed in Table II. All
parameters of distributed model are validated using 3D EM
solver and Raphael [12]. The LC values are further refined by
comparing the extracted values of the entire structure and each
part. Also, equations in [11] are used to different parameter
values for three sections of the IC stripline.
Fig. 8. S41 simulation result of DUTs using 3D EM solver
The wires which are lower than signal line show 0.5 dB less
coupling at 2 GHz compared to the wires which are 0.4 mm
higher than signal line in [11]. This result shows that
interconnect design should be considered for minimizing EM
disturbance.
III.
SIMULATION OF EQUIVALENT CIRCUIT MODEL
A. Definition of equivalent circuit model
With the availability of the equivalent circuit model, IC
designer can analyze the effect of RF interference at the circuit
simulation stage. Also, an intuitive interpretation is possible
with LC parameters of equivalent circuit model. In this section,
the improved lumped-element LC circuit model is proposed to
analyze the coupling between IC stripline and DUT.
An equivalent lumped-element circuit of IC stripline is
proposed in [11]. In this work, the equivalent circuit models of
the three region of the IC stripline, coupling dominant region
and other side parts of the active conductor, are replaced by the
distributed T-model. Electromagnetic coupling between active
Fig. 9. Proposed distributed LC model for coupling
TABLE II.
PARAMETER OF EQUIVALENT CIRCUIT MODEL
Csub
[fF]
Csl
[fF]
43.38
29.04
Straight Line
12-curved Line
Large-pate Line
Ccoupl
[fF]
Cic
[fF]
1.38
23.66
1.42
22.96
1.78
29.70
Lsub
[pH]
Lsl
[pH]
96.80
114.96
Lic
[pH]
M
[pH]
169.72
7.960
207.76
7.559
138.76
7.672
APEMC 2015
B. S-parameter analysis using equivalent circuit
The S-parameter results from the simulation of the
equivalent circuit are shown in Figure 10. The coupling
characteristics of three DUTs in the equivalent circuit
simulation are same as those of the 3D EM simulation. The
S31 of large-plate line and the S41 of straight line shows the
highest coupling. Because the maximum difference of S31 and
S41 among three models is below 3dB, the average parameter
of three models can be representing the ICs using same
package.
IV.
CONCLUSION
In this paper, the S-parameter analysis results of IC stripline
method with different types of DUTs are presented. Among the
five DUTs, the DUT with the largest capacitive coupling shows
the highest noise injection from IC stripline to package and IC.
Also, the equivalent distributed lumped-element circuit model
is proposed to model the inductive and the capacitive coupling.
This model can accurately predict the S-parameters obtained
from 3D EM simulation results. One of the advantages of
equivalent circuit model is that IC designer can apply the
equivalent circuit model to evaluate the EMC characteristics of
DUT. The proposed equivalent circuit represents the coupled
electromagnetic field from IC stripline to ICs. Future research
includes the fabrication and measurement of IC stripline
method for different types of ICs.
ACKNOWLEDGEMENT
(a) S31 result of equivalent circuit
(b) S41 result of equivalent circuit
This work was supported by the National Research
Foundation of Korea (NRF) grant funded by the Korea
government (MSIP) (No. NRF-2014R1A2A2A01006595).
Fig. 10. S-parameter result of equivalent circuit
The 3D EM and equivalent circuit simulation results of
each DUT case are compared in Figure 11. Both simulation
results of S31 representing near-end coupling and S41 showing
far-end coupling are matched well. This proposed model is
applicable to frequencies up to 3 GHz which is the maximum
range of IC stripline specified in IEC standards. The
comparison between single element and 50 segments of largeplate line case is shown in Figure 11(d). The single element
shows the deviation at frequencies over 2GHz.
(a) The result of straight line
(b) The result of 12-curved line
(c) The result of large-plate line
(d) Equivalent model comparison
Fig. 11. S-parameter comparison between 3D EM solver and equivalent
circuit
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