B-4-17
2012 年　電子情報通信学会総合大会
A Study on Imbalance Component and EM Radiation from
Asymmetrical Differential-Paired Lines with Equi-Distance Routing
Yoshiki Kayano, Yasunori Tsuda and Hiroshi Inoue
Akita University, Japan
l =137
w=100
FR-4 ( ε r=4.5, h =1.53)
(Reverse side is ground plane)
l =100
Logical
Logical
Line 2 ( w t= 1.9)
Port 1
Port 2
s=1.0
Line 1 ( w = 1.9)
I. Introduction
For actual differential-signaling (DS) techniques
such as low-voltage differential-signaling (LVDS), the ideal balance
or symmetrical topology cannot be established, and hence, an imbalance component is excited in practical high-density packaging systems e.g. [1], [2]. Hence, effective methods for predicting and suppressing EMI as well as maintaining SI over a broad band are required. So far, the authors have discussed the characteristics of the
EM radiation from a PCB driven by LVDS [3], [4]. This paper focuses
on the imbalance component and EM radiation generated by asymmetrical differential-paired lines with equi-distance routing, which
depends on the PCB layout of the design stage.
II. Geometry under Study
The differential-paired lines with
different layouts were prepared for the discussion as typical equidistance routing. The geometries of the PCBs under study are illustrated in Fig. 1. a) is a basic symmetrical structure as the “ideally
balanced” case, called PCB1; b), c) and d) are asymmetrical topology
with equi-distance and different bend routing region.
Frequency responses of |Scd21 |,
III. Results and Discussion
which is defined as the conversion from differential-mode (balance
component) to common-mode (imbalance component), are shown in
Fig. 2. Although the geometric length of each line is the same as
shown in Fig. 1 (PCB5 (n=1, 2 and 3)), the |Scd21 | is increased as
the number of bend region is increased. This may result from the
phase-difference of propagation signal between the differential-paired
lines, due to discontinuity of the DM impedance, and difference of net
propagation-path due to EM coupling in bend region.
The horizontal component of far-electric fields at 3 m is
measured in an anechoic chamber, in order to discuss the correlation between imbalance component and EM radiation from the
PCB. The differential-paired lines are driven by an LVDS driver (NS
DS90LV047A) connected to a crystal oscillator (3.3 V amplitude and
25.0 MHz oscillation frequency). The differential-paired lines are
terminated with 100 Ω SMT resistor as bridge termination. The measured frequency response of far-electric field is shown in Fig. 3. The
radiation from the “PCB5 (n=1)” case is not small compared with that
from the “PCB5 (n=2, 3)” cases. This fact does not correspond to the
feature of imbalance component evaluated from the |Scd21 |. Once the
phase-difference of propagation signal between the differential-paired
lines arises, a cancellation effect of DS for EM radiation at observation point will be deteriorated dramatically, and hence EM radiation
increases. Although equi-distance routing is considered as a suitable
method for improvement of SI performance at the end of paired lines
such as eye-diagram, it does not work as suppressing the EMI.
IV. Conclusion
This paper reported the basic characteristics of
imbalance component and EM radiation from a practical differentialpaired lines with asymmetrical equi-distance routing. The consequences indicate that the measurement of |Scd21 | is not the enough
parameter for predicting the EM radiation. Predicting and identifying
the dominant radiation component are the future subjects for mitigating EMI and developing guidelines in high-speed electronic designs.
The authors sincerely thank to Akita IndusAcknowledgments
trial Technology Center, for their support of measurements in an anechoic chamber, and Cyberscience Center, Tohoku University, and
General Information Processing Center, Akita University, for their
support with computer resources. This research was partially supported by TELECOM ENGINEERING CENTER.
2012/3/20 〜 23　岡山市
Logical
Port 1
l b=24.0
Logical
Port 2
s=1.0
24.0
t
7.5 30.0
25.0
30.0 7.5
b) PCB5: equi-distance routing ( n =1)
a) PCB1: ideally balanced
y
z
x
l b=24.0
Logical
Port 1
Logical
Port 2
Logical
Port 1
l b=24.0
Logical
Port 2
8.0
12.0
6.0
10.0
7.5 30.0
25.0
30.0 7.5
c) PCB5: equi-distance routing ( n =2)
7.5 30.0
25.0
30.0 7.5
d) PCB5: equi-distance routing ( n =3)
Fig. 1 Geometry of the PCB under study (in mm).
0
equi−distance routing
−10
|Scd21| [dB]
−20
n=3
−30
−40
n=2
n=1
−50
balanced
−60
Experiment
FDTD
−70
−80 7
10
8
10
9
10
10
Frequency [Hz]
10
Far−electric field Eφ (90, 90) [dBµV/m]
Fig. 2 Frequency response of |Scd21 |.
25
20
15
10
PCB1
PCB5(n=1)
PCB5(n=2)
PCB5(n=3)
5
noise floor level
0
0
200
400
600
Frequency [MHz]
800
1000
Fig. 3 Frequency response of far-electric field (hori. comp.).
References [1] H. Johnson and M. Graham, High-Speed Signal
Propagation: Advanced Black Magic, Prenticel Hall, 2003. [2] C.
Gazda, et al., IEEE Trans. Adv. Packag., 33, 4, pp.969–978, 2011.
[3] Y. Kayano and H. Inoue, EMCJ2011-87, 2011. [4] Y. Kayano, K.
Mimura and H. Inoue, Trans. JIEP, 4, 1, 2011.
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