Filtering for Modular Data/Power ports
Overview
(RJ11 through RJ45 sizes)
Steward’s new line of “Slimline” Common Mode Chokes provide an effective EMI solution for
filtering Data/Power modular connectors.
Steward’s CM2718 for use with standard 4 line single module application, CM3818 for use
with 6 line single module applications (including 4 line data & 2 line power), and CM5018 for
use with a full RJ45 8 & 10 line single module application will provide the lowest cost, smallest
footprint EMI solution available on the market today.
Discussion
Modular jack ports (all of which have tight transmission specifications) support several very different protocols which generate a wide
range of EMI issues. Modular jacks range from the RJ11 2 & 4 line application to the RJ45 8 & 10 line types. The most common data
port is the RJ45. The RJ45 is used to support a broad range of serial data transmission (10 Mbs thru 250 Mbs) and, in some cases,
current loads. These ports have created several layers of EMI issues that need to be addressed.
Signal lines
- The various data protocols have a broad range of carrier frequencies to support 10 / 100 base T Ethernet up to the
1Gbs data (4 X 250 Mbs) transmission rates.
Power Lines
- Though currently a limited application, power can be handled by two or more conductors in the connector. These
power lines are a source of some unwanted EMI. The main issue, as in all power applications, is conducted common mode noise;
so the use of a Common Mode Choke to provide filtration has proven to be the best solution.
1.
PROBLEM:
The geometry of the typical filtered connector utilizes a group of wound toroids configured as common mode
chokes which tends to create too much Normal Mode Impedance. This causes failure in transmission signal
integrity due to excessive differential impedance on the line. The reason this occurs is due to the need to use small
toroids wound with a large number of turns. This configuration usually provides from 1400 to 1800 ohms peak to
obtain a broad band filter of greater then 100 ohms from 10 MHz to 1 GHz. The resulting high peak performance
curve has high Q, and therefore, high inter-winding capacitance leading to poor normal mode performance.
STEWARD SOLUTION:
Steward’s “Slimline” Common Mode Chokes have the lowest Normal mode impedance in the industry today (See
Data Performance curves on last page). Steward’s unique part geometry provides superior performance and
minimum net impedance at 10MHz, 100MHz and 250MHz. These chokes also provide a considerable amount of
broadband Common Mode Filtration. For example the 200 ohm parts yield more then 100 ohms of pure Common
Mode rejection from 10 MHz to 1 GHz. The net circuit impedance (Normal Mode) has less than 60 ohms impedance
from 10 to 250 Mhz, less than 25 ohms @ 100 MHz, and less than 5 ohms @ 10 MHz. Steward ferrite materials
currently used in all Steward multi-line products have a volume resistively (ohms per cm) that effectively removes
electrical crosstalk. Also, the geometry used by Steward minimizes inter-winding capacitance, the primary source of
crosstalk in most common mode chokes.
2.
PROBLEM:
The large footprint required for a separate Common Mode Choke and shielded modular connector requires far too
much board space compared to the typical shielded / filtered modular connector.
STEWARD SOLUTION:
Steward’s new “Slimline” Common Mode Chokes when, combined with the use of a standard Shielded RJ45
modular connector, has a smaller footprint than the standard RJ45 filtered/shielded modular assembly. This
provides a net DECREASE in footprint over the currently accepted solution by as much as 27% for a typical 4 line
filtered solution versus a shielded/filtered modular assembly.
3.
PROBLEM:
The shielded/filtered modular connector is very costly, due to its construction.
STEWARD SOLUTION:
The combined cost of a “Slimline” Common Mode Choke with a standard shielded modular connector will provide
approximately a 40% decrease in the cost per filtered line, over a filtered/shielded assembly.
Steward
U.S.A.
• Telephone: +1-423-867-4100 • Fax +1-423-867-4102 • Internet: http://www.steward.com
SCOTLAND
• Telephone: +44-(0)-1506-414200 • Fax +44-(0)-1506-410694
SINGAPORE
• Telephone: +(65)-337-9667 • Fax +(65)-337-9686
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Figure 1
Typical 4 Line Application (Ethernet Port)
CM2718
Shielded RJ45 Connector
Figure 2
Typical 6 Line Application (Ethernet Port)
CM3818
Shielded RJ45 Connector
Figure 3
Typical 8 Line Application (Ethernet Port)
CM5018
Shielded RJ45 Connector
Board Space Comparison for a 4 Line Application
Typical Filtered and Shielded RJ45 Connector
(approx. 0.495 in
2
of board space)
Typical Shielded 4 line RJ45 Connector with
Steward
CM2718R201R-00
(Steward solution: approx. connector area = .281 in
2
,
approx. common mode choke area = .079in
2
approx. combined area = 0.360 in
2
of board space)
27% Less Printed Circuit Board area required
Steward
U.S.A.
• Telephone: +1-423-867-4100 • Fax +1-423-867-4102 • Internet: http://www.steward.com
SCOTLAND
• Telephone: +44-(0)-1506-414200 • Fax +44-(0)-1506-410694
SINGAPORE
• Telephone: +(65)-337-9667 • Fax +(65)-337-9686
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CM2718R800R-00, CM3818R800R-00, CM5018R800R-00
Z, R, X
L
vs. Frequency
Impedance, Resistance, Inductive Reactance
120
CM2718R800R-00, CM3818R800R-00, CM5018R800R-00
Z, vs. Frequency
Open, Common, and Normal Mode
400
Impedance (W)
Impedance (W)
Normal
200
Z
60
R
Open
Common
X
L
0
1
10
100
1000
0
1
10
100
1000
10000
Frequency (MHz)
CM2718R121R-00, CM3818R121R-00, CM5018R121R-00
Z, R, X
L
vs. Frequency
Impedance, Resistance, Inductive Reactance
200
Frequency (MHz)
CM2718R121R-00, CM3818R121R-00, CM5018R121R-00
Z, vs. Frequency
Open, Common, and Normal Mode
600
Normal
Impedance (W)
100
Z
R
Impedance (W)
300
Open
Common
X
L
0
1
10
100
1000
0
1
10
100
1000
10000
Frequency (MHz)
CM2718R201R-00, CM3818R201R-00, CM5018R201R-00
Z, R, X
L
vs. Frequency
Impedance, Resistance, Inductive Reactance
240
Frequency (MHz)
CM2718R201R-00, CM3818R201R-00, CM5018R201R-00
Z, vs. Frequency
Open, Common, and Normal Mode
500
Impedance (W)
Z
120
R
Impedance (W)
250
Common
Normal
Open
X
L
0
1
10
100
1000
0
1
10
100
1000
10000
Frequency (MHz)
Frequency (MHz)
Steward produces an extensive line of solution focussed ferrite products for Inductive and EMI Filtering Applications. Products include ferrite EMI
cable cores, connector plates, unique common mode chokes, high current thru-hole and surface mount components, impedance chip beads,
surface mount inductors, toroid inductor cores and ferrite powders. Please consult our web site or contact your nearest Steward office or represen-
tative for additional information.
Steward
5 Cochrane Square
Brucefield Industry Park
Livingston EH54 9DR
Scotland, UK
Phone: +44-(0)-1506-414200
Fax: +44-(0)-1506-410694
Internet: http://www.steward.com
e-mail: europe@steward.com
Steward
1200 East 36th Street
P.O. Box 510
Chattanooga, Tennessee 37401-0510
U. S. A.
Phone: +1-423-867-4100
Fax: +1-423-867-4102
Internet: http://www.steward.com
e-mail: americas@steward.com
Steward
47 Hill Street, #08-07
SCCCI Building
Singapore
179365
Phone: +65-337-9667
Fax: +65-337-9686
Internet: http://www.steward.com
e-mail: asia@steward.com
e-mail: stewarda@pacific.net.sg
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