Murata Noise Suppression in Onboard Ethernet 100Base-T1
Onboard Ethernet includes communication systems used in automobiles. A variety of interface standards can be used, depending on the application. Some examples of communication systems are CAN/LIN, FlexRay, MOST, and Ethernet. Onboard Ethernet standards include 100Base-T1 with one pair and 100Base-TX with two pairs. But unwanted noise can become an issue, so Murata researched ways to suppress noise in onboard Ethernet 100Base-T1 applications.
Onboard Ethernet Tables
Necessity of Noise Suppression in Onboard Ethernet
Differential transmission noise
In differential transmissions including Ethernet, noise occurs due to a common mode current caused by various factors.
Ethernet Problems
The cables used for Ethernet are different from USB and HDMI cables.
Noise Standards of Onboard Devices
Onboard devices have a shorter antenna distance and stricter limit values than consumer products.
Differential transmission noise
Ethernet problems
Noise standards of onboard devices
Recommendation
A common mode choke coil is an effective way to suppress noise in a differential transmission. Murata recommends the DLW43MH series as the optimal common mode choke coil for 100Base-T1 noise suppression.
Common Mode Current Diagram
Users can also selectively drop just the common mode.
Radiation Noise Evaluation - Test Condition
The noise suppression effect of the common mode choke coil was confirmed with radiation noise measurements.
Radiation Noise Test Condition
Radiation Noise Test Results
Conductive Noise Evaluation - Test Condition
Ethernet Test Board
Test Board Circuit
Radiation Noise Test - Measurements Results
Radiation Noise Test Results Summary
Noise increases across some frequencies with the CAN and FlexRay compliant DLW43SH101XK2, and the noise suppression effect is insufficient. However, the noise can be effectively suppressed by using the 100Base-T1 compliant DLW43MH201XK2
DPI Evaluation
The immunity improvement effect of the common mode choke coil was confirmed by performing a DPI (Direct Power Injection) test.
DPI Test Condition
DPI Test Board
DPI Measurement Results
Summary
• Because onboard Ethernet uses non-shielded cables that easily radiate noise and onboard noise standards must be supported, noise suppression is required.
• CISPR25 Class5 radiation noise standards can be met by using the 100Base-T1-compliant DLW43MH201XK2. It displays a higher level of noise suppression for conductive noise and DPI than the common mode choke coils for CAN and FlexRay.
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Related Products
Murata DLW Common Mode Choke Coils
Offers high impedance in the high-frequency band for more effective noise suppression.