Noise suppression technologies/case study introduction (Automotive)

Automotive Ethernet for ADAS Noise suppression measures for 1000Base-T1 (4)

8. Testing of Immunity (DPI) Measures

Production of DLW32SH101XK2 has been discontinued.

A DPI (Direct Power Injection) test was conducted using the same 1000Base-T1 EMC test board as conducted emission.

Testing of Immunity (DPI) Measures_image


1 - 1000MHz



Power Step



1000Base-T1 EMC Test Board

DC Power Supply


Signal Generator


Power Amplifier

BSA1040-100 (1-400MHz)   
BLWA4010-100 (400-1000MHz)

Common mode noise is conducted out from an external source to the signal line on the 1000Base-T1 EMC test board, and a control PC is used to confirm whether any communication errors occurred.

Testing of Immunity (DPI) Measures_image2

In the same way as the conducted emission, the DLW32MH101XT2 (CMCC for 1000Base-T1), DLW43MH201XK2 (CMCC for 100Base-T1), and DLW32SH101XK2 (CMCC for CAN) were used as test CMCCs.

Differential Mode Transmission Characteristics_image
Sdd21(Differential Mode Transmission Characteristics)
Common Mode Transmission Characteristics_image
Scc21(Common Mode Transmission Characteristics)
Differential Mode Reflection Characteristics_image
Sdd11(Differential Mode Reflection Characteristics)
Mode Conversion Characteristics_image
Ssd12(Mode Conversion Characteristics)

1000Base-T1 DPI Test Results

At low frequencies of 2 MHz and less, the CMCCs exhibited differences in performance levels, but for other frequencies, there was no difference in performance, and all CMCCs satisfied the limit values.

1000Base-T1 DPI Test Results_image

1000Base-T1 DPI Test Results

The differences in the CMCCs at 2 MHz and less are thought to be due to common mode attenuation (Scc21). Differences in the mode conversion characteristics did not affect the results in the DPI test.

1000Base-T1 DPI Test Results

9. Key Points for Testing of Immunity (DPI) Measures

100Base-T1 DPI Test Results

After 1000Base-T1, the DPI test was also conducted for 100Base-T1. The CMCC for 100Base-T1 satisfied the limit values. However, the CMCC for CAN performed worse than the CMCC for 100Base-T1 at low frequencies of 1 MHz and less, and it also did not meet the limit values at 8 to 60 MHz, and failed the test.

100Base-T1 DPI Test Results_image

The differences at 2 MHz and less are thought to be due to common mode attenuation (Scc21). Also, the differences at 8 to 60 MHz are thought to be due to the mode conversion characteristics.

100Base-T1 DPI Test Results_image2

Noise Entry Mechanism

One factor why the mode conversion characteristics of the CMCC affected the test results for 100Base-T1 is that the common mode noise that entered from an external source was converted to differential mode noise, which distorted the signal waveform, resulting in a communication error.

Noise Entry Mechanism_image

Notes on Board Design

In the same way as conducted emissions, in addition to the CMCC, this may also be caused by mode conversion due to imbalances on the board, and so careful attention is needed in board design.

Notes on Board Design_image
Key Points in Occurrence of Mode Conversion

10. Conclusion

  • For the automotive Ethernet standard 1000Base-T1, high performance is required in the CMCCs used for noise suppression, and the mode conversion characteristics are particularly important.
  • In evaluation of conducted emissions, a CMCC having mode conversion characteristics that meets the required values for 1000Base-T1 is needed for suppressing noise. The limit values are not satisfied when using CMCCs for CAN or for 100Base-T1.
  • Even in the CMCC for 1000Base-T1, the mode conversion characteristics can worsen due to variations in the board design and installed components, resulting in increased noise. For this reason, careful attention on this point is necessary in the design process.
  • In the DPI test, which is an immunity test, the required performance for the CMCC is lower than that for conducted emissions, but the noise resistance varies by the PHY, and so the one with lower mode conversion characteristics is preferred.

Automotive Ethernet CMCCs Mentioned in This Article


For 1000Base-T1

1. Effective for suppressing noise emitted from signal lines in automobile networks.

2. Fully compatible with the 1000Base-T1 automotive Ethernet standard

3. Operating temperature range for automotive applications: -40°C to 125°C

Product Details Page



For 100Base-T1

1. L4.5×W3.2×T2.7 mm, Compact type with dimensional tolerance of ±0.2 mm

2. Provides common mode inductance of 200 μH (at 0.1 MHz) despite its compact size

3. Significant improvement in mode conversion characteristics

Product Details Page


Compatible interfacePart numberSizeCommon mode
Rated current
1000Base-T1DLW32MH101XT23.2×2.5mm100μH typ100mA
100Base-T1DLW43MH201XK24.5×3.2mm200μH typ110mA

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