Common mode noise filter NFG0QHB242HS2
Noise suppression technologies/case study introduction (Consumer)
Noise suppression measures for differential interface--intrasystem EMC (electromagnetic compatibility)-- (2)
INDEX
- 1. Popularization of differential interface and wireless communication modules
- 2. Noise issues with differential interfaces
- 3. Measures to suppress radiated noise
- 4. Noise picked up by Wi-Fi antenna (1): Investigation with simple board
- 5. Noise picked up by Wi-Fi antenna (1): Results of the investigation with simple board
- 6. Noise picked up by Wi-Fi antenna (2): Investigation with actual device
- 7. Noise picked up by Wi-Fi antenna (2): Results of the investigation with actual device
- 8. Investigation of intrasystem EMC with actual device
- 9. Investigation results of intrasystem EMC with actual device
- 10. Effect on a signal waveform
- 11. Result of eyemask test for USB 3.2
- 12. Summary
6. Noise picked up by Wi-Fi antenna (2): Investigation with actual device
Noise picked up by an antenna was evaluated by using an electronic device with USB 3.2 support and equipped with a Wi-Fi antenna.
The antenna used for the evaluation was the one incorporated into the device.
The extent that the noise radiated from the evaluation board wirings was picked up by the antenna was investigated during transmission through USB 3.2.
Furthermore, the effects of this measure were compared with those derived from CMCC.
7. Noise picked up by Wi-Fi antenna (2): Results of the investigation with actual device
Green vs. red (standard)
When the CMCC was placed away from the noise source, the noise was not improved.
Blue vs. red (standard)
When the CMCC was placed close to the noise source, the noise was improved by approximately 5 dB.
The result indicated that the noise differed by 5 dB even when the actual device was used, depending on the position the CMCC was installed.
8. Investigation of intrasystem EMC with actual device
Wi-Fi reception sensitivity was evaluated by using an electronic device with USB 3.2 support and equipped with a Wi-Fi antenna.
During communication through USB 3.2, Wi-Fi communication was performed between the electronic device and the Wi-Fi test set. During the Wi-Fi communication, we confirmed whether the receiving sensitivity would deteriorate in a case where the USB 3.2 communication was not performed. Furthermore, the effects of this measure were compared with those derived from CMCC.
9. Investigation results of intrasystem EMC with actual device
Green vs. red (standard)
When a CMCC was placed away from the noise source, reception sensitivity was improved by approximately 1dB.
Blue vs. red (standard)
When a CMCC was placed close to the noise source, reception sensitivity was improved by approximately 8dB.
As a result, Wi-Fi reception sensitivity in the actual device differed by 7dB depending on where the CMCC was set up.
10. Effect on a signal waveform
In a USB 3.2 compliance test, we confirmed whether the insertion of a CMCC affects a signal waveform. In the test, eye patterns were evaluated in an environment for testing the compliance of the waveform of USB 3.2.
11. Result of eyemask test for USB 3.2
In the eyemask tests for Keysight SDA and USB-IF, it was found that even the use of a common mode choke coil, NFG0QHB372, did not have any adverse effect on the waveform.
12. Summary
Evaluation of noise picked up by antenna
- During the transmission of USB 3.2 signals, noise picked up in the 2.4 GHz range is monitored.
- Installing a CMCC close to the noise source improves antenna interference in the 2.4 GHz range.
- On the other hand, installing a CMCC close to a USB connector, which is away from the CPU, cannot sufficiently improve the interference.
Evaluation of Wi-Fi reception sensitivity
- During the transmission of USB 3.2 signals, Wi-Fi reception sensitivity deteriorated in the 2.4 GHz range.
- Installing a CMCC close to the noise source improved Wi-Fi reception sensitivity in the 2.4 GHz range.
- On the other hand, when a CMCC was installed away from the noise source, reception sensitivity was not improved.
Single integrity
- There is no problem with signal waveform quality as long as an appropriate CMCC is selected.
The evaluation and investigation show that the position to install a CMCC is important for noise suppression measures for the intrasystem EMC.
Our recommended common mode choke coils
The following CMCCs are recommended for noise suppression in differential transmission lines.
Due to this function, common mode noise can be effectively eliminated without affecting the signal waveform. Furthermore, the measure has been recommended by several IC makers.