Noise suppression technologies/case study introduction (Consumer)
Noise suppression measures for differential interface--intrasystem EMC (electromagnetic compatibility)-- (1)
- 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
1. Popularization of differential interface and wireless communication modules
In recent years, digital devices such as smartphones have been required to transmit high-resolution and large-volume data inside and outside them. Accordingly, various differential interfaces have been adopted.
On the other hand, such digital devices have become equipped with wireless communication modules for transmitting data between the devices and the Internet. Of the modules, Wi-Fi modules have been popularized as popular wireless communication modules.
2. Noise issues with differential interfaces
The intrasystem EMC has been more noticeable due to the speeding up of differential interfaces and the popularization of wireless communications.
Intrasystem EMC: Phenomenon in which noise emitted from USB 3.2 interferes with the Wi-Fi antenna in a device and deteriorates the quality of Wi-Fi communication
EMC for public standards: Phenomenon in which noise emitted from the actual device or USB 3.2 cable exceeds the limit values of public standards
3. Measures to suppress radiated noise
Insert a common mode choke coil (CMCC) into the differential interface. Each CMCC becomes more effective when it is installed close to the noise source.
Noise source of Tx signal = USB IC side
Noise source of Rx signal = USB connector side
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.
4. Noise picked up by Wi-Fi antenna (1): Investigation with simple board
The noise picked up by an antenna was evaluated during transmission through USB 3.2 using an evaluation board equipped with a USB Type-C connector. The signal source was a USB 3.2-compatible notebook PC with SSD used for its sink device. In addition, an omni antenna was set up 5 cm away from the evaluation board.
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.
5. Noise picked up by Wi-Fi antenna (1): Results of the investigation with simple board
Green vs. red (standard)
When a CMCC was placed away from the noise source, the noise was improved by approximately 2 dB.
Blue vs. red (standard)
When a CMCC was placed close to the noise source, the noise was improved by approximately 5 dB.
The result indicated that the noise differed by 3 dB, depending on the position the CMCC was installed.