EMI Suppression Filters (EMC and Noise Suppression)Noise suppression measures for differential interface--intrasystem EMC (electromagnetic compatibility)-- (1)

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.

The intrasystem EMC has been more noticeable due to the speeding up of differential interfaces and the popularization of wireless communications.

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.

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.

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.

The result indicated that the noise differed by 3 dB, depending on the position the CMCC was installed.