Common-mode filters with integrated ESD protection (ECMF)

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Today’s high speed communication interfaces are built using a differential mode. (see figure 1)

To speed up data transmissions, a first approach is to reduce the signal amplitude. The smaller the signal amplitude, the  more the single-ended transmission is sensitive to noise.  In contrary, a differential transmission uses a pair of lines to transmit signals of an equal amplitude in reverse phase (D+, D-) and receive the differential. This transmission method is less sensitive to the noise our ground effect. Also, the magnetic field around the two lines is cancelled, reducing spurious radiation. For these reasons, the differential transmission mode is used for most high-speed data transmission applications.

 

For high-speed datalines like MIPI DSI or CSI, HDMI TMDS lines or USB superspeed signals, ST has developed a range of Common Mode Filters with integrated ESD protection tailored to reject a wide range of frequency bands (700 MHz LTE, 2.4 GHz Bluetooth, 2.4 and 5 GHz Wi-Fi, to name a few) with a deep level of attenuation.

Designed as RF antenna desense medication in applications where the high-speed differential links generate radiated noise at frequencies of the RF antenna, our common-mode filters are strongly recommended for applications where an RF receiver coexists with a high-speed differential dataline.

Benefits of our common-mode filters with integrated protection:

  • Improved ESD clamping thanks to dual clamping structure (ESD diode and serial resistor of inductance)
  • Improved receiver sensitivity by removing common mode noise in useful antenna bandwidth
  • Space and BOM savings by integrating both the ESD protection diodes and the common mode filter

When subjected to common-mode noise, high-speed differential lines generate unwanted radiated noise. Common-mode filters prevent differential lines from radiating and interfering with other RF signals nearby.

 

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