App note from Abracon about EMI filtering with CMCs. Link here
Common mode chokes are used in both power and signaling circuits. Data lines in electronic communications systems usually exist as pairs where they transmit signals of equal amplitude but opposite polarity. These lines are known as differential signals or pairs, such that the transmitted signal is sensed at the receiver by taking the voltage difference between the two lines.
A common mode choke is a passive electromagnetic device that permits the passage of the desired electrical signals through data or power lines while filtering out the unwanted high-frequency noise signal from external sources or other circuits of the system.