Common mode choke for signal line（Signal Line CMC）
FAQ
Frequently Asked Questions
What certifications does VOOHU Electronics hold?
VOOHU Electronics holds ISO 9001:2015 international quality management system certification, ISO 14001:2015 environmental certification, RoHS environmental certification, REACH certification, and CE certification.
How can I quickly find the right product for my project?
On the VOOHU official website, you can quickly select products online by product category or by parameter filters (such as data rate, package, operating temperature, current, etc.). You can also visit the "Solution" page to view recommended solutions matching your needs. For further support, contact our technical support team directly with your application scenario, and we will recommend the optimal solution for you.
What is the difference between a signal line CMC and a power line CMC?
They work on the same principle but have different design priorities. Signal line CMCs (such as the WHAC and WHLC series) are mostly small chip packages with low current ratings and strictly controlled parasitics; the focus is on suppressing common mode noise without degrading the integrity of high-speed differential signals. Power line CMCs, by contrast, emphasize high current-carrying capability and high common mode impedance in the low frequency band.
On which interfaces are signal line common mode chokes typically used?
They are commonly used on various differential signal lines such as USB, HDMI, LVDS, CAN, RS485, and Ethernet. Connected in series with the differential pair, they filter out common mode noise picked up by or radiated from cables, improving EMI performance and immunity to interference.
Why can differential signals pass through while common mode noise is suppressed? And what is mode conversion?
For differential signals, the currents in the two windings flow in opposite directions, so the magnetic flux cancels and the impedance is low; common mode noise currents flow in the same direction, so the flux adds up and the impedance is high. However, if the two windings are asymmetric (deviations in turns or winding position), part of the differential signal is converted into a common mode component (i.e., mode conversion, specified by Scd21/Ssd21), which becomes a new radiation source. For high-speed interfaces, check the manufacturer's mode conversion specifications during selection.
Does adding a common mode choke to high-speed differential lines (e.g., Gigabit Ethernet, USB 3.x) affect signal quality?
It does have an impact - the key is keeping it under control. The CMC's differential mode insertion loss, parasitic capacitance, and impedance discontinuity can degrade the eye diagram, and the higher the data rate, the more sensitive the signal. When selecting, make sure the differential mode cutoff frequency is at least 3-5 times the signal's fundamental frequency, check the differential mode insertion loss curve (e.g., -3 dB bandwidth), and place the device as close to the connector as possible to avoid introducing discontinuities in the middle of impedance-controlled traces.
