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Common mode chokes for radio module?

eem2am

Aug 3, 2009
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Hi,
We are using the ESP32-C3-MINI-1 chip as a wi-fi transceiver.

ESP32-C3-MINI-1 Transceiever datasheet:
https://www.espressif.com/sites/default/files/documentation/esp32-c3-mini-1_datasheet_en.pdf
Forgetting for a moment that about the RF side of thsi chip, ..the chip receives/transmits data by copper tracks into its pins 30 and 31 respectively.
These signals go to a connector which accomodates a cable which goes off board. We are concerned about this cable acting as an antenna and creating a radiated emissions problem.
As such, we wish to put a common mode choke(s)/ferrite bead in these traces, right by the connector. Can you recomend any ferrite beads or common mode chokes for this? I presume since there are three lines (RX,TX and GND), that really a common mode choke is not practical, and that a ferrite bead in each line would be best?
 

Harald Kapp

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Nov 17, 2011
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I presume since there are three lines (RX,TX and GND), that really a common mode choke is not practical, and that a ferrite bead in each line would be best?
I agree. Common mode choles are good for preventing common mode noise on differential lines. Your signals are not differential. On the contrary, should it so happen that the transmitted signal is equal or very similar to the received signal (this may happen or not, depending on what's going on in your communication), a common mode choke would suppress the signal.
This paper on "IMPROVING NOISE IMMUNITY FOR SERIAL INTERFACE" may help youalong.
 
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