DocID025260 Rev 1

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AN4356

Solution to avoid antenna desense

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Solution to avoid antenna desense

The best method to prevent antenna desense is to insert a common mode filter on the link.

This device includes two coupled inductances acting like a subtracter for common mode

noise thanks to the magnetic flux accumulation, inducing high impedance for it. The

differential signal is not affected (Figure 9).

Figure 9. Common mode filter basics

The common mode filter is efficient on all the common mode noise induced on the link:

•

Conduction noise

•

Radiated noise

•

Noise induced by skew

Figure 10. Common mode filter against various noise sources

The magnetic flux induced by common

mode current increases the impedance

and cancels common mode noise.

The magnetic flux induced by differential

mode current cancels each other. Low

impedance is achieved.

t

t

t

t

D+

D-

[D+]-[D-]

[D+]+[D-]

Transmitter

Receiver

Differential signals

Skew

t

t

t

t

t

t

t

t

D+

D-

Conduction noise

Coupled RF

Coupled noise

RF spike

CMF

Filtered signal