DocID026455 Rev 1

7/21

AN4511

Common mode filters

21

so

Equation 5

Equation 6

and

Equation 7

The filter presents a low resistive impedance equal to DC resistance of inductances

therefore a low attenuation of the high-speed differential signal (see Figure 6).

Equation 8

and

Equation 9

The filter presents a high inductive impedance, therefore a high rejection of the common

mode noise (see Figure 6).

ML

=

Z

1

R

1

j

ω L

1

M

–

() R

1

≈

()

+

=

Z

2

R

2

j

ω L

2

M

–

() R

2

≈

()

+

=

Z

1

R

1

j

ω L

1

M

+

() R

1

j

ω 2L

×

+

=

+

=

Z

2

R

2

j

ω L

2

M

+

() R

2

j

ω 2L

×

+

=

+

=