Technical information

USBUF01P6

4/9

2.1.1

EMI filtering

Current FCC regulations requires that class B computing devices meet specified maximum

levels for both radiated and conducted EMI.

●

Radiated EMI covers the frequency range from 30 MHz to 1GHz.

●

Conducted EMI covers the 450 kHz to 30 MHz range.

For the types of devices utilizing the USB, the most difficult test to pass is usually the

radiated EMI test. For this reason the USBUF01P6 device is aiming to minimize radiated

EMI.

The differential signal (D+ and D-) of the USB does not contribute significantly to radiated or

conducted EMI because the magnetic field of both conductors cancels each other.

The inside of the PC environment is very noisy and designers must minimize noise coupling

from the different sources. D+ and D- must not be routed near high speed lines (clocks

spikes).

Induced common mode noise can be minimized by running pairs of USB signals parallel to

each other and running grounded guard trace on each side of the signal pair from the USB

controller to the USBUF device.

If possible, locate the USBUF device physically near the USB connectors. Distance between

the USB controller and the USB connector must be minimized.

The USBUF01P6 ensures a filtering protection against electro-magnetic and radio

frequency Interference thanks to its low-pass filter structure. This filter is characterized by

the following parameters:

●

cut-off frequency

●

insertion loss

●

high frequency rejection.

Figure 3.

USBUF01P6 typical

attenuation curve.

Figure 4.

Measurement configuration.

f/Hz

1.0M

3.0M

10.0M

30.0M

100.0M

300.0M

1.0G

3.0G

-25.00

-22.50

-20.00

-17.50

-15.00

-12.50

-10.00

-7.50

-5.00

-2.50

0.00

dB

-

-

-

-

-

-

-

-

-

-

TEST BOARD

50

Ω

Vg

50

Ω