AN-1109

Application Note

Rev. 0 | Page 4 of 20

PREAMP ON

LOG

5

dB/

#ATN

0dB

VA SB

SC FC

ACORR

40dBµV

47dBµV

37dBµV

AVG BW 300kHz

30dBµV

REF 60.0dBµV

ACTV DET: PEAK

MEAS DET: PEAK

MKR 873.3MHz

38.56dBµV

REF LEVEL

60.0dBµV

CHAMBER EN55022, CLASS B, RADIATED EMISSIONS PRESCAN

START

L

30.0MHz

#1F BW 120kHz

STOP

1.0000GHz

SWP 909ms

CISPR 22 CLASS A

CISPR 22 CLASS B

Figure 5. Anechoic Chamber Emissions from a Standard 4-Layer Board with

4-Channel ADuM1402 at 1 Mbps

PREAMP ON

LOG

5

dB/

#ATN

0dB

40dBµV

VA SB

SC FC

ACORR

30dBµV

47dBµV

37dBµV

REF 50.0dBµV

ACTV DET: PEAK

MEAS DET: PEAK

MKR 682.7MHz

23.38dBµV

REF LEVEL

50.0dBµV

CHAMBER EN55022, CLASS B, RADIATED EMISSIONS PRESCAN

START

L

30.0MHz

#1F BW 120kHz

STOP

1.0000GHz

SWP 909ms

CISPR 22 CLASS A

CISPR 22 CLASS B

AVG BW 300kHz

Figure 6. Anechoic Chamber Emissions from a Low Noise 4-Layer Board with

300 pF Stitching Capacitance and 4-Channel ADuM1402 at 1 Mbps

The emissions data for this board, as shown in Figure 5, passes

CISPR 22 Class A emissions standards by approximately 6 dBμV

in the 30 MHz to 230 MHz range (40 dBμV requirement). In

contrast, Figure 6 shows the results of a low noise, 4-layer board

using a 300 pF stitching capacitance. This was tested under the

same conditions as the standard board but passes CISPR 22

Class A and CISPR 22 Class B by a wide margin. The EMI

Mitigation Techniques section describes how to use some recom-

mended PC layout techniques like those used on the low noise

board to control radiated emissions.