AN-1109
Application Note
CHAMBER EN55022, CLASS B, RADIATED EMISSIONS PRESCAN
CHAMBER EN55022, CLASS B, RADIATED EMISSIONS PRESCAN
REF LEVEL
60.0dBµV
ACTV DET: PEAK
MEAS DET: PEAK
REF LEVEL
50.0dBµV
ACTV DET: PEAK
MEAS DET: PEAK
MKR 873.3MHz
MKR 682.7MHz
38.56dBµV
23.38dBµV
REF 60.0dBµV
PREAMP ON
REF 50.0dBµV
PREAMP ON
LOG
5
dB/
#ATN
0dB
LOG
5
dB/
#ATN
0dB
40dBµV
47dBµV
37dBµV
CISPR 22 CLASS A
47dBµV
37dBµV
CISPR 22 CLASS A
CISPR 22 CLASS B
40dBµV
30dBµV
30dBµV
CISPR 22 CLASS B
VA SB
SC FC
ACORR
VA SB
SC FC
ACORR
START 30.0MHz
#1F BW 120kHz
STOP 1.0000GHz
SWP 909ms
START 30.0MHz
#1F BW 120kHz
STOP 1.0000GHz
SWP 909ms
L
AVG BW 300kHz
L
AVG BW 300kHz
Figure 5. Anechoic Chamber Emissions from a Standard 4-Layer Board with
4-Channel ADuM1402 at 1 Mbps
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.
Rev. 0 | Page 4 of 20
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