Hello ADI support,
By comparing table 4-5 (1 Mb/s, 3.3V) with 6-7 (10 Mb/s, 3.3V) of AN-1109, emissions from the ADuM140x scale up with channel bit rate like:
45-28=17 dB/dec for the standard board
(45-16)-(28-11) = 12 dB/dec for the optimized board
230 .. 1000 MHz
53-36 = 17 db/dec for the standard board
(53-24)-(36-7) = 0 dB for the optimized board
1. If I am not wrong in interpreting the results, it looks like the optimized board does a better job at higher frequencies (> 230 MHz) than at lower frequencies, where common mode emissions dominate.
Can you explain this behaviour?
2. The optimized board barely meets CISPR 22 class B limits at 10 Mb/s in the lower frequency range. Now the ADuMx can reach 90 Mb/s.
Should emission levels scale up as stated above in the 30-230 MHz range, is it at all possible to meet class B EMC specifications with bit rates higher than 40 Mb/s up to the specified limit? Do you have any measurement data for these cases?