Before installing
the EMI filter |
 |
|
As shown, the 37 MHz clock signal generates higher frequency harmonics.
It is these high frequency harmonics that can cause EMI issues.
Therefore a filter that will minimize the high frequency harmonics
without distorting the signal waveform is required. The NFW31SP107X1E4
(EMI filter for signal lines, cut-off frequency: 100 MHz) is selected
and installed on the signal line. Since higher harmonics are also
conducted to the power supply line of the oscillator, the BLM18BB751SN1
(Chip Ferrite Bead, 750 ohms at 100 MHz) is also installed on the
power supply line. This solution suppresses the higher harmonics
from the 37-MHz clock signal by as much as 15 dB. Using a filter
with a high constant greatly distorts the clock signal waveform,
adversely affecting circuit operation. Therefore, it is necessary
to check the waveform and then select a filter with an appropriate
constant. |
