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When installing an extension board with a cable, noise may be conducted
to the cable through the GND line due to the boards GND fluctuations. This
results in high level noise emission. Therefore, the board's GND must be
stabilized with connections between the metal fitting (which is connected
to the metal case of the personal computer) and a GND with low impedance.
In addition, EMI filters are installed on the cable connector port.
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Noise suppression effects produced when improving the GND
and installing EMI filters on the cable connector port |
Before improving
the GND |
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After improving
the GND |
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Connecting the metal
chassis and the board |
After installing
the EMI filter |
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Installing an EMI filter
on the cable connector port |
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| When the board's GND impedance is high and the return current is flowing,
potential difference develops. This makes the board's GND unstable and causes
noise emission. To stabilize the board's GND, the GND impedance is reduced
by increasing the number of connection points between the GND and chassis.
In this example, the GND is improved by increasing the number of connection
points between the board and chassis, and then an EMI filter, NFM21CC222R1H3
is installed on the cable ports connected to the peripherals. This suppresses
the noise level by as much as 10 dB. |
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