Data Sheet

Module：EWN-8258FAT1CA1
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13
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12.
3 Motherboard interference avoidance
Moth
erboard interference comes from: high-speed data interface (HDMI), the Operating
frequency of main chip, DDR, DC-DC power supply. The method of avoiding interference according
to the characteristics of various signals is also different. The main methods of interference avoidance
include:
1. ke
eping away from the source of interference;
2. Addin
g shields to avoid interference leakage;
3. Re
asonable layout to eliminate interference.
12.3.1 Interface interference
When HDMI uses the 74.2MHz frequency, its 33x frequency is in the 2.4G band of BT, which will
seriously interfere with the BT signal. If the HDMI frequency is 148.5MHz, although the 16x frequency
is not in the BT band, the isolation of the frequency is not good, and the BT signal will be interfered to
some extent. If the distance between the HDMI interface and the BT module on the PCB is less than
5cm, the HDMI output display will interfere with the BT signal, resulting in problems such as BT
connection failure and throughput drop. Therefore, keep the location of the BT module away from
the HDMI port on the hardware layout to avoid interference.
At the same time, if the BT antenna is built-in the motherboard, its placement must also be
carefully considered to be far from the interface interference. If the antenna is placed in an incorrect
position, even if the module is shielded, the interference signal is coupled through the antenna,
which will eventually result in a lower BT throughput. (Note: In addition to interference, the
placement of the internal antenna should also evaluate the effect of the metal interface, motherboard,
and housing material on the antenna impedance.)