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Bus lines contain many lines that switch on and off simultaneously.
Especially on data and address bus lines, an instantaneous large current
flows into the GND and power supply lines. Therefore, it is necessary
to suppress the current flow on the signal lines. The BLM Series (Chip
Ferrite Bead) is generally used for this purpose. On the control bus
line, especially at high operating speeds and high noise levels, a
filter with resistance components is used, such as the NFR21G Series
(Chip "EMIFIL®"). |
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Noise suppression effects produced when installing the BLM18AG601SN1
(Chip Ferrite Bead, 600 ohms at 100 MHz) on the data bus lines |
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Before installing
the EMI filter |
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The many signal lines of a data bus switch on and off simultaneously.
This causes instantaneous large return currents to flow into
the GND and power supply line, resulting in noise generation.
To suppress current flow on the bus lines, the BLM18AG601SN1
(Chip Ferrite Bead, 600 ohms at 100 MHz) is installed on the
data bus lines. This suppresses the noise level by approximately
3 to 4 dB. Since the operating speed of the bus lines is relatively
low in this example, a Chip Ferrite Bead(Standard Type) is used.
However, when a filter with excessively high impedance is used
on a high-speed data bus line, the signal waveform is distorted,
causing the circuit to malfunction. Therefore, using a Chip
Ferrite Bead(For High-speed Signals) is most effective. |
After installing
the EMI filter |
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