The A-to-D and D-to-A conversion technologies have been applied to portable audio equipment with the enhancement of the scale of integration of memory and the progress of signal compression techniques.
The MP3 is one of such technologies. (It uses Compact Flash, Memory Stick, and SD as recording media.) The following noise suppression measures are applicable to these solid state audio players.
One of radiant noises is those from the cable from a headphone or an earphone. The higher harmonics in an internal digital processing circuit leaks from ground, a power supply, or a signal line to an audio line, and are intensively radiated from a headphone cable.
Since the voice frequency is as low as 20kHz or below, chip ferrite beads with an impedance near 600ohm (at 100MHz) are frequently used to suppress radiant noise.
Since some types of ferrite may distort sound signals, however, care must be taken to select the material. The BLM_B Series accommodating high-speed signals are recommended to prevent this.
The three-line common mode choke coil DLM2HG Series have been newly introduced to the market. The choke coil is capable of suppressing radiant noise through a sound signal circuit and further preventing voice distortion.
| No EMI Filter on L, R and Ground |
BLM18BB601SN on L, R and Ground |
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|---|---|---|
| Radiation |  |
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Noise Suppression Examples in Home Electronics
