Conclusion

AN3141

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Doc ID 17004 Rev 1

5

Conclusion

Mobile phone LCD or camera links can radiate on the RX frequencies, which can impact

mobile phone sensitivity.

To evaluate this radiation, a spectrum measurement has been performed at RX GSM

frequencies, on a digital signal having 1.8 ns rise and fall time. The measurement identifies

a power of -92 dBm at 940 MHz, on a single line, and 50

Ω environment. This is huge

regarding the requested sensitivity on GSM band.

To reduce this noise, filtering is needed. It must respect the signal integrity, and filter RX

band frequencies.

EMIF08-LCD04M16, EMIFxx-LCD02F3 and EMIFxx-LCD03F3 have been designed to filter

parallel LCD and camera links, while fully respecting signal integrity. Time domain

measurement shows a very low impact on the signal.

Frequency domain measurements with filters show attenuation at RX band frequencies:

●

From -92 dBm without filter to -120 dBm with EMIF10-LCD02F3, RC type filter, at

F=940 MHz

●

From -92 dBm without filter to -126 dBm with EMIF08-LCD04M16, LC type filter, at

F=940 MHz

●

From -92 dBm without filter to a power lower than -130 dBm with EMIF10-LCD03F3, LC

type filter, at F=940 MHz

Consequently, using filters, before the flex connection, reduces the emission of the flex at

RX frequencies.

Using LC type filters:

●

Does not impact the signal integrity

●

Decreased the reception frequency range power to an insignificant value

Consequently, the RF system sensitivity is not affected. It remains at its own value.