EMI Suppression Filters (EMC and Noise Suppression)Examples of Noise Suppression against LTE Noise

The measurement results of noise received by antennas indicated coupling of broadband noise.

Then we evaluated the adjacent electromagnetic field distribution to identify noise source locations and examined them. As a result, we consider that noise is coupled with antennas due to the noise on the data line and the power line near the flexible cable of the LCD data line.

We selected an L-type filter suited for high-impedance circuits. Since multiple signals are arranged in parallel in the signal line, we selected an array type of 4-circuit configuration with high mounting effect.

After anti-noise measures have been taken, we measured and evaluated the noise level received by antennas with a spectrum analyzer.
As shown in the green graph of the measurement result, the broadband noise value is close to the floor level, indicating that noise suppression exerts an effect.

We found that the noise source is the switching noise of the power supply. Therefore, we selected a ferrite bead to be inserted into the power line of the flat cable that propagates the switching noise.

As a result of measurement and evaluation of the noise level received by antennas after measures were taken, 1.5MHz-cycle noise is eliminated as shown by the yellow data and a value close to the floor level is obtained, indicating that noise was reduced by the effect of the ferrite bead.

After we measured the antenna's receiving sensitivity before and after measures and implemented noise suppression, we evaluated whether the improvement effect was produced.
The measurement result shows that the improvement effect of 3.3 dB (main antenna) and 6.6 dB (sub antenna) was produced.

The adjacent electromagnetic field distribution evaluation result also shows that the electromagnetic field distribution near the flexible cable of the LCD data line is reduced.

The result of measurement of noise received by antennas using a spectrum analyzer showed that 2136-MHz noise is coupled with both main and sub antennas.
The subsequent evaluation of the adjacent electromagnetic field distribution showed that high distribution is present near the data line of the camera module.
The measured noise was generated at a 24-MHz cycle. Since this cycle is the same as the camera module driving clock frequency, the 2136-MHz noise received by the antennas is the harmonic component of the camera module clock frequency.

The noise source was the camera module clock frequency. Therefore, a ferrite bead for high-GHz band high-speed signals was inserted into the clock line. Furthermore, a 68Ω damping resistor was inserted to shape the waveform because ringing occurred on the clock waveform.

The antenna receiving sensitivity measurement result after measures have been implemented shows that the improvement effect of 1.5 dB (main antenna) and 3.7 dB (sub antenna) was produced.

The adjacent electromagnetic field distribution evaluation result also shows that the electromagnetic field distribution near the flexible cable of the camera module is reduced.