**6.5 Component and signaling cable considerations**

Two components (local oscillator and clock chip circuit) on motherboard probably will need an extra local shield placed on it to pass regulatory testing if the components radiate overlimit spurious noise. Hence the mechanical chassis design should also provide sufficient space with height clearance to accommodate this kind of SMT shield/can.

The camera module is also a potential RF noise source of the system, especially when it is located in the proximity of antennas. A mechanical shielding solution – sheet metal, EMI paint, foil, and/or magnesium walls should be considered to isolate the EMI noise from the antennas as shown in Figure 46. Although most of the camera modules equipped with metal shielded enclosure, but the glass which cover the CCD gate, transfer gate may leak or coupling the magnetic field to the nearby traces through the glass aperture.

Fig. 46. Shielded enclosure and loop probe for noise measurement of camera module.

LVDS is now a popular signaling system that can deliver information at very high speed over twisted pair copper cables. LVDS technology uses the voltage difference between two wires to carry signal information for high-speed data transfer through the panel hinge to minimize EMI related problems. In order to minimize the aforementioned EMI problems, we can utilize LVDS cables with the following mechanical recommendations:


210 Wireless Communications and Networks – Recent Advances

Grounding the motherboard to the chassis wherever possible (screw holes, connectors, etc.) will help reduce EMI radiation from the motherboard. The grounding contacts should follow EMC design guidelines for length to width ratio requirement to prevent from adding a radiation structure rather than providing a noise-reduction ground point. Every effort should be made for each screw and contact point of the motherboard to the chassis for a

The grounding of the heat sink also raises a problem for ESD, EMI, and platform noise of wireless devices, therefore improvement should be made in the grounding of the heat sink (cooler). The improvement should include: enabling better DC grounding at "spring

Two components (local oscillator and clock chip circuit) on motherboard probably will need an extra local shield placed on it to pass regulatory testing if the components radiate overlimit spurious noise. Hence the mechanical chassis design should also provide sufficient

The camera module is also a potential RF noise source of the system, especially when it is located in the proximity of antennas. A mechanical shielding solution – sheet metal, EMI paint, foil, and/or magnesium walls should be considered to isolate the EMI noise from the antennas as shown in Figure 46. Although most of the camera modules equipped with metal shielded enclosure, but the glass which cover the CCD gate, transfer gate may leak or

contact" points, and no non-grounded arms longer than 7mm are allowed.

space with height clearance to accommodate this kind of SMT shield/can.

coupling the magnetic field to the nearby traces through the glass aperture.

Fig. 46. Shielded enclosure and loop probe for noise measurement of camera module.

Fig. 45. Metal plate for LCD panel shielding purpose.

**6.5 Component and signaling cable considerations** 

good chassis ground point.


The use of LVDS system must be cautious that most of the LVDS cables have good degree of balance for the fundamental frequency, but the balanced pair becomes unbalanced for those frequencies higher than 10 harmonics when the harmonic signal across the LVDS cable. Therefore it will usually generate the common mode voltage resulting in common mode radiation, and the shield of the LVDS cable become ground return.

The impedance mismatching at DDR2 or DDR3 memory socket usually causes higher noise current distribution around the socket area. These magnetic filed may couple to the WWAN module when the shielding effectiveness of WWAN module's shielded enclosure is not adequate as shown in Figures 47-49. Lower impedance will tmake dI/dt increase and dramatically increase the current drawn from supply (not good for the design of power distribution system), while higher impedance will emit more EMI and also become more susceptible to external interference.

Fig. 47. RF module location and bearby field distribution.

Fig. 48. Embedded antenna mini-coaxial cable and noise distribution.

Fig. 49. Circuit ground and chassis ground.
