Voltage Regulator Module Current Loop Radiation; Radiation Cancellation Of A Differential Line - Intel Quark SoC X1000 Design Manual

Figure 53.

Radiation Cancellation of a Differential Line

17.3.2

Voltage Regulator Module Current Loop Radiation

The noise from voltage regulator module (VRM) is typically around 50~300MHz.The
two noise peaks at 125 and 250 MHz shown in
can cause both signal integrity (SI) and EMI issues (see
different coupling paths. Besides the coupling paths elimination, the issues can be
resolved effectively by mitigating VRM noise from the source.
simplified VRM circuit. The VRM EMI noise can be detrimental when its harmonics
coincide with the resonant frequency of the input decoupling path which encompasses
input decoupling capacitors and the top and bottom transistors. A practical way to
mitigate the VRM noise without sacrificing VR efficiency is to have minimal parasitic
PCB inductance of the current loop indicated above. Several good layout practices are
listed in the followings: Have a solid ground plane immediately underneath the VRM
circuit and connect the VRM ground to the solid ground plane through vias. These Vias
should be placed close to the low-side FET.
• Place the decoupling capacitors very close to the top transistor. The ground pin of
the capacitors should be connected to the solid ground plane right underneath.
• Use at least two decoupling capacitors to reduce overall parasitic inductance from
the capacitors themselves.
• If transistors are placed at different layers, ground vias should be placed close to
the phase node vias.
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Intel Quark™ SoC X1000
PDG
110
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Intel Quark™ SoC X1000—Electromagnetic Interference
Figure 54 are an example. VRM noise
Figure 55) through the same or
Figure 56 shows a
June 2014
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