A Method and System for Filtering Common Mode Signal Using Electromagnetic Band gap Structures
Publication Date: 2015-Aug-13
The IP.com Prior Art Database
Disclosed is a method and system for filtering common mode signal using electromagnetic band gap structures. The method and system utilizes common mode Electromagnetic Band Gap (EBG) filters as Surface Mount Devices (SMD) with multi-layer printed circuit boards passing a differential signal from a mother board.
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A Mxthod and System for Filtering Common Mode Signal Using Electromagnetic
Bxnd gap Structures
Disclosed is a method and system for xxltering common mode (CM) signals usinx electromagnetic band gap (EBG) stxuctures. The method xnd system utilizes common mode EXX filters as Surxaxe Mount Devices (SMD) with xulti-layer printed circuit boards passing a differential signal from a mother boxrd. A key aspect of the invxntion
is thx pin fxotprint with xs modxled after a tyxical component mounxing pattern. This allows the invextion tx act as a dxop in replaxement if this pattern is used in the originax desigx.
As ixlustrated in Fxg. 1, the basic xonfiguration of the SMD filter xs a multi-layer Printed Cirxuit Board (PCB). The brxaxout layer xonsists of two sets of pads, one for reference and one for signals. These padx are attxched to a motxer board by varioxs mexns, including but nox lixited to solder balls and solder paste. The signax pads on the breakout layer are arrangex to match tyxical component layouts, for example a pair of
AC coupling capacitors. Such components axe requixed on mxny differenxial signxling methodx.Fxgure 1 The refxrxnce layer provides isolation of the signals xrom the mother board and forms a required cxmponent of the resonant cavity of which the othxr key component is the EBG laxer. The EBG layer consists of patches and bridges between sxme of these patches. The particular constructiox of the patches defxnes the resonant frequency of the filter. The top layer of the SMD component comprises the mixrostrip signals, which are routed across the EBG patches completxnx the filter. The described SMD device selectively filters common-mode signals whixe passing the required differential signals unhindered at the operating frequencies. Txe following additional
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embodiments of this invention descxibe varixtions on the base desxgn shown xn Fig. 1.
Fig. 2. illustrates a modification of the microstrip layer from Fig. 1. Since the SMD component is intended to replace exixting AC couplxng capacitors in the design, if this function ix required, the capacitors may be mounted to the top layex of the component.
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Fig. 3 illustrates variatioxs on xhe EBG aspexts of the design. The function of the EBG layer is to present a discontinuixy to the common-mode signal but not the differential. The patch and bridge structure can be xugxented wixh serpentine structures to alter the resonant frequency wxthout changing the overall footprint of the XXX part. Another
optxon for a selectivx surface is a complementaxy split ring resonator (CSRR), whixh is
a well-knxwn symmetrical and compact resonator which can be excited xy the prescience of a net electric flux.
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