COMMON MODE NOISE SUPPRESSION METHOD AND APPARATUS

RELATED APPLICATIONS

[001] This application claims priority from US provisional patent serial number 62/236, 156 filing date October 2 2016 which is incorporated herein in its entirety.

BACKGROUND

[002] Data Communications Cables

[003] Modern data communication cables are designed to prevent: (a) Alliance crosstalk between pairs within the same cable, and crosstalk between cables, and (b) Radiation

susceptibility and radiation emission from the cable.

[004] Currently available high-speed cables resolve both problems by costly shielding. Low- cost solutions of these problems are demanded by the industry.

Common Mode Choke (CMC)

[005] Modern CMCs are designed to suppress common-mode currents, while providing minimum distortion and attenuation to differential- mode currents. Graph 10 of figure 2 illustrates the impedance vs. frequency relationship of the Murata DLP11SNXXXHL2 series.

[006] This Murata design addresses the problem of impedance mismatch, but the problem of differential-signal resonance remains unresolved (see oval encircling the problem part of the signal attenuation curve).

[007] As can be seen, the differential signal is attenuated by 6dB and more starting with 600MHz. This spectrum distortion cannot be compensated completely by active equalizing techniques (oriented to compensate monotonously growing with frequency attenuation of interconnection cables), and there is a demand for CMCs with enhanced differential-mode attenuation performance.

[008] Use of CMCs on high-speed balanced video signals interfaces causes various major problems: (A) Signal waveform distortion due to signal reflections due to impedance mismatch introduced by CMCs to differential signal; (B) Signal waveform distortion due to resonance-like differential signal attenuation response at higher part of the signal spectrum. This phenomenon is also called dispersion; (C) Excessive radiated emissions due to limited common-mode attenuation.

[009] One of the best-performance high-speed CMCs currently available on market are currently manufactured by Murata (Japan & USA) and TDK (Japan). SUMMARY

[0010] There may be provided a method for design of data communication cable and common mode noise choke, as illustrated in the claims.

[0011] According to an embodiment of the invention there may be provided a common mode noise suppressing device, that may include a group of conductors for conveying differential mode signals and common mode noise; and at least one common mode noise trap that may include at least one conductive shield and at least one common mode noise attenuator; wherein the at least one conductive shield partially surrounds the group of conductors thereby leaving at least one conductive path for a propagation of at least one current resulting from the common mode noise to the at least one common mode noise attenuator; and wherein the at least one conductive shield may be positioned between the group of conductors and the at least one common noise attenuator.

[0012] The at least one common mode noise attenuator may be configured to absorb the at least one current resulting from the common mode noise.

[0013] The at least one conductive shield may include (a) a first electrically conductive layer that may include first electrically conductive segments that may be isolated from each other, and (b) a second electrically conductive layer that may include second electrically conductive segments that may be isolated from each other; wherein the at least one common mode noise attenuator may include (a) a first layer of an electromagnetic attenuating material , and (b) a second layer of the electromagnetic attenuating material; wherein the first electrically conductive layer may be positioned between the group of conductors and the first layer of electromagnetic attenuating material; and wherein the second electrically conductive layer may be positioned between the group of conductors and the second layer of electromagnetic attenuating material.

[0014] A length, along the longitudinal axis of the first electrically conductive layer, of a first electrically conductive segment does not exceed 5 millimeters or may have any other dimension.

[0015] The common mode noise suppressing device may include dielectric material that may be positioned between the first electrically conductive layer and the second electrically conductive layer; a first additional electrically conductive layer and a second additional electrically conductive plate; wherein the first layer of the electromagnetic attenuating material may be positioned between the first additional electrically conductive layer and the first layer of electromagnetic attenuating material; and wherein the second layer of an electromagnetic attenuating material may be positioned between the second additional electrically conductive layer and the second layer of electromagnetic attenuating material.

[0016] The at least one common noise trap may span along at least a majority of a length of the group of conductors.

[0017] The at least one conductive shield may include (a) a first electrically conductive layer that may include first electrically conductive segments that may be isolated from each other, and (b) a second electrically conductive layer with that may include second electrically conductive segments that may be isolated from each other; wherein the at least one common mode noise attenuator may include multiple electromagnetic attenuating material elements; wherein the group of conductors may be positioned between the first electrically conductive shield and the second electrically conductive shield; and wherein multiple first electrically conductive segments and multiple second electrically conductive segments may be positioned between sets of electromagnetic attenuating material elements of the multiple electromagnetic attenuating material elements. The elements of attenuation materials should be preferably located in areas, in which segments of shielding conductive layers physically separate them from signal conductors, and there is no line of sight between them and said signal conductors.

[0018] Each set of electromagnetic attenuating material elements may include a pair of spaced apart sets of electromagnetic attenuating material layers.

[0019] The group of conductors, the first electrically conductive shield and the second electrically conductive shield may be folded. Said segments of the first and the second conductive layers may either produce closed conductive loops around the group of the signal conductors, or may not produce closed conductive loops around the group of the signal conductors.

[0020] The group of conductors, the first electrically conductive shield and the second electrically conductive shield may be spaced apart from each other.

[0021] The at least one common mode noise trap may include multiple spaced apart common mode noise traps, wherein each common noise trap surround a portion of the group of conductors.

[0022] A distance between a pair of adjacent common mode noise traps may be smaller than a length of each common mode noise trap. [0023] The multiple common noise traps span along at least a majority of a length of the group of conductors.

[0024] The group of conductors may be isolated.

[0025] The at least one common mode noise trap may include a common noise trap that may be winded around the group of conductors.

[0026] The at least one common mode noise trap may include a common noise trap follows a spiral path around the group of conductors.

[0027] The group of conductors may be in proximity with magnetic cores. In this cases, magnetic cores may operate as absorbing material.

[0028] Signal conductors and shielding layers may be implemented as a flexible printed transmission line.

[0029] The at least one common mode noise trap may include an inner electrically conductive shield , an outer electrically conductive shield; wherein the at least one common mode noise attenuator may include an inner electromagnetic attenuating element and an outer

electromagnetic attenuating element; wherein the inner electrically conductive shield partially surrounds the inner electromagnetic attenuating element; wherein the outer electrically conductive shield partially surrounds the inner electrically conductive shield; wherein the outer electromagnetic attenuating element partially surrounds the outer electrically conductive shield; and wherein the inner electrically conductive shield and the outer electrically conductive shield may be spaced apart from each other.

[0030] The inner electrically conductive shield preferably contacts the inner electromagnetic attenuating element and wherein the outer electrically conductive shield preferably contacts the outer electromagnetic attenuating element.

[0031] A pair of conductors of the group of conductors may enter through at least one aperture formed by the outer electrically conductive shield and at least partially surround the inner electrically conductive shield.

[0032] The pair of conductors surrounds the inner electrically conductive shield multiple times.

[0033] The pair of conductors may include the first conductor and the second conductor, wherein the first conductor at least partially surrounds the inner electrically conductive shield while positioned at a first conductor layer; and wherein the second conductor at least partially surrounds the inner electrically conductive shield while positioned at a second conductor layer that may be spaced apart from the first conductor layer.

[0034] The common mode noise suppressing device may include multiple different layers that form the inner electrically conductive shield, the outer electrically conductive shield, the inner electromagnetic attenuating element and the outer electromagnetic attenuating element.

[0035] The different layers may be manufactured by metal-ceramic manufacturing process.

[0036] According to an embodiment of the invention, there may be provided a common mode noise suppressing device, which may include a group of conductors for conveying differential mode signals and common mode noise; and at least one common mode noise trap that may include at least one conductive shield and at least one common mode noise attenuator; wherein the at least one conductive shield may partially surround the group of conductors thereby leaving at least one conductive path for a propagation of at least one current resulting from the common mode noise to the at least one common mode noise attenuator; and wherein the at least one conductive shield may be positioned between the group of conductors and the at least one common noise attenuator.

[0037] The least one common mode noise attenuator may be a ring shaped magnetic core.

[0038] According to an embodiment of the invention there may be provided a method for common mode noise suppression, the method may include conveying by a group of conductors differential mode signals and common mode noise; and attenuating the common mode noise by at least one common mode noise trap that may include at least one conductive shield and at least one common mode noise attenuator; wherein the at least one conductive shield partially surrounds the group of conductors thereby leaving at least one conductive path for a propagation of at least one current resulting from the common mode noise to the at least one common mode noise attenuator; and wherein the at least one conductive shield may be positioned between the group of conductors and the at least one common noise attenuator.

[0039] The attenuating of the common mode noise may include passing currents induced by the common mode noise through the at least one common noise attenuator.

[0040] The device design may include preventing currents induced by the differential mode signals to be in interaction with the at least one common noise attenuator.

[0041] According to an embodiment of the invention there may be provided a method for manufacturing a common mode noise suppressing device; the method may include manufacturing multiple layers that form an inner electrically conductive shield, an outer electrically conductive shield, an inner electromagnetic attenuating element and an outer electromagnetic attenuating element; wherein the inner electrically conductive shield partially surrounds the inner electromagnetic attenuating element; wherein the outer electrically conductive shield partially surrounds the inner electrically conductive shield; wherein the outer electromagnetic attenuating element partially surrounds the outer electrically conductive shield; and wherein the inner electrically conductive shield and the outer electrically conductive shield may be spaced apart from each other.

[0042] The common mode noise suppressing device may be, for example, a common-mode choke, a cable, and the like.

[0043] Any combination of any of the devices and/or elements that forms the devices, may be provided.

[0044] According to an embodiment of the invention there may be provided an at least one common noise trap that once integrated with (or combined with or connected to) a group of conductors forms a common mode noise suppressing device. The group of conductors is configured to convey differential mode signals and common mode noise. The at least one common mode noise trap may include at least one conductive shield and at least one common mode noise attenuator. Wherein once integrated with (or combined with or connected to) the group of conductors the at least one conductive shield partially surrounds the group of conductors thereby leaving at least one conductive path for a propagation of at least one current resulting from the common mode noise to the at least one common mode noise attenuator; and wherein the at least one conductive shield may be positioned between the group of conductors and the at least one common noise attenuator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0046] FIG. 1 illustrates currents driven through a pair of conductors; [0047] FIG. 2 illustrates an impedance versus frequency relationship of Murata

DLPl lSNxxxHL2 series.

[0048] FIG. 3 illustrates a prior art balanced communication line;

[0049] FIG. 4 illustrates a common mode noise suppressing device according to an embodiment of the invention;

[0050] FIGs. 5A and 5B illustrate common mode noise suppressing device and currents that flow through a common mode noise suppressing device according to an embodiment of the invention;

[0051] FIGs. 6-7, 8A, 8B and 9-16 illustrate common mode noise suppressing devices and their components according to various embodiments of the invention;

[0052] FIGs. 17-32 illustrate a common mode noise suppressing device and portions of the common mode noise suppressing device according to various embodiments of the invention;

[0053] FIG. 33 illustrates a method according to an embodiment of the invention;

[0054] FIG. 34 illustrates a method according to an embodiment of the invention; and

[0055] FIG. 35 illustrates a common mode noise suppressing device according to an

embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0056] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0057] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings.

[0058] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0059] Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.

[0060] Any reference in the specification to a method should be applied mutatis mutandis to a system capable of executing the method.

[0061] Any reference in the specification to a system should be applied mutatis mutandis to a method that may be executed by the system.

[0062] According to various embodiments of the invention there is provided a common mode noise choke and data communication cable, whereas each of them may include (a) a group of conductors for conveying differential mode signals and that may occasionally convey also common mode noise; and (b) at least one common mode noise trap that may include at least one conductive shield and at least one common mode noise absorber. The common mode noise absorber can be made of an attenuating material (also referred to as lossy material).

[0063] The at least one conductive shield partially surrounds the group of conductors thereby leaving at least one conductive path for a propagation of at least one current resulting from the common mode noise to the at least one common mode noise attenuator.

[0064] The conductive paths may include, for example, gaps 123 and 124 of figure 19 and their surroundings; apertures 23 and 24 of figures 4 and 6 and their surroundings; conductive layer 81 and the gaps between traps 80(1), 80(2) and 80(3) of figure 8; conductive layer 81 and the gap between windings 80'(1), 80'(2) and 80'(3) of figure 9; gap 91 and its surrounding of figure 11 ; gap 99' and its surrounding of figure 13; gap 205 and its surrounding of figure 14; gap 999 and its surrounding of figure 15; gap 216 and its surrounding of figure 16. It is noted that any reference herein to the term "surrounding" refers especially to conductive materials that are proximate to the gap.

[0065] The at least one conductive shield is positioned between the group of conductors and the at least one common noise attenuator. [0066] The group of conductors may include two or more conductors, dedicated for conveyance of balanced differential-mode signal currents.

[0067] The at least one common mode choke and data communication cable can include one, two or more than two common mode noise traps.

[0068] Signal current are currents induced by signal driver(s), as necessary for the circuit intended functionality.

[0069] DM current(s) - Differential Mode currents driven in pair of conductors carrying signal current, whereas in most cases DM currents are functional currents. DM current in one conductor is equal in amplitude and exactly in anti-phase to the DM current in the other conductor comprising the pair of wires.

[0070] CM current(s) are Common Mode currents driven in pair of conductors, whereas CM current in one conductor is equal in amplitude and exactly in-phase with the CM current in the other conductor comprising the pair of wires.

[0071] Screen current(s) are currents induced in the metallic screen introduced in this invention by DM currents and CM currents.

[0072] Differential mode (DM) and Common Mode (CM) currents may be defined as follows (Clayton R. Paul, Introduction to Electromagnetic Compatibility, Second Edition, page 528):

[0073] Consider a pair of parallel wires 11 and 12 or PCB lands of length L and separation S shown in Figures 1 and 3.

[0074] The two conductors are placed in the xz plane and are parallel to the z axis. Suppose that the currents at the same cross section are directed to the right and denoted as I and I ₂ ■ We will concentrate on frequency-domain emissions, so that the currents will be the phasor currents.

[0075] These can be decomposed into differential-mode and common-mode components by writing h — h: + ID Eqn. (la)

Eqn. (lb) [0076] Given the currents I and I ₂ , we can decompose them into their differential- mode component I _D and their common- mode component I _c by solving set of equations ( 1) to give equations (2a) and (2b):

/„ — J ~ Eqn. (2a)

[0077] Common Mode Choke (CMC) is an electronic component used for maximum possible suppression of CM noise in balanced transmission lines, while providing minimum attenuation to DM currents.

[0078] 3dB operational frequency band is the frequency interval, within which DM signal attenuation does not exceed 3dB.

[0079] There are provided several Common Mode suppression structures used for noise suppression in balanced transmission lines. Balanced transmission line structures are not limited by two-conductors structure, and may have any integer number of pairs of electrical conductors.

[0080] The noise suppression structures covered within the body of this invention features the following typical performance parameters:

[0081] The frequency 3dB operational band should be as wide as possible. For example, typical 3dB operational band is desired to spread up to 3GHz, i.e. Differential Mode (DM) insertion loss is below 3dB in the whole 0 - 3GHz operational frequency band

[0082] Common Mode (CM) attenuation in the operational frequency band should be as high as possible, within constrains of DM loss being less than 3dB. Common mode loss is a frequency- dependent parameter, and is dictated primarily by magnetic and absorption materials properties, as well as by the structure geometry. It is a primary goal of the present invention to develop noise-suppression structures with CM attenuation typically 10 times (in dBs expression) greater, compared with the DM loss. For example, DM insertion loss is 3dB, and CM insertion loss is typically 30dB.

[0083] In addition, there is a goal to develop CMC common mode noise choke with minimal physical dimensions and cost, enabling full manufacturing automation. [0084] The novel CMCs design disclosed in this patent is for use on high-speed data communications transmission lines with typically 90Ω, 100Ω, 120 Ω or other characteristic impedances.

[0085] Currently commercially available CMCs provide miniature size, but suffer from DM impedance mismatch and from significant DM propagation loss rise above typically 500MHz. Both factors limit their application for a number of important high-speed signal applications.

[0086] The disclosed design has been based on several principles:

[0087] A. Conductors carrying DM current should form balanced transmission line with controlled characteristic impedance. This line has characteristic impedance satisfying impedance matching condition for DM signal at the common mode noise choke input and output ports. In general, according to the present invention, the transmission line characteristic impedance may vary along the line length inside the common mode noise choke structure;

[0088] B. Electromagnetic fields and currents generated by DM signal should be spatially confined in areas filled with low-loss dielectric materials (the balanced transmission line area). In the disclosed design, this DM fields confinement is achieved by use of special metallic shields, providing natural electromagnetic boundaries for electromagnetic fields generated by DM currents;

[0089] C. CM noise attenuation is achieved primarily by dissipation of electromagnetic field generated by CM currents in absorbing materials, located outside of the region occupied by fields generated by DM currents. Electromagnetic field generated by CM in transmission line area is coupled to the area filled with absorbing material via specially designed irregularities (in a form of cuts) in the metallic shields, used for confinement of DM fields;

[0090] D. The CM field is preferably confined within the area filled with absorption material by means of an additional electromagnetic shield. This measure results in more intensive CM attenuation and prevents undesirable CM field irradiation into an outer space.

[0091] Following is a detailed disclosure of the CM suppression apparatus and of several preferred embodiments.

[0092] The operational principle of the proposed common mode noise choke is based on assumption that ground plane metallic losses are much smaller at high frequencies compared with losses caused by ferrite or other lossy material. The novel CMC design enables induction of Eddy current in ferrite only by the common mode currents, but it prevents Eddy currents development by differential mode currents flowing in the transmission line.

[0093] The proposed solution is to add a new metallic screen element in the novel CMC construction. The metallic screen has cuts in direction transverse to direction of signal propagation in the balanced transmission line.

[0094] For convenience of further discussion, it is proposed to call the side of screen which is facing current-carrying conductors, the front side, while the other side will be called the rear side.

[0095] In figure 4, both ground planes of coplanar transmission line played a role of

electromagnetic screen between the transmission line and absorbing material. Both ground planes 21 and 22 were cut periodically or randomly to provide apertures 23 and 24 respectively.

[0096] Two layers of absorbing material 41 and 42 were added above the upper ground plane 21 and beneath the bottom ground plane 22 respectively. Two additional ground planes 51 and 52 (preferably without cuts) were added on both sides of the resultant structure, to confine within the absorbing material electromagnetic fields generated by CM currents.

[0097] The longitudinal axis of the common mode noise choke 60 is denoted 15.

[0098] Similar CM suppression apparatus exists in all other embodiments disclosed by this patent application.

[0099] Let us consider paths of differential- and common-mode currents induced on the metallic screen.

[00100] DM current induces oppositely-directed currents in metallic screen, so that the net current is zero.

[00101] As demonstrates above drawing 5A, distribution of eddy currents induced by DM current induced in the shield is in a form of closed loops. Currents induced by DM do not cross the gap in the shield. On the opposite, in case of eddy currents induced by the common mode, the induced in the screen currents start on its outer side and continue on its inner side. In this part of its path, the CM currents interact with lossy (preferably ferrite) material, and are partially dissipated.

[00102] As can be seen, there is practically no interaction between the DM currents path and RF absorbing material, while interaction of CM with the absorber is similar for the case of traditional design not employing metallic screen. [00103] For lesser interaction of DM currents with absorbing material, the absorbing material may be preferably removed (not shown in figure 5A) in areas along the axis z, occupied by gaps between screens. In this way, there is no line of site between the absorbing material and the current-carrying conductors.

[00104] Totally four optional structures are described in this application, but the disclosed above design principles may be applied for design of other CM suppression apparatus.

[00105] Basic Linear Structure

[00106] The basic linear structure according to an embodiment of the invention differs from the prior art balanced coplanar transmission line, known from prior art.

[00107] Physical parameters of this transmission line have been selected to achieve the desired characteristic impedance.

[00108] Figure 4 illustrates a basic linear structure operating like a common mode choke

60 according to an embodiment of the invention.

[00109] In the linear structure 60 transverse slots (apertures 23 and 24) were cut in the metallic ground planes of original transmission line. The original transmission line, typically featuring controlled characteristic impedance, is produced by two current-carrying conductors 11 and 12, low-loss dielectric material layers 31 and 32 and top and bottom ground planes 21 and 22.

[00110] Two layers of absorbing material 41 and 42 have been added above and beneath the two ground planes.

[00111] Two new ground planes 51 and 52 were added above the upper layer of absorbing material and below the lower layer of absorbing material.

[00112] Figure 5A illustrates the operational principle of the CM suppression device shown in figure 4, according to an embodiment of the invention.

[00113] Figure 5B illustrates a simpler (in relation to figure 4) suppression device according to an embodiment of invention, with additional ground planes 51 and 52 in figure 4 removed.

[00114] Common Mode Choke

[00115] Figure 6 illustrates a common mode noise suppression choke 61 that includes multiple folded repetitions according to an embodiment of the invention. [00116] The common mode noise choke 61 of figure 6 includes first metallic shield 21 with multiple spaced apart apertures 23, and a second metallic shield 22 with multiple spaced apart apertures 24, multiple electromagnetic attenuating material elements such as spaced apart attenuating material layers 41, 42, 43 and 44.

[00117] For lesser interaction of DM currents with absorbing material, the absorbing material in layers 41, 42, 43 and 44 may be preferably removed in void areas 411, 412, 421, 422, 431, 432, 441, 442. These voids in absorbing materials should be located along the folded transmission line structure across gaps 23 between screens 21 '( 1), 2 (2), 2 (3), 2 (4), 2 (5), 21'(6), 21'(7) and by gaps 24 between screens 22'(1), 22'(2), 22'(3), 22'(4), 22'(5), 22'(6), 22'(7), 22'(8), 22'(9). In this way, line of site between the absorbing material and the current- carrying conductors is eliminated.

[00118] Figure 6 is a cross sectional view and illustrates only one current-carrying conductor 11 of the group of conductors. Conductor 11 is positioned between the first metallic shield 21 and the second metallic shield 22.

[00119] Multiple portions of the current-carrying conductor (for example the horizontal portions of the conductor 11) are positioned between sets of electromagnetic attenuating material elements of the multiple electromagnetic attenuating material elements.

[00120] In figure 6 each set of electromagnetic attenuating material elements comprises a pair of spaced apart sets of electromagnetic attenuating material layers - such as pair of layers 41 and 42, pair of layers 42 and 43, pair of layers 43 and 44, and the like.

[00121] Figure 6 also shows additional metallic layer 51. The bottom parts of the common mode noise choke 61 are not shown.

[00122] This folded structure has been designed in order to produce a compact CMC component. The total structure thickness is dependent on a number of folds N.

[00123] An alternative of above edge-coupled strip line transmission line is a broadside- coupled structure, shown in figure 7.

[00124] A model dimensions, shown below in Fig. 7 have been selected to match to 100Ω characteristic impedance.

[00125] For example, for dielectric material with dielectric constant E _r = 11, the total structure cross-section dimensions are as shown in Figure 7: [00126] Noise Suppression Lossy Cable

[00127] Figures 8A, 8B and 9 illustrate cable structure featuring electromagnetic properties of a common mode choke suppressor according to an embodiment of the invention.

[00128] In this embodiment, pair of wires 11 and 12 that form a transmission line is designed with isolation layers 73 of proper thickness that surround conductors 11 and 12 respectively, yielding characteristic impedance of desired value.

[00129] Figure 8A and 8B illustrate spaced apart traps 80(1), 80(2) and 80(3) surround conductors 11 and 12 and are configured to absorb the CM energy. In figure 9 multiple traps are implemented as multiple windings (80'(1), 80'(2) and 80'(3)) of thin dielectric tape surrounding conductors 11 and 12. Metallic shielding pads 800'(1), 800'(2) and 800'(3) with layered sections of absorbing material above the pads, are also shown.

[00130] In figures 8A-and 9 each trap includes an inner metallic shield layer 81 and an outer absorbing layer 82.

[00131] In figure 8B an additional shielding layer 83 surrounds the traps so that the lossy material layer 82 is positioned between conductive layer 81 and the additional shielding layer 83.

[00132] The additional shielding layer 83 can be made of a conductive material. The additional shielding layer may or may not be terminated (bonded) to local chassis of electronic boxes on either side of the cable. In case that the additional shielding layer 83 is not terminated - this saves the cable shield termination costs, traditionally associated with use of conventional shielded cables.

[00133] The additional shielding layer can include multiple segments, may include apertures, may be formed as a mesh, and the like.

[00134] It has been found that the higher the addition of the additional shielding layer can substantially increase the CM attenuation. This phenomenon may be explained by better confinement of electromagnetic field generated by CM currents inside the lossy material.

[00135] Traps are located along the cable length, so that gaps are produced between adjacent gaps.

[00136] The operational principle of this cable, operating as a CM suppression apparatus, has been already explained in above sections.

[00137] This embodiment can be used in high-speed data communication cables [00138] The novel CM suppression design idea based on separation of DM and CM induced currents routes, is suitable for CM suppression on numerous types of balanced signal lines, primarily on high-speed balanced data communication pairs of wires.

[00139] It is known from prior art, that imperfectly balanced transmission lines, carrying high-speed communication signals, are prone to generate undesirable radiated emissions. The use of the same design idea, disclosed in this patent, may be beneficial for suppression of Common Mode in high-speed data communication cables. These CM-suppression elements may be periodically integrated in the cable, along its length. This measure may suppress common mode generation in the cable due to its inherent imbalance. Radiated emissions due to CM current generated by the cable imbalance cannot be completely suppressed by CM chokes located only on the cable ends, and should be suppressed immediately on the site of its generation. This is exactly what the proposed CM suppression apparatus does: it suppresses the CM currents along the whole cable length, in along their generation. The CM current attenuation provided by the apparatus may be relatively small, but should prevail the rate of the CM generation in the cable, due to the cable imbalance.

[00140] The CM currents suppression results in two positive affects:

[00141] A Alliance crosstalk between pairs and between cables is reduced

[00142] B Radiated emission from the cable is reduced.

[00143] The proposed method does not have a goal to improve the cable imbalance, which is costly and becomes a formidable task for high operational frequencies, but to dissipate CM currents generated by the cable imbalance. This dissipation should be done along all cable length. It is another goal of this invention to provide low-cost method and apparatus to suppress effectively the common mode currents along the whole cable length.

[00144] The proposed method is to use periodical, as dense as necessary-located along the cable, dissipative traps for the common mode currents energy. One of possible traps construction in one of its preferred embodiments is demonstrated in Figures 8A, 8B and 9.

[00145] Figures 8A, 8B and 9 show the private case of two wires, but the method may be easily extended to an arbitrary number of wires. For example, in case of LAN cables, these traps may be added on each pair of wires, and/or over the whole cable, composed of up to 4 twisted pairs. This approach may reduce pair-to-pair alliance crosstalk, as well as a level of radiated emissions. Cylindrical traps are added periodically along the wires, preferably tightly over the wires isolation, i.e. with minimal air gaps. This arrangement may be considered as a distributed common-mode choke structure. The traps operation is based on the principle of CMC described above for the case of lumped CMCs. Differential- mode currents induced on the inner conductive layer of each trap generate circular Eddy currents only on the inner side, adjacent to the wires. On the contrary, CM currents in the wires, induce currents on the inner side of the conductive layer, but then proceed on the outer side of the conductive layer, i.e. in close proximity with lossy material. Eventually, current induced by the common mode in the trap flows in closed loop composed of two sections: (A) on the conductive layer inner side, practically without loss and (B) on the outer side of the conductive layer, with significantly greater loss.

[00146] The trap effectiveness has resonant behavior due to reflections from the trap edges. Maximum loss occurs at resonant frequencies. Traps may be with varying length, in order to cover broader frequency range of effective CM energy absorption.

[00147] Moreover, several layers of lossy traps may be added to improve the CM attenuation performance.

[00148] As in the case of the novel CMC design, several types of lossy materials may be proposed: (A) ferrite bulk or powder material, (B) ferrite thin film, (C) amorphous metal tape, (D) amorphous metal powder immersed in some isolating binder material, (E) resistive metal films and (F) carbon-based composition coating, etc.

[00149] The preferred embodiment of the trap design is shown in Figures 10A, 10B, 11,

12 and 13.

[00150] Conductive layer 81 and lossy layers 82 are deposited on a flexible plastic substrate 83 and form tape 85. The conductive layer 81, with preferably transverse cuts in it, is in close proximity with the pair of current-carrying conductors 71 and 72. The current-carrying conductors 71 and 72, low-los dielectric layer 84 and ground plane 81 for balanced transmission line with controlled differential-mode characteristic impedance. The lossy layer 82 is made of lossy material, preferably in a thin layer form. The layer of lossy material preferably occupies the same area as the conductive material. The last, external layer is the plastic tape, supporting above conducting and lossy layers. Both conductive and lossy layers are patterned as patches, thus preventing unrestricted propagation of currents induced by the common mode in longitudinal direction. [00151] In an additional preferred embodiment, overall shield may be added over the bottom or top sides of plastic substrate 83 (not shown in FIG. 10A), as required for better confinement of electromagnetic field generated by CM currents within absorbing material.

[00152] In an additional preferred embodiment, the plastic tape with printed on it and isolated from each other metallic patches, similar to tape 85, may also be turned as a spiral over the current - carrying wires in one or more layers. The outer layer of absorptive material may be applied preferably over the outer side of metallic patches. This solution may be used as an addon instant mitigation of EMI problems, occurring due to cables conductive and radiated susceptibility or emissions.

[00153] In an additional preferred embodiment, tape similar to 85 may be used, wherein the lossy material layer 82 is replaced or enforced by powder of lossy material embedded into the cable plastic jacket.

[00154] Flexible Printed Transmission Line Wound over Magnetic Core

[00155] One of the preferred transmission line embodiments is manufactured by flexible printed circuit technology, as shown in Fig.lOB. Current-carrying conductors 71 and 72, flexible low=loss dielectric layer 84 and ground plane 81 form balanced transmission line with controlled characteristic impedance. In literature such structure is called Balanced Grounded Coplanar

Transmission Line (BGCTL). Cuts are done in the ground plane 81, preferably in transverse direction.

[00156] In order to obtain effect of CM attenuation, the flexible transmission line 86 is turned over (typically) ferrite cylindrical core having absorbing properties in the desired frequency band. The ferrite core should be on the ground plane side of the tape 86. In this way, ground plane 81 eliminates interactions of DM currents with ferrite core.

[00157] The transmission line 86 may be manufactured by flexible PCB technology. This technology is adequate to manufacture BGCTL. Typical dielectric material is Capton, with dielectric constant er = 4.6.

[00158] In another preferred transmission line embodiments, the flexible transmission line

86 is manufactured without ground plane 81 , but one or more metallic screens 91 and 92 were added over two cylindrical surfaces of the closed magnetic core 96, as shown in Figure 11. This figure also shows windings of flexible PCB over the screens. Figure 12 is a side and top view of the apertures metallic shields 93 and 94. [00159] In figure 11 there are two magnetic parts 91 and 92 forming a single closed-loop magnetic core. Two cylindrical branches of the core are surrounded by metallic shields 93 and 94, respectively. Flexible printed circuits board 95 that conveys conductors, surrounds these two shields.

[00160] The transmission line is preferably manufactured by methods of flexible printed circuit board technology, whereas controlled impedance is achieved by proper selection of several physical parameters:

a) W - trace width

b) S - spacing between traces comprising the transmission line

c) T - metal layers thickness

d) H - thickness of dielectric layer

e) A - flexible print width.

[00161] Above parameters are selected to produce balanced transmission line with desired

DM characteristic impedance. For example, for CMC used for noise suppression in Ethernet link, the required characteristic impedance is 100Ω.

[00162] The flexible PCB is manufactured in a form of narrow strip. The strip is then turned over metallic shields 93 and 94, whereas said shields are wrapped around cylindrical branches 91 and 92 of the ferrite core. Signal-carrying conductors printed on the flexible PCBs are conductively attached by welding or soldering to the component's terminals 97 and 98. The signal-carrying traces 95 are preferably located on the side, which is not in contact with the ferrite core, i.e. isolated from the ferrite core by the metallic shield layer 93 and 94. This measure prevents interaction between the magnetic core and field generated by balanced signal flowing in the transmission line, thus reducing DM signal propagation loss in the CMC transmission line structure. As a result, the CMC insertion loss is close to that of transmission line of the same physical length, when measured without ferrite cores, located in close proximity.

[00163] Coplanar symmetrical transmission line was selected for the reason that it is balanced, and may be built of a flexible PCB with a single printed layer.

[00164] Use of flexible PCB makes cylindrical shape with circular cross-section optimal for the ferrite core. The most popular core shape with cylindrical sections and closed path for magnetic flux. Pot-core is an alternative core shape. [00165] Some magnetic manufacturers produce Common Mode Chokes and inductors, in which ferrite cores are glued to each other to provide a closed magnetic loop. One example of such core design is given in Figure 13.

[00166] Flow of common-mode currents on the metallic screen is shown in Figure 14.

[00167] Method and Apparatus for Enhancement of CMC Operational Bandwidth.

[00168] Traditionally, common mode chokes employ magnetic cores manufactured of a homogenous magnetic material (ferrite). Different ferrite materials have different frequency characteristics, such, one material type may have high RF energy suppression in lower frequency band, whereas the other in high frequency band. The material ability to absorb magnetic field energy is characterized by an imagery part of magnetic permeability, novel common mode suppression device may employ a combination of various ferrite materials, covering different frequency bands and thus resulting in enhanced effective operational bandwidth. Thus, two structures in figures 13 and 14 employ Magnetic Material #1 (207) with large imaginary part of magnetic permeability (Ιηι(μκι)) in lower frequency band, and Magnetic Material #2 (206) with large imaginary part of magnetic permeability (μκι) in higher frequency band. In this way, device effective operational bandwidth may be enhanced. In Fig. 13 magnetic core sections made of different magnetic materials 91(1), 91(2), 91(3) and 91(4) are stacked along the cylindrical structure (axis Z). In Fig. 14 magnetic core sections made of different magnetic materials occupy coaxial cylindrical volumes, whereas volume adjacent to an inner side of metallic shield is occupied with material 206 exhibiting higher-frequency attenuation properties. Correspondingly, material with lower-frequency properties 207, occupy central areas, remote from the metallic screen.

[00169] Figure 13 illustrates a common mode noise suppression device in which the magnetic core includes multiple (fours) spaced apart elements 91( 1), 91(2), 91(3) and 91(4) that can be made of different materials.

[00170] Figure 14 illustrates a cross sectional view of a common mode noise suppressing device according to an embodiment of the invention.

[00171] Figure 14 illustrates a magnetic core 207 surrounded by an outer layer of material that has absorption properties in higher frequencies, surrounded by dielectric material in which there is a metallic screen 203 with gap 205, the dielectric layer is surrounded by current carrying conductor 205 that has an input port 201 and an output port 202. For lesser DM signal losses, magnetic materials 206 and 207 may be deliberately removed from areas, which are in close proximity to gap 205.

[00172] Figure 15 illustrates common mode device 87, whereas magnetic material core has a shape of toroid 99, metallic shield with the circular gap 999 partially envelopes the magnetic core, and flexible balanced transmission line 88 is turned several times around the said conductive shield. The circular gap should be cut in the shielding conductive envelop in a way preventing generation of closed conductive loop around the magnetic core, and enabling penetration of eddy currents, generated by CM currents, on the inner side of conductive shield. It is important to note, that the device in FIG. 16 serves as a CM & DM separator. The device extracts CM currents components from a mixture of DM and CM currents appearing on input port. The DM current component in the primary winding does not induce any significant current into the secondary port, while the CM current component is effectively induced. Such device may be applied for CM detection, including CM data communication.

[00173] Figure 16 illustrates a cross sectional view of a common mode noise suppressing device according to an embodiment of the invention.

[00174] Figure 16 illustrates a cylindrical magnetic core 218 surrounded by

several turns of an inner isolated signal conductor 217 with balanced output port 215, that serves as secondary windings of RF transformer, ^

a metallic screen 213 with gap 216, and

the outer preferably isolated current carrying conductor 214, that has an input balanced port 211-212.

Two conductors comprising the output port 215 extend the conductive screen 213 through gap 216.

[00175] Figure 16 shows only a single turn of current-carrying wires over and underneath the conductive shield, whereas in actual applications, number of turns in primary and secondary windings may be arbitrary, and may be selected optimal for achievement of design goals. One of design benefits is a completely electromagnetically shielded construction, whereas an inner coil 217 is effectively shielded against environmental electromagnetic noise by shielding layer 213.

[00176] Monolithic Miniature Common Mode Choke

[00177] Figures 17-32 illustrates a common mode noise choke 100 according to various embodiments of the invention. [00178] Figure 17 is a three dimensional view of common mode noise choke 100. Figure

18 illustrates balanced input port 101-102 and balanced output port 103-104, the first signal- carrying conductor 111, the second signal- carrying conductor 112, the first arm 113 that couples the first output terminal 103 to the first signal- carrying conductor 111, the second arm 114 that couples the second output terminal 104 to the second current-carrying conductor 112. Figure 19 shows an inner metallic shield 121 with the gap 123, an outer metallic shield 122 and an outer aperture 124 formed in the outer metallic shield 122. Both gaps 123 and 124 prevent generation of closed conducive loop around magnetic core 141 and 142, shown in FIG. 26, and enable interaction between eddy currents, generated in the screen by CM, and absorbing magnetic material. It should be noticed that both metallic shields should be electrically bonded to the ground plane of the PCB hosting this common-mode choke device. This measure ensures enhanced CMC performance. Special grounding electrodes should be added in the CMC design (these grounding terminals are not shown in figures).

[00179] Figures 20-32 illustrates, from top to bottom, thirteen different layers 100(1)-

110(13) of common mode noise choke 100.

[00180] The number of layers and the composition of each layer may differ from those illustrated in figures 20-32.

[00181] The following list of components and the following table illustrate the different layers and components of the common mode noise choke 100:

101 first input port. 102 second input port 103 first output port

104 second output port 111 first conductor 112 second conductor

113 first arm 114 second arm 121 inner metallic shield

122 outer metallic shield 123 aperture of inner metallic shield

124 aperture of outer metallic shield 131 dielectric material

141 inner electromagnetic attenuating element;

142 outer electromagnetic attenuating element;

151 upper additional metallic layer 152 lower additional metallic layer

161 first metallic plate 162 second metallic plate.

First isolating layer with via hole 100(3) 101-104, 113, 121, 122, 123, 124, 131, 141, 142

First ground plane layer 100(4) 101-104, 113, 121, 122, 123, 124, 131, 141, 142,

161

First signal (+) isolating layer 100(5) 101-104, 113, 121, 122, 123, 124, 131, 141, 142 with via hole

First conductor layer 100(6) 101-104, 111, 121, 122, 123, 124, 131, 141, 142

Isolating layer 100(7) 101-104, 121, 122, 123, 124, 131, 141, 142

Second conductor layer 100(8) 101-104, 112, 121, 122, 123, 124, 131, 141, 142

Second signal (-) isolating layer 100(9) 101-104, 114, 121, 122, 123, 124, 131, 141, 142 with via hole

Second ground plane layer 100(10) 101-104, 114, 121, 122, 123, 124, 131, 141, 142,

162

Second isolating layer with via 100(11) 101-104, 114, 121, 122, 123, 124, 131, 141, 142 hole

Second signal (-) input trace 100(12) 101-104, 114, 121, 122, 123, 124, 131, 141, 142

Ferrite lower layer 100(13) 101-104, 152

TABLE 1

[00182] Electrical isolation between current-carrying conductors and conductive screens may be achieved by use of various isolating dielectric materials. In this specific embodiment, transmission line (both signal traces and screen layer) are manufactured using metal-ceramic technology, similar to that employed of Multi-Layer Ceramic Capacitors (MLCC)

manufacturing, while the magnetic core material may be manufactured either separately, or in the same multilayer wet printing, 3D printing (or similar) processes.

[00183] In the latter case, which comprises an additional preferred embodiment, paste of magnetic material is co-fired with the metallic and isolating layers.

[00184] The basic metallic screen idea may be implemented in a number of manufacturing technologies:

[00185] A. Metallic deposition on magnetic cores with following laser cuts or selective etching

[00186] B. Metal-ceramic monolithic design, whereas metallic, isolating and ferrite parts are manufactured by wet paste printing (or similar) technique [00187] C. Flexible PCB winding over cylindrical sections of magnetic core, whereas conductive screen is manufactured as a metallic spring attached to the same section. This approach has an advantage of better control of the winding transmission line characteristic impedance.

[00188] Depositions of lossy materials (magnetic, resistive or other lossy layer) on the rear

(outer) side of the conductive screen, may be done by numerous ways, and will not be discussed here.

[00189] The monolithic CMC structure is composed of several layers. Each layer may be manufactured by one of available technologies, like Multilayer Ceramic (MLC), 3D Printing, etc.

[00190] The new common mode noise choke operates also as a DM & CM modes separator.

[00191] Refer to embodiment shown in FIG. 16. The newly proposed common mode noise choke possesses properties of spatial separator between currents induced on the screen by Differential and Common mode currents. At each turn of current-carrying currents over the screen, it provides for currents induced in the metallic screen by CM currents, an option either to be reflected by the gap or to proceed flowing on the screen opposite side. The common mode current on the screen, will prefer the second option. On the other side, currents induced by DM currents, practically do not appear on the other side of the screen. The screen gap does not cause any significant perturbation to the DM signal currents in both wires comprising the signal- carrying pair, and remains nearly transparent for DM currents.

[00192] In this sense, the newly proposed common mode noise choke, operates as a mode spatial separator. It may perform several functions, some of them are in addition to these traditionally performed by classic Common Mode Chokes: Attenuation of energy induced in the screen by CM currents. Phase delay of currents induced in the screen by CM currents. Diversion of the currents induced by CM currents to other physical paths. Being a part of common mode noise choke which role is to measure CM currents induced in the conductive screens.

[00193] Let us consider each additional function separately.

[00194] Attenuation of energy induced in the screen by CM currents

[00195] Such attenuation may be provided by lossy material located on the rear side of the screen. The lossy material should be in tight contact with the screen rear side for the maximum attenuation effect. A variety of materials and shapes are valid for dissipation of the common mode energy: (A) Bulk (as in traditional CMC design) or thin layer (novel design feature) of ferrite or other materials, (B) Amorphous metal tape, (C) Resisting material, like Nickel-Chrome, etc., (D) Lossy materials based on amorphous metal powder immersed in isolating binder compound, (E) A combination of bulk ferrite with a thin/thick films coating of

absorbing/resistive materials over the rear side of metallic screen.

[00196] Selection of optimal material depends on the design goals. Resistive layers deposition has several advantages over traditional ferrite materials: (A) they are light- weighted, (B) they operate starting with practically zero and up to very high (microwave) frequencies, (C) are relatively low-cost.

[00197] In case of resistive coating, surface resistance may be varied. Optimum value must be selected to provide impedance matching with the CM source impedance. In this case, the CM attenuation shall be optimal.

[00198] Phase delay of currents induced in the screen by CM currents

[00199] Currents induced on the screen by CM currents flow an additional physical length as compared with currents on the front side of the screen. This property may be used for intentional phase delay in future applications.

[00200] Diversion of the currents induced by CM currents to other physical paths

[00201] Once currents induced on the screen by CM current are physically separated from currents induced by DM currents, it is feasible to divert them to some other physical direction. This feature enables to design a device (such as device 330 of figure 35 that includes input port 331, and two different mode output ports 332 and 333). The device is able to receive a mixture of Differential-Mode and Common-Mode currents at its input port, and to convey these modes into two different output ports. An illustration of this idea is provided on 33. Such devices may be used for common-mode data communication, e.g. PLC. They may be beneficial also as a sensing element of apparatus used for tracking hidden cables and metallic pipes.

[00202] Mode splitting device has a goal to convey differential mode to Port 2 and common mode to Port 3 with minimum attenuation, which means that Sddl2 and Sccl3 parameters should be as close to OdB as possible. On the contrary, common mode transmission from port 1 to port 2 (Sccl2), as well as differential transmission from port 1 to port 3 (Sddl3), should be kept as low as possible. Therefore, in respect to common mode, and under assumption that source impedance driving Port #1 and loads terminating Ports #2 and #3, the device operates as a conventional transformer with turns ratio 1: 1. Operational frequency bandwidth of such a device may be comparable with this of conventional RF transformers, known from prior art.

[00203] Measurement of CM currents induced in the conductive screens

[00204] Such measurement function may be beneficial as a substitute of conventional RF current probes. The new method of CM current measurement may result in physically smaller current probes with broader operational bandwidth and flatter frequency response.

[00205] Figure 33 illustrates method 310 for common mode noise suppression, according to an embodiment of the invention.

[00206] Method 310 may be executed by any one of the common mode noise chokes illustrated in any of the previous figures.

[00207] Method 310 may start by step 312 of conveying by a group of conductors differential mode signals and common mode noise.

[00208] Step 312 may be followed by step 314 of attenuating the common mode noise by at least one common mode noise trap that comprises at least one conductive shield and at least one common mode noise attenuator; wherein the at least one conductive shield partially surround the group of conductors thereby leaving at least one conductive path between the group of conductors and the common noise attenuator; and wherein the at least one conductive shield is positioned between the group of conductors and the at least one common noise attenuator.

[00209] Step 314 may include passing currents induced by the common mode noise through the at least one common noise attenuator.

[00210] Step 314 may include preventing currents induced by the differential mode signals to pass through the at least one common noise attenuator.

[00211] Figure 34 illustrates method 320 for manufacturing a common mode noise choke, according to an embodiment of the invention.

[00212] Method 320 may be used to manufacture the common mode noise choke of figure

14.

[00213] Method 320 may start by step 312 of manufacturing multiple layers that form an inner metallic shield, an outer metallic shield, an inner electromagnetic attenuating element and an outer electromagnetic attenuating element; wherein the inner metallic shield partially surrounds the inner electromagnetic attenuating element; wherein the outer metallic shield partially surrounds the inner metallic shield; wherein the outer electromagnetic attenuating element partially surrounds the outer metallic shield; and wherein the inner metallic shield and the outer metallic shield are spaced apart from each other.

[00214] Step 312 may be followed by coupling the multiple layers to a ferrite layer.

[00215] The common mode suppression, as disclosed in this application, may be employed in manufacturing of Printed Circuit Boards (PCBs). In particular, the technique may be effective, for example in the following cases:

a) PCBs incorporating relatively long (for example - exceeding 100 mm) high-speed balanced transmission lines (like backplanes for digital communication systems, central office equipment, etc.);

b) EMI filter sections embedded in inner layers of PCB, and located in areas

adjacent to connectors with high-speed data contents (like HDMI, 1G Base-T, 10G Base-T, PCI Express, etc.)

[00216] PCB with long runs of high-speed balanced pairs and employing the novel CM suppression mechanism, feature:

a) Reduced radiated and conducted emissions

b) Enhanced signal integrity parameters, like:

i. Reduced sensitivity to transmission line irregularities like bends, turns; ii. Enhanced balance, including compensation of imbalanced caused by manufacturing tolerances and proximity of asymmetrically located via holes, etc.

iii. Reduced crosstalk between balanced pairs and other traces (both balanced and single-ended run on the same PCB, including enhanced jitter resulting due to reduced crosstalk.

[00217] The application in high-speed PCBs is illustrated in Fig. 5B and in figures 36-38.

The novel noise-suppression mechanism may be employed on any type of balanced high-speed transmission lines, located either in an outer PCB layers, or in inner PCB layers.

[00218] Figure 36 demonstrates the inner-layer embodiment of the design idea, and is a cross sectional view of a device 420 that includes the following sequence (from top to bottom):

a) Top solid ground layer 421.

b) Top layer of absorbing material 422. c) Top ground plane with traverse cuts 423.

d) Top lossless dielectric layer.

e) Multiple (for example three) balanced pairs of transmission lines 411, 412 and 413.

f) Bottom lossless dielectric layer. The top and bottom dielectric layers are collectively denoted 427.

g) Bottom ground plane with traverse cuts 424.

h) Bottom layer of absorbing material 425.

i) Bottom solid ground layer 426.

[00219] The balanced pairs of transmission lines are positioned within a gap between

(while contacting) top and bottom lossless dielectric layers 427.

[00220] In comparison to figure 5 A - Upper and bottom solid ground planes 426 and 421 are added for better confinement of CM electromagnetic field in absorption layer and isolation from other PCB layers (not shown in the figure).

[00221] Particles of absorptive material may be embedded into pre-preg epoxy material with typical filling ratio (by volume) typically within the range from 5% to 75%. Typical absorbing materials are soft ferrite micrometer and nanometer powder, amorphous metal powder and flakes, carbon powder, etc.

[00222] Figure 37 is a top view of some of the components of device 410. Figure 37 illustrates top ground plane with transverse cuts 423 as well as traverse cuts 429 that are normal to balanced pairs of transmission lines 411, 412 and 413 - but may also be oriented in a non- normal angle.

[00223] Figure 37 illustrates a short section with typical dimensions, whereas all other layers are removed for clarity. Each transverse cut may be done over a single balanced pair of transmission lines. In some applications, longer transverse cuts stretched over two or more balanced pairs, are avoided in order to prevent increased coupling between these pairs.

Nevertheless, in some kinds of practically important applications, such crosstalk is not important, and longer transverse cuts may be used.

[00224] The term "balanced" means that functional signal propagated not between the single PCB trace and the PCB ground plane, but between two (typically symmetrical) PCB traces. In this cases, ground planes play secondary roles, and may impact the transmission line characteristic impedance, but most of signal energy is confined between symmetrical parallel- running traces.

[00225] Figures 38 and 39 illustrate the application of the CM suppression technique for

EMI common-mode filtering of high-speed signal interfaces. In this case, PCB traces that include a balanced signal pairs are designed as microstrips, i.e. as traces located in the PCB outer layers.

[00226] Figure 39 is a top view that illustrates a PCB 450 that includes a high speed transceiver 451 (may be a chip - IC) that is coupled via an EMI filter structure 453 to a connector 452. For clarity, only one balanced transmission line is shown. In practical applications, any number of balanced transmission lines may be treated in a similar way. A cross sectional view of the EMI filter structure 453 with three balanced transmission lines is provided in figure 38.

[00227] The EMI filter structure 453 includes (from top to bottom) a first balanced pair

431, a top lossless dielectric layer 444, a ground plane with transverse cuts 443, a layer of absorbing materials 442 and a solid ground plane 441.

[00228] It should be noticed that currently, arsenal of components for common-mode suppression is limited by Common Mode Chokes (CMCs). Selection of CMCs for high-speed applications is very limited, and their attenuation performance is very humble. The CMC performance is limited, since in current CMC design there is tight relationship between attenuation of Common Mode (CM) and Differential Mode (DM).

[00229] When using the novel CM suppression method this relationship is diminished to minimum, and large CM suppression (up to 20-30dB, typically) may be achieved without significantly compromising DM signal loss.

[00230] Figure 40 is a cross sectional view, figure 41 is a side view and figure 42 is a top view of a device 460 according to an embodiment of the invention. This embodiment addresses the new planar design of Common Mode Choke (CMC) based on the same idea of common mode noise suppression. The suggested CMC design enables also planar multilayer

implementation suitable for multilayer metal-ceramic manufacturing.

[00231] Figures 40 and 41 illustrates a device that absorbs common mode current energy in the central layer of absorbing material (absorbing material 465 - is a layer that is positioned between the top ground pane 474 and the bottom ground plane 472. The balanced transmission line is implemented as two edge-coupled conductors over ground plane, whereas the slab occupying the space between the ground plane conductors and the signal-carrying conductors is a low-loss dielectric material. Pair of two coupled conductors is turned around the absorbing slab, like it is usually done in inductors employing magnetic cores. In our case, ground plane serves for physical isolation between the differential-mode currents and the absorbing material, which leads to low differential-mode losses. On the contrary, common-mode currents induce currents in the ground planes, which circulate around the ground planes, penetrating also on the ground plane side, which is in tight contact with absorbing material. This mechanism is responsible for high degree of the common mode absorption.

[00232] For higher common mode attenuation, additional transverse cuts may be done in metallic ground planes. These cuts are shown in the drawing.

[00233] It is important to note that ground planes 473 and 474 should be electrically bonded to the ground plane(s) of the PCB hosting this CMC device.

[00234] Please note that contact pads used for the component installation on the host PCB is not shown in the drawing.

[00235] The device incorporates a central slab 465 of lossy material, typically

manufactured of ferrite, metal powder, or any other RF and microwave lossy material. The slab 465 is surrounded in its top and bottom sides by two metallic layers 473 and 474. These layers serve as a ground plane for balanced transmission line 470. In figure 40, windings 470 form a single balanced transmission line with controlled characteristic impedance. For this reason, spacing between pair of traces and thickness of low-loss dielectric layers 463 and 464 are selected properly, in order to ensure the required value of characteristic impedance.

[00236] Transverse cuts may be, or may not be cut in the ground metallic layers. Arbitrary number of cuts may be done, as may be considered practical, under constraints of limited space in typically miniature SMT device. For example, figure 42 shows a single cut in upper and lower ground planes. More cuts typically introduce greater common mode noise attenuation, while resulting in somewhat greater differential-mode loss. Therefore, number of cuts should be selected based on a compromise between the common-mode and differential mode attenuation. Figure 41 shows the side view of the same CMC structure, including connections between top and bottom layers of this planar structure. For enhanced broadband performance, these vertical sections of balanced transmission line should also be designed with desired value of

characteristic impedance, to prevent undesirable differential-mode signal reflections. It should be noted, that signal traces should be isolated from top and bottom ground planes by low-loss dielectric material 475, show in figure 42, but (for clarity of explanations) not shown in the figure 41.

Please refer to figure 42. The differential balanced signal inputs the CMC structure at port 471, performs several rotation around the planar structure, and outputs at the port 472. On the contrary, common-mode noise current tends to perform additional flow surrounding the top and bottom ground planes, thus contacting with the absorbing material slab. This causes high common-mode attenuation, as compared with low-loss differential mode propagation.

[00237] In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.

[00238] Moreover, the terms "front," "back," "top," "bottom," "over," "under" and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

[00239] Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality.

[00240] Any arrangement of components to achieve the same functionality is effectively

"associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial

components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality. [00241] Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

[00242] Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same common mode noise choke. Alternatively, the examples may be implemented as any number of separate integrated circuits or separate common mode noise chokes interconnected with each other in a suitable manner.

[00243] However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

[00244] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms "a" or "an," as used herein, are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[00245] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.