Method and apparatus for implementing common mode cable noise suppression for medium range frequencies

The present invention relates generally to the field of electromagnetic interference (EMI) noise suppression, and more particularly, relates to a method, apparatus, and a localized in-line cable filter system for implementing electromagnetic cable noise suppression including common mode medium range frequencies suppression.

Electromagnetic emissions can create problems in various electronic systems. Electromagnetic emissions are often coupled to a cable internally and/or externally and often times cannot be removed at the receiving peripheral. Also the coupled interference can be coming from a source that is not under the developer's control.

Ferrite cores often are used for reducing electromagnetic emissions. However, a ferrite core only may not provide enough series impedance to drop the common mode emissions to allow the electronic system to pass required standards for electromagnetic emissions.

A need exists for an effective mechanism for implementing electromagnetic cable noise suppression including common mode medium range frequencies suppression.

Principal aspects of the present invention are to provide a method, apparatus, and localized in-line cable filter system for implementing electromagnetic cable noise suppression. Other important aspects of the present invention are to provide such method, apparatus, and localized in-line cable filter system for implementing electromagnetic cable noise suppression substantially without negative effect and that overcome many of the disadvantages of prior art arrangements.

In brief, a method, apparatus, and a localized in-line cable filter system are provided for implementing electromagnetic cable noise suppression. The localized in-line cable filter system includes at least one electromagnetic interference (EMI) filter element connected between a cable and a current return path member. An insulation displacement terminal connects the EMI filter element to the cable. The EMI filter element and current return path member provide a low impedance connection toward a source.

In accordance with features of the invention, the current return path member includes a grounding conductor connected to the source. A bonding strap connected to the source can provide the current return path member.

In accordance with features of the invention, the current return path member returns current to the source, while minimizing the loop current path distance. The current return path member connection to the source has a minimized or short length from the EMI filter element to the source.

In accordance with features of the invention, when used with a ribbon cable, the localized in-line cable filter system can include a respective EMI filter element connected between a respective cable or wire conductor of the ribbon cable and a shielding or bonding strap current return path. A wire conductor of the ribbon cable can provide the current return path member.

The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein:

FIG. 1 is a perspective view not to scale illustrating an exemplary localized in-line cable filter system in accordance with the preferred embodiment;

FIG. 2 is a perspective view not to scale illustrating interior details of the exemplary localized in-line cable filter system in accordance with the preferred embodiment;

FIG. 3 is a partial perspective view of the exemplary localized in-line cable filter system of FIG. 1 illustrating insulation displacement connector and filter circuit apparatus in accordance with the preferred embodiment; and

FIGS. 4 and 5 are front and side views of the insulation displacement connector and filter circuit connection apparatus of FIG. 3 in accordance with the preferred embodiment.

In accordance with features of the preferred embodiments, placement of contact decoupling capacitors is enabled after the portion on the cable where the cable is coupled to a source. A localized in-line cable filter circuit is provided. The filter circuit allows the noise current to be shunted back to the source, which is best condition while the series ferrite core provides an impedance to lower the current down the line that is opposite to the source side of the cable.

In accordance with features of the preferred embodiments, the noise current is coupled onto the cable and is coupled back to the source by the localized in-line cable filter circuit via a shield or bond connection that may be separate or may be wrapped around the source side of the cable. The use of discrete capacitors enabled by the preferred embodiments is needed for various frequencies, usually medium range frequencies lower than 1000 Mhz. A low impedance path is provided via the bonded and/or shielded connection back toward the interfering source. This is usually the best connection since coming back to the chassis forces the current through a smaller circuitous route than through the earthed connections.

Having reference now to the drawings, in FIG. 1 , there is shown an exemplary localized in-line cable filter system generally designated by the reference character 100 for implementing electromagnetic cable noise suppression of the preferred embodiment.

The localized in-line cable filter system 100 includes an electromagnetic interference (EMI) filter generally designated by 102 connected between a cable generally designated by 104 and a current return path member 106 . The return current path member 106 advantageously is arranged to return the current to the source in a minimized or smallest loop possible. The return current path member 106 is formed, for example, from a thin sheet of metal, a metal mesh member, or a wire conductor.

The localized in-line cable filter system 100 preferably includes a ferrite core generally designated by 108 surrounding the cable 104 on the side of the EMI filter 102 opposite from the source. As shown in FIG. 1 , the EMI filter 102 is formed by a pair of respective mating housing or clamp members 110 , 112 . A pair of respective ferrite core members 114 , 116 preferably forms the ferrite core 108 for easy assembly with the cable 104 .

While a ribbon cable 104 is shown, it should be understood that the present invention is not limited to the use of a ribbon cable, various cable arrangements can be used with the localized in-line cable filter system 100 for implementing electromagnetic cable noise suppression of the preferred embodiment. For example, the localized in-line cable filter system 100 can be used with a free cable, which is a non-ribbon arrangement.

The return current path member 106 can be implemented with, for example, one or more cable conductors, such as predefined conductor or wire within the ribbon cable. The return current path member 106 advantageously can be implemented with, for example, a bonding strap or a shielded connection that may be separate or wrapped around the source side of the cable 104 .

Referring also to FIG. 2 , the lower housing or clamp member 110 of the EMI filter 102 is shown with the upper insulation displacement clamp member 112 removed. An opening or passageway 202 for receiving the ribbon cable 104 (not shown in FIG. 2 ) is defined between the ferrite core members 114 , 116 forming the ferrite core 108 . The lower housing member 110 includes a plurality of insulation displacement terminals 204 arranged in dual, staggered rows.

As shown in FIG. 2 , a plurality of EMI filter elements 210 are arranged in dual, staggered rows within the lower housing member 110 , with a respective EMI filter element 210 in line with each of insulation displacement terminals 204 . Each EMI filter element 210 preferably is implemented with a discrete value capacitor or other equivalent circuit EMI filter element.

The lower housing member 110 includes an opening or passageway 212 for receiving the return current path member 106 . The lower housing member 110 includes a pair of keying or positioning features 214 for cooperative engagement with mating features of the upper housing member 112 . The lower housing member 110 and upper housing member 112 are formed of an electrically insulative material, such as a plastic material.

Referring to FIG. 3 , the localized in-line cable filter system 100 includes insulation displacement connector and filter circuit apparatus generally designated by the reference character 300 .

Referring also to FIGS. 4 and 5 , there are shown detailed views of the insulation displacement connector and filter circuit connection apparatus 300 in accordance with the preferred embodiment.

Apparatus 300 includes at least one insulation displacement terminal 204 connected between a cable 302 of the ribbon cable 104 and the respective discrete value capacitor or other equivalent circuit EMI filter element 210 . A conductor member 304 connects the capacitor or EMI filter element 210 to the return current path member 106 .

The capacitor or EMI filter element 210 provides a return path for the coupled current through the bonding strap 106 . The return path strap 106 preferably is short with respect to the wavelength of the problem frequency and should return the current to the source in the smallest loop possible.

While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims.