Low profile filter

[0002] This application claims the benefit of priority to U.S. provisional patent application Ser. No. 60/420,532, filed on Oct. 23, 2002, now pending.

[0003] The present invention relates to electromagnetic filters and methods of providing electromagnetic filters.

[0004] It is known in the prior art to use an inductor and a capacitor circumferentially disposed about a feedthrough conductor in order to filter unwanted electromagnetic energy from a signal being carried by the conductor. In some prior art devices, the capacitor is circumferentially disposed about the inductor, and the inductor is circumferentially disposed about the conductor. Such an arrangement provides a compact filter, but the electromagnetic characteristics of that filter may be dictated by the reactance intrinsic to the ground design.

[0005] Also in the prior art is the use of discoidal capacitors, circumferentially disposed about a feedthrough conductor. When used in combination with an inductor, the discoidal capacitors are set apart from the inductor, and this increases the size of the electromagnetic filter.

[0006] The invention may be embodied in an electromagnetic filter for use with a feedthrough conductor. An inductor having a metallized surface is disposed about the conductor, and a capacitor is joined to the inductor. A first conductive contact electrically connects one set of capacitor plates to the metallized surface and a second conductive contact electrically connects another set of capacitor plates to the feedthrough conductor.

[0007] The invention may be embodied in a method of providing an electromagnetic filter. An inductor may be provided, and coated to provide a metallized surface. A capacitor is electrically connected to a first conductive contact and a second conductive contact. The capacitor may be joined to the inductor and the first conductive contact may be electrically connected to the metallized surface. The second conductive contact may be joined to the feedthrough conductor.

[0008] For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0009] FIG. 1 is a cross-sectioned perspective view of a metallized inductor according to the invention;

[0010] FIG. 2 is a partially cross-sectioned perspective view of an electromagnetic filter according to the invention;

[0011] FIG. 3 is partially cross-sectioned perspective view of an electromagnetic filter according to the invention; and

[0012] FIG. 4 is a flow chart depicting a method according to the invention.

[0013] The invention may be embodied as an electromagnetic filter. FIG. 1 shows an inductor 10 with a metallized surface 13. As shown in FIGS. 2 and 3, the inductor 10 may be disposed about a feedthrough conductor 16. The metallized surface 13 may be formed by electroplating the inductor 10. The metallized surface 13 may be at a first electric potential and the conductor 16 may be at a second electric potential. It should be noted that for the inductor 10, the metallized surface 13 does not extend so as to be positioned between the feedthrough conductor 16 and the inductor 10.

[0014] A capacitor 19 may be joined to the inductor 10 so as to fix the position of the capacitor 19 relative to the inductor 10. The metallized surface 13 may be used to join the capacitor 19 to the inductor 10. However, a non-metallic material may be used to join the capacitor 19 to the inductor 10.

[0015] The capacitor 19 may have a first plate 20 and a second plate 21. A first conductive contact 22 may electrically connect the metallized surface 13 to the first plate 20. The capacitor 19 may also have a dielectric material 24, which separates the plates 20, 21. A second conductive contact 25 may electrically connect the feedthrough conductor 16 and the second plate 21. The metallized surface 13 may be associated with a first electric potential, for example ground, and the second conductive contact 25 may be electrically connected to the feedthrough conductor 16. In this manner, a pi filter may be provided. By placing the ground on the inductor, additional parasitics may be eliminated.

[0016] The capacitor 19 may be positioned so as not to be disposed about the inductor 10. Instead, the capacitor 19 may be disposed about the feedthrough conductor 16 at a first axial location 28 of the feedthrough conductor 16, while the inductor 10 is disposed about a second axial location 31 of feedthrough conductor 16. In FIGS. 2 and 3, the first axial location 28 is shown being different from the second axial location 31. An additional capacitor 34 may be joined to the metallized surface 13 of the inductor 10, and the additional capacitor 34 may be positioned at a third axial location 34. Both capacitors 19, 34 may be positioned at axial locations of the feedthrough conductor 16 that are different from the axial location of the inductor 10. For example, the capacitors 19, 34 may have axial locations that result in the inductor 10 being positioned axially between the capacitors 19, 34.

[0017] FIG. 2 shows that the capacitors 19, 34 may each be a single capacitor circumferentially disposed about the feedthrough conductor 16. As shown in FIG. 3, in lieu of a single circumferentially disposed capacitor 19, two or more discrete capacitors 19A, 19B maybe positioned around the feedthrough conductor 16, each discrete capacitor 19A, 19B being positioned at an axial location different from the axial location of the inductor 10. Further, in lieu of a single circumferentially disposed additional capacitor 34, two or more discrete capacitors 34A, 134B may be positioned around the feedthrough conductor 16, each discrete capacitor 34A, 34B being positioned at an axial location different from the axial location of the inductor 10. The capacitors 19A, 19B, 34A, 34B may be joined to a substrate 23, which in turn may be joined to the inductor 10.

[0018] The invention also includes a method of providing an electromagnetic filter. In such a method, an inductor is provided 100 and a portion of the inductor is coated 103 to provide a metallized surface on the inductor. The metallized surface may be provided by electroplating the inductor 10. A capacitor is provided 106, and electrically connected to a first conductive contact and a second conductive contact. The first conductive contact may be associated with a first plate and the second conductive contact may be associated with a second plate, the plates being separated by a dielectric material. The capacitor may be joined 109 to the metallized inductor, and the first conductive contact may be electrically connected 112 to the metallized surface. The electrical connection between the first conductive contact and the metallized surface may be provided by soldering. The second conductive contact is electrically connected 115 to the feedthrough conductor. The electrical connection between the second conductive contact and the feedthrough may be provided by soldering.

[0019] Although the present invention has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present invention may be made without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.