PLANAR PULSE TRANSFORMER

Abstract: A planar pulse transformer is formed upon a substrate (20) having at leat one opening (22) formed therein and has a magnetically permeable core (10) having at least one portion thereof disposed within the opening of the substrate. Preferably, at least one primary winding (150) and at least one secondary winding (152) at least partially encircle the core. The primary and secondary windings are comprised entirely of metallization layers so as to simplify the fabrication process and reduce costs.

Description: P ANAR PULSE TRANSFORMER Field of the Invention The present invention relates generally to hybrid circuit fabrication and more particularly to a planar pulse transformer specifically designed for use in hybrid circuit applications. Background of the Invention Hybrid circuits, wherein discreet components, i.e., resistors, capacitors, inductors, diodes, transistors, etc., are utilized in combination with integrated circuits, are well known. Hybrid circuit construction affords the advantage of integrating both discreet components and integrated circuits on a single substrate so as to simplify packaging requirements and facilitate the construction of volume-efficient circuitry. Pulse transformers for use in such hybrid construction are also well known. Such pulse transformers are typically capable of operating over a wide range of frequencies and are typically used to transfer non-sinusoidal pulses, generally without materially changing their waveforms. Such transformers are commonly utilized in circuit isolation applications. However, contemporary pulse transformers are generally formed as discrete components which must be mounted upon a substrate during the formation of hybrid circuitry thereupon. As such, contemporary pulse transformers are comparatively expensive (since they must be purchased as separate, discrete components) and are typically not packaged in a volume-efficient manner. Although it is known to form transformers directly upon the substrate, rather than utilizing prefabricated components, according to contemporary methodology such construction is complex and costly. Examples of such integrally formed transformers are disclosed in United States Patent Numbers 4,103,267; 4,777,465; 4,342,976; and 3,771,042. However, the transformers described in these patents utilize a toroidal type of core which is of one piece construction and thus must be mounted upon either the top or bottom surface of the substrate. Such construction necessitates that the windings be formed at least partially from conductors other than metalization layers formed directly upon the substrate. A portion of the windings of such transformers is generally comprised of wire. Examples of transformers having windings fabricated entirely of wire are disclosed in United States Patent Numbers 3,851,287; 3,691,497; 4,455,545; and 5,161,098. Such construction requires that wires be wound about a core and is thus inherently more complex than desired. It is also known to form a transformer utilizing metalization layers entirely for the windings thereof, rather than wire as in the above-referenced patents. One example of such a transformer is disclosed in United States Patent Number 5,015,972. However, the construction of the device of United States Patent Number 5,015,972 does not facilitate the use of magnetically permeable core so as to enhance the magnetic coupling of the primary and secondary windings thereof and thus the efficiency of the transformer is compromised. As such, it is beneficial to provide means for forming pulse transformers having magnetically permeable cores directly upon a hybrid circuit substrate so as to eliminate the need for wire windings and thus substantially reduce the cost thereof and also so as to enhance the volume efficiency of the circuitry. Summary of the Invention The present invention specifically addresses and alleviates the above-mentioned deficiencies associated with the prior art. More particularly, the present invention comprises a planar pulse transformer comprising a ceramic substrate having two openings formed therein. A ferrite core comprises a U core section having two legs, each leg extending through one of the openings of the substrate, and an I core section extending between the two legs of the U core section. At least one primary winding comprising at least one turn is formed as a metalization layer upon the substrate and at least partially encircles a first one of the legs. Similarly, at least one secondary winding comprising at least one turn is formed as a metalization layer upon the substrate and at least partially encircles a second one of the legs. The metalization layer may be formed upon either side of the substrate, or both sides thereof, as desired. The windings of the planar pulse transformer are formed as metalization layers upon the ceramic substrate wherein each metalization layer is separated from adjacent metalization layers via an insulating glass layer according to well known methodologies. The core, formed generally in the shape of a torus, passes through the substrate such that it also passes through the first and second windings formed thereupon. As such, the only prefabricated component of the planar pulse transformer of the present invention is the core itself, the windings being formed entirely via metalization upon the substrate. This substantially reduces the costs of the planar pulse transformer. Additionally, the volume efficiency of the planar pulse transformer is substantially enhanced, since the planar pulse transformer of the present invention is disposed at least partially within the substrate of the hybrid circuit, rather than being formed entirely upon the surface thereof, and also since the windings of the transformer do not typically extend substantially above the surface of the substrate. These, as well as other advantages of the present invention, will be more apparent from the following description and drawings. It is understood that changes in the specific structure shown and described may be made within the scope of the claims without departing from the spirit of the invention. Brief Description of the Drawings Figure 1 is a perspective view of the core of the planar pulse transformer of the present invention showing the U core section and the I core section exploded away from one another; Figure 2 is a perspective view of the substrate of the planar pulse transformer of the present invention showing two openings formed therein through which the core extends and also showing the bonding pads by which the planar pulse transformer is connected to other substrates or hybrid components placed upon the same or other substrates; Figure 3 is a perspective view of the core of Figure 1 inserted through the openings of the substrate of Figure 2; Figure 4 shows the first metalization layer for a substrate having two planar pulse transformers of the present invention formed thereupon, wherein the uppermost planar pulse transformer is ultimately to comprise two primary windings and two secondary windings, while the lowermost planar pulse transformer is to ultimately comprise four primary windings and two secondary windings; Figure 5 is the second metalization layer associated with the two planar pulse transformers of Figure 4; Figure 6 is the third metalization layer associated with the two planar pulse transformers of Figures 4 and 5; and Figure 7 is the fourth metalization layer associated with the two planar pulse transformers of Figures 4-6. Detailed Description of the Preferred Embodiment The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiment and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the function and sequence of steps for constructing and operating the invention in connection with the illustrated embodiment. It is to be understood, however, that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. The planar pulse transformer of the present invention is illustrated in Figures 1-7 which depict a preferred embodiment of the invention. Referring now to Figure 1, the planar pulse transformer of the present invention comprises a 2-part core 10. The core 10 comprises a U core section 12 and an I core section 14 configured such that when the I core section 14 is attached to first 16 and second 18 legs of the U core section 12, the core 10 is generally shaped as a torus. However, the core may be substantially rectangular in configuration (as illustrated in Figures 1 and 3) rather than having the rounded surfaces of a torus, so as to facilitate expensive manufacture thereof. Indeed, those skilled in the art will appreciate that the core may have various different configurations, other than those described and illustrated. The purpose of the core is to provide magnetically permeable material which serves as a flux guide for the windings of the transformer. Various different core shapes and configurations are well known in the art and are contemplated herein. Referring now to Figure 2, the substrate 20 generally comprises a planar member 30, preferably formed of a ceramic material. Those skilled in the art will appreciate that various other insulating materials are likewise suitable for use as the substrate. First 22 and second 24 openings are formed within the substrate 20 such that the two legs 16 and 18 of the U core fit therethrough. First bonding pads 26 and second bonding pads 28 are formed upon the upper surface 30 of the substrate 20 so as to facilitate electrical interconnection of the planar pulse transformer of the present invention with other substrates and/or hybrid electrical components. Parts of bonding pads 26 and 28 are electrically connected to the primary and secondary windings of each planar pulse transformer. Referring now to Figure 3, the core 10 is attached to the substrate 20 by positioning the first 16 and second 18 legs of the U core section 12 through the first 22 and second 24 openings, respectively, of the substrate and then attaching the I core section 14 to the distal ends of the first 16 and second 18 legs. The I core section 14 is preferably attached to the U core section 12 via a non-conductive epoxy such that the I core section is in intimate contact with the distal ends of the U core section 12. The core 10 is optionally also held in position with respect to the substrate 30 via such non-conductive epoxy. A plurality of such cores 10 may be formed upon a single substrate 20 so as to facilitate the formation of multiple transformers thereupon. Metalization patterns (as shown in Figures 4-7) are formed upon the upper surface 30 of the substrate 20 so as to define the windings of the planar pulse transformer. Thus, the windings of the planar pulse transformer of the present invention are formed entirely of such metalization patterns, rather than utilizing wire to form at least a portion of the windings according to contemporary methodology. A plurality of primary windings and a plurality of secondary windings may optionally be utilized, as desired. Selected pairs of the first bonding pads 26 provide electrical interconnection to corresponding primary windings and selected pairs of bonding pads 28 provide electrical interconnection to secondary windings. As those skilled in the art will appreciate, each winding may comprise a desired number of turns, formed upon separate metalization layers, preferably separated by glass insulating layers. Thus, a desired number of windings may be formed by simply alternating metalization and glass insulation layers, as desired. The conductors or windings are fabricated via the screening of metalization layers onto a ceramic substrate via contemporary methodology. Thus, according to the present invention, standard hybrid circuit manufacturing techniques are utilized to form the planar pulse transformer of the present invention, thereby substantially reducing the cost thereof. The transformer core 10 is preferably formed of a ferrite material, preferably laminated iron or steel plates, as is common in contemporary transformer construction. The size and type of material is determined by the requirements for each specific application. As mentioned above, the windings are made utilizing standard hybrid construction techniques. Optionally, the conductors are formed so as to extend to the top metalization layer for interconnection to other substrates via the use of bonding pads or for connection to other hybrid components placed upon the same substrate. Referring now to Figures 4-7, metalization layers required for the formation of two planar pulse transformers, each having a plurality of single turn primary and secondary windings, is illustrated. With particular reference to Figure 4, the substrate 120 comprises first 122, second 124, third 126, and fourth 128 openings formed therein. The first 122 and second 124 openings receive a first core (not shown) and the third 126 and fourth 128 openings receive a second core (not shown), so as to facilitate the formation of two separate planar pulse transformers. The first metalization layer comprises a first primary winding 150 and a first secondary winding 152 for the first planar pulse transformer and a first primary winding 154 for the second planar pulse transformer. First 156 and second 158 fiducial facilitate the alignment of screens during subsequent processing steps. The distal ends of each winding are positioned such that they may be brought up to the next layer during subsequent processing steps according to well known methodology. The process of applying metalization layers is performed so as to bring each separate primary winding of the first or upper transformer to the upper surface so as to facilitate interconnection with other components and/or substrates is discussed. As those skilled in the art will appreciate, the routing of the secondary winding of the first planar pulse transformer and the primary and secondary windings of the second planar pulse transformer is analogous to that of the routing of the first and second primary windings of the first planar pulse transformer. The first 160 and second 162 ends of the first primary winding of the first planar pulse transformer are positioned such that during the subsequent application of the insulating glass layer, they are exposed, i.e., not covered with glass, so as to facilitate their being brought up to the next metalization layer. With particular reference to Figure 5, the first ends 166 and 168 of bridging traces 165 and 167, respectively, contact the ends 160 and 162 of the first primary winding formed upon the first metalization layer and extend to second ends 170 and 172 thereof to facilitate contact with the third metalization layer. Second primary winding 174 is formed as part of the second metalization layer. First 176 and second 178 ends of the second primary winding 174 are positioned so that they may similarly contact the third metalization layer. With particular reference to Figure 6, first 180, second 182, third 184, and four 186 bridging traces facilitate interconnection between adjacent metalization layers as discussed above. With particular reference to Figure 7, first 190, second 192, third 193, and fourth 194 bridging traces facilitate interconnection with the fourth metalization layer and define bond pads to facilitate interconnection of the first 150 and second 174 primary windings of the first planar pulse transformer with other substrates and/or hybrid components. Thus, two planar pulse transformers are formed upon substrate 130 utilizing four metalization layers, according to the present invention. Those skilled in the art will appreciate that various different metalization and glass insulation patterns are likewise suitable for facilitating such construction. Thus, it is understood that the exemplary planar pulse transformers described herein and shown in the drawings represent only a presently preferred embodiment of the invention. Indeed, various modifications and additions may be made to such embodiment without departing from the spirit and scope of the invention. For example, both the core and the windings may be of various configurations other than those illustrated and described herein. Also, the present invention may be configured as various different types of transformers or inductive devices, including autotransfor ers. These and other modifications and additions may be obvious to those skilled in the art and may be implemented so that the present invention may be used in a variety of different applications.

Claims: WHAT IS CLAIMED IS: 1. A transformer comprising: a) a substrate having at least one opening formed thereon; b) a magnetically permeable core having at least a portion thereof disposed with the opening of said substrate; c) at least one winding at least partially encircling said core. 2. The transformer as recited in Claim 1 wherein said at least one winding comprises: a) at least one primary winding; and b) at least one secondary winding. 3. The transformer as recited in Claim 1 wherein said substrate comprises a ceramic substrate. 4. The transformer as recited in Claim 1 wherein said substrate comprises two openings formed therein and said core comprises: a) an I core section; b) a U core section having two legs; and c) said U core section is positioned such that each leg thereof is disposed within one of the two openings of said substrate and said I core section extends between the two legs. 5. The transformer as recited in Claim 1 wherein said core is comprised of a ferrite material. 6. The transformer as recited in Claim 2 wherein at least one of said primary and secondary windings comprise a plurality of turns. 7. The transformer as recited in Claim 2 wherein said at least one primary winding is comprised a plurality of primary windings. 8. The transformer as recited in Claim 2 wherein said at least one secondary winding is comprised a plurality of secondary windings. 9. The transformer as recited in Claim 2 wherein said primary and secondary windings comprise metalization layers. 10. The transformer as recited in Claim 2 wherein said primary and secondary windings comprise a plurality of metalization layers separated by glass insulation layers. 11. The transformer as recited in Claim 1 wherein said core comprises a two-part core which is assembled so as to capture a portion of the substrate between each part thereof. 12. The transformer as recited in Claim 2 wherein said at least one primary winding and said at least one secondary winding are comprised entirely of metalization layers. 13. A planar pulse transformer comprising: a) a ceramic substrate having two openings formed therein; b) a ferrite core comprising: (i) a U core section having two legs, each leg extending through one of the openings of said substrate; (ii) an I core section extending between the two legs; c) at least one primary winding comprising at least one turn formed as a metalization layer upon said substrate and at least partially encircling a first one of said legs; and d) at least one secondary winding comprising at least one turn formed as a metalization layer upon said substrate and at least partially encircling a second one of said legs.

Inventors: KRUSE NEILS A, KRUSE, NEILS, A.
Applicants: NORTHROP GRUMMAN CORP, NORTHROP GRUMMAN CORPORATION
Application year: 1995
Main classification: H01F27
IPC codes: H01F17, H01F19, H01F27