WO1991007765A1

WO1991007765A1 - A planar transformer and a splitter/combiner using same

Info

Publication number: WO1991007765A1
Application number: PCT/US1990/004716
Authority: WO
Inventors: Robert C. Kane
Original assignee: Motorola, Inc.
Priority date: 1989-11-22
Filing date: 1990-08-22
Publication date: 1991-05-30

Abstract

A planar transformer (100) having substantially co-planar primary (301) and secondary windings (304) is formed through a deposition process on a substrate (101). This transformer has particular utility in a splitter/combiner structure.

Description

A PLANAR TRANSFORMER AND A SPLITTER/COMBINER

USING SAME Technical Field

This invention relates generally to transformers, and to splitters/combiners that make use of transformers.

Background of the Invention

Transformers are well understood in the art. Transformers typically include a primary and a secondary winding, wherein movement of current through the primary induces a voltage in the secondary winding. ^' Transformers are typically comprised of discrete elements wherein the primary and secondary windings include wound coils of conductor. Typically, such transformer embodiments require a significant amount of space, and also require separate handling during the fabrication and manufacturing stage of a product using such transformers.

Accordingly, a need exists for a transformer that can be preferably constructed during the same fabrication process used to form other components on a substrate. Further such a transformer should be particularly amenable to use in a splitter/combiner that could also be formed during the same fabrication process.

Summary of the Invention

These and other needs are substantially met through provision of the planar transformer disclosed herein, particularly as used in conjunction with a splitter/combiner. Pursuant to this invention, the transformer is comprised of a primary formed on a substrate, and a secondary that is also formed on that same substrate in a substantially co-planar orientation with respect to the primary.

In one embodiment of the invention, the planar transformer can be configured in conjunction with a splitter/combiner. Pursuant to one embodiment, the splitter/combiner includes a number of conductive surfaces formed on a substrate, wherein some of the conductive surfaces are transmission lines, and others are not. Certain of the conductive paths that are not transmission lines are oriented with respect to one another so as to be able to allow for inductive coupling therebetween. So configured, a well balanced signal splitter or signal combiner can be achieved through use of planar elements formed on a substrate, thereby taking advantage of the planar transformer configuration.

Brief Description of the Drawings

Fig. 1 comprises a side elevational view of one embodiment of the invention; Fig. 2 comprises a side elevational view of another embodiment of the invention;

Fig. 3 comprises a top plan enlarged view of a planar transformer; and Fig. 4 comprises a top plan enlarged view of a signal combiner and/or signal splitter constructed in accordance with the invention.

Best Mode For Carrying Out The Invention

The planar transformer (100) can be seen in Fig. 1 as being formed on one surface (103) of a substrate (101). Depending upon the application intended, this substrate (101 ) may be comprised of an insulating material, or of a material having a permeability greater than free space, such as an appropriate ferrite substance. (Additional detail regarding the planar transformer (100) itself will be provided below.) If desired, and as appropriate to the particular application,. a second substrate (102) can be provided and brought into joinder with the planar transformer (100) as depicted in Fig. 2. In the embodiment depicted in Fig. 2, the first substrate (101 ), and/or the second substrate (102), may be comprised of a material having a permeability greater than free space.

The primary and secondary for the planar transformer (100) will now be described in more detail with reference to Fig. 3.

The primary (301 ) has been arranged as a single annular shaped conductive path that has been formed on one surface of the substrate (101 ) through an appropriate deposition process, as well understood in the art. Input terminals (302 and 303) to the primary (301 ) are provided to allow energy to be input to the primary. In this embodiment, the primary consists of a single winding. If desired, additional windings could be formed.

The secondary (304) comprises four substantially concentric annular shaped conductive paths formed about (or interwound with) the primary (301 ) such that two of the secondary winding paths are to the interior of the primary (301 ), and two of the secondary conductive paths are to the exterior of the primary (301 ). Terminals (306 and 307) are again provided to allow access to any signals induced within the secondary by the primary. In this embodiment, there are four secondary turns to the one primary turn. Other ratios could of course be selected to suit an appropriate application. Regardless of the number of turns, however, it is important to note that both the primary (301 ) and the secondary (306) are substantially co-planar with respect to one another, and can both be formed during a deposition process, which may be the same disposition process that forms conductive paths for other purposes on the substrate (101).

In the embodiment depicted, the spacing between the conductive paths has been set at 0.0254 cm (0.010"). The primary conductor (301 ) has a width of 0.0762 cm (0.030"), while the secondary conductor (304) has a width of 0.0381 cm (0.015"). The primary conductor (301) has been made wider than the secondary conductor (304) in order to support the anticipated current carrying needs of the device in a particular application. A splitter/combiner (400) that makes integral use of the planar transformer will now be described with reference to Fig. 4. On a first side (103) of the substrate (101), a first conductor (401) having a width, in this embodiment, of 0.26924 cm (0.106") bifurcates at a junction point (402) into two conductive paths (403 and 404) that will act as primaries (or secondaries, depending upon whether the device functions as a splitter or a combiner, respectively) for two separate planar transformers (405 and 410). Each of these primaries (403 and 404) then couples via conductors (406 and 407) to other conductive paths (41 1 and 412) that are situated closely to the primaries (403 and 404) and that function as secondaries (or primaries). Lastly, each of these secondary paths (411 and 412) couple to second and third conductive paths (413 and 414, respectively).

The opposite side (104) of the substrate (101 ) has a ground plane disposed thereover with the exception of an area (416) that is opposite the transformers (405 and 410). So configured, all of the conductive traces will constitute microstrip, with the exception of the transformer windings, such that all of the paths function as transmission lines (with the exception of the planar transformers).

It will be noted that jumper points (408 and 409) would require a conductor connected therebetween in order to complete the conductive path indicated.

The device described operates as a signal splitter in the following manner. A signal provided to the first conductor (401) will split between the two paths constituting the primary windings (403 and 404) of the two planar transformers (405 and 410). This will in turn induce a flow of current in their associated secondaries (412 and 411), which current is available at the second and third conductors (413 and 414). If desired, an appropriate energy dissipating mechanism, such as a resistor (417), may be coupled between the two paths to dissipate energy that might otherwise contribute to a non-optimum path termination.

This structure functions as a combiner by placing inputs on the second and third conductors (414 and 413), thereby placing a current through the associated transformer windings (412 and 41 1) which, in this configuration, function as primaries to induce an associated current flow in their respective secondaries (403 and 404), which signals are then combined at the junction (402) to the first path (401 ). Again, the energy dissipating mechanism (417) can be utilized to effectively balance the signals. What is claimed is:

Claims

1. A transformer, comprising:

A) a substrate;

B) a primary formed on the substrate;

C) a secondary formed on the substrate, wherein the secondary is substantially co-planar with respect to the primary.

2. The transformer of claim 1 , wherein,

A) the substrate has a first major surface and a second major surface;

B) the primary is formed on the first major surface;

C) the secondary is formed on the first major surface.

3. The transformer of claim 2 wherein the secondary is interwound with respect to the primary.