Wideband planar transformer

• US 7,821,374 B2
• Filed: 01/04/2008
• Issued: 10/26/2010
• Est. Priority Date: 01/11/2007
• Status: Active Grant

• Current Assignee: PlanarMag, Inc. (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: Keyeye Communications
• Inventors: Pham, Anh-Vu, McConnell, Stephen M., Harrison, William Lee
• Primary Examiner(s): Enad; Elvin G
• Assistant Examiner(s): CHAN, TSZFUNG JACKIE
• Application Number:
  US12/006,822
• Publication Number:
  US 20090002111A1
• Time in Patent Office: 1,026 Days
• Field of Search: 336/192, 336/200, 336/229, 336/232
• US Class Current: 336/229
• CPC Class Codes: H01F 17/0033 with the coil helically wound around a magnetic core
• CPC Class Codes: H01F 19/04 Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range resonant circuits H03H
• CPC Class Codes: H01F 2027/2814 with only part of the coil or of the winding in the printed circuit board, e.g. the remaining coil or winding sections can be made of wires or sheets
• CPC Class Codes: H01F 30/16 Toroidal transformers
• CPC Class Codes: H01F 41/046 structurally combined with ferromagnetic material
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor

Abstract

A method of arranging and fabricating parallel primary and secondary coils of a wideband planar transformer is provided. The spacing and width of the coils are disposed to extend the bandwidth from DC to GHz and allow for high frequency coupling when the core permeability dramatically drops and achieves low reflected energy and low loss over a wide bandwidth. A bottom mold having a pattern of hole-pairs with conductive elements inserted vertically couples to a top mold such that a middle portion of the conductive elements spans between the top and bottom molds. Dielectric material envelopes the middle portion and a displacement feature of the mold creates a vacancy. A ferrite element is deposited to the vacancy. A second top mold spans the bottom mold and dielectric material is deposited to create a molded assembly. A deposited patterned conductive coating connects the element ends to define the transformer coils.

Claims

1. A wideband planar transformer comprising:

a. a ferrite material wherein said ferrite material has a closed-loop circuitous shape; and

b. a pair of balanced symmetric coupled transmission lines inter-wound about said ferrite material, wherein said pair of balanced symmetric coupled transmission lines comprises a capacitance between each said transmission line and a mutual inductance between each said transmission line, wherein said pair of coupled transmission lines form a pair of balanced symmetric coupled differential lines, wherein said pair of balanced symmetric coupled transmission lines inter-wound about said ferrite material provide a distributed inductance about said ferrite material, wherein trace widths of each said transmission line and gaps between said pair of balanced symmetric coupled transmission lines are matched to provide said differential coupling across a range from DC to multi-GHz, wherein said pair of coupled differential lines have an impedance proportional to a ratio of said distributed inductance over said coupling capacitance, wherein said ratio is disposed to match a differential input impedance and a differential output impedance in said wideband planar transformer,

wherein each said transmission line comprises a specific impedance,

wherein said specific impedance is dependent on an inductance of each said line and a capacitance of each said line.

2. The wideband planar transformer of claim 1, wherein said closed-loop circuitousshape comprises a toroid shape, wherein said coupled transmission lines comprise teardrop-shape conductors arranged with a small teardrop end near a center of said ferrite material and a large teardrop end away from said center of said ferrite material.

3. The wideband planar transformer of claim 2, wherein said conductive elements are disposed inside said ferrite material and outside said ferrite material, wherein said inside conductive elements are connected to said small teardrop end and said outside conductive elements are connected to said large teardrop end.

4. The wideband planar transformer of claim 1, wherein said coupled transmission lines comprise teardrop-shape conductors, wherein said teardrop-shape conductors comprise conductive coatings that form generally parallel said coupled transmission lines, wherein said coupled transmission lines comprise primary and secondary coils, wherein a coil spacings and coil widths are optimized to control leakage inductance and winding capacitance to lower reflected energy.

5. The wideband planar transformer of claim 1 wherein said coupled transmission lines comprise a primary coil and a secondary coil, wherein a first center tap is connected to a center coil of said primary coil and a second center tap is connected to a center coil of said secondary coil, wherein each half of each said coupled transmission line is made symmetric by said first center tap and said second center tap.

6. The wideband planar transformer of claim 1, wherein said coupled transmission lines are disposed to provide voltage isolation while maintaining said impedance.