Capacitively balanced inductive charging coil

Abstract

An inductor coil includes a wire which is wound in alternating layers such that the surface area of the wire in each winding viewed from above or below the coil is substantially equal in each half of the coil defined by a line bisecting the center point in each layer. The layers are also wound in a serpentine fashion to balance the capacitance between layers. The substantially equal surface area of wire in each half of a coil layer and in adjacent coil layers results in a balanced capacitance of the coil which, in turn, results in reduced common mode noise.

We claim: 
     
         1 . An inductive coil comprising:
 a length of electrically conductive wire forming at least one winding in a planar layer, the layer including a center point, the at least one winding comprising:   a first half of the winding; and   a second half of the winding contiguous with the first half; wherein:   the wire crosses itself at an edge of the first and second halves.   
     
     
         2 . The inductive coil of  claim 1  wherein the winding is approximately circular. 
     
     
         3 . The inductive coil of  claim 1  wherein the winding is a symmetric geometric shape. 
     
     
         4 . The inductive coil according to  claim 1  further comprising at least one additional coil formed by the wire. 
     
     
         5 . The inductive coil according to  claim 4  wherein the at least one additional coil is a spirally wound coil. 
     
     
         6 . The inductive coil according to  claim 1 , further including:
 at least one adjacent planar layer; wherein   both of the layers include a plurality of windings made from a continuous length of the wire; and   the wire from the first half crosses the wire from the second half.   
     
     
         7 . An inductive coil comprising:
 first and second adjacent coil layers formed from a single wire; wherein   the first layer defines a plane bisected by a line through a center point of the plane, the line defining a first half and a second half of the at least one layer,   the first layer comprises a plurality of windings made from a continuous length of wire that crosses itself;   the wire forms a first winding of the at least one layer before crossing itself; and   the wire forms a second winding of the at least one layer after crossing itself.   
     
     
         8 . The inductive coil according to  claim 7 , wherein:
 The second layer comprises:
 a first half; and 
 a second half; wherein: 
   a surface area of the wire comprising the first portion is approximately equal to a surface area of the wire comprising the second portion; and   the wire crosses itself between windings.   
     
     
         9 . The inductive coil according to  claim 7  wherein the coil layers are approximately circular. 
     
     
         10 . The inductive coil according to  claim 7  wherein the coil layers include a symmetric geometric shape. 
     
     
         11 . The inductive coil according to  claim 7  wherein the at least one of the coil layers is a conventional spirally wound coil. 
     
     
         12 . A portable electronic device comprising:
 a housing;   electronic components associated with the housing;   an inductive coil including a length of electrically conductive wire formed into at least one winding in a planar layer, the layer including a center point in the planar layer, each the winding including:   a first portion comprising approximately one half of the winding as determined by a line through the center point parallel with the planar layer; and   a second portion comprising another half of the winding in the planar layer opposite to the first portion;   wherein the length of wire comprising the first portion is approximately equal to the length of wire comprising the second portion.   
     
     
         13 . The portable electronic device according to  claim 12  wherein the winding is approximately circular. 
     
     
         14 . The portable electronic device according to  claim 12  further including at least one additional coil. 
     
     
         15 . The portable electronic device according to  claim 14  wherein the at least one additional coil is a conventional spirally wound coil. 
     
     
         16 . The portable electronic device according to  claim 12  further including:
 at least one adjacent planar layer; wherein: 
 both of the layers include a plurality of windings made from a continuous length of wire, the wire from the first half crossing the wire from the second half and forming a first half of a winding in the adjacent layer. 
 
     
     
         17 . A method for forming an inductive coil comprising the steps of:
 operating a rotating mandrel;   wrapping a wire length on the mandrel;   translating the wire in conjunction with the step of wrapping to alternate the wire in adjacent layers; and   forming the wrapped wire into an inductive coil.   
     
     
         18 . The method of  claim 17  wherein the step of translating includes:
 winding the wire into a first half of a first winding layer; 
 winding the wire into a second half of a second winding layer; 
 winding the wire thence into a first half of the first winding layer; wherein 
 the wire alternates between layers in a serpentine manner. 
 
     
     
         19 . The method of  claim 17  wherein the step of translating includes alternating approximately each half of a wire winding such that the length of wire comprising a first half portion of the winding is approximately equal to the length of wire comprising a second half portion of the winding. 
     
     
         20 . The method of  claim 17  wherein the step of translating includes forming a conventional spiral wound winding in at least one adjacent layer.