Micro-scale planar-coil transformer with shield

Abstract

Micro-scale planar-coil transformers including one or more shields are disclosed. The one or more shields can block most common-mode current from crossing from one side to another side of a transformer. Reduction of common-mode current crossing the transformer results in reduction of dipole radiation, which is the main component of electromagnetic interference (EMI) in some transformers.

1 . A micro-scale planar-coil transformer arranged on a substrate having an upper surface, comprising:
 a first planar coil arranged in a first layer occupying a first area in a plane parallel to the upper surface;   a second planar coil arranged in a second layer; and   a shield arranged in an intermediate layer, the intermediate layer being between the first and second layers;   wherein a projection onto the first planar coil of a region enclosed by a perimeter of the shield covers a second area of the coil that is less than the first area.   
     
     
         2 . The micro-scale planar-coil transformer of  claim 1 , wherein a ratio of the second area to the first area is at least partially based on a ratio of a second common-mode voltage ripple amplitude of the second planar coil to a first common-mode voltage ripple amplitude of the first planar coil, the second common-mode voltage ripple amplitude being less than the first common-mode voltage ripple amplitude. 
     
     
         3 . The micro-scale planar-coil transformer of  claim 2 , wherein the ratio of the second area to the first area and the ratio of the second common-mode voltage ripple amplitude to the first common-mode voltage ripple amplitude comprise substantially complementary percentages. 
     
     
         4 . The micro-scale planar-coil transformer of  claim 3 , wherein the ratio of the second common-mode voltage ripple amplitude to the first common-mode voltage ripple amplitude is substantially equal to a coupling coefficient of the first and second planar coils. 
     
     
         5 . The micro-scale planar-coil transformer of  claim 1 , comprising only three metallization layers, the three metallization layers comprising the first layer, the second layer, and the intermediate layer. 
     
     
         6 . The micro-scale planar-coil transformer of  claim 1  comprising an overpass portion of the first coil arranged in the intermediate layer. 
     
     
         7 . The micro-scale planar-coil transformer of  claim 1 , wherein the first planar coil is electromagnetically coupled to the second planar coil and wherein the micro-scale planar-coil transformer further comprises:
 a third planar coil arranged in the second layer and coupled to the second planar coil; and   a fourth planar coil electromagnetically coupled to the third planar coil and arranged in the first layer.   
     
     
         8 . A micro-scale planar-coil transformer arranged on a substrate having an upper surface, comprising:
 a first side of a transformer comprising a first planar coil arranged in a first layer and configured to couple to a first electrical ground;   a second side of the transformer comprising a second planar coil arranged in a second layer and configured to couple to a second electrical ground;   a first shield arranged in a first intermediate layer and configured to couple to the first electrical ground, the first intermediate layer being between the first and second layers; and   a second shield arranged in a second intermediate layer and configured to couple to the second electrical ground, the second intermediate layer being between the first and second layers.   
     
     
         9 . The micro-scale planar-coil transformer of  claim 8 , wherein:
 the first planar coil occupies a first area in a plane parallel to the upper surface; and   a projection onto the first planar coil of a region enclosed by a perimeter of the first shield covers a second area of the first coil that is equal to the first area.   
     
     
         10 . The micro-scale planar-coil transformer of  claim 9 , wherein:
 the second planar coil occupies a third area in a plane parallel to the upper surface; and   a projection onto the second planar coil of a region enclosed by a perimeter of the second shield covers a fourth area of the second coil that is equal to the third area.   
     
     
         11 . The micro-scale planar-coil transformer of  claim 8 , comprising only four metallization layers, the four metallization layers comprising the first layer, the second layer, the first intermediate layer and the second intermediate layer. 
     
     
         12 . The micro-scale planar-coil transformer of  claim 8 , comprising an overpass portion of the first coil arranged in the first intermediate layer. 
     
     
         13 . A micro-scale planar-coil transformer arranged on a substrate having an upper surface, comprising:
 a first planar coil arranged in a first layer occupying a first area in a plane parallel to the upper surface;   a second planar coil arranged in a second layer; and   a shield arranged in an intermediate layer, the intermediate layer being between the first and second layers,   wherein a projection onto the first planar coil of a region enclosed by a perimeter of the shield encloses a second area that is equal to the first area.   
     
     
         14 . The micro-scale planar-coil transformer of  claim 13 , wherein a second common-mode voltage ripple amplitude of the second coil is greater than a first common-mode voltage ripple amplitude of the first coil that is substantially zero. 
     
     
         15 . The micro-scale planar-coil transformer of  claim 13 , wherein the second coil and the shield are configured to couple to a first electrical ground. 
     
     
         16 . The micro-scale planar-coil transformer of  claim 13 , wherein the shield is a first shield and the first planar coil is electromagnetically coupled to the second planar coil and wherein the micro-scale planar-coil transformer further comprises:
 a third planar coil arranged in the second layer and coupled to the second planar coil;   a fourth planar coil electromagnetically coupled to the third planar coil and arranged in the first layer occupying a third area in the plane parallel to the upper surface; and   a second shield arranged in the intermediate layer,   wherein a projection onto the fourth planar coil of a region enclosed by a perimeter of the second shield encloses a fourth area that is equal to the third area.   
     
     
         17 . A micro-scale planar-coil transformer, comprising:
 a first planar coil arranged in a first layer;   a second planar coil arranged in a second layer; and   means for reducing dipole radiation between the first and second planar coils.   
     
     
         18 . The micro-scale planar-coil transformer of  claim 17 , wherein the means for reducing dipole radiation between the first and second planar coils comprises means for blocking common-mode current between the first and second planar coils. 
     
     
         19 . The micro-scale planar-coil transformer of  claim 17 , wherein the means for reducing dipole radiation between the first and second planar coils comprises means for exposing the second planar coil to a portion of a first common-mode voltage ripple amplitude of the first planar coil, the portion being substantially equal to a second common-mode voltage ripple amplitude of the second planar coil. 
     
     
         20 . The micro-scale planar-coil transformer of  claim 19 , wherein a ratio of the portion to the first common-mode voltage ripple amplitude is substantially equal to a coupling factor of the first and second planar coils.