be used further although the first spiral winding 204 is depicted as having approximately 1 5 turns and the second spiral winding 216 is depicted as having approximately 4 5 turns for clarity the number of turns in each winding may be tailored to suit individual application needs micro transformer 200 may pack the windings as closely together vertically as the design rules for a given process will allow to minimize overall circuit size while helping ensure a close magnetic coupling between the windings the winding layers may alternate so that a primary winding is proximate to a secondary winding similarly as shown in a variation depicted in fig2 b concentrically wound primary and secondary windings may be placed proximately on a common layer vias may connect their inner terminals to another layer for example as previously described the overall magnetic field resulting from currents flowing through the conductive windings may be oriented substantially perpendicular to the substrate the diameter of the individual spiral windings may be made relatively large compared to the separation between the individual spiral windings to achieve tighter magnetic coupling similarly symmetry between the primary windings and the secondary windings however many spirals each may comprise may be maximized to avoid degradation of the magnetic coupling in practice magnetic coupling ratios of 0 8 may be achieved with reasonable spiral sizes such a micro transformer may have an exemplary power transfer efficiency of ten to fifteen percent alternating currents that switch at a frequency from ten mhz to 20 mhz for example may be used.