Contactless USB — A capacitive power and bidirectional data transfer system

This paper extends the Universal Serial Bus (USB) standard to the contactless domain by combining bidirectional data communication with a capacitive power transfer interface. This work first addresses the power transfer with analysis, simulations, and experiment, based on a secondary side phase feedback series resonant topology. This gives the advantage of simple circuitry to regulate output voltage over large parametric variations of the capacitive interface. Secondly this work presents the data communication analysis, simulations and experiment where differential mode voltage containing the data information rides on top of the larger power voltage. An experimental prototype was built to deliver 1.25W of power with 53% overall efficiency over a total of 300pF capacitance with an area of 52cm², also realizing 100Mb/s bidirectional data communication.