ZERO-CROSSING SLOTTED FOREIGN OBJECT DETECTION

Systems, methods and apparatus for wireless charging are disclosed. A method for operating a charging device includes providing a charging current to a resonant circuit when a receiving device is present on a surface of the wireless charging device, providing a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or to transitions of a current in the resonant circuit through a zero ampere level, providing a measurement slot by decreasing or terminating the charging current for a period of time, and determining whether an object other than the receiving device is present on a surface of the charging device based on measurements of samples of voltage or current captured based on timing provided by the zero-crossing signal, wherein the samples are captured during the measurement slot.