External object detection sensing circuit for wireless power transmission system

The invention relates to an external object detection sensing circuit for a wireless power transmission system. A wireless power circuit operable in a transceiver mode and a Q factor measurement mode, and including a bridge coupled to a coil and having an output coupled to a rectified voltage node. In the Q factor measurement mode, the excitation circuit drives the coil with a pulse signal. The protection circuit couples the coil to the first node when in the Q factor measurement mode and decouples the coil from the first node when in the transceiver mode. The Q-factor sensing circuit includes an amplifier having an input coupled to a first node and a common mode voltage (Vcm), and generating an output signal having an output voltage. A comparator generates a comparison output indicative of a Vcm cross of the voltage at the first terminal of the coil, a processing circuit generates an enable signal based on the comparison output, and an analog-to-digital converter digitizes the output voltage when enabled for