Foreign objection detection sensing circuit for wireless power transmission systems

A wireless power circuit operable in transceiver mode and in Q-factor measurement mode includes a bridge rectifier having first and second inputs coupled to first and second terminals of a coil, and an output coupled to a rectified node. An excitation circuit coupled to the first terminal, in Q-factor measurement mode, drives the coil with a pulsed signal. A protection circuit couples the first terminal to a first node when in Q-factor measurement mode and decouples the first terminal when in transceiver mode. A controller causes the bridge rectifier to short the first and second terminals to ground during Q-factor measurement mode. A sensing circuit amplifies voltage at the first node to produce an output voltage, and in response to the voltage at the first node rising to cross a rising threshold voltage, digitizes the output voltage. The digitized output voltage is used in calculating a Q-factor of the coil.