Foreign objection detection sensing circuit for wireless power transmission systems

A wireless power circuit operable in a transceiver mode and in a Q-factor measurement mode, comprising:

• a coil having first and second terminals;
• a bridge rectifier having a first input and a second input coupled to the first terminal and second terminal of the coil, respectively, and having an output coupled to a rectified voltage node;
• an excitation circuit coupled to the first terminal of the coil and configured to drive the coil with a pulsed signal in the Q-factor measurement mode;
• a protection circuit coupling the first terminal of the coil to a first node in the Q-factor measurement mode and decoupling the first terminal of the coil from the first node in the transceiver mode;
• a controller configured to cause the bridge rectifier to short the first and second terminals of the coil to ground during Q-factor measurement mode;
• and
• a Q-factor sensing circuit configured to:
• amplify voltage at the first node to produce an output signal having an output voltage;
• and
• in response to the voltage at the first node rising to cross a rising threshold voltage, take a sample of the output voltage to produce a digitized output voltage, and provide the digitized output voltage useful in calculating a Q-factor of the coil.