Q-factor determination for foreign object detection circuit in wireless charging system

A method for a node in a wireless charging system to determine the presence of a metal foreign object, themethod comprising:

• plotting values, by a sample and hold circuit, of a sinusoidal waveform generated by a resonant circuit of the node wherein the sample and hold circuit locates and samples peak value positions along the sinusoidal waveform;
• using the plotted values to generate an estimated sinusoidal waveform by a processor,
• wherein the estimated sinusoidal waveform is a curve fitting between upper peaks and lower peaks of the peak value positions along the sinusoidal waveform;
• using values from the estimated sinusoidal waveformto calculate a Q factor value by the processor;
• and
• using the Q factor value to detect the presence ofthe metal foreign object.