Zero Crossing Period of FSK Waveforms with Small Power Perturbation Brought by the Magnetically Coupled Series Resonant Circuits

The received signal waveform in a magnetic resonance wireless power transfer circuit with the input frequency discretely shifted is analyzed to demodulate FSK signal to binary data. First, components of the signal are presented based on frequency characteristic with two maximal transferred power. Second, it is shown how zero crossing period to determine the output value of bit regularly varies in two separated spans of time. Third, their interval, where there occurs non-regular change of zero crossing period, is evaluated. Two norms are proposed to formulate the upper and the lower limits of the interval. Finally, the range where zero crossing periods exist is analyzed and clearly expressed with an inequality.