Bidirectional communication demodulation for wireless charging system

In a wireless charging system comprising a power transmitter and a power receiver, wherein a primary coil in the power transmitter wirelessly transmits a power signal to a secondary coil in the power receiver, a method implemented by one of the power transmitter and the power receiver for recovering binary data modulated on the power signal using a bi-phase digital encoding scheme, the method comprising:

• (a) processing an analog signal corresponding to voltage in a first coil of the wireless charging system using analog circuitry to generate a processed analog signal, wherein the first coil is one of the primary coil and the secondary coil;
• (b) sampling the processed analog signal to generate a sequence of digital samples;
• (c) detecting transitions in the sequence of digital samples associated with the bi-phase digital encoding scheme by applying two or more different transition-detection filters to the sequence of digital samples;
• and
• (d) decoding the detected transitions to recover the binary data, wherein the two or more different transition-detection filters comprise two or more of:
• a first transition-detection filter algorithm comprising detecting a transition only if amplitudes of the digital samples are determined to correspond to expected sample amplitudes;
• a second transition-detection filter algorithm comprising:
• (A1) calculating a first average of a first N of the digital samples, N>1;
• (A2) calculating a second average of a subsequent N of the digital samples;
• (A3) calculating a first difference between the first and second averages;
• and
• (A4) detecting a first transition candidate when the magnitude of the difference exceeds a first specified threshold value;
• a third transition-detection filter algorithm comprising:
• (C1) detecting a valid low-to-high transition only if a most-recent bit 0 in the binary data was encoded at a high sample level;
• and
• (C2) detecting a valid high-to-low transition only if the most-recent bit 0 in the binary data was encoded at a low sample level;
• a fourth transition-detection filter algorithm comprising:
• (B1) calculating a first weighted average using a first set of the digital samples corresponding to a sliding window;
• (B2) calculating a second weighted average using a second set of the digital samples corresponding to the sliding window;
• (B3) calculating a second difference between the first and second weighted averages;
• and
• (B4) detecting a second transition candidate when the magnitude of the second difference exceeds a second specified threshold value;
• and
• a fifth transition-detection filter algorithm comprising detecting a transition only if timing of the transition is determined to correspond to an expected transition time.

In a wireless charging system comprising a power transmitter and a power receiver, wherein a primary coil in the power transmitter wirelessly transmits a power signal to a secondary coil in the power receiver, a method implemented by one of the power transmitter and the power receiver for recovering binary data modulated on the power signal using a bi-phase digital encoding scheme, the method comprising:

• (a) processing an analog signal corresponding to voltage in a first coil of the wireless charging system using analog circuitry to generate a processed analog signal, wherein the first coil is one of the primary coil and the secondary coil;
• (b) sampling the processed analog signal to generate a sequence of digital samples;
• (c) detecting transitions in the sequence of digital samples associated with the bi-phase digital encoding scheme by applying two or more different transition-detection filters to the sequence of digital samples;
• and
• (d) decoding the detected transitions to recover the binary data, wherein step (b) comprises:
• periodically sampling the processed analog signal at a sequence of sampling times separated by a normal sampling interval corresponding to an integer multiple of a cycle of the processed analog signal;
• and
• the sampling times are based on results of a calibration process in which the processed analog signal is sampled at calibration sampling times separated by a calibration sampling interval that is different from the normal sampling interval to generate a sequence of calibration samples that approximates samples generated by sampling the processed analog signal multiple times over a single cycle of the processed analog signal.