Zero-crossing amplitude shift keying demodulation
Systems, methods and apparatus for wireless charging are disclosed. A charging device has a resonant circuit comprising one or more transmitting coils, a driver circuit configured to provide a charging current to the resonant circuit, a zero-crossing detector configured to provide a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or corresponding to transitions of a current in the resonant circuit through a zero ampere level and an Amplitude Shift Keying demodulator. The demodulator may be configured to receive a plurality of samples of voltage or current in the resonant circuit captured at times determined by the edges included in the zero-crossing signal, and demodulate a modulated signal obtained from the charging current using the plurality of samples of voltage or current in the resonant circuit.
1. A method for operating a wireless charging device, comprising:
providing a charging current to a resonant circuit when a receiving device is present on a surface of the wireless charging device;
providing a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or to transitions of a current in the resonant circuit through a zero ampere level;
sampling voltage or current in the resonant circuit at a plurality of sample points identified using the edges included in the zero-crossing signal, wherein the sampling is performed at a frequency corresponding to a fundamental frequency of the current or voltage in the resonant circuit; and
demodulating a modulated signal obtained from the charging current using a plurality of samples of voltage or current obtained by the sampling of the voltage or current in the resonant circuit, wherein the modulated signal is modulated using Amplitude Shift Keying (ASK).
2. The method of claim 1 , wherein the zero volt level corresponds to a current amplitude midway between maximum and minimum amplitudes of an alternating current (AC) measured in the resonant circuit.
3. The method of claim 1 , wherein the zero volt level corresponds to a voltage level midway between maximum and minimum amplitudes of an AC voltage measured across the resonant circuit.
4. The method of claim 1 , further comprising:
capturing a sample of voltage or current in the resonant circuit following after a delay that follows an edge in the zero-crossing signal.
5. The method of claim 4 , wherein the delay is calculated to cause sampling of the voltage or current when the voltage or current has a maximum amplitude.
6. The method of claim 1 , further comprising:
using a series of samples of voltage in the resonant circuit to demodulate the modulated signal.
7. The method of claim 1 , further comprising:
using a series of samples of current in the resonant circuit to demodulate the modulated signal.
8. The method of claim 1 , further comprising:
determining phase differences between a series of samples of voltage in the resonant circuit and a corresponding series of samples of current in the resonant circuit; and
demodulating the modulated signal based on the phase differences.
9. A charging device, comprising:
a resonant circuit comprising at least one transmitting coil;
a driver circuit configured to provide a charging current to the resonant circuit;
a zero-crossing detector configured to provide a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or corresponding to transitions of a current in the resonant circuit through a zero ampere level; and
an Amplitude Shift Keying demodulator configured to:
receive samples of voltage or current in the resonant circuit captured at a plurality of sample points determined by the edges included in the zero-crossing signal, wherein the samples are captured at a frequency corresponding to a fundamental frequency of the current or voltage in the resonant circuit; and
demodulate a modulated signal obtained from the charging current using the samples of voltage or current in the resonant circuit.
10. The charging device of claim 9 , wherein the zero volt level corresponds to a current amplitude midway between maximum and minimum amplitudes of an alternating current (AC) measured in the resonant circuit.
11. The charging device of claim 9 , wherein the zero volt level corresponds to a voltage level midway between maximum and minimum amplitudes of an AC voltage measured across the resonant circuit.
12. The charging device of claim 9 , wherein each of the samples of voltage or current in the resonant circuit is captured following after a delay that follows an edge in the zero-crossing signal.
13. The charging device of claim 12 , wherein the delay is calculated to cause sampling of the voltage or current when the voltage or current has a maximum amplitude.
14. The charging device of claim 9 , wherein the Amplitude Shift Keying demodulator is further configured to:
use a series of samples of voltage in the resonant circuit to demodulate the modulated signal.
15. The charging device of claim 9 , wherein the Amplitude Shift Keying demodulator is further configured to:
use a series of samples of current in the resonant circuit to demodulate the modulated signal.
16. The charging device of claim 9 , wherein the Amplitude Shift Keying demodulator is further configured to:
determine phase differences between a series of samples of voltage in the resonant circuit and a corresponding series of samples of current in the resonant circuit; and
demodulate the modulated signal based on the phase differences.