Adaptive passive ping
Systems, methods and apparatus for wireless charging are disclosed. A charging device has a charging circuit that includes a charging coil located proximate to a surface of the charging device, a pulse generating circuit, and a controller. The pulse generating circuit may be configured to provide a pulsed signal to the charging circuit, where each pulse in the pulsed signal includes a plurality of cycles of a clock signal that has a frequency greater or less than a nominal resonant frequency of the charging circuit. The controller may be configured to detect a change in resonance of the charging circuit based on a difference in response of the charging circuit to first and second pulses transmitted in the pulsed signal. The controller may be further configured to determine that a chargeable device has been placed in proximity to the charging coil based on the difference in responses.
1. A method for detecting an object, comprising:
transmitting a pulsed signal using a resonant circuit in a wireless charging device, wherein each pulse in the pulsed signal comprises a plurality of cycles of a clock signal that has a frequency that is greater than a nominal resonant frequency of the resonant circuit;
for each pulse in the pulsed signal:
generating a measurement signal representative of quality factor (Q factor) of the resonant circuit during transmission of the each pulse; and
filtering the measurement signal to obtain a filtered measurement signal indicative of Q factor of the resonant circuit during transmission of the each pulse; and
determining that a chargeable device has been placed in proximity to a coil of the resonant circuit when a first Q factor of the resonant circuit is different from a second Q factor of the resonant circuit, wherein the first Q factor is measured during transmission of a first pulse and the second Q factor is measured during transmission of a previously-transmitted second pulse.
2. The method of claim 1 , wherein the first Q factor exceeds a threshold value when the chargeable device has been placed in proximity to the coil of the resonant circuit.
3. The method of claim 2 , wherein the second Q factor is less than the threshold value before the chargeable device has been placed in proximity to the coil of the resonant circuit.
4. The method of claim 1 , further comprising:
detecting a change in the measurement signal between transmission of the first pulse and transmission of the second pulse; and
determining that the chargeable device has been placed in proximity to the coil of the resonant circuit when the change in the measurement signal exceeds a threshold difference value.
5. The method of claim 1 , further comprising:
providing a low-pass filtered version of the measurement signal and a filtered version of the measurement signal to respective inputs of a comparator; and
determining that the chargeable device has been placed in proximity to the coil of the resonant circuit when the comparator indicates a difference between its inputs.
6. The method of claim 5 , wherein the low-pass filtered version of the measurement signal is obtained from a low-pass filter configured to block higher frequency components of the measurement signal.
7. The method of claim 5 , wherein the comparator comprises a hysteresis circuit.
8. The method of claim 1 , wherein the measurement signal is obtained by measuring current in the resonant circuit.
9. The method of claim 1 , wherein the measurement signal is obtained by measuring voltage in the resonant circuit.
10. The method of claim 1 , further comprising:
using the resonant circuit to transmit an active ping in accordance with standards-defined specifications for charging the chargeable device; and
identifying the chargeable device from information encoded in a modulated signal received from the chargeable device,
wherein the clock signal has a frequency that is greater than nominal resonant frequency defined by the standards-defined specifications.
11. A charging device, comprising:
a resonant circuit that includes a charging coil located proximate to a surface of the charging device;
a pulse generating circuit configured to provide a pulsed signal to the resonant circuit, wherein each pulse in the pulsed signal comprises a plurality of cycles of a clock signal that has a frequency that is greater than a nominal resonant frequency of the resonant circuit;
a measurement circuit configured to provide a measurement signal indicative of Q factor of the resonant circuit during transmission of each pulse in the pulsed signal;
a filter configured to provide a filtered measurement signal indicative of Q factor of the resonant circuit during transmission of the each pulse;
comparison logic configured to compare a first Q factor measured during transmission of a first pulse and a second Q factor is measured during transmission of a previously-transmitted second pulse; and
a controller configured to determine that a chargeable device has been placed in proximity to a coil of the resonant circuit when the first Q factor of the resonant circuit is different from the second Q factor of the resonant circuit.
12. The charging device of claim 11 , wherein the first Q factor exceeds a threshold value when the chargeable device has been placed in proximity to the coil of the resonant circuit.
13. The charging device of claim 12 , wherein the second Q factor is less than the threshold value before the chargeable device has been placed in proximity to the coil of the resonant circuit.
14. The charging device of claim 11 , wherein the controller is further configured to:
detect a change in the measurement signal between transmission of the first pulse and transmission of the second pulse; and
determine that the chargeable device has been placed in proximity to the coil of the resonant circuit when the change in the measurement signal exceeds a threshold difference value.
15. The charging device of claim 11 , wherein the comparison logic is further configured to:
determine that the chargeable device has been placed in proximity to the coil of the resonant circuit based on a comparison of provide a low-pass filtered version of the measurement signal with a filtered version of the measurement signal.
16. The charging device of claim 15 , further comprising:
a low-pass filter configured to provide the low-pass filtered version of the measurement signal by blocking higher frequency components of the measurement signal.
17. The charging device of claim 15 , wherein the comparison logic comprises a hysteresis circuit.
18. The charging device of claim 11 , wherein the measurement signal is obtained by measuring current in the resonant circuit.
19. The charging device of claim 11 , wherein the measurement signal is obtained by measuring voltage in the resonant circuit.
20. The charging device of claim 11 , wherein the controller is further configured to:
use the resonant circuit to transmit an active ping in accordance with standards-defined specifications for charging the chargeable device; and
identify the chargeable device from information encoded in a modulated signal received from the chargeable device,
wherein the clock signal has a frequency that is greater than nominal resonant frequency defined by the standards-defined specifications.