Adaptive passive ping

Abstract

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.

What is claimed is: 
     
         1 . A method for detecting an object, comprising:
 using a gating signal to control a duration and a repetition rate at which bursts of a stimulation signal are provided to a resonant circuit, wherein frequency of the stimulation signal differs from a nominal resonant frequency of the resonant circuit;   during each burst of the stimulation signal:
 generating a measurement signal representative of quality factor (Q factor) of the resonant circuit; and 
 filtering the measurement signal to obtain a filtered measurement signal; and 
   determining that a chargeable device has been placed on a charging surface of a wireless charging device in proximity to a coil of the resonant circuit based on a reduction in the Q factor of the resonant circuit as indicated by the filtered measurement signal.   
     
     
         2 . The method of  claim 1 , wherein a frequency spread between the frequency of the stimulation signal and the nominal resonant frequency of the resonant circuit is proportionate to the nominal resonant frequency. 
     
     
         3 . The method of  claim 1 , further comprising:
 selecting a frequency spread between the frequency of the stimulation signal and the nominal resonant frequency of the resonant circuit based on a trade-off between signal-to-noise ratio (SNR) and power consumption.   
     
     
         4 . The method of  claim 1 , further comprising:
 selecting a frequency spread between the frequency of the stimulation signal and the nominal resonant frequency of the resonant circuit based on a trade-off between SNR and time needed for energy in each burst of the stimulation signal to decay in the resonant circuit.