Wireless power transmitter and method of controlling the same

1. A wireless power transmitter, comprising:

a resonator configured to transmit a detection signal;

a period detector configured to detect a period of oscillation of an oscillation signal caused by remnants of the detection signal, and generate a pulse signal substantially corresponding to the oscillation signal; and

a controller configured to receive the pulse signal from the period detector, and determine whether an external charging object is approaching in response to a change in the period of the oscillation signal, wherein the determining of whether the external charging object is approaching comprises determining whether the external charging object is approaching in response to a detected change in a pulse width of the pulse signal.

2. The wireless power transmitter of claim 1 , wherein the resonator is further configured to transmit the detection signal as a substantially sine shaped wave, at a substantially constant frequency, and

the period detector is further configured to detect the period of the oscillation signal after transmitting the detection signal.

3. The wireless power transmitter of claim 1 , wherein the controller is further configured to determine that the external charging object is approaching in response to another period of an oscillation signal caused by remnants of another detection signal, transmitted after the detection signal, being longer than the period of the oscillation signal caused by the detection signal.

4. The wireless power transmitter of claim 1 , wherein the period detector is further configured to detect a period of a first waveform of the oscillation signal, and

determine that the external charging object is approaching in response to the period of the first waveform changing.

5. The wireless power transmitter of claim 1 , wherein the period detector is further configured to compare the oscillation signal with a reference value to generate the pulse signal.

6. The wireless power transmitter of claim 5 , wherein the period detector comprises:

a voltage divider connected to the resonator and configured to divide a voltage level of an output signal of the resonator at a constant ratio; and

a comparator configured to compare an output of the voltage divider with the reference value to generate the pulse signal.

7. A method of controlling a wireless power transmitter, the method comprising:

generating a detection signal;

detecting a period of oscillation of an oscillation signal caused by remnants of the detection signal, wherein the detecting of the period of oscillation of the oscillation signal comprises generating a pulse signal corresponding to the oscillation signal; and

determining whether an external charging object is approaching in response to a change in the period of the oscillation signal, wherein the determining of whether the external charging object is approaching comprises determining whether the external charging object is approaching in response to a detected change in a pulse width of the pulse signal.

8. The method of claim 7 , wherein the detection signal is generated to be a resonance signal which is transmitted at a constant frequency through a resonator, and

the detecting of the period of the oscillation signal comprises detecting the oscillation signal after transmitting the detection signal.

9. The method of claim 7 , wherein the determining of whether the external charging object is approaching comprises:

detecting another period of another oscillation signal caused by remnants of another detection signal transmitted after the detection signal; and

determining that the external charging object is approaching in response to the other period being longer than the period.

10. The method of claim 7 , wherein the detecting of the period of the oscillation signal comprises:

detecting a period of a first waveform of the oscillation signal.

11. The method of claim 10 , wherein the determining of whether the external charging object is approaching comprises:

determining that the external charging object is approaching in response to the period of the first waveform of the oscillation signal changing.

12. The method of claim 7 , wherein the detecting of the period of the oscillation signal comprises:

comparing the oscillation signal with a preset reference value;

outputting a voltage having a first level in response to the oscillation signal being greater than the reference value;

outputting a voltage having a second level in response to the oscillation signal being equal to the reference value or less; and

time-continuously outputting the voltage having the first level or the voltage having the second level to generate the pulse signal.