Patent Publication Number: US-2023163635-A1

Title: Wireless power transmission device and operating method of wireless power transmitter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0160718, filed on Nov. 19, 2021, Korean Patent Application No. 10-2022-0008693, filed on Jan. 20, 2022, and Korean Patent Application No. 10-2022-0032236, filed on Mar. 15, 2022, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
     FIELD 
     The inventive concepts relate to an electronic device, and more particularly, to a wireless power transmission device and a method of operating a wireless power transmitter. 
     BACKGROUND 
     Wireless charging means that power is transferred between a transmitter that transmit wireless power and a receiver. If a user puts a foreign object made of metal, such as a coin or a key, near the transmitter, the foreign object may absorb power from the magnetic field, so an accident due to heat may occur. Accordingly, to inhibit or prevent heat generation due to foreign objects in a wireless charging system, it is desirable or necessary to detect foreign objects. In addition, when a foreign object is detected, it is desirable or necessary to lower the power delivery level or stop the power delivery. 
     SUMMARY 
     The inventive concepts provide a wireless power transmission device that implements a test signal for detecting a foreign object without adding additional hardware and a method of operating a wireless power transmitter. 
     In addition, the inventive concepts provide a wireless power transmission device for quickly and accurately detecting a foreign object and a method of operating a wireless power transmitter. 
     According to an aspect of the inventive concepts, a wireless power transmission device for supplying wireless power to a wireless power reception device includes a converter circuit configured to generate a test signal, the test signal having a test frequency based on an input current generated from a power source, a resonant tank configured to transmit wireless power in response to the test signal, a current sensing circuit configured to sense the input current when the wireless power is transmitted, and a controller configured to control the converter circuit to generate the test signal, calculate a quality factor of the resonant tank based on the sensed input current, compare the quality factor with a stored reference quality factor, and control the converter circuit to reset the test frequency or transmit a digital ping signal to the wireless power reception device according to a result of comparing the quality factor with the stored reference quality factor. 
     According to another aspect of the inventive concepts, a wireless power transmission device for supplying power to the wireless power reception device includes a power source connected between a first node and ground, a current sensing circuit connected between the first node and a second node, a converter circuit including a first transistor connected between the second node and a third node, a second transistor connected between the second node and a fourth node, a third transistor connected between the third node and the ground, and a fourth transistor connected between the fourth node and the ground, a resonant tank connected between the third node and the fourth node, and a controller connected to an output terminal of the current sensing circuit and connected to a gate electrode of each of the first to fourth transistors, wherein the controller is configured to output a first switching signal to the gate electrode of the first transistor, output a second switching signal to the gate electrode of the second transistor, output a third switching signal to the gate electrode of the third transistor, and output a fourth switching signal to the gate electrode of the fourth transistor, wherein at least one signal group of a first signal group including the first and third switching signals and a second signal group including the second and fourth switching signals is a square wave having a test frequency and a test duty ratio, and wherein a phase difference between two switching signals included in the at least one signal group is 180 degrees. 
     According to another aspect of the inventive concepts, an operating method of a wireless power transmitter for controlling a resonant tank includes setting a test frequency of a test signal applied to the resonant tank, calculating a quality factor of the resonant tank by applying the test signal to the resonant tank, comparing the quality factor with a stored reference quality factor, and resetting the test frequency or performing an operation of wirelessly transmitting power according to a result of comparing the quality factor with the stored reference quality factor. 
     According to another aspect of the inventive concepts, an operating method of a wireless power transmitter for controlling a resonant tank includes sensing an input current to the resonant tank by applying a test signal to the resonant tank, setting a test resonance frequency based on the sensed value of the input current, calculating a quality factor based on the sensed value and the test resonance frequency; comparing the quality factor with a reference quality factor selected according to the test resonance frequency among a plurality of specified reference quality factors, and resetting the test signal or performing an operation of wirelessly transmitting power according to a result of comparing the quality factor with the reference quality factor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some example embodiments of the inventive concepts will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a view for explaining a wireless power transmission/reception system according to an example embodiment of the present inventive concepts; 
         FIGS.  2 A and  2 B  are schematic equivalent circuit diagrams of a resonant tank included in a wireless power transmission device; 
         FIG.  3    is a graph schematically showing a coil current input to a resonant tank included in a wireless power transmission device according to an example embodiment of the present inventive concepts according to frequency; 
         FIG.  4    is a circuit diagram, as an example, for implementing a wireless power transmission device according to an example embodiment of the present inventive concepts; 
         FIG.  5    is a diagram for explaining an example embodiment of an operation timing between switching signals, a voltage and a current applied to a resonant tank, and an input current; 
         FIG.  6    is a view for explaining another example embodiment of an operation timing between switching signals, a voltage and a current applied to the resonant tank, and an input current; 
         FIG.  7    is a circuit diagram, as an example, for implementing a wireless power reception device according to an example embodiment of the present inventive concepts; 
         FIG.  8    is a flowchart for explaining a method of operating a wireless power transmitter, according to an example embodiment of the present inventive concepts; 
         FIG.  9    is a flowchart illustrating an example embodiment of calculating a quality factor; 
         FIGS.  10 A and  10 B  are graphs schematically illustrating a potential difference, an input current, a flag signal, and a rectified voltage applied to a resonant tank according to the example embodiment shown in  FIG.  9   ; 
         FIG.  11    is a flowchart for explaining another example embodiment of calculating a quality factor; 
         FIGS.  12 A and  12 B  are graphs schematically illustrating a potential difference, an input current, a flag signal, and a rectified voltage applied to a resonant tank according to the example embodiment shown in  FIG.  11   ; 
         FIG.  13    is a flowchart for explaining another example embodiment of calculating a quality factor; 
         FIGS.  14 A and  14 B  are graphs schematically illustrating a potential difference, an input current, a flag signal, and a rectified voltage applied to a resonant tank according to the example embodiment shown in  FIG.  11   ; 
         FIG.  15    is a diagram schematically illustrating a wireless power transmission device, an electronic device including a wireless power reception device, and a foreign object; 
         FIG.  16    is a diagram schematically illustrating a wireless power transmission device, an electronic device including a wireless power reception device, and a magnetic member; 
         FIG.  17 A  is a graph schematically showing a coil current according to the presence or absence of a magnetic member according to frequency in a wireless power reception device; 
         FIG.  17 B  is a graph schematically showing a quality factor according to the presence or absence of a magnetic member according to frequency in a wireless power reception device; 
         FIG.  18 A  is a graph schematically showing coil current according to the presence or absence of a magnetic member and the presence or absence of a foreign object in a wireless power reception device according to frequency; 
         FIG.  18 B  is a graph schematically illustrating a quality factor according to the presence or absence of a magnetic member and the presence or absence of a foreign object in a wireless power reception device according to frequency; 
         FIGS.  19 A and  19 B  are graphs schematically illustrating an operation of transmitting wireless power that may be performed according to whether a packet is received from a wireless power reception device; 
         FIG.  20    is a graph schematically illustrating whether detection of a foreign object has passed or failed; 
         FIG.  21    is a flowchart for explaining a method of operating a wireless power transmitter, according to another example embodiment of the present inventive concepts; and 
         FIG.  22    is a flowchart for describing in detail an operation method of the wireless power transmitter shown in  FIG.  21   . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, some example embodiments of the present inventive concepts will be described in detail with reference to the accompanying drawings. 
       FIG.  1    is a diagram for explaining a wireless power transmission/reception system according to an example embodiment of the present inventive concepts. 
     Referring to  FIG.  1   , a wireless power transmission/reception system  10  may include a wireless power transmission device  100  and a wireless power reception device  110 . 
     The wireless power transmission device  100  may supply wireless power to the wireless power reception device  110 . 
     The wireless power transmission device  100  may provide wireless power to the wireless power reception device  110  through a contactless method. The contactless method may be, for example, a wireless charging standard (e.g., Alliance for Wireless Power (A4WP)) that follows separate short-range wireless communication. However, the inventive concepts are not limited thereto, and in another example embodiment, the contactless method may be a wireless charging standard (e.g., Wireless Power Consortium (WPC), Power Matters Alliance (PMA), and the like) that does not use separate short-range wireless communication. 
     The wireless power transmission device  100  may transmit wireless power and receive information data from the wireless power reception device  110  through a contactless method. 
     The wireless power transmission device  100  may include a power supply circuit  101 , a current sensing circuit  102 , a memory  103 , a controller  104 , a converter circuit  105 , and a TX resonant tank  106 . 
     The power supply circuit  101  may be a power supply for supplying power to the wireless power transmission device  100 . In one example embodiment, the power supply circuit  101  may be implemented as a DC voltage source. In another example embodiment, the power supply circuit  101  may be implemented as a direct current source. 
     The current sensing circuit  102  may sense an input current generated by the power supply circuit  101  when wireless power is transmitted to the wireless power reception device  110 . The current sensing circuit  102  may provide a sensed value corresponding to the sensed input current to the controller  104 . The sensed value corresponding to the sensed input current may be, for example, a value corresponding to a DC component of the input current. 
     The memory  103  may store sensed values obtained by the current sensing circuit  102 . The memory  103  may store data for wireless power transmission. Data for transmitting wireless power may include, for example, a duty ratio and frequency of a signal for transmitting wireless power. The memory  103  may store data for detecting a foreign object, and the data for detecting a foreign object will be described later with reference to  FIG.  4   . The memory  103  may be implemented as a volatile memory, such as dynamic random-access memory (RAM) (DRAM), static RAM (SRAM), or the like. However, the inventive concepts are not limited thereto, and the memory  103  may be implemented as a non-volatile memory. The memory  103  may be disposed outside the controller  104 , but is not limited thereto and may be included in the controller  104 . 
     The controller  104  may control the converter circuit  105  to transmit wireless power to the wireless power reception device  110 . For example, the controller  104  may transmit a plurality of switching signals each having a turn-on level or a turn-off level to the converter circuit  105 . 
     The controller  104  may detect a foreign object by using a quality factor of the TX resonant tank  106  as the test signal is transmitted to the TX resonant tank  106 . In particular, the controller  104  may control the converter circuit  105  to generate a test signal. Then, the controller  104  may calculate the quality factor of the TX resonant tank  106  based on the input current sensed by the current sensing circuit  102 . Then, the controller  104  may compare the quality factor with a pre-stored reference quality factor. The controller  104  may control the converter circuit  105  to reset the test frequency or transmit a digital ping signal to the wireless power reception device  110 , according to the comparison result. 
     The test signal may be a voltage or current applied to the TX resonant tank  106 . For example, the test signal may be a voltage (or a potential difference between both inputs) applied to the input of the TX resonant tank  106 . For example, the test signal may be a current flowing through the input of the TX resonant tank  106 . In an example embodiment, the test signal may be a square wave having a test duty ratio included in a range of a test frequency and a pre-stored duty ratio. However, the inventive concepts are not limited thereto. The test frequency and the test duty ratio may be set by the controller  104 , respectively, and vary. 
     The quality factor of the TX resonant tank  106  may be referred to as “sharpness”, “Q factor”, “selectivity”, “goodness”, “quality coefficient”, “quality factor”, and the like. 
     The digital ping signal may be a signal transmitted from the wireless power transmission device  100  to the wireless power reception device  110  when a wireless power transmission operation is normally performed. 
     In some example embodiments, the controller  104  may control the converter circuit  105  to sequentially generate a signal having a frequency in a pre-stored frequency range as a test signal, sequentially store the sensed value corresponding to the sensed input current as the signal is sequentially generated, set the frequency as the test resonance frequency when the input current corresponding to the greatest value among the stored sensed values is sensed, calculate at least one cut-off frequency based on the stored sensed values, and calculate the quality factor based on the test resonance frequency and the at least one cut-off frequency. In particular, as an example embodiment for calculating the cut-off frequency is described, the controller  104  may set a frequency as the at least one cut-off frequency when an input current corresponding to at least one sensed value smaller by 3 dB (or more or less dB) than the greatest value (e.g., 3 dB less than the greatest value) among the stored sensed values is sensed. The description of the embodiment above will be given later in detail with reference to  FIG.  9   . 
     In another example embodiment, the controller  104  may control the converter circuit  105  to generate a signal having an initial frequency stored in advance (e.g., desired, pre-stored, predetermined, specified, etc.) as a test signal, store a sensed value corresponding to an input current sensed as a signal is generated, calculate the amount of change of the sensed input current per unit time using the sensed value, and calculate the quality factor by resetting the test frequency according to whether the sign of the change amount has changed or calculating the test resonance frequency and bandwidth based on the stored sensed value. The description of the embodiment above will be given later in detail with reference to  FIG.  11   . 
     In another example embodiment, the controller  104  may control the converter circuit  105  to sequentially output a first test signal having a resonance frequency of a pre-designed resonant tank and a second test signal having a pre-designed cut-off frequency before the wireless power transmission device  100  is shipped, and accordingly, store a first sensed value and a second sensed value and detect a foreign object by comparing sizes between the first sensed value and the second sensed value. The description of the example embodiment above will be given later in detail with reference to  FIG.  13   . 
     The converter circuit  105  may generate a test signal based on the input current generated by the power supply circuit  101 . 
     The TX resonant tank  106  may transmit a digital ping signal or provide wireless power based on the voltage (or current) generated by the converter circuit  105 . The TX resonant tank  106  may transmit wireless power in response to the test signal. 
     The wireless power reception device  110  may include an RX resonant tank  111 , an RX rectifier  112 , and an RX load circuit  113 . 
     The RX resonant tank  111  may be magnetically coupled to the TX resonant tank  106  to receive wireless power. The RX resonant tank  111  may output a voltage (and current) based on the received wireless power (e.g., according to the received wireless power, in response to the received wireless power, etc.). 
     The RX rectifier  112  may rectify the AC voltage (and current) output from the RX resonant tank  111  into a DC voltage to generate a rectified voltage. 
     The RX load circuit  113  may be a circuit representing a load generated in the wireless power reception device  110 . 
       FIGS.  2 A and  2 B  are schematic equivalent circuit diagrams of a resonant tank included in a wireless power transmission device. In particular,  FIG.  2 A  is an equivalent circuit diagram between a wireless power transmission device and a wireless power reception device, and  FIG.  2 B  is an equivalent circuit diagram between a wireless power transmission device and a foreign object. 
     Referring to  FIGS.  1  and  2 A , a wireless power transmitter  210  and a TX resonant tank  220  may be included in the wireless power transmission device  100  shown in  FIG.  1   . 
     The wireless power transmitter  210  may include the power supply circuit  101 , the current sensing circuit  102 , the memory  103 , the controller  104 , and the converter circuit  105  illustrated in  FIG.  1   . 
     The TX resonant tank  220  may include a transmission capacitor CP, a transmission inductor LP, and a transmission resistor RP. In an embodiment, the transmit capacitor CP, the transmit inductor LP, and the transmit resistor RP may be connected in series to form a resonant circuit. However, the inventive concepts are not limited thereto, and in another example embodiment, the transmission capacitor CP, the transmission inductor LP, and the transmission resistor RP may be configured as a resonant circuit by a parallel or series-parallel combination. 
     The resonance frequency Fres of the TX resonant tank  220  may be calculated by substituting the values of the transmission inductor LP and the transmission capacitor CP into [Equation 1] below. 
     
       
         
           
             
               
                 
                   
                     F 
                     res 
                   
                   = 
                   
                     1 
                     
                       
                         
                           L 
                           P 
                         
                         ⁢ 
                         
                           C 
                           P 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     The quality factor Q of the TX resonant tank  220  may be calculated by substituting the values of the transmission capacitor CP, the transmission inductor LP, and the transmission resistor RP into the following [Equation 2]. 
     
       
         
           
             
               
                 
                   
                     
                       
                         Q 
                         = 
                           
                         
                           
                             1 
                             
                               R 
                               P 
                             
                           
                           ⁢ 
                           
                             
                               
                                 L 
                                 P 
                               
                               
                                 C 
                                 P 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         
                           
                             F 
                             res 
                           
                           BW 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, Fres is the resonance frequency and BW is the bandwidth. 
     The TX resonant tank  220  may be magnetically coupled to the RX resonant tank  230 . When the TX resonant tank  220  and the RX resonant tank  230  are magnetically coupled, a mutual inductance M may occur. 
     Referring to  FIGS.  1  and  2 A , the RX resonant tank  230 , the wireless power receiver  240 , and a load resistor RL may be included in the wireless power reception device  110  illustrated in  FIG.  1   . 
     The RX resonant tank  230  may include a reception capacitor CS, a reception inductor LS, and a reception resistor RS. In some example embodiments, the reception capacitor CS, the reception inductor LS, and the reception resistor RS may be connected in series to form a resonant circuit. However, the inventive concepts are not limited thereto. 
     The wireless power receiver  240  may include the RX rectifier  112  illustrated in  FIG.  1   . 
     The load resistor RL may correspond to the RX load circuit  113  illustrated in  FIG.  1   . 
     The TX resonant tank  220 , the RX resonant tank  230 , the wireless power receiver  240 , and the load resistor RL, for example, may be implemented with an equivalent circuit  221  including an equivalent capacitor CTRX, an equivalent inductor LTRX, and an equivalent resistor RTRX connected in series. 
     The equivalent inductor LTRX may be expressed as in [Equation 3] below, and the equivalent resistor RTRX may be expressed as [Equation 4] below. 
     
       
         
           
             
               
                 
                   
                     L 
                     TRX 
                   
                   = 
                   
                     
                       
                         L 
                         P 
                       
                       + 
                       
                         
                           
                             - 
                             
                               w 
                               3 
                             
                           
                           ⁢ 
                           
                             C 
                             S 
                           
                           ⁢ 
                           
                             
                               M 
                               2 
                             
                             ( 
                             
                               
                                 
                                   w 
                                   2 
                                 
                                 ⁢ 
                                 
                                   C 
                                   S 
                                 
                                 ⁢ 
                                 
                                   L 
                                   S 
                                 
                               
                               - 
                               1 
                             
                             ) 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   
                                     w 
                                     2 
                                   
                                   ⁢ 
                                   
                                     C 
                                     S 
                                   
                                   ⁢ 
                                   
                                     L 
                                     S 
                                   
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             
                               w 
                               2 
                             
                             ⁢ 
                             
                               
                                 
                                   C 
                                   S 
                                   2 
                                 
                                 ( 
                                 
                                   
                                     R 
                                     S 
                                   
                                   + 
                                   
                                     R 
                                     L 
                                   
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                     ≅ 
                     
                       L 
                       P 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     3 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               
                 
                   
                     R 
                     TRX 
                   
                   = 
                   
                     
                       
                         R 
                         P 
                       
                       + 
                       
                         
                           
                             w 
                             4 
                           
                           ⁢ 
                           
                             C 
                             S 
                             2 
                           
                           ⁢ 
                           
                             
                               M 
                               2 
                             
                             ( 
                             
                               
                                 R 
                                 S 
                               
                               + 
                               
                                 R 
                                 L 
                               
                             
                             ) 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   
                                     w 
                                     2 
                                   
                                   ⁢ 
                                   
                                     C 
                                     S 
                                   
                                   ⁢ 
                                   
                                     L 
                                     S 
                                   
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             
                               w 
                               2 
                             
                             ⁢ 
                             
                               
                                 
                                   C 
                                   S 
                                   2 
                                 
                                 ( 
                                 
                                   
                                     R 
                                     S 
                                   
                                   + 
                                   
                                     R 
                                     L 
                                   
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                     ≅ 
                     
                       R 
                       P 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, w is the angular frequency and M is the mutual inductance. In some example embodiments, when the load resistor RL is sufficiently large, the equivalent inductor LTRX may approximate the transmission inductor LP, and the equivalent resistor RTRX may approximate the transmission resistor RP. Since the equivalent inductor LTRX and the equivalent resistor RTRX approximate the transmission inductor LP and the transmission resistor RP, respectively, the quality factor Q of the equivalent circuit  221  may approximate the quality factor Q of the TX resonant tank  220 . In addition, the resonance frequency of the equivalent circuit  221  may be reduced by shielding the wireless power receiver  240 . 
     Referring to  FIGS.  1  and  2 B , a material of a foreign object may be a metal having conductivity. Since a foreign object, which is a metal, absorbs a magnetic field, the metal foreign object may be implemented as an equivalent circuit  250  including an equivalent inductor LFO and an equivalent resistor RFO, as shown in  FIG.  2 B . The equivalent inductor LFO and the equivalent resistor RFO may be connected in series, but are not limited thereto. 
     The equivalent circuit  222  to the TX resonant tank  220  and the equivalent circuit  250  may be implemented with, for example, a transmission capacitor CP, an equivalent inductor LPFO, and an equivalent resistor RPFO connected in series. 
     The input impedance ZIN for the equivalent circuit  222  may be expressed as in [Equation 5] below. 
     
       
         
           
             
               
                 
                   ZIN 
                   = 
                   
                     
                       
                         R 
                         P 
                       
                       + 
                       
                         jwL 
                         P 
                       
                       + 
                       
                         1 
                         
                           jwC 
                           P 
                         
                       
                       + 
                       
                         
                           
                             ( 
                             wM 
                             ) 
                           
                           2 
                         
                         
                           
                             R 
                             FO 
                           
                           + 
                           
                             jwL 
                             FO 
                           
                         
                       
                     
                     = 
                     
                       
                         ( 
                         
                           
                             R 
                             P 
                           
                           + 
                           
                             
                               
                                 
                                   ( 
                                   wM 
                                   ) 
                                 
                                 2 
                               
                               ⁢ 
                               
                                 R 
                                 FO 
                               
                             
                             
                               
                                 R 
                                 FO 
                                 2 
                               
                               + 
                               
                                 
                                   ( 
                                   
                                     wL 
                                     FO 
                                   
                                   ) 
                                 
                                 2 
                               
                             
                           
                         
                         ) 
                       
                       + 
                       
                         jw 
                         ⁡ 
                         ( 
                         
                           
                             L 
                             P 
                           
                           - 
                           
                             
                               
                                 
                                   ( 
                                   wM 
                                   ) 
                                 
                                 2 
                               
                               ⁢ 
                               
                                 L 
                                 FO 
                               
                             
                             
                               
                                 R 
                                 FO 
                                 2 
                               
                               + 
                               
                                 
                                   ( 
                                   
                                     wL 
                                     FO 
                                   
                                   ) 
                                 
                                 2 
                               
                             
                           
                         
                         ) 
                       
                       + 
                       
                         1 
                         
                           jwC 
                           P 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, w is the angular frequency and M is the mutual inductance. At this time, a value of the equivalent inductor LPFO decreases and a value of the equivalent resistor RPFO increases. Therefore, with respect to the resonance frequency Fres and the quality factor Q of the TX resonant tank  220 , the resonance frequency Fres of the equivalent circuit  222  increases, and the quality factor Q of the equivalent circuit  222  decreases. 
       FIG.  3    is a graph schematically showing a coil current input to a resonant tank included in a wireless power transmission device according to an example embodiment of the present inventive concepts according to frequency. 
     Referring to  FIGS.  1 ,  2 A,  2 B, and  3   , when a foreign object is not around the wireless power transmission device  100 , the current according to the frequency may be expressed as a spectrum, as shown in  FIG.  3    (Empty). The current may be, for example, a current input to the TX resonant tank  106 . A spectrum, such as Empty shown in  FIG.  3   , may have a resonance frequency Fres, two cut-off frequencies FL and FH, and a bandwidth BW. The current value at the resonance frequency Fres is the greatest value, and the current value at the resonance frequency Fres may be times the current value at the two cut-off frequencies FL and FH. One cut-off frequency FL of the two cut-off frequencies FL and FH is less than the resonance frequency Fres, and the other cut-off frequency FH of the two cut-off frequencies FL and FH is greater than the resonance frequency Fres. The bandwidth BW may be a difference value between the two cut-off frequencies FL and FH. Alternatively, the bandwidth BW may be twice the difference value between any one of the two cut-off frequencies FL and FH and the resonance frequency Fres. 
     When only the wireless power reception device  110  is present with respect to the wireless power transmission device  100 , the current according to the frequency may be expressed as a spectrum, as shown in  FIG.  3    (with power reception device). In some example embodiments, since the inductance of the equivalent circuit is increased by shielding of the wireless power reception device  110 , the resonance frequency Fres&#39; may be less than the resonance frequency Fres. However, the quality factors may be similar or identical enough to ignore errors. 
     When only a foreign object is present with respect to the wireless power transmission device  100 , the current according to the frequency may be expressed as a spectrum, as shown in  FIG.  3    (with foreign object). In some example embodiments, the resonance frequency increases, and the greatest value of the current and the quality factor decrease. 
     When present together with a foreign object and the wireless power reception device  110  with respect to the wireless power transmission device  100 , a current according to a frequency may be expressed as a spectrum, as shown in  FIG.  3    (with power reception device and foreign object). In some example embodiments, the resonance frequency, the greatest value of the current, and the quality factor also decrease. 
     Since the quality factor Q decreases when there is a foreign object, the wireless power transmission device  100  may detect the presence or absence of the foreign object by using the quality factor Q of the TX resonant tank  220 . 
       FIG.  4    is a circuit diagram, as an example, for implementing a wireless power transmission device according to an example embodiment of the present inventive concepts. 
     Referring to  FIGS.  1  and  4   , the wireless power transmission device (e.g., the wireless power transmission device  100  shown in  FIG.  1   ) may include a power source  310 , a current sensing circuit  320 , a memory  330 , a controller  340 , a converter circuit  350 , and a resonant tank  360 . 
     The power source  310  may be connected between the first node N 1  and the ground. In particular, for example, one end of the power source  310  may be electrically connected to the first node N 1 , and the other end of the power source  310  may be electrically connected to the ground. In an example embodiment, the power source  310  may be implemented as a DC voltage source, but is not limited thereto. The power source  310  implemented as a direct voltage source may apply a DC voltage to the first node N 1 . 
     The current sensing circuit  320  may be connected between the first node N 1  and the second node N 2 . In an example embodiment, the current sensing circuit  320  may include a sensing transistor STR and an amplifier AMP. However, the inventive concepts are not limited thereto. The sensing transistor STR may be implemented as an N-type Metal Oxide Semiconductor Field Effect Transistor (MOSFET), but is not limited thereto. A first electrode (e.g., a drain electrode) of the sensing transistor STR may be electrically connected to the first node N 1 , and a second electrode (e.g., a source electrode) of the sensing transistor STR may be electrically connected to the second node N 2 . The sensing control signal SC may be transmitted to the gate electrode of the sensing transistor STR. The sensing control signal SC may have a turn-on level or a turn-off level. In some example embodiments, when the wireless power transmission device  100  is powered on, the sensing control signal SC has a turn-on level, the sensing transistor STR is turned on, and the input current IIN flows from the first node N 1  to the second node N 2 . The amplifier AMP may amplify a signal corresponding to a difference between the voltage applied to the first node N 1  and the voltage applied to the second node N 2  and output the amplified signal. The amplified signal may be transmitted to the controller  340 . A first input terminal of the amplifier AMP may be electrically connected to the first node N 1 , and a second input terminal of the amplifier AMP may be electrically connected to the second node N 2 . 
     The capacitor CD may be connected between the second node N 2  and the ground. In particular, for example, a first terminal of the capacitor CD may be electrically connected to the second node N 2 , and a second terminal of the capacitor CD may be electrically connected to a ground. The capacitor CD may constantly maintain the voltage generated by the power source  310 . Alternatively, the capacitor CD may maintain constant a voltage to be applied to the converter circuit  350  (e.g., a voltage applied to the second node N 2 ). 
     The bridge current IBRG may be input to the converter circuit  350  through the second node N 2 . 
     The memory  330  may store data for detecting a foreign object. For example, the memory  330  may include initial frequency data Finit, frequency step data Fstep, test duty ratio data Dt, reference quality factor data Qth, end frequency data Fend, frequency range data Frange, design resonance frequency data Fdgn, design bandwidth data BWdgn, and bridge circuit operation type data BRGtyp. The initial frequency data Finit is an initial value for initially setting the test frequency of the test signal, that is, data representing the initial frequency. The frequency step data Fstep is data representing a change amount for changing a preset test frequency. The test duty ratio data Dt is data representing a value for setting the duty ratio of the test signal. The reference quality factor data Qth is data representing a value of the reference quality factor. The end frequency data Fend is data representing the last value for finally setting the test frequency of the test signal, that is, the end frequency. For example, when a frequency range is set, the end frequency may be a smallest value or a greatest value of the frequency range. The frequency range data Frange is data representing a range value for setting a test frequency of a test signal. The design resonance frequency data Fdgn is data representing a predesigned (or, alternatively desired, specified, predetermined, etc.) resonance frequency before the wireless power transmission device  100  is shipped. The design bandwidth data BWdgn is data representing a bandwidth designed in advance before the wireless power transmission device  100  is shipped. The bridge circuit operation type data BRGtyp is data representing an operation method of the converter circuit  350 . The operation method of the converter circuit  350  may be, for example, a half-bridge circuit operation or a full-bridge circuit operation, but is not limited thereto. 
     The controller  340  may be connected to an output terminal of the current sensing circuit  320 . The controller  340  may be connected to the gate electrode of each of first to fourth transistors TR 1 , TR 2 , TR 3 , and TR 4 . The controller  340  may transmit the sensing control signal SC to the sensing transistor STR. The controller  340  may output the first to fourth switching signals S 1 , S 2 , S 3 , and S 4 . For example, the controller  340  may output the first switching signal S 1  to the gate electrode of the first transistor TR 1 , output the second switching signal S 2  to the gate electrode of the second transistor TR 2 , output the third switching signal S 3  to the gate electrode of the third transistor TR 3 , and output the fourth switching signal S 4  to the gate electrode of the fourth transistor TR 4 . The controller  340  may receive a sensed value corresponding to the input current sensed by the current sensing circuit  320 . The controller  340  may store the sensed value therein or store the sensed value in the memory  330 . The controller  340  may receive data from the memory  330 . The controller  340  may include a micro controller unit (MCU) that performs an operation of calculating the quality factor, a logic circuit that outputs the first to fourth switching signals S 1 , S 2 , S 3 , and S 4 , and various registers. 
     The converter circuit  350  may be connected between the second node N 2  and the ground. In an example embodiment, the converter circuit  350  may include a plurality of switches. For example, the converter circuit  350  may include first to fourth transistors TR 1 , TR 2 , TR 3 , and TR 4 . The first to fourth transistors TR 1 , TR 2 , TR 3 , and TR 4  may be implemented as N-type MOSFETs, but are not limited thereto. The first electrode of the first transistor TR 1  may be electrically connected to the second node N 2 , and the second electrode of the first transistor TR 1  may be electrically connected to the third node N 3 . The first electrode of the second transistor TR 2  may be electrically connected to the second node N 2 , and the second electrode of the second transistor TR 2  may be electrically connected to the fourth node N 4 . The first electrode of the third transistor TR 3  may be electrically connected to the third node N 3  and the second electrode of the third transistor TR 3  may be connected to a ground. The first electrode of the fourth transistor TR 4  may be electrically connected to the fourth node N 4 , and the second electrode of the fourth transistor TR 4  may be connected to the ground. The first to fourth switching signals S 1 , S 2 , S 3 , and S 4  may be transmitted to the gate electrode of each of the first to fourth transistors TR 1 , TR 2 , TR 3 , and TR 4 , respectively. Each transistor may be turned on in response to a turn-on level of each switching signal. The converter circuit  350  may operate as a half-bridge circuit or as a full-bridge circuit according to the timing method of the first to fourth switching signals S 1 , S 2 , S 3 , and S 4 . The converter circuit  350  may provide the transmission coil current IC_TX to the TX resonant tank  360 , in response to the first to fourth switching signals S 1 , S 2 , S 3 , and S 4 . The converter circuit  350  herein may be referred to as a bridge circuit. 
     The TX resonant tank  360  may be connected between the third node N 3  and the fourth node N 4 . In particular, for example, the TX resonant tank  360  includes a transmission capacitor CP, a transmission inductor LP, and a transmission resistor RP connected in series, and one end of the transmission capacitor CP may be electrically connected to the third node N 3 , and one end of the transmission resistor RP may be electrically connected to the fourth node N 4 . 
       FIG.  5    is a diagram for explaining an example embodiment of an operation timing between switching signals, a voltage and a current applied to a resonant tank, and an input current. In particular,  FIG.  5    is a timing diagram of signals for the converter circuit  350  to operate as a half bridge. 
     Referring to  FIGS.  4  and  5   , the first signal group may be referred to as a group including first and third switching signals S 1  and S 3 . The second signal group may be referred to as a group including the second and fourth switching signals S 2  and S 4 . In some example embodiments, one signal group of the first signal group and the second signal group may be a square wave having a test frequency Ft and a test duty ratio. Referring to  FIG.  5   , for example, the first and third switching signals S 1  and S 3  may be square waves, and the second and fourth switching signals S 2  and S 4  may have a constant level. However, the inventive concepts are not limited thereto, and the first and third switching signals S 1  and S 3  may have a constant or substantially constant level, and the second and fourth switching signals S 2  and S 4  may be square waves. The square wave may be a waveform having one level (e.g., turn-on level, logic high level HIGH, etc.) and another level (e.g., turn-off level, logic low level LOW, etc.) during one period. The duty ratio of the square wave may be determined according to the previously stored test duty ratio data Dt. The period Tt of the square wave may be the reciprocal of the test frequency Ft. When the first and third switching signals S 1  and S 3  are square waves, a phase difference between the first and third switching signals S 1  and S 3  may be 180 degrees. For example, the first switching signal S 1  may have a logic high level HIGH (or turn-on level) and the third switching signal S 3  may have a logic low level LOW (or turn-off level). In some example embodiments, when the first signal group is a square wave, any one of the second and fourth switching signals S 2  and S 4  has a turn-on level that turns on the transistor, and another one of the second and fourth switching signals S 2  and S 4  may have a turn-off level. For example, the second switching signal S 2  may have a logic low level LOW (or turn-off level) and the fourth switching signal S 4  may have a logic high level HIGH (or turn-on level). However, the inventive concepts are not limited thereto, and when the first and third switching signals S 1  and S 3  are square waves, the second switching signal S 2  may have a logic high level HIGH and the fourth switching signal S 4  may have a logic low level LOW. 
     The first voltage V 1  @ N 4  applied to the fourth node N 4  may have a logic low level LOW. Since the third switching signal S 3  is at a turn-on level, the voltage level applied to the third node N 3  by turning on the third transistor TR 3  is the ground level. Accordingly, the voltage level of the first voltage V 1  @ N 4  applied to the fourth node N 4  may be the ground level. The second voltage V 2  @ N 3  applied to the third node N 3  may be a square wave having a test frequency Ft. A potential difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  may be a test signal. 
     When the voltage level of the first switching signal S 1  is the turn-on level, the voltage level of the second switching signal S 2  is the turn-off level, the voltage level of the third switching signal S 3  is the turn-off level, and the voltage level of the fourth switching signal S 4  is the turn-on level, a voltage level of the first voltage V 1  @ N 4  may be lower than a voltage level of the second voltage V 2  @ N 3 . 
     When the voltage level of the first switching signal S 1  is the turn-off level, the voltage level of the second switching signal S 2  is the turn-off level, the voltage level of the third switching signal S 3  is the turn-on level, and the voltage level of the fourth switching signal S 4  is the turn-on level, a voltage level of the first voltage V 1  @ N 4  may be the same as the voltage level of the second voltage V 2  @ N 3 . 
     The transmission coil current IC_TX may be an alternating current, as shown in  FIG.  5   . The magnitude of the transmission coil current IC_TX may be expressed as the magnitude of the potential difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  with respect to the magnitude of the input impedance (e.g., ZIN). The frequency when the magnitude of the input impedance is the smallest or the transmission coil current IC_TX is the greatest may be a resonance frequency. Since the resonance frequency is required to calculate the quality factor Q, it is desirable or necessary to obtain information on the magnitude of the input impedance ZIN. 
     In addition, the bridge current IBRG and the input current IIN may have waveforms as shown in  FIG.  5   . The DC component IBRG_DC of the bridge current IBRG may be expressed as in [Equation 6] below. 
     
       
         
           
             
               
                 
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     Here, ft may be the test frequency, D may be a duty ratio of the test signal, Z(ft) may be an impedance (or input impedance) at the test frequency, and A(D) may be a coefficient (constant) for the duty ratio. That is, the DC component IBRG_DC of the bridge current IBRG may include information on the magnitude of the input impedance. 
     The magnitude of the DC component IBRG_DC of the bridge current IBRG may be the same or substantially the same as the magnitude of the DC component IIN_DC of the input current IIN. Accordingly, information on the input impedance is obtained by sensing the DC component IIN_DC of the input current IIN. When the magnitude of the input impedance is the smallest, the DC component IIN_DC of the input current IIN may be the largest. 
     As described above, by implementing the test signal shown in  FIG.  5    only with the converter circuit  350  without separate hardware, there is an effect of reducing the manufacturing cost and promoting integration. 
     The test signal may be weak enough that the wireless power reception device  110  does not wake up. When the wireless power reception device  110  wakes up by a test signal, a foreign object may be incorrectly determined because the quality factor is reduced by the load resistor RL. 
     As described above, when the test signal is weakly generated, the quality factor Q is more accurately calculated, and there is an effect of more accurately detecting a foreign object. 
       FIG.  6    is a diagram for explaining another example embodiment of an operation timing between switching signals, a voltage and a current applied to a resonant tank, and an input current. In particular,  FIG.  6    is a timing diagram of signals for the converter circuit  350  to operate as a full bridge. 
     Referring to  FIGS.  4  and  6   , the first signal group and the second signal group may be square waves having a test frequency and a test duty ratio. In some example embodiments, the phase difference of the first signal group may be 180 degrees, and the phase difference of the second signal group may also be 180 degrees. Moreover, the phase difference between the first switching signal S 1  and the fourth switching signal S 4  is 0 degrees (or 360 degrees), and the phase difference between the second switching signal S 2  and the third switching signal S 3  is also 0 degrees (or 360 degrees). For example, when the first switching signal S 1  and the fourth switching signal S 4  may have a turn-off level, the second switching signal S 2  and the third switching signal S 3  may have a turn-on level. 
     The first voltage V 1  @ N 4  applied to the fourth node N 4  and the second voltage V 2  @ N 3  applied to the third node N 3  may be a square wave having a test frequency Ft. In addition, a phase difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  may be 180 degrees. A potential difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  may be a test signal. As the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  are generated, the transmission coil current IC_TX is as shown in  FIG.  6   . 
     When the voltage levels of the first switching signal S 1  and the fourth switching signal S 4  are turn-off levels and the voltage levels of the second switching signal S 2  and the third switching signal S 3  are turn-on levels, a voltage level of the first voltage V 1  @ N 4  may be higher than a voltage level of the second voltage V 2  @ N 3 . 
     When the voltage levels of the first switching signal S 1  and the fourth switching signal S 4  are turn-on levels and the voltage levels of the second switching signal S 2  and the third switching signal S 3  are turn-off levels, a voltage level of the first voltage V 1  @ N 4  may be lower than a voltage level of the second voltage V 2  @ N 3 . 
     The test signals shown in  FIGS.  5  and  6    may have a test duty ratio, and the test duty ratio may be included in a preset (or alternatively, desired, specified, predetermined, etc.) duty ratio range. As the value of the test duty ratio is closer to the smallest value of the duty ratio range, the test signal is weak enough that the wireless power reception device  110  does not wake up, and since the quality factor Q is calculated more accurately, there is an effect of more accurately detecting a foreign object. On the other hand, as the value of the test duty ratio is closer to the greatest value of the duty ratio range, it is possible to accurately sense the input current IIN, and since the quality factor Q is calculated more accurately, there is an effect of more accurately detecting a foreign object. 
     As described above, by implementing the test signal shown in  FIG.  6    only with the converter circuit  350  without separate hardware, there is an effect of reducing the manufacturing cost and promoting integration. 
       FIG.  7    is a circuit diagram, as an example, for implementing a wireless power reception device according to an example embodiment of the present inventive concepts. 
     Referring to  FIGS.  1 ,  4  and  7   , the wireless power reception device  110  may include an RX resonant tank  410 , a reception rectification circuit  420 , and a load resistor RL. 
     The RX resonant tank  410  may include a reception capacitor CS, a reception inductor LS, and a reception resistor RS connected in series, as shown in  FIG.  2 A . As the RX resonant tank  410  and the TX resonant tank  360  shown in  FIG.  4    are magnetically coupled, a reception coil current IC_TX may flow in the RX resonant tank  410 . 
     The reception rectification circuit  420  may be an example of the reception rectification circuit  112  shown in  FIG.  1   . The reception rectification circuit  420  may include first to fourth diodes D 1 , D 2 , D 3 , and D 4  and a rectification capacitor CR. In another embodiment, the reception rectification circuit  420  may include transistors instead of the first to fourth diodes D 1 , D 2 , D 3 , and D 4 . The first diode D 1  may be connected between the rectification capacitor CR and the first receiving node AC 1 _RX. The second diode D 2  may be connected between the rectification capacitor CR and the second reception node AC 2 _RX. The third diode D 3  may be connected between the first reception node AC 1 _RX and the ground. The fourth diode D 4  may be connected between the second reception node AC 2 _RX and the ground. The rectification capacitor CR may be connected between a node to which the first diode D 1  and the second diode D 2  are connected and a ground. When the reception coil current IC_RX is generated, the reception rectification circuit  420  may generate a rectified voltage VRECT and a rectified current IRECT. 
     The load resistor RL may be connected between the rectification capacitor CR and the ground. 
       FIG.  8    is a flowchart for explaining a method of operating a wireless power transmitter, according to an example embodiment of the present inventive concepts. 
     Referring to  FIGS.  2 A,  2 B,  4  and  8   , an operating method of a wireless power transmitter includes setting the characteristics of the test signal applied to the resonant tank S 100 , applying a test signal to the resonant tank to calculate the quality factor of the resonant tank S 110 , comparing the quality factor to the pre-stored reference quality factor S 120 , and resetting the test frequency according to the comparison result (S 120 , NO, and S 100 ) or performing an operation of transmitting wireless power S 130 . 
     In operation S 100 , the wireless power transmitter  210  sets the characteristics of the test signal input to the resonant tank (e.g., the TX resonant tank  220 ). Here, the characteristic of the test signal may be a test frequency Ft of the test signal. In addition, the characteristic of the test signal may further include a test duty ratio of the test signal. 
     In operation S 110 , the wireless power transmitter  210  applies a test signal to the resonant tank to calculate a quality factor of the resonant tank. A method of calculating the quality factor will be described later with reference to  FIGS.  9 ,  11 , and  13   . 
     In operation S 120 , the wireless power transmitter  210  compares the quality factor with a pre-stored (or alternatively, desired, specified, etc.) reference quality factor. In particular, for example, the wireless power transmitter  210  determines whether the quality factor is greater than the reference quality factor. The reference quality factor data Qth may be stored, for example, in the memory  330  illustrated in  FIG.  4   . 
     If the quality factor is greater than the reference quality factor (S 120 , YES), in operation S 130 , the wireless power transmitter  210  performs an operation of transmitting wireless power. 
     If the quality factor is less than or equal to the reference quality factor (S 120 , NO), operation S 100  is performed. Resetting the test frequency may mean changing the test frequency or setting the test frequency to an initial value. 
       FIG.  9    is a flowchart illustrating an example embodiment of calculating a quality factor. 
     Referring to  FIGS.  4  and  9   , in operation S 200 , the controller  340  sets the test frequency Ft of the test signal to the initial test frequency Finit, and sets the test duty ratio D of the test signal to the test duty ratio Dt. The initial test frequency Finit is included in a pre-stored frequency range, and may be, for example, a smallest value or a greatest value of the frequency range. The test signal is a square wave having a test duty ratio in a preset (or alternatively, desired, specified, etc.) duty ratio range. 
     In operation S 210 , the converter circuit  350  applies a test signal to the TX resonant tank  360 , the current sensing circuit  320  senses the input current IIN, and the controller  340  stores a sensed value corresponding to the sensed input current. In particular, the controller  340  controls the converter circuit  350  to generate a test signal, and stores the sensed value corresponding to the input current IIN sensed by the current sensing circuit  320  internally or in the memory  330 . 
     In operation S 220 , the controller  340  checks whether the set test frequency Ft is an end frequency Fend. If the test frequency Ft is not the end frequency Fend (S 220 , NO), in operation S 230 , the controller  340  sets a new test frequency by adding a frequency step Fstep to the set test frequency Ft. In another example embodiment, the controller  340  sets a new test frequency by subtracting a frequency step Fstep from the set test frequency Ft. Operations S 210 , S 220 , and S 230  are repeatedly performed until the test frequency Ft reaches the end frequency Fend. That is, the controller  340  controls the converter circuit  350  to sequentially generate a signal having a frequency in a pre-stored frequency range as a test signal, the converter circuit  350  applies the test signal to the resonant tank  360 , the current sensing circuit  320  sequentially senses the input current sensed as the test signal is sequentially generated, and the controller  340  sequentially stores sensed values corresponding to the sensed input current. 
     If the test frequency Ft is the end frequency Fend (S 220 , YES), in operation S 240 , the controller  340  sets a greatest value among the stored sensed values as a greatest input current, and sets a test frequency at the greatest input current as a test resonance frequency Fres. In particular, the controller  340  sets the input current corresponding to the greatest value among the stored sensed values as the greatest input current, and sets the frequency as the test resonance frequency when the greatest input current is sensed. 
     In operation S 250 , the controller  340  calculates the bandwidth BW based on the frequencies FL and FH when the input current is 1/√{square root over (2)} times (or 0.707 times) the greatest input current. In particular, for example, the controller  340  obtains at least one sensed value smaller by 3 dB (or more or less dB) than the greatest value (or greatest input current) among the stored sensed values, and sets a frequency when an input current corresponding to the at least one sensed value is sensed as the at least one cut-off frequency. In addition, when the number of cut-off frequencies is two, the controller  340  calculates a difference between the cut-off frequencies as a bandwidth. Alternatively, when the number of cut-off frequencies is one, the controller  340  calculates twice the difference between the cut-off frequency and the test resonance frequency as a bandwidth. 
     In operation S 260 , the controller  340  calculates the quality factor Q using the test resonance frequency and bandwidth. A method of calculating the quality factor Q is the same as described above with reference to [Equation 2]. 
       FIGS.  10 A and  10 B  are graphs schematically illustrating a potential difference, an input current, a flag signal, and a rectified voltage applied to a resonant tank according to the embodiment shown in  FIG.  9   . In particular,  FIG.  10 A  is a graph showing signals that may occur when there is no foreign object, and  FIG.  10 B  is a graph showing signals that may occur when a foreign object is detected. 
     Referring to  FIGS.  2 A,  4  to  6  and  10 A , in an example embodiment, the operation of the wireless power transmitter  210  may include a first phase (Q FACTOR CALCULATION PHASE), a second phase (Q FACTOR JUDGE PHASE), and a third phase (DIGITAL PING OPERATION PHASE). 
     The first phase (Q FACTOR CALCULATION PHASE) may be a period during which an operation for calculating the quality factor Q is performed. In particular, in the first phase (Q FACTOR CALCULATION PHASE), a potential difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  is provided to the TX resonant tank  220  as a test signal, and accordingly, the input current IIN may be sensed. The input current IIN @ Fres at the test resonance frequency is the largest, and the input current at the test resonance frequency IIN @ Fres is 3 dB greater than the input current at the cut-off frequencies IIN @ FL and IIN @ FH. The voltage level of the rectified voltage VRECT generated by the reception rectification circuit  420  is lower than the voltage level of the preset (or alternatively, desired, specified, etc.) wake-up voltage VRX_WKP. The preset wake-up voltage VRX_WKP may be a voltage required for the wireless power receiver  240  to wake up. The flag signal FLAG may be a signal generated by the controller  340 . In particular, when the controller  340  includes an MCU and a logic circuit, the MCU transmits a flag signal FLAG having a turn-on level (or logic high level) to the logic circuit, and the logic circuit may output the first to fourth switching signals S 1 , S 2 , S 3 , and S 4  to transmit a digital ping signal. 
     The second phase (Q FACTOR JUDGE PHASE) may be a period during which an operation of comparing the calculated quality factor with a preset reference quality factor is performed. In particular, in the second phase (Q FACTOR JUDGE PHASE), the generation of the test signal is stopped. Accordingly, the input current IIN may or may not have a very small value, and the rectified voltage VRECT may or may not have a very small voltage level. If the quality factor is greater than the reference quality factor, the voltage level of the flag signal FLAG is changed from a logic low level to a logic high level. 
     The third phase (DIGITAL PING OPERATION PHASE) may be a period during which an operation for transmitting a digital ping signal is performed. In particular, in the third phase (DIGITAL PING OPERATION PHASE), the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  may have the same or substantially the same shape as the waveform shown in  FIG.  6   . However, the potential difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  is greater than the magnitude of the test signal. The input current IIN flows while maintaining a constant or substantially constant level. The voltage level of the rectified voltage VRECT is higher than the voltage level of the preset wake-up voltage VRX_WKP. The wireless power receiver  240  wakes up. 
     On the other hand, referring to  FIGS.  2 A,  4  to  6  and  10 B , if there is a foreign object, the operation of the wireless power transmitter  210  may include a first phase (Q FACTOR CALCULATION PHASE) and a second phase (Q FACTOR JUDGE PHASE). 
     In the first phase Q FACTOR CALCULATION PHASE, the greatest value of the input current IIN is smaller than the greatest value of the input current IIN shown in  FIG.  10 A . In the second phase (Q FACTOR JUDGE PHASE), when it is determined that the quality factor is smaller than the reference quality factor, the voltage level of the flag signal FLAG maintains a logic low level. After the second phase (Q FACTOR JUDGE PHASE), when the first phase (Q FACTOR CALCULATION PHASE) arrives, and until the foreign object is removed, the first phase (Q FACTOR CALCULATION PHASE) and the second phase (Q FACTOR JUDGE PHASE) are repeated. 
       FIG.  11    is a flowchart for explaining another example embodiment of calculating a quality factor. 
     Referring to  FIGS.  4  and  11   , operations S 300  and S 310  are the same as operations S 200  and S 210  described above with reference to  FIG.  9   . 
     In operation S 320 , the controller  340  calculates the amount of change in the input current per unit time using the sensed value. The amount of change of the input current per unit time may be referred to as a slope (dIIN/dt). 
     In operation S 330 , the controller  340  determines whether the sign of the slope is changed. The change in the sign of the slope may mean that the sign of the slope is changed from positive to negative or changed from negative to positive. By determining whether the sign of the slope is changed, the greatest input current, test resonance frequency, quality factor, etc. may be calculated more quickly, and as a result, it is effective to quickly check whether a foreign object is detected. On the other hand, if it is checked whether the sign of the slope is changed, the sensed input current tends to continue to increase or decrease. 
     If the sign of the slope does not change, that is, if the sign of the slope is constant (S 330 , NO), in operation S 340 , the controller  340  calculates a frequency step Fstep stored in advance at the initial frequency, and resets the calculated frequency to the test frequency. Operation S 340  may be the same as operation S 230  described above with reference to  FIG.  9   . Until the sign is changed, changing the frequency (e.g., operation S 340 ), storing the sensed value (e.g., operation S 310 ), and calculating the amount of change per unit time (e.g., operation S 320 ) are repeated. 
     When the sign is changed (S 330 , YES), in operation S 350 , the controller  340  sets the corresponding sensed value as the greatest input current, and sets the test frequency at the greatest input current as the test resonance frequency Fres. In particular, when the sign is changed, the controller  340  sets the input current corresponding to the stored sensed value as the greatest input current, and sets the frequency as the test resonance frequency when the greatest input current is sensed. 
     In operation S 360 , the controller  340  calculates the bandwidth BW based on the frequencies FL and FH when the input current is 
     
       
         
           
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     times (or 0.707 times) the greater input current. The controller  340  searches for a sensed value smaller than the stored sensed value by 3 dB when a sign is changed from among the stored sensed values. Then, the controller  340  performs a cut-off frequency when an input current corresponding to the sensed value is sensed. Then, the controller  340  calculates twice the difference between the cut-off frequency FL or FH and the test resonance frequency Fres as the bandwidth. On the other hand, since the sensed input current continues to increase or decrease, one cut-off frequency FL or FH is calculated. 
     Operation S 370  is the same or substantially the same as operation S 260  described above with reference to  FIG.  9   . 
     As described above, there is a benefit in that the time for calculating the quality factor may be reduced. 
       FIGS.  12 A and  12 B  are graphs schematically illustrating a potential difference, an input current, a flag signal, and a rectified voltage applied to a resonant tank according to the example embodiment shown in  FIG.  11   . In particular,  FIG.  12 A  is a graph showing signals that may occur when there is no foreign object, and  FIG.  12 B  is a graph showing signals that may occur when a foreign object is detected. 
     Referring to  FIGS.  2 A,  4  to  6  and  12 A , in the first phase (Q FACTOR CALCULATION PHASE), a potential difference between the first voltage V 1  @ N 4  and the second voltage V 2  @ N 3  is provided to the TX resonant tank  220  as a test signal, and accordingly, the input current IIN may be sensed. When the sign of the slope of the input current IIN is changed, the test resonance frequency Fres may be searched, and when the input current IIN @ Fres at the test resonance frequency is sensed, the input current at the cut-off frequency IIN @ FL or IIN @ FH may also be identified. The description of the rectified voltage VRECT and the flag signal FLAG is the same or substantially the same as described above with reference to  FIGS.  10 A and  10 B . 
     Descriptions of the second phase (Q FACTOR JUDGE PHASE) and the third phase (DIGITAL PING OPERATION PHASE) are the same or substantially the same as those described above with reference to  FIGS.  10 A and  10 B . 
     On the other hand, referring to  FIGS.  2 A,  4  to  6  and  12 B , if there is a foreign object, in the first phase (Q FACTOR CALCULATION PHASE), the greatest value of the input current IIN is smaller than the greatest value of the input current IIN shown in  FIG.  12 A , and in the second phase (Q FACTOR JUDGE PHASE), if it is determined that the quality factor is smaller than the reference quality factor, the first phase (Q FACTOR CALCULATION PHASE) and the second phase (Q FACTOR JUDGE PHASE) are repeated until the foreign object is removed. 
       FIG.  13    is a flowchart for explaining another example embodiment of calculating a quality factor. 
     Referring to  FIGS.  4  and  13   , in operation S 400 , the controller  340  sets the test frequency Ft of the test signal to the resonance frequency Fdgn of the previously designed resonant tank, sets the bandwidth BW of the test signal to a previously designed bandwidth BWdgn, and sets the test duty ratio D of the test signal to the test duty ratio Dt. The resonance frequency Fdgn is referred to as a first test frequency, the predesigned bandwidth BWdgn is referred to as a first bandwidth, and a first signal having the first test frequency is referred to as a first test signal. 
     In operation S 411 , the converter circuit  350  applies a first test signal to the TX resonant tank  360 , and the current sensing circuit  320  senses the input current IIN, and the controller  340  stores a first sensed value corresponding to the sensed input current. 
     In operation S 412 , the controller  340  sets the test frequency of the test signal as the cut-off frequency. At this time, the cut-off frequency is greater than the resonance frequency Fdgn of the previously designed resonant tank. The cut-off frequency is referred to as the first cut-off frequency. In particular, the controller  340  calculates a first cut-off frequency greater than the resonance frequency Fdgn by adding half (½) of the pre-designed bandwidth BWdgn to the resonance frequency Fdgn of the pre-designed resonant tank. The first cut-off frequency is set as the second test frequency. 
     In operation S 413 , the converter circuit  350  applies a second test signal to the TX resonant tank  360 , and the current sensing circuit  320  senses the input current IIN, and the controller  340  stores a second sensed value corresponding to the sensed input current. 
     In operation S 414 , the controller  340  compares the first sensed value with the second sensed value. In particular, the controller  340  checks whether the first sensed value is smaller than the second sensed value. When only a foreign object exists with respect to the wireless power transmission device  100 , the current according to the frequency may be expressed as a spectrum, as shown in  FIG.  3    (with foreign object). A case where the second sensed value is greater than the first sensed value corresponds to a case where only the wireless power transmission device  100  and the foreign object are magnetically coupled, such that this has the effect of detecting foreign objects faster. 
     If the first sensed value is smaller than the second sensed value (S 414 , YES), the test frequency is reset while operation S 400  is performed. 
     Until the first sensed value is greater than or equal to the second sensed value, setting the test frequency (e.g., operation S 400 ), storing the first sensed value (e.g., operation S 411 ), setting the second test frequency (e.g., operation S 412 ), and storing the second sensed value (e.g., operation S 413 ) are repeated. 
     If the first sensed value is greater than or equal to the second sensed value (S 414 , NO), in operation S 420 , the controller  340  subtracts a frequency step of a pre-stored (or alternatively, stored, desired, specified, etc.) positive number from the frequency when the first sensed value is greater than or equal to the second sensed value. For example, the controller  340  subtracts a pre-stored positive frequency step Fstep from the first cut-off frequency. 
     In operation S 421 , the converter circuit  350  applies a signal having the subtracted frequency to the TX resonant tank  360  as a test frequency, and the current sensing circuit  320  senses an input current, and the controller  340  stores a sensed value corresponding to the sensed input current. In this case, the sensed value corresponding to the sensed input current is referred to as a second sensed value. Operation S 421  is the same or substantially the same as operation S 210  described above with reference to  FIG.  9    or S 310  described above with reference to  FIG.  11   . 
     In operation S 422 , the converter circuit  350  calculates the amount of change in the sensed input current per unit time using the second sensed value. Operation S 422  is the same or substantially the same as operation S 320  described above with reference to  FIG.  11   . 
     Operation S 423  is the same as operation S 330  described above with reference to  FIG.  11   . That is, depending on whether the sign of the slope is changed, a frequency step is subtracted from the subtracted frequency, or a quality factor is calculated based on the subtracted frequency and a sensed value. If the sign of the slope is constant (S 423 , NO), operation S 420  is performed. Until the sign is changed, subtracting the positive frequency step (e.g., operation S 420 ), storing the sensed value (e.g., operation S 421 ), and calculating the amount of change per unit time (e.g., operation S 422 ) are repeated. 
     If the sign of the slope is changed (S 423 , YES), in operation S 424 , the controller  340  sets the input current corresponding to the stored sensed value as the greatest input current, and sets the test frequency as the test resonance frequency when the greatest input current is sensed. Operation S 424  is the same as operation S 350  described above with reference to  FIG.  11   . 
     Operations S 425  and S 426  are the same or substantially the same as operations S 360  and S 370  described above with reference to  FIG.  11   . At this time, when the input current corresponding to the sensed value smaller by 3 dB than the stored sensed value is sensed when the sign is changed, that test frequency is referred to as the second cut-off frequency, and the bandwidth calculated using the second cut-off frequency and the test resonance frequency is referred to as a second bandwidth. 
     As described above, there is a benefit that a foreign object may be detected more quickly. 
       FIGS.  14 A and  14 B  are graphs schematically illustrating a potential difference, an input current, a flag signal, and a rectified voltage applied to a resonant tank according to the example embodiment shown in  FIG.  11   . In particular,  FIG.  14 A  is a graph showing signals that may occur when there is no foreign object, and  FIG.  14 B  is a graph showing signals that may occur when a foreign object is detected. 
     Referring to  FIGS.  2 A,  4  to  6  and  14 A , in the first phase (Q FACTOR CALCULATION PHASE), the input current at the test resonance frequency IIN @ Fres and the input current at the cut-off frequency (e.g., IIN @ FH) may also be identified. The rectified voltage VRECT, the flag signal FLAG, the second phase (Q FACTOR JUDGE PHASE), and the third phase (DIGITAL PING OPERATION PHASE) have been described above with reference to  FIGS.  10 A and  10 B . 
     Meanwhile, referring to  FIGS.  2 A,  4  to  6  and  14 B , if there is a foreign object, the first phase (Q FACTOR CALCULATION PHASE) and the second phase (Q FACTOR JUDGE PHASE) are repeated until the foreign object is removed. 
       FIG.  15    is a diagram schematically illustrating a wireless power transmission device, an electronic device including a wireless power reception device, and a foreign object. 
     Referring to  FIG.  15   , a foreign object  2000  may exist on the wireless power transmission device  1000 . The foreign object  2000  may be a metal coin, but is not limited thereto. The electronic device  3000  may include the wireless power reception device  110  described above with reference to  FIG.  1   . When the wireless power transmission device  1000 , the foreign object  2000 , and the electronic device  3000  are magnetically coupled, the wireless power transmission device  1000  may detect the presence of the foreign object  2000  based on the quality factor. Until the foreign object  2000  is removed from the wireless power transmission device  1000 , the wireless power transmission device  1000  may stop transmitting wireless power to the electronic device  3000 . 
     As described above, by implementing a test signal for detecting a foreign object without adding additional hardware, there is an effect of reducing manufacturing cost and promoting integration. 
     In addition, as described above, there is an effect of inhibiting or preventing an accident due to heat by quickly and accurately detecting a foreign object in the wireless charging system. 
       FIG.  16    is a diagram schematically illustrating a wireless power transmission device, an electronic device including a wireless power reception device, and a magnetic member. 
     Referring to  FIG.  16   , a wireless power reception device  2001  may exist on a wireless power transmission device  1001 . The wireless power reception device  2001  may be, for example, a wearable electronic device such as a smart watch. The wireless power reception device  2001  may include a magnetic member  2002 . The magnetic member  2002  may be, for example, a magnet, but is not limited thereto, and may mean an entire member made of a magnetic material. When the wireless power reception device  2001  includes the magnetic member  2002 , the wireless power transmission device  1001  and the wireless power reception device  2001  may be more easily coupled. When the wireless power transmission device  1001  and the wireless power reception device  2001  are easily coupled, a wireless charging operation may be easily performed between the wireless power transmission device  1001  and the wireless power reception device  2001 . Meanwhile, the wireless power reception device  2001  may also include the same or substantially the same material as the magnetic member  2002 . 
     The wireless power transmission device  1001  may perform an operation (e.g., a foreign object detection operation) performed by the wireless power transmission device  100  described above with reference to  FIG.  1   . However, when the wireless power reception device  2001  includes the magnetic member  2002 , the wireless power transmission device  1001  may detect the magnetic member  2002  as a foreign object. It is desirable or necessary to inhibit or prevent the magnetic member  2002  from being detected as a foreign object. 
       FIG.  17 A  is a graph schematically showing a coil current according to the presence or absence of a magnetic member according to frequency in a wireless power reception device, and  FIG.  17 B  is a graph schematically showing a quality factor according to the presence or absence of a magnetic member according to frequency in a wireless power reception device. 
     Referring to  FIGS.  3 ,  16  and  17 A , when the wireless power reception device  2001  does not include the magnetic member  2002  and a foreign object is not around the wireless power transmission device  1001  (e.g., refer to RX shown in  FIG.  17 A ), the input current IIN generated in the wireless power transmission device  1001  may be expressed as a first spectrum according to frequency, similar to that described above with reference to  FIG.  3   . In some example embodiments, the resonance frequency for the input current IIN may be included in the first resonance frequency range. In an example embodiment, the smallest value of the first resonance frequency range may be “F1l”, and the greatest value of the first resonance frequency range may be “F1h”. “F1l” and “F1h” may be natural numbers. 
     When the wireless power reception device  2001  includes a magnetic member  2002  and a foreign object is not around the wireless power transmission device  1001  (e.g., see MRX shown in  FIG.  17 A ), the input current IIN generated in the wireless power transmission device  1001  may be expressed as a second spectrum. In some example embodiments, the resonance frequency for the input current IIN may be included in the second resonance frequency range. In an example embodiment, the smallest value of the second resonance frequency range may be “F2l”, and the greatest value of the second resonance frequency range may be “F2h”. “F2l” and “F2h” may be natural numbers. 
     The greatest value of the first resonance frequency range (e.g., “F1h”) may be less than or equal to the smallest value of the second resonance frequency range (e.g., “F2l”). For example, the greatest value (e.g., “F1h”) of the first resonance frequency range may be equal to the smallest value (e.g., “F2l”) of the second resonance frequency range. 
     Depending on whether the wireless power reception device  2001  includes the magnetic member  2002 , a resonance frequency for the input current IIN may vary. Therefore, if there is no foreign object other than the magnetic member  2002 , when the resonance frequency for the input current IIN is obtained, it may be checked whether the wireless power reception device  2001  includes the magnetic member  2002 . 
     Referring to  FIG.  17 B , when a foreign object is not around the wireless power transmission device  1001 , a quality factor when the wireless power reception device  2001  does not include a magnetic member  2002  (e.g., see RX shown in  FIG.  17 B ) may be relatively larger than a quality factor (e.g., see MRX shown in  FIG.  17 B ) when the wireless power reception device  2001  includes the magnetic member  2002 . 
     When it is checked whether the wireless power reception device  2001  includes the magnetic member  2002  using the resonance frequency for the input current IIN, it is desirable to set the value of the standard quality factor for identifying foreign objects differently. When the wireless power reception device  2001  includes the magnetic member  2002 , it is desirable to set the value of the reference quality factor relatively low in order not to detect the magnetic member  2002  as a foreign object. For example, the first reference quality factor Qth 1  when the wireless power reception device  2001  does not include the magnetic member  2002  (e.g., refer to RX shown in  FIG.  17 B ) may be set to be greater than or equal to the second reference quality factor Qth 2  when the wireless power reception device  2001  includes the magnetic member  2002  (e.g., refer to MRX illustrated in  FIG.  17 B ). 
       FIG.  18 A  is a graph schematically showing coil current according to the presence or absence of a magnetic member and the presence or absence of a foreign object in a wireless power reception device according to frequency, and  FIG.  18 B  is a graph schematically illustrating a quality factor according to the presence or absence of a magnetic member and the presence or absence of a foreign object in a wireless power reception device according to frequency. 
     Referring to  FIGS.  3 ,  16 ,  17 A and  18 A , when the wireless power reception device  2001  includes a magnetic member  2002  and there is no foreign object around the wireless power transmission device  1001 , the input current IIN is the same as that in  FIG.  17 A  (e.g., see MRX shown in  FIG.  18 A ). When the wireless power reception device  2001  includes a magnetic member  2002  and a foreign object exists around the wireless power transmission device  1001  (e.g., see MRX+FO shown in  FIG.  18 A ), the resonance frequency for the input current IIN may be greater than the greatest value (e.g., “F2h”) of the second resonance frequency range. In some example embodiments, if the resonance frequency for the input current IIN is greater than the greatest value of the second resonance frequency range (e.g., “F2h”), it may be determined that the wireless power transmission device  1001  has detected a foreign object. Even if the resonance frequency for the input current IIN is included in the second resonance frequency range, a foreign object may exist around the wireless power transmission device  1001 . 
     When the wireless power reception device  2001  does not include the magnetic member  2002  and a foreign object exists around the wireless power transmission device  1001 , the resonance frequency for the input current IIN may be included in the first resonance frequency range (e.g., see RX+FO# 2  illustrated in  FIG.  18 A ). Alternatively, when the wireless power reception device  2001  does not include the magnetic member  2002  and a foreign object exists around the wireless power transmission device  1001 , the resonance frequency for the input current IIN may be included in the second resonance frequency range (e.g., refer to RX+FO# 1  shown in  FIG.  18 A ). 
     Referring to  FIG.  18 B , when the wireless power reception device  2001  includes a magnetic member  2002  and a foreign object is not around the wireless power transmission device  1001 , the quality factor for the input current IIN is the same or substantially the same as that in  FIG.  17 B  (e.g., see MRX shown in  FIG.  18 B ). 
     When the wireless power reception device  2001  includes a magnetic member  2002  and a foreign object exists around the wireless power transmission device  1001 , the quality factor for the input current IIN may be smaller than the second reference quality factor Qth 2  as shown in  FIG.  18 B  (e.g., refer to MRX+FO shown in  FIG.  18 B ). 
     When the wireless power reception device  2001  does not include the magnetic member  2002  and a foreign object exists around the wireless power transmission device  1001 , the resonance frequency for the input current IIN may be included in the first resonance frequency range (e.g., see RX+FO# 2  illustrated in  FIG.  18 B ). In this case, the quality factor for the input current IIN may be smaller than the first reference quality factor Qth 1 . 
     In some example embodiments, when the wireless power reception device  2001  does not include the magnetic member  2002  and a foreign object exists around the wireless power transmission device  1001 , the resonance frequency for the input current IIN may be included in the second resonance frequency range (e.g., refer to RX+FO# 1  shown in  FIG.  18 B ). In addition, the quality factor for the input current IIN may be greater than the second reference quality factor Qth 2 . In a situation where the resonance frequency for the input current IIN is included in the second resonance frequency range, if the wireless power transmission device  1001  compares the quality factor with respect to the input current IIN and the second reference quality factor Qth 2  to determine whether a foreign object is detected, a misjudgment may occur. 
       FIGS.  19 A and  19 B  are graphs schematically illustrating an operation of transmitting wireless power that may be performed according to whether a packet is received from a wireless power reception device. 
     Referring to  FIGS.  18 A,  18 B and  19 A , the operating phases of the wireless power transmission device  1001  and the wireless power reception device  2001  for wireless power transmission may be divided into a selection phase, a ping phase, an identification and configuration phase, and a power transfer phase. 
     In some example embodiments, the wireless power reception device  2001  may include a magnetic member  2002  (e.g., a magnet), and in some example embodiments, the wireless power reception device  2001  may transmit a packet PKT indicating that it is a reception device including the magnetic member  2002  in the power transmission state to the wireless power transmission device  1001 . After receiving the packet PKT, the wireless power transmission device  1001  may continue to transmit wireless power (e.g., see “WIRELESS POWER TRANSMITTING” shown in  FIG.  19 A ). 
     As described above with reference to  FIGS.  18 A and  18 B  (e.g., see MRX shown in  FIG.  18 B ), when the resonance frequency for the input current IIN is included in the second resonance frequency range and the quality factor for the input current IIN is greater than the second reference quality factor Qth 2 , since the wireless power reception device  2001  may transmit the aforementioned packet PKT to the wireless power transmission device  1001 , the wireless power transmission device  1001  may detect a foreign object with respect to the wireless power reception device  2001  including the magnetic member  2002  according to whether a packet PKT is received. 
     Referring to  FIGS.  1  and  19 B , in some example embodiments, the wireless power reception device  2001  may transmit a signal CEP including a control error packet to the wireless power transmission device  1001  in a power transmission state. The wireless power transmission device  1001  may stop transmitting wireless power in response to the signal CEP including the control error packet. And, the wireless power transmission device  1001  may reset the test signal. 
     As described above with reference to  FIGS.  18 A and  18 B  (e.g., see RX+FO# 1  shown in  FIG.  18 B ), when the resonance frequency for the input current IIN is included in the second resonance frequency range and the quality factor for the input current IIN is greater than the second reference quality factor Qth 2 , since the wireless power reception device  2001  may not transmit the aforementioned packet PKT to the wireless power transmission device  1001  or transmit a signal CEP including the aforementioned control error packet to the wireless power transmission device  1001 , the wireless power transmission device  1001  may detect a foreign object according to whether a signal CEP including a control error packet is received (or whether the aforementioned packet PKT is not received). 
       FIG.  20    is a graph schematically illustrating whether detection of a foreign object has passed or failed. 
     Referring to  FIG.  20   , a foreign object detection pass area FOD PASS may be an area in which a foreign object is not detected. In the case of foreign object detection pass area FOD PASS, a resonance frequency may be included in the first resonance frequency range (e.g., “F1l” to “F1h”) and the quality factor may be greater than or equal to the first reference quality factor Qth 1 . 
     The foreign object detection fail area FOD FAIL may be an area in which a foreign object is detected. In the case of foreign object detection fail area FOD FAIL, a resonance frequency may be included in the first resonance frequency range (e.g., “F1l” to “F1h”) and the quality factor may be smaller than the first reference quality factor Qth 1 . Alternatively, in the case of a foreign object detection fail area FOD FAIL, the resonance frequency may be included in the second resonance frequency range (e.g., “F1h” (or “F2l”) to “F2h”) and the quality factor may be smaller than the third reference quality factor Qth 3 . Alternatively, in the case of the foreign object detection fail area FOD FAIL, the resonance frequency may be greater than the greatest value (e.g., “F2h”) of the second resonance frequency range. 
     The first reference quality factor Qth 1  may be greater than or equal to the second reference quality factor Qth 2 , and the second reference quality factor Qth 2  may be greater than the third reference quality factor Qth 3 . 
     The foreign object detection pass/fail area FOD PASS/FAIL @ PKT may be an area in which a foreign object is detected or not according to whether the wireless power transmission device  1001  receives the packet PKT described above with reference to  FIG.  19 A  from the wireless power reception device  2001 . In the foreign object detection pass/fail area FOD PASS/FAIL @ PKT, the resonance frequency is included in the second resonance frequency range (e.g., “F1h” (or “F2l”) to “F2h”), and the quality factor may be less than the second reference quality factor Qth 2  and greater than or equal to the third reference quality factor Qth 3 . 
     In some example embodiments, the frequency search range may include a first resonance frequency range (e.g., “F1l” to “F1h”) and a second resonance frequency range (e.g., “F1h” (or “F2l”) to “F2h”). 
     Hereinafter, an operation method of the wireless power transmitter for detecting a foreign object according to whether the wireless power reception device  2001  includes the magnetic member  2002  will be described. 
       FIG.  21    is a flowchart for explaining a method of operating a wireless power transmitter, according to another example embodiment of the present inventive concepts. 
     Referring to  FIG.  21   , the operating method of the wireless power transmitter may include sensing the input current by applying a test signal to the resonant tank S 1000 , setting the test resonance frequency based on the sensed value for the input current S 1100 , calculating a quality factor based on the sensed value and the test resonance frequency S 1200 , comparing the quality factor with a reference quality factor selected according to a test resonance frequency among a plurality of preset reference quality factors S 1300 , and resetting the test signal or performing an operation of wirelessly transmitting power according to the comparison result S 1400 . 
     Operation S 1000  is, for example, as described above with reference to operations S 200  and S 210  shown in  FIG.  9   . 
     Operation S 1100  is, for example, as described above with reference to operations S 220 , S 230 , and S 240  shown in  FIG.  9   . 
     Operation S 1200  is, for example, as described above with reference to operations S 250  and S 260  shown in  FIG.  9   . 
     In operation S 1300 , if the test resonance frequency is included in the first resonance frequency range as described above with reference to  FIG.  20   , the selected reference quality factor may be the first reference quality factor (e.g., Qth 1  shown in  FIG.  20   ). When the test resonance frequency is included in the second resonance frequency range, as described above with reference to  FIG.  20   , the selected reference quality factor may be a second reference quality factor (e.g., Qth 2  illustrated in  FIG.  20   ) or a third reference quality factor (e.g., Qth 3  illustrated in  FIG.  20   ). 
     Operation S 1400  is the same as described above with reference to operations S 100 , S 120 , and S 130  shown in  FIG.  8   . 
       FIG.  22    is a flowchart for describing in detail an operation method of the wireless power transmitter shown in  FIG.  21   . 
     Referring to  FIGS.  20 ,  21 , and  22   , operation S 2000  is, for example, the same as operation S 210  described above with reference to  FIG.  9   . 
     Operation S 2100  is, for example, the same or substantially the same as operations S 220 , S 230 , and S 240  described above with reference to  FIG.  9   . Alternatively, in another example embodiment, operation S 2100  is the same or substantially the same as operation S 320 , operation S 330 , operation S 340 , and operation S 350  described above with reference to  FIG.  11   . 
     The wireless power transmitter (e.g., the wireless power transmission device  100  shown in  FIG.  1   ) checks whether the test resonance frequency is included in a preset frequency search range S 2200 . The frequency search range may include, as described above with reference to  FIG.  20   , a first resonance frequency range (e.g., “F1l” to “F1h”) and a second resonance frequency range (e.g., “F1h” (or “F2l”) to “F2h”). 
     The test resonance frequency may be a frequency greater than a frequency search range (e.g., “F1l” to “F2h” illustrated in  FIG.  20   ). That is, if the test resonance frequency is not included in the frequency search range (S 2200 , NO), operation S 2000  is performed. 
     If the test resonance frequency is included in the frequency search range (S 2200 , YES), operation S 2300  is performed. Operation S 2300  is the same or substantially the same as operation S 1200  described above with reference to  FIG.  21   . 
     The wireless power transmitter determines whether the test resonance frequency is included in the first resonance frequency range (e.g., “F1l” to “F1h” shown in  FIG.  20   ) S 2400 . 
     When the test resonance frequency is included in the first resonance frequency range (S 2400 , YES), the wireless power transmitter compares whether the quality factor is greater than a first reference quality factor (e.g., the first reference quality factor Qth 1  illustrated in  FIG.  20   ) S 2500 . 
     If the quality factor is less than or equal to the first reference quality factor (S 2500 , NO), operation S 2000  is performed. 
     If the quality factor is greater than the first reference quality factor (S 2500 , YES), operation S 2600  is performed. Operation S 2600  is, for example, the same or substantially the same as operation S 130  described above with reference to  FIG.  8   . 
     If the test resonance frequency is not included in the first resonance frequency range (S 2400 , NO), that is, the test resonance frequency is in the second resonance frequency range (e.g., “F1h” (or “F2l”) to “F2h” shown in  FIG.  20   ), the wireless power transmitter compares whether the quality factor is greater than a second reference quality factor (e.g., the second reference quality factor Qth 2  illustrated in  FIG.  20   ) S 2700 . The second reference quality factor may be less than or equal to the first reference quality factor. Referring to  FIG.  20   , for example, the second reference quality factor Qth 2  may be the same as the first reference quality factor Qth 1 . However, the inventive concepts are not limited thereto. 
     If the quality factor is greater than the second reference quality factor (S 2700 , YES), operation S 2600  is performed. 
     If the quality factor is less than or equal to the second reference quality factor (S 2700 , NO), the wireless power transmitter compares whether the quality factor is greater than the third reference quality factor S 2800 . The third reference quality factor Qth 3  may be, for example, smaller than the second reference quality factor Qth 2  with reference to  FIG.  20   . 
     If the quality factor is greater than the third reference quality factor (S 2800 , YES), the wireless power transmitter checks whether a packet (e.g., the packet PKT illustrated in  FIG.  19 A ) is received from the outside (e.g., the wireless power reception device  2001  shown in  FIG.  16   ) S 2900 . 
     When the packet is received (S 2900 , YES), operation S 2600  is performed. When a packet is not received or a signal including a control error packet (e.g., a signal CEP shown in  FIG.  19 B ) is received (S 2900 , NO), operation S 2000  is performed. 
     As described above, even when the wireless power reception device  2001  includes the magnetic member  2002 , by accurately detecting a foreign object around the wireless power transmission device  1001 , there is an effect of inhibiting or preventing malfunctions and accidents due to heat. 
     It will be understood that elements and/or properties thereof described herein as being “substantially” the same and/or identical encompasses elements and/or properties thereof that have a relative difference in magnitude that is equal to or less than 10%. Further, regardless of whether elements and/or properties thereof are modified as “substantially,” it will be understood that these elements and/or properties thereof should be construed as including a manufacturing or operational tolerance (e.g., ±10%) around the stated elements and/or properties thereof. 
     One or more of the elements disclosed above may include or be implemented in one or more processing circuitries such as hardware including logic circuits; a hardware/software combination such as a processor executing software; or a combination thereof. For example, the processing circuitries more specifically may include, but is not limited to, a central processing unit (CPU), an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FGPA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, application-specific integrated circuit (ASIC), etc. 
     While aspects of the inventive concepts have been particularly shown and described with reference to some example embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the scope of the inventive concepts.