Abstract:
A wireless power reception device and a wireless communication method thereby are provided. The wireless communication method by the wireless power reception device may comprise the steps of: receiving a wireless power signal from a wireless power transmission device; measuring the strength of the wireless power signal; modulating the amplitude of the wireless power signal according to the measured strength of the wireless power signal; and performing communication with the wireless power transmission device by using the signal having the amplitude modulated.

Description:
BACKGROUND OF THE INVENTION 
     Field of the invention 
       [0001]    The present invention relates to wireless charging, and more particularly, to a contactless power reception device. 
         [0002]    Related Art 
         [0003]    In recent years, supply of portable electronic devices including a smart phone, a laptop, an MPEG-1 audio layer (MP3) player, a headset, and the like has been spread. However, since the portable electronic devices operate by consuming power stored in battery cells (e.g., a primary cell, a secondary cell, and the like), the battery cell needs to be charged or replaced in order to continuously operate the portable electronic devices. 
         [0004]    A method of charging the battery cell is generally divided into a contact type charging method of charging the battery cell by using a power supply line and a power supply terminal and a contactless charging method of charging the battery cell with wireless power induced by a magnetic field generated from a primary coil of a wireless power transmitting apparatus by using a wireless power reception device. However, in the contact type charging method, an instant discharge phenomenon occurs as different potential differences are generated at both terminals when a charger and a battery are coupled to or separated from each other and the power supply terminal is exposed to the outside, and as a result, fire may occur when foreign materials are accumulated in the power supply terminal and the battery is naturally discharged and the life-span and the performance of the battery deteriorate due to moisture. Accordingly, in recent years, in order to solve the problems, a research into the contactless charging method has been in active progress. 
         [0005]    As one of technologies associated with the contactless charging method, “Contactless Charging System” of Korean Patent Registration No. 10-0971705 discloses that a wireless power signal is transmitted by determining measuring a delay time up to a time of receiving a response signal corresponding to a request signal from a time of outputting the request signal through a primary-side core unit and comparing the measured delay time with a reference stand-by time when a load change is sensed in the primary-side core unit of a contactless power transmission device and thereafter, determining that a corresponding object is a foreign material when the measured time is shorter than the reference stand-by time and determining that the corresponding object is a normal contactless power reception device when the measured time is longer than the reference stand-by time. 
         [0006]    In the magnetic induction type contactless charging system, the wireless power reception device generally communicates with the wireless power transmission device by an amplitude-shift keying (ASK) modulation method. In detail, when the amplitude of the wireless power signal which the wireless power reception device receives from the wireless power transmission device is modulated, the modulated signal is induced to a transmitting coil of the wireless power transmission device. The wireless power transmission device performs communication by detecting the modulated signal induced to the transmitting coil. However, in the contactless charging system, as the intensity of the wireless power signal transmitted from the wireless power transmitting apparatus increases, distortion occurs in the modulated signal and this causes a communication error between the wireless power transmitting apparatus and the wireless power receiving apparatus. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a wireless power reception device which can smoothly communicate with a wireless power transmission device even when the strength of wireless power transmitted from the wireless power transmission device increases in a contactless charging system. 
         [0008]    The present invention also provides a wireless communication method which enables a wireless power reception device and a wireless power transmission device to smoothly communicate with each other even when the strength of wireless power transmitted from the wireless power transmission device increases in a contactless charging system. 
         [0009]    In an aspect, a wireless communication method by a wireless power reception device is provided. The wireless power reception device includes: receiving a wireless power signal from a wireless power transmission device; measuring the strength of the wireless power signal; modulating the amplitude of the wireless power signal according to the measured strength of the wireless power signal; and performing communication with the wireless power transmission device by using the signal having the amplitude modulated, and the modulating of the amplitude of the wireless power signal may be performed by a modulator included in the wireless power reception device according to the measured strength of the wireless power signal and the modulator may be implemented to include at least one resistor and at least one transistor. 
         [0010]    The at least one transistor may be implemented by a metal oxide silicon field effect transistor (MOSFET). 
         [0011]    The modulator may be implemented to be configured in a direct current (DC) terminal of the wireless power reception device. 
         [0012]    The modulator may be implemented to be configured in an alternating current (AC) terminal of the wireless power reception device. 
         [0013]    The modulator may be implemented to include two or more transistors and two or more resistors. 
         [0014]    In another aspect of the present invention, a wireless power reception device is provided. The wireless power reception device includes: at least one secondary core receiving a wireless power signal transmitted from a wireless power transmission device; a rectifier rectifying the received wireless power signal; a detection circuit measuring the strength of the wireless power signal by monitoring an output of the rectifier a plurality of modulators modulating the amplitude of the wireless power signal; and a controller controlling communication with the wireless power transmission device by using the signal having the amplitude modulated by the modulator, and the modulator may be implemented to include at least one resistor and at least one transistor. 
         [0015]    The at least one transistor may be implemented by a metal oxide silicon field effect transistor (MOSFET). 
         [0016]    The modulator may be implemented to be configured in a direct current (DC) terminal of the wireless power reception device. 
         [0017]    The modulator may be implemented to be configured in an alternating current (AC) terminal of the wireless power reception device. 
         [0018]    The modulator may be implemented to include two or more transistors and two or more resistors. 
         [0019]    According to the present invention, since a wireless power reception device modulates the amplitude of a wireless power signal according to the strength of the wireless power signal transmitted from a wireless power transmission device to prevent a modulated signal from being distorted, smooth wireless communication is available even when strong wireless power signal are transmitted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a diagram illustrating a contactless charging system according to the present invention. 
           [0021]      FIG. 2  is a block diagram illustrating a wireless power transmission device included in the contactless charging system. 
           [0022]      FIG. 3  is a circuit diagram illustrating a wireless power reception device included in the contactless charging system. 
           [0023]      FIG. 4  is a block diagram illustrating a wireless power reception device according to an embodiment of the present invention. 
           [0024]      FIG. 5  is a circuit diagram illustrating the wireless power reception device according to the embodiment of the present invention. 
           [0025]      FIG. 6  is a block diagram illustrating a wireless power reception device according to another embodiment of the present invention. 
           [0026]      FIG. 7  is a circuit diagram illustrating the wireless power reception device according to the embodiment of  FIG. 6 . 
           [0027]      FIG. 8  is a block diagram illustrating a wireless power reception device according to yet another embodiment of the present invention. 
           [0028]      FIG. 9  is a circuit diagram illustrating the wireless power reception device according to the embodiment of  FIG. 8 . 
           [0029]      FIG. 10  is a flowchart illustrating a wireless communication method of a wireless power reception device according to an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0030]    The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In addition, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0031]    Throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, terms including “unit”, and the like disclosed in the specification mean a unit that processes at least one function or operation and this may be implemented by hardware or software or a combination of hardware and software. 
         [0032]    A term called “wireless power” used in the present specification means predetermined type of energy associated with an electric field, a magnetic field, an electromagnetic field, and the like transmitted from a transmitter to a receiver without using physical electromagnetic conductors. The wireless power may be called a power signal or a wireless power signal and mean an oscillating magnetic flux enclosed by a primary coil at a transmitting side and a secondary coil at a receiving side. Hereinafter, a wireless power receiving apparatus and a wireless communication method in a contactless charging system for wirelessly charging devices including a mobile phone, a cordless phone, a smart phone, an MP3 player, a laptop, a headset, and the like will be described as an example. A fundamental principle of wireless power transmission includes both a magnetic induction coupling method and a magnetic resonance coupling (that is, resonance induction) method using frequencies less than 30 MHz. However, various frequencies including frequencies at which a license-exemption operation is permitted at comparative higher radiation levels, for example, less than 135 kHz (LF) or 13.56 MHz (HF) may be used. 
         [0033]      FIG. 1  is a diagram illustrating a contactless charging system according to the present invention. 
         [0034]    Referring to  FIG. 1 , the contactless charging system  100  includes a wireless power transmission device  110  and one or more wireless power reception devices  150 - 1  to  150 -n (herein, n is a natural number). 
         [0035]    The wireless power transmission device  110  includes a primary core. The primary coil may include at least one primary coil. The wireless power transmission device  110  may have a predetermined appropriate shape, but one preferred embodiment may be a flat platform having a power transmission surface. The respective wireless power reception devices  150 - 1  to  150 -n are positioned on the platform or near the platform to receive wireless power from the wireless power transmission device  110 . 
         [0036]    The respective wireless power reception devices  150 - 1  to  150 -n may be separated from the wireless power transmission device  110 . When the respective wireless power reception devices  150 - 1  to  150 -n are positioned near the wireless power transmission device  110 , the respective wireless power reception devices  150 - 1  to  150 -n include the secondary core coupled with an electromagnetic field generated by the primary core of the wireless power transmission device  110 . The secondary core may include one or more secondary coils. 
         [0037]    The wireless power transmission device  110  transmits power to the wireless power reception devices  150 - 1  to  150 -n without a direct contact. In this case, the primary core and the secondary core are magnetic induction coupled or magnetic resonance coupled to each other. The primary coil or the secondary coil may have predetermined appropriate shapes. As one example, the primary coil and the secondary coil may be copper wires wound around a high magnetic permeability formation such as ferrite or an amorphous material, but are not limited thereto. 
         [0038]    The wireless power reception devices  150 - 1  to  150 -n are connected with external load (not illustrated, also referred to as an actual load of the wireless power reception device) to supply the power wirelessly received from the wireless power transmission device  110  to the external load. For example, each of the wireless power reception devices  150 - 1  to  150 -n may transport the received power to an object which consumes or stores the power, such as a portable electric or electronic device or a rechargeable battery cell or battery 
         [0039]      FIG. 2  is a block diagram illustrating a wireless power transmission device included in the contactless charging system. Hereinafter, the wireless power transmission device will be described in more detail with reference to  FIG. 2 . 
         [0040]    The wireless power transmission device  200  may include a primary core  210 , an electric driving circuit  220 , a controller  230 , and a current measurement circuit  240 . 
         [0041]    The primary core  210  transmits a signal for detecting the wireless power receiving apparatus and a wireless power signal. 
         [0042]    The electric driving circuit  220  is connected to the primary core  210  to apply electric driving signals to the primary core so that the electromagnetic field is generated in the primary core  210 . 
         [0043]    The controller  230  is connected to the electric driving circuit  220  to generate a control signal  231  to control an alternating current (AC) signal required when the primary core  210  generates an induction magnetic field or causes magnetic resonance. The controller  230  may control an operation frequency, and voltage, current, and/or a duty cycle in the wireless power transmission device  200  according to a power control signal received from the wireless power reception device. 
         [0044]    The current measurement circuit  240  measures current that flows on the primary core  220 . The current measured by the current measurement circuit  240  may be alternating current (AC). As one example, the current measurement circuit  240  may be a current sensor. Alternatively, the current measurement circuit  240  may be a transformer that lowers high current that flows on the primary core  210  to low current and uses the low current. Further, the current measured by the current measurement circuit  240  may be direct current (DC). 
         [0045]    The controller  230  may obtain information transmitted by the wireless power reception device by using a current or voltage value measured by the current measurement circuit  240 . The wireless power reception device may continuously or periodically transmit to the wireless power transmission device  200  a power control signal to request an increase of the power or a power control signal to request a decrease of the power until required power is satisfied by varying the load. When the wireless power transmission device  200  receives the power control signal to request the increase of the power from the wireless power reception device through the load variation, the wireless power transmission device  200  decreases the power control signal to an appropriate magnitude by using the transformer or a voltage distributor and performs envelope detection by using a detector and thereafter, makes the power control signal pass through a low-pass filter to detect the signal form the wireless power reception device. In addition, the strength of the current which flows on the primary core  210  may be increased so as to transmit higher power as a response to the power control signal. In more detail, the controller  230  may adjust the control signal so as to apply an AC signal having a larger magnitude than a reference AC signal in order to make higher current flow on the primary core  210 . On the contrary, when the controller  230  receives the power control signal to request the decrease of the power from the wireless power reception device, the controller  230  may adjust the control signal so as to apply an AC signal lower than the reference AC signal to the primary core  210  so that power lower than the current transmission power is transmitted. 
         [0046]      FIG. 3  is a circuit diagram illustrating a wireless power reception device included in the contactless charging system. Hereinafter, a structure of the wireless power reception device will be described in more detail with reference to  FIG. 3 . 
         [0047]    The wireless power reception device  300  may include a secondary core  310 , a modulator  320 , a controller  330 , a rectifier  340 , and a regulator  350 . 
         [0048]    The secondary core  310  may be configured by at least one secondary coil. The secondary core  310  may receive a wireless power signal transmitted from the primary core of the wireless power transmission device. 
         [0049]    The modulator  320  may be configured by an AC terminal of the wireless power reception device  300  as illustrated in  FIG. 3  and modulate the amplitude of the wireless power signal received through the secondary core  310 . To this end, the modulator  320  may include a capacitor  321  and a transistor  322 . For example, the modulator  320  turns on/off the transistor  322  connected to the capacitor  321  to modulate the amplitude of the wireless power signal received through the secondary core  310 . The signal with the modulated amplitude may be induced to the primary core of the wireless power transmission device through the secondary core  310 . 
         [0050]    The controller  330  which is used for controlling an operation of the wireless power reception device  300  may control power supplied to a load connected to the wireless power reception device  300  as one example. Further, the controller  330  may perform communication with the wireless power transmission device by controlling the modulator  320 . 
         [0051]    The rectifier  340  may rectify AC power received by the secondary core  310  to direct current (DC) power. The power rectified by the rectifier  340  may be supplied to the load which is connected or mounted onto or included in the wireless power reception device  300 . The rectifier  340  may be implemented by a half-bridge, a full-bridge, or the like as illustrated in  FIG. 3 . In  FIG. 3 , as an example, it is illustrated that the rectifier  340  includes a plurality of diodes, but the diode of the rectifier  340  may be replaced with the transistor such as a field effect transistor (FET). 
         [0052]    The regulator  350  is configured at a rear terminal of a bridge including a plurality of diodes to supply the direct current (DC) power received through the bridge to the load connected or mounted onto or included in the wireless power reception device  300 . Herein, the bridge may serve to convert input AC voltage to DC voltage and be implemented by the half-bridge, the full-bridge, or the like. 
         [0053]    Meanwhile, although not illustrated in  FIG. 3 , the wireless power reception device  300  may include a detection circuit which measures strength of the wireless power signal transmitted from the wireless power transmission device by monitoring an output of the rectifier  340 . 
         [0054]    When the strength of the wireless power signal detected from the detection circuit is larger than or smaller than a predetermined control point, the controller  330  may transmit information on power control so that the wireless power signal with predetermined strength may be received by modulating the amplitude of the wireless power signal received from the wireless power reception device by means of the modulator  320 . Alternatively, when the strength of the wireless power signal detected from the detection circuit is beyond the predetermined range, the controller  330  may allow the strength of the wireless power signal to be maintained within the predetermined range by modulating the amplitude of the wireless power signal received from the wireless power reception device by means of the modulator  320 . In this case, as illustrated in  FIG. 3 , when the capacitor  321  is used in the modulator  320 , constant impedance for a change in frequency is maintained, and thus even though the frequency is changed, the modulator  320  may perform constant amplitude modulation. However, when a resistor instead of the capacitor  321  is used in the modulator  320 , a response time may be minimized according to the used resistor, but since the impedance is changed according to a frequency, when a full band is used, distortion according to the frequency may be caused. Further, even though the capacitor  321  is used in the modulator  320 , the magnitude of the power received from the wireless power transmission device is larger than a predetermined value, the signal modulated by the modulator  320  may be distorted. Since the distortion of the modulated signal causes communication failure between the wireless power transmission device and the wireless power reception device  300 , the wireless power reception device according to the present invention may include components described below for smooth communication. 
         [0055]      FIG. 4  is a block diagram illustrating a wireless power reception device according to an embodiment of the present invention and  FIG. 5  is a circuit diagram illustrating the wireless power reception device according to the embodiment of the present invention. Hereinafter, the wireless power reception device according to the embodiment of the present invention will be described in detail with reference to  FIGS. 4 and 5 . 
         [0056]    First, referring to  FIG. 4 , a wireless power reception device  400  according to an embodiment of the present invention may include a secondary core  410 , a rectifier  420 , a regulator  430 , a detection circuit  440 , a controller  450 , and a modulator  460 . The wireless power reception device  400  is connected to an external load  470  to supply power wirelessly received from the wireless power transmission device to a load  470 . 
         [0057]    The secondary core  410  may include at least one secondary coil receiving the wireless power signal transmitted from the wireless power transmission device. 
         [0058]    The rectifier  420  may rectify AC power received by the secondary core  410  to direct current (DC) power. The power rectified by the rectifier  420  may be supplied to the load  470  which is connected or mounted onto or included in the wireless power reception device  400 . The rectifier  420  may be implemented by a half-bridge, a full-bridge, or the like. 
         [0059]    The regulator  430  is configured at a rear terminal of a bridge including a plurality of diodes to supply direct current (DC) power received through the bridge to the load connected or mounted onto or included in the wireless power reception device  300  through the regulator  430 . Herein, the bridge may serve to convert input AC voltage to DC voltage and be implemented by the half-bridge, the full-bridge, or the like and the regulator  430  converts the DC voltage of the rectifier into stable DC voltage and supplies the DC voltage to the load. 
         [0060]    The detection circuit  440  monitors the DC voltage output from the rectifier  420  in connected with the rear terminal of the rectifier  420  to measure the strength of the wireless power signal transmitted from the wireless power transmission device. 
         [0061]    The controller  450  may control communication with the wireless power transmission device by using a signal with the amplitude modulated by the modulator  460  based on the strength of the wireless power signal measured by the detection circuit  440 . 
         [0062]    The modulator  460  may modulate the amplitude of the wireless power signal transmitted from the wireless power transmission device. 
         [0063]    Hereinafter, the wireless power reception device of  FIG. 4  will be described in more detail with reference to the circuit diagram of  FIG. 5 . In  FIG. 5 , as an example, a case where a secondary core  510  includes one secondary coil is illustrated. Referring to  FIG. 5 , a modulator  560  is positioned between a rectifier  520  and using the plurality of diodes or FETs and a regulator  530  to modulate the DC power which is the output of the rectifier  520 . Further, the modulator  560  may include one resistor  561  and one or more transistors  562  and  563 . Since the modulator  560  includes the resistor  561 , the response time may be minimized according to the used resistor. However, since the impedance varies depending on the frequency, when the full band is used, the distortion depending on the frequency may be caused, but since the modulator  560  is connected to the DC terminal of the diode bridge in series as illustrated in  FIG. 5 , the modulator varies the current amount in the direction in which the signal flows to prevent the frequency from being distorted even with the high power. Further, the modulator  560  may include a PNP transistor  563  and a controller  550  is connected to a base terminal of the PNP transistor  563  to switch the modulator  560  and analoguely control the magnitude of amplitude modulation according to a load change amount through the current control. Meanwhile, in  FIG. 5 , it is illustrated that the rectifier  520  includes a plurality of diodes, but the diode of the rectifier  520  may be replaced with the transistor such as a field effect transistor (FET). 
         [0064]    Meanwhile,  FIG. 6  is a block diagram illustrating a wireless power reception device according to another embodiment of the present invention and  FIG. 7  is a circuit diagram illustrating the wireless power reception device according to the embodiment of  FIG. 6 . Hereinafter, the wireless power reception device according to the embodiment will be described in detail with reference to  FIGS. 6 and 7 . 
         [0065]    First, referring to  FIG. 6 , the wireless power reception device  600  according to the embodiment of the present invention may include a secondary core  610 , a rectifier  620 , a regulator  630 , a detection circuit  640 , a controller  650 , and a modulator  660 . The wireless power reception device  600  is connected to an external load  670  to supply power wirelessly received from the wireless power transmission device to the load  670 . 
         [0066]    The secondary core  610  may include at least one secondary coil receiving the wireless power signal transmitted from the wireless power transmission device. 
         [0067]    The rectifier  620  may rectify AC power received by the secondary core  610  to direct current (DC) power. The power rectified by the rectifier  620  may be supplied to the load  670  which is connected or mounted onto or included in the wireless power reception device  600 . The rectifier  620  may be implemented by a half-bridge, a full-bridge, or the like. 
         [0068]    The regulator  630  is configured at a rear terminal of a bridge including a plurality of diodes to supply the direct current (DC) received through the bridge to the load connected or mounted onto or included in the wireless power reception device  600 . Herein, the bridge may serve to convert input AC voltage to DC voltage and be implemented by the half-bridge, the full-bridge, or the like. 
         [0069]    The detection circuit  640  monitors the DC voltage in connected with the rear terminal of the rectifier  620  to measure the strength of the wireless power signal transmitted from the wireless power transmission device. 
         [0070]    The controller  650  may control communication with the wireless power transmission device by using a signal with the amplitude modulated by the modulator  660  based on the strength of the wireless power signal measured by the detection circuit  640 . 
         [0071]    The modulator  660  may modulate the amplitude of the wireless power signal transmitted from the wireless power transmission device. 
         [0072]    Hereinafter, the wireless power reception device of  FIG. 6  will be described in more detail with reference to the circuit diagram of  FIG. 7 . A modulator  760  includes first and second modulation modules  765  and  770 . The modulator  760  is configured to be positioned between a secondary corer  710  and a rectifier using a plurality of diodes to modulate AC power which is an output of the core  710 . In this case, the first and second modulation modules  765  and  770  may include one or more resistors  788  and  771  and one or more transistors  767  and  772 , respectively. Since the modulator  760  includes the resistors  766  and  771 , a response time may be minimized according to the used resistors  766  and  771 . However, since the impedance varies depending on the frequency, when a full band is used, distortion depending on the frequency may be caused, but the response time and frequency modulation may be more actively controlled by using two or more resistors  766  and  771  and two or more transistors  767  and  772 . The first and second modulation modules  765  and  770  may modulate the amplitude of the wireless power signal received through the secondary core  710  by turning on/off or analoguely controlling the transistor connected to the resistor. The signal with the modulated amplitude may be induced to the primary core of the wireless power transmission device through the secondary core  710 . Further, the first and second modulation modules  765  and  770  may include one or more PNP transistors  768  and  773  and a controller  750  is connected to base terminals of respective PNP transistors  768  and  773  included in the first and second modulation modules  765  and  770  to control a current flow of the modulator  760 . Accordingly, the modulator  760  is switched by the controller  750  and the magnitude of the amplitude modulation is analoguely controlled according to a load change amount through a current control to enable stable communication. 
         [0073]    Meanwhile,  FIG. 8  is a block diagram illustrating a wireless power reception device according to yet another embodiment of the present invention and  FIG. 9  is a circuit diagram illustrating the wireless power reception device according to the embodiment of the present invention. Hereinafter, the wireless power reception device according to the embodiment will be described in detail with reference to  FIGS. 8 and 9 . 
         [0074]    First, referring to  FIG. 8 , the wireless power reception device  800  according to the embodiment of the present invention may include a secondary core  810 , a rectifier  820 , a regulator  830 , a detection circuit  840 , a controller  850 , and a modulator  860 . The wireless power reception device  800  is connected to an external load  870  to supply power wirelessly received from the wireless power transmission device to the load  870 . 
         [0075]    The secondary core  810  may include at least one secondary coil receiving the wireless power signal transmitted from the wireless power transmission device. 
         [0076]    The rectifier  820  may rectify AC power received by the secondary core  810  to direct current (DC) power. The power rectified by the rectifier  820  may be supplied to the load  870  which is connected, installed, or included to the wireless power reception device  800  by the regulator  830 . The rectifier  820  may be implemented by a half-bridge, a full-bridge, or the like. 
         [0077]    The regulator  830  is configured at a rear terminal of a bridge including a plurality of diodes to supply the direct current (DC) power received through the bridge to the load connected or mounted onto or included in the wireless power reception device  800 . Herein, the bridge may serve to convert input AC voltage to DC voltage and be implemented by the half-bridge, the full-bridge, or the like. 
         [0078]    The detection circuit  840  monitors the DC voltage in connected with the rear terminal of the rectifier  820  to measure the strength of the wireless power signal transmitted from the wireless power transmission device. 
         [0079]    The controller  850  may control communication with the wireless power transmission device by using a signal with the amplitude modulated by the modulator  860  based on the strength of the wireless power signal measured by the detection circuit  840 . 
         [0080]    The modulator  860  may modulate the amplitude of the wireless power signal transmitted from the wireless power transmission device. 
         [0081]    Hereinafter, the wireless power reception device of  FIG. 9  will be described in more detail with reference to the circuit diagram of  FIG. 9 . Referring to  FIG. 9 , a modulator  960  may include two resistors  961  and  962  and two transistors  963  and  964 . The two transistors  963  and  964  may be a metal oxide silicon field effect transistor (MOSFET). Further, since the modulator  960  includes the resistors  961  and  962 , the response time may be minimized according to the used resistors  961  and  962 . Further, the current flow may be more actively controlled by switching on/off two transistors  963  and  964 . Further, the modulator  960  configured as illustrated in  FIG. 9  may perform modulation through a controller  950 . 
         [0082]      FIG. 10  is a flowchart illustrating a wireless communication method of a wireless power reception device according to an embodiment of the present invention. 
         [0083]    Referring to  FIG. 10 , the wireless power reception device receives the wireless power signal from the wireless power transmission device (S 1010 ). In the case of receiving the wireless power signal, the wireless power transmitted from the primary coil of the wireless power transmission device may be received by the secondary coil of the wireless power reception device. 
         [0084]    Next, the wireless power reception device measures the strength of the received wireless power signal (S 1020 ). The measured power may be alternating current (AC) or AC voltage. As one example, the wireless power signal may be measured by a current sensor or a voltage sensor. 
         [0085]    Next, the wireless power reception device modulates the amplitude of the wireless power signal according to the measured strength of the wireless power signal (S 1030 ). The wireless power signal may be modulated by the modulator. 
         [0086]    As one example, in the wireless power reception device, the modulator is configured to be positioned between the rectifier using a plurality of diodes or FETs and the regulator to modulate the DC power which is the output of the rectifier. In this case, the modulator may include one resistor and one or more transistors. Since the modulator includes the resistor, the response time may be minimized according to the used resistor. Since the modulator is connected to a DC terminal of a diode bridge in series, the modulator varies a current amount in a direction in which a signal flows without an influence by the frequency to enable smooth communication even with high power. Further, the modulator may include the PNP transistor and the controller is connected to the base terminal of the PNP transistor to control the current flow of the modulator. 
         [0087]    As another example, the wireless power reception device is configured to be positioned between the secondary core and the rectifier using the plurality of diodes to modulate the AC power which is the output of the secondary core. In this case, the modulator may include two or more resistors and two or more transistors. Since the modulator includes the resistor, the response time may be minimized according to the used resistor. However, since the impedance varies depending on the frequency, when the full band is used, the distortion depending on the frequency may be caused, but the response time and frequency modulation may be more actively controlled by using two or more resistors and two or more transistors. 
         [0088]    Next, the wireless power reception device performs communication with the wireless power transmission device by using the signal with the modulated amplitude (S 1040 ). In detail, the signal with the modulated amplitude may be induced to the primary core of the wireless power transmission device from the secondary core of the wireless power reception device and the wireless power transmission device may control transmission power by detecting the signal induced in the primary core. 
         [0089]    According to the present invention, since the wireless power reception device modulates the amplitude of the wireless power signal according to the strength of the wireless power signal transmitted from the wireless power transmission device to prevent a modulated signal from being distorted, smooth wireless communication is available even when strong wireless power signals are transmitted. 
         [0090]    The above description just illustrates the technical spirit of the present invention and various changes and modifications can be made by those skilled in the art to which the present invention pertains without departing from an essential characteristic of the present invention. Therefore, the exemplary embodiments disclosed in the present invention are used to not limit but describe the technical spirit of the present invention and the scope of the technical spirit of the present invention is not limited by the exemplary embodiments. The scope of the present invention should be interpreted by the appended claims and it should be analyzed that all technical spirit in the equivalent range thereto is intended to be embraced by the scope of the present invention.