Abstract:
An electronic device includes a contactless integrated circuit card function unit, a contactless charging function unit, and a switching unit. The contactless integrated circuit card function unit includes a clamp circuit and realizes a contactless integrated circuit card function. The clamp circuit suppresses excessive voltage of a signal received at an antenna whose operating frequency is a predetermined frequency. The contactless charging function unit commonly uses the antenna and realizes a contactless charging function. The switching unit invalidates or reduces the function of the clamp circuit when the contactless charging function unit is used.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority of Provisional Application Ser. No. 61/309,653, filed Mar. 2, 2010, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to techniques for efficiently sharing necessary hardware when both contactless integrated circuit (IC) card technology and wireless charging technology are included in an electronic device. 
         [0004]    2. Description of the Related Art 
         [0005]    Electronic devices represented by recent cellular phone terminals have a contactless IC card function such as a function called the “NFC/FeliCa” function, and these electronic devices have become more and more popular in various applications such as commuter passes, electronic tickets, and electronic money. “NFC” stands for Near Field Communication and is a short-distance wireless communication standard for performing bidirectional data communication at a very short distance of about 10 cm by using radio waves at 13.56 MHz. “FeliCa”, which is a registered trademark of Sony Corporation, is the name of contactless IC card technology developed by Sony Corporation and is employed in NFC. 
         [0006]    At the same time, wireless charging technology for charging cellular phone terminals without using cables has recently been proposed. Japanese Unexamined Patent Application Publication No. 2007-249305 discloses techniques for contactlessly charging an electronic device from a charging apparatus by using electromagnetic coupling. 
       SUMMARY OF THE INVENTION 
       [0007]    It has been proved that the following problems occur when both the wireless charging technology and the contactless IC card technology as described above are to be included in an electronic device. 
         [0008]    That is, realization of the contactless IC card function involves a loop antenna for wireless communication, a radio-frequency (RF) block for rectification and waveform shaping, and a baseband block that converts an analog signal into a digital signal (and vice versa) and processes these signals. 
         [0009]    Also, realization of the wireless charging technology generally involves a loop antenna and a charging block that has the mechanism capable of accumulating power induced in the antenna and efficiently feeding the power to a battery. Hardware serving as the core of the wireless charging technology has a structure similar to that of the contactless IC card technology. 
         [0010]    It is expected in the future that various problems will occur when the wireless charging function is to be included in a cellular phone terminal with the contactless IC card function. 
         [0011]    The first problem is the availability of space for mounting an antenna (loop antenna for wireless charging). Since multiple antennas and various devices for realizing various functions have already been present in the cellular phone terminal, there is not much space remaining. It is thus very difficult to mount an additional large loop antenna. 
         [0012]    The second problem is the interference between the wireless charging function and the contactless IC card function which uses an operating frequency similar to that used by the wireless charging function. The contactless IC card technology is originally a communication system that employs a radio frequency band of 13.56 MHz. Communication between a reader and a card/tag is realized by causing the antenna to resonate at 13.56 MHz. 
         [0013]    At the same time, the wireless charging function employs a similar principle, and mutual effects on each other are thus inevitable. More specifically, a clamp circuit is mounted on a contactless IC card chip to prevent damage to the chip due to excessive input when a magnetic field is received from an external reader/writer. 
         [0014]    However, because the clamp circuit automatically discards the excessive input power higher than the necessary amount, if the contactless IC card function shares the antenna with the wireless charging function, power to be supplied to a charging circuit is restricted by the clamp circuit, resulting in very low efficiency of transferring power to the charging side. 
         [0015]    Because of these reasons, it is necessary to devise a new mechanism that allows both the functions to share the same antenna and to coexist while minimizing mutual effects upon each other. 
         [0016]    It is desirable to provide techniques for allowing a contactless IC card antenna to be shared as an antenna for a wireless charging function without causing problems. 
         [0017]    According to one exemplary embodiment, the specification discloses an electronic device including a contactless integrated circuit (IC) card function unit configured to be connected to an antenna element and process a signal received at the antenna; a clamp circuit included in the contactless IC card function unit, the clamp circuit configured to suppress excessive voltage of the signal received via the antenna; a contactless charging function unit configured to be connected to the antenna and a battery of the electronic device, and charge the battery by receiving an electromotive force induced at the antenna; a switching module configured to eliminate or reduce the function of the clamp circuit; and a control unit connected to the switching module and configured to determine whether the contactless IC card function unit is in use or the contactless charging function is in use and control the switching module based on the determination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a conceptual diagram of a short-distance communication system which serves as a precondition to an embodiment of the present invention and which includes an electronic device that has two functions, i.e., a contactless IC card function and a wireless charging function, and a reader/writer; 
           [0019]      FIGS. 2A and 2B  are illustrations of antenna types; 
           [0020]      FIG. 3A  is a diagram illustrating a structure example of an electronic device according to an embodiment of the present invention; 
           [0021]      FIG. 3B  is a diagram illustrating a specific example of the structure of the electronic device illustrated in  FIG. 3A ; 
           [0022]      FIG. 4  is a diagram illustrating a structure example in which a selector illustrated in  FIG. 3B  is replaced by a switch; 
           [0023]      FIG. 5  is a diagram illustrating an example in which an antenna and a tuning unit are connected to a charging block side in the structure illustrated in  FIG. 4 ; 
           [0024]      FIG. 6  is a sequence diagram illustrating exchange of signals between a contactless charger and the units of the electronic device according to the embodiment of the present invention; 
           [0025]      FIG. 7  is a diagram illustrating a structure example of the electronic device according to a second embodiment of the present invention; and 
           [0026]      FIG. 8  is a sequence diagram illustrating exchange of signals between the contactless charger and the units of the electronic device according to the second embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Preferred exemplary embodiments of the present invention will now be described in detail with reference to the drawings. 
         [0028]      FIG. 1  is a conceptual diagram of a short-distance communication system which serves as a precondition to an embodiment of the present invention and which includes an electronic device  100  that has two functions, i.e., a contactless IC card function and a wireless charging function, and a reader/writer  200 . 
         [0029]    The electronic device  100  includes an antenna  101 , a tuning unit  110 , an amplifier  121 , a filter  122 , a filter  131 , a drive circuit  151 , a modulation circuit  152 , a memory  153 , a central processing unit (CPU)  154 , a demodulation unit  155 , a load switch (SW)  156 , and a clamp circuit  157 . 
         [0030]    The elements  151  to  157  are included in a contactless IC card large-scale integrated circuit (LSI) (NFC/FeliCa LSI)  150 . The contactless IC card LSI  150  is a large-scale integrated circuit that includes the drive circuit  151 , the modulation circuit  152 , the memory  153 , and the CPU  154  which realizes an upper layer of a wireless communication protocol. It is not necessary that these circuits be configured as LSI; these circuits may be built as independent elements. These elements constitute a contactless IC card function unit of an embodiment of the present invention. The other elements of a cellular phone terminal are publicly available and are thus not shown in the drawings. 
         [0031]    A sending block  130  of a reader/writer function includes part of the elements of the contactless IC card LSI  150 , the filter  131 , the tuning unit  110 , and the antenna  101 . 
         [0032]    The antenna  101  is a single element for both sending and receiving signals. As illustrated in  FIGS. 2A and 2B , the antenna  101  may be a type formed by vertically winding coils around a plate-shaped ferrite ( FIG. 2B ) or a loop type formed by winding coils in a plane ( FIG. 2A ). Either type may be employed as an antenna used in an electronic device according to an embodiment of the present invention. 
         [0033]    The tuning unit  110  is a block for obtaining a resonant frequency of 13.56 MHz together with an inductance component in an antenna unit. Generally, a capacitor is connected in parallel with a loop antenna of the antenna unit. 
         [0034]    A receiving block  120  shared between a reader/writer and a contactless IC card of the electronic device  100  includes part of the elements of the contactless IC card LSI  150 , the tuning unit  110 , and the antenna  101 . This part of the contactless IC card LSI  150  is an LSI including the amplifier  121  for amplifying response data that is from a card and that has been amplitude-shift-keying (ASK) modulated, the filter  122  for shaping the waveform, and the demodulation unit  155  for extracting data. This LSI also serves as a circuit that extracts a clock frequency of a carrier received from the external reader/writer  200 . 
         [0035]    When a response is to be sent to the reader/writer  200  side at the time at which the card function is ON, the response is modulated by repeatedly turning ON and OFF the load using the load SW  156  to change a load resistance of the antenna  101 . The modulated waveform seems to be an impedance change at the tip of an antenna  201  of the reader/writer  200  side and is transmitted as an amplitude difference of voltage and current. The amplitude difference is converted into digital data and is processed. 
         [0036]    To prevent damage to the chip due to excessive input when a magnetic field is received from the external reader/writer  200 , the clamp circuit  157  has a function of suppressing a voltage greater than or equal to a certain amount in order to suppress excessive voltage of the received signal. 
         [0037]    When the electronic device  100  functions as a reader/writer, the element  200  represents a contactless IC card or an NFC device. 
         [0038]      FIG. 3A  is a diagram illustrating the relationship between the electronic device  100  according to the embodiment and a reader/writer-charger  165  with an external charger function. The basic principle of charging in this example is power transfer using electromagnetic induction. That is, two coil antennas that face each other are provided between the charging side (the reader/writer-charger  165  in the example illustrated in  FIG. 3A ) and the side to be charged (the electronic device  100 ), and alternating current (AC) is caused to flow through the coil (an antenna  164 ) at the power sending side. Accordingly, a magnetic flux change occurs in the coil (antenna  164 ) at the power sending side, and an electromotive force occurs in the other coil (the antenna  101 ), resulting in the flow of current. That is, energy is transmitted contactlessly through a magnetic flux change. The power excited at the antenna  101  is smoothed by a rectifier circuit  161 , controlled by a charging control circuit  162  to be an appropriate amount of voltage and current, and is supplied to a secondary battery  163  (the elements  161  to  163  are shown in  FIG. 3B ). The secondary battery  163  is charged with voltage and current from the charging control circuit  162 . 
         [0039]      FIG. 3B  illustrates a structure example of the electronic device  100  according to the embodiment. The same reference numerals are given to elements that are the same as or similar to those illustrated in  FIG. 1 , and overlapping descriptions thereof are omitted. In this structure, a charging block  160  for wireless charging (contactless charging function unit), a selector  170  that selects a transfer path from the antenna  101 , and a charging control unit  158  that appropriately controls the selector  170  in accordance with a communication partner are added to the system illustrated in  FIG. 1 . The charging control unit  158  and the selector  170  constitute a unit that removes effects of the contactless IC card function unit when power is charged contactlessly. 
         [0040]    The charging block  160  includes the rectifier circuit  161 , the charging control circuit  162 , and the secondary battery  163 . 
         [0041]    Next, the operation of the embodiment will be described. 
         [0042]      FIG. 4  illustrates the electronic device  100  in which the selector  170  illustrated in  FIG. 3B  is replaced by a switch  170 ′. Normally, the antenna  101  and the tuning unit  110  are connected to the contactless IC card LSI  150  side. In this example, the section that is in charge of turning the switch  170 ′ is the contactless IC card LSI  150 . The entire control is performed by the contactless IC card LSI  150  serving as a master. That is, the antenna  101  and the tuning unit  110  are connected to the charging block  160  only when it is determined that there is a necessity to start charging upon a request from an external charger (reader/writer-charger  165  illustrated in  FIG. 3 ) to start charging. This entire processing is controlled by the contactless IC card LSI  150 . The charging control unit  158  controls the charging control circuit  162  and the switch  170 ′ on the basis of a processing result obtained by the CPU  154 . 
         [0043]      FIG. 5  illustrates an example in which the antenna  101  and the tuning unit  110  are connected to the charging block  160  side due to the turning of the switch  170 ′. The remaining elements are the same as those illustrated in  FIG. 4 . 
         [0044]    Next, an algorithm from a charging start request to the actual start of charging will be briefly described. 
         [0045]    Normally, wireless communication using NFC is started by a polling command from a reader/writer (R/W) side. Though the actual command to be used varies according to the RF standard to be used, the basic flow is the same. The embodiment of the present invention assumes that the charger side complies with an NFC wireless protocol, and the protocol is the extension of the current specifications. It is also assumed that a determination bit representing the presence/absence of a charger function is included in information in a frame. 
         [0046]      FIG. 6  is a sequence diagram illustrating exchange of signals between a contactless charger (reader/writer-charger  165 ) and the units of the electronic device  100  according to the embodiment. The state of a magnetic field (RF) generated by the coil antenna  164  at the reader/writer-charger  165  side in accordance with time is illustrated on the right of  FIG. 6 . It is assumed that there are three levels, i.e., 0, 1, 2, for the power intensity of the carrier where 0&lt;1&lt;2: 
         [0047]    level 0: off (standby) 
         [0048]    level 1: communication of contactless IC card function 
         [0049]    level 2: contactless charging 
         [0050]    First, a polling command is sent wirelessly from the contactless charger  165  (S 11 ). This corresponds to REQA of ISO 14443A or a polling command of FeliCa. In response to this polling command, when the electronic device  100  is a device conforming to the contactless charging function, a CHG bit (CHG=1 in this case) in a frame is set, and a response is sent (S 12 ). As a precondition, a specific bit in a frame of the polling command is defined as a CHG bit. In this example, it is assumed that the charger  165  side has been able to check whether the partner device (electronic device  100 ) is a device that conforms to the contactless charging function. Next, the charger  165  sends a request command REQ for starting charging to the contactless IC card LSI  150  (S 13 ). The contactless IC card LSI  150  has been storing, in the internal memory  153 , an ON/OFF default value indicating whether to use the contactless charging function. In accordance with this information, the contactless IC card LSI  150  sends ACK/NACK (S 14 ). When the contactless charging function is OFF, the process may be terminated after a certain time has elapsed (time out). When the electronic device  100  has the contactless charging function, the contactless charging ON/OFF default value can be set by a user to selectively validate/invalidate the function. When the electronic device  100  does not have the contactless charging function, the default value is set to OFF. 
         [0051]    When ACK is sent from the contactless IC card LSI  150 , a command START_CHG for starting charging is sent from the charger  165  side (S 15 ). The contactless IC card LSI  150  sends ACK in response to this command (S 16 ), and the charger  165  side prepares to transfer power. Power transfer actually starts after a certain interval (standby state illustrated in  FIG. 6 ). During the interval, the contactless IC card LSI  150  sends a control signal SELECT_CHG=1 to the switch  170 ′ (S 17 ) and turns the switch  170 ′ toward the charging block  160  side. Thereafter, the contactless IC card LSI  150  also sends a control signal CHG_EN=1 to the charging control circuit  162  and enables the charging control circuit  162  (S 18 ). Accordingly, charging (power transfer) from the charger  165  starts (S 19 ). 
         [0052]    A charging ending sequence may take the following two cases. 
         [0053]    The first case is simply that the charging control circuit  162  in the charging block  160  automatically detects that the secondary battery  163  has been fully charged and accordingly the charging control circuit  162  informs the charging control unit  158  in the contactless IC card LSI  150  that charging has been completed. 
         [0054]    The second case is when the antenna  101  connected to the contactless IC card LSI  150  is physically separated from the antenna  164  of the charger  165  and there is no longer power transfer from the charger  165 . In this case, the charging control circuit  162  detects a voltage level from the rectifier circuit  161  (RF detector) in the charging block  160  and, when this level falls below a certain threshold, informs the charging control unit  158  in the contactless IC card LSI  150  thereof. In response to this, the charging control unit  158  turns the switch  170 ′ to default, i.e., toward the common receiving block  120  side. 
         [0055]    According to the first embodiment described above, the switch  170 ′ is turned toward the common receiving block  120  side in a period in which contactless charging is not performed, as illustrated in  FIG. 4 . Thus, the clamp circuit  157  can efficiently function in a desired manner, and the contactless IC card LSI  150  can be protected against excessive voltage. Also in this state, the charging block  160  is completely separated from the transfer path from the antenna  101 . Thus, there is no effect on the receiving block  120  side. The switch  170 ′ is turned toward the charging block  160  side in a period in which contactless charging is performed, as illustrated in  FIG. 5 . Thus, the clamp circuit  157  is completely separated from the transfer path from the antenna  101 , resulting in prevention of deterioration of the charging efficiency of the charging block  160  due to the clamp circuit  157 . 
         [0056]      FIG. 7  illustrates a structure example of the electronic device  100  according to a second embodiment of the present invention. The same reference numerals are given to elements that are the same as or similar to those illustrated in the above-described other drawings, and overlapping descriptions thereof are omitted. This embodiment relates to a method in which a unit (selector  170 ) that selects the transfer path of the circuit is not used. Specifically, a clamp circuit  157   a  that can perform control to switch the level of voltage to suppress (clamp voltage) or to be selectively invalidated is provided as the clamp circuit  157  included in the contactless IC card LSI  150 . That is, in this embodiment, the charging control unit  158  and the clamp circuit  157   a  constitute a unit that removes effects of the contactless IC card function unit when power is charged contactlessly. The clamp circuit  157   a  includes three pairs (A, B, and C) of a resistor and a constant-voltage element (Zener diode in  FIG. 7 ) and a switch D that grounds one of these pairs. The number of pairs is not limited to three. The voltage values (clamp voltages) of the constant-voltage elements of the individual pairs are set to different levels. It is assumed that at least one of the voltage values of the constant-voltage elements of the three pairs is higher than a voltage value when the contactless IC card function is used. When charging is performed, such a constant-voltage element is selected. When there is only one pair, a constant-voltage element with a normal voltage value is used, and selective invalidation operation of the clamp circuit  157   a  is performed using the switch D. 
         [0057]    More specifically, it is assumed that the relationship among thresholds of a voltage level (clamp voltages of the individual pairs) Vth at which the clamp circuit  157   a  operates is A&gt;B&gt;C. In this case, Vth is set to B or C when, for example, communication using NFC is performed. When charging is performed (that is, when the contactless charging function unit is used), the clamp circuit  157   a  is switched to A, thereby restricting the function of the clamp circuit  157   a . That is, the threshold of the voltage level at which the clamp circuit  157   a  operates is increased. Accordingly, useless consumption of power at the contactless IC card LSI  150  side can be prevented as much as possible during charging. 
         [0058]    Charging can be most efficiently performed when the threshold of the clamp circuit  157   a  is set to none of A to C, and the clamp circuit  157   a  is invalidated (OFF). This method is effective when the charging block  160  side has entered a state in which power supplied from the contactless charger  165  can be certainly consumed and no excessive voltage is applied to the contactless IC card LSI  150  side. 
         [0059]      FIG. 8  is a sequence diagram illustrating exchange of signals between the contactless charger (reader/writer-charger  165 ) and the units of the electronic device  100  according to the second embodiment. The same reference numerals are given to elements that are the same as or similar to those illustrated in  FIG. 6 , and overlapping descriptions thereof are omitted. In the sequence diagram of  FIG. 8 , steps S 11  to S 16  are the same as those illustrated in  FIG. 6 . Thereafter in the standby state, instead of an instruction to turn the switch  170 ′ in step S 17  in  FIG. 6 , an instruction to switch the clamp circuit  157   a  is given in step S 17   a  in the sequence diagram of  FIG. 8 . In the example described above, the clamp circuit  157   a  is switched to A or invalidated using the switch D. 
         [0060]    With the structure illustrated in  FIG. 7 , an electromotive force discarded by the contactless IC card LSI  150  when charging is performed can be minimized. That is, the antenna  101  and the tuning unit  110  can be shared between the two functions. Since the selector  170  is not used in this embodiment, an output of the tuning unit  110  remains connected to the clamp circuit  157   a  when charging is performed. Since power excited at the tip of the antenna  101  is consumed at the charging block  160 , protection of the contactless IC card LSI  150  does not become insufficient even when the clamp circuit  157   a  is invalidated or the threshold of the voltage level at which the clamp circuit  157   a  operates is increased. 
         [0061]    Although the preferred exemplary embodiments of the present invention have been described above, various modifications or changes other than those described above can be made. For example, although the cellular phone terminal has been described as the electronic device, the electronic device is not limited to the cellular phone terminal. The embodiments of the present invention are applicable to any electronic device such as a digital camera, a camcorder, a game machine, a portable player, or a headset. 
         [0062]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.