Abstract:
A wireless communication device includes: a first case having an antenna; and a second case connected to the first case, and having a first conductor at a position that is opposite to the antenna when the first case and the second case overlay each other, a second conductor at a position different from the position at which the first conductor is disposed, and a switch that switches an electrical connection state of the first conductor and the second conductor, wherein the switch switches the electrical connection state to disconnect state when the switch detects that the first case and the second case overlay each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-285129 filed on Dec. 21, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a wireless communication device that has an antenna in its case. 
       BACKGROUND 
       [0003]    To meet demands for portability and ease of operation, a mobile terminal device such as a mobile telephone uses a so-called folding structure in which divided cases are mutually connected by a hinge so as to openable and closable. The antenna characteristics of an antenna mounted in this type of mobile terminal device are important parameters in maintaining stable communication characteristics and assuring other communication quality. 
         [0004]    As for an antenna mounted in a mobile communication device, a communication terminal in which two cases each have a conductor is disclosed, the conductors of the two cases being capacitively, inductively, or conductively coupled to each other. 
         [0005]    The antenna in the communication terminal described in, for example, Japanese Laid-open Patent Publication No. 2004-134975 is assumed to be pulled out when the antenna is used. With recent communication terminals, however, built-in antennas are mainly used to meet a demand for small cases. 
         [0006]      FIGS. 1A and 1B  illustrate the principle of operation used when the technology described in Japanese Laid-open Patent Publication No. 2004-134975 is applied to a folding-type mobile telephone having a built-in antenna.  FIG. 1A  is a side view when the cases of this type of folding-type mobile telephone are open. With a mobile terminal device  2 , which is an exemplary folding-type mobile telephone, a fixed part (case on the keyboard side)  4  and a movable part (case on the display side)  6  are mutually connected by a hinge  8  so as to be openable and closable. 
         [0007]    In  FIG. 1B , the folding-type mobile telephone is represented with an antenna circuit. In an antenna operation with the cases open, a metal or a material including a metal in the fixed part  4  forms a first antenna element  40 , and a metal or a material including a metal in the movable part  6  forms a second antenna element  60 . A built-in antenna  16  operates as a resonator. The first antenna element  40  and second antenna element  60  resonate with the built-in antenna  16 . For functional reasons for the mobile terminal device  2 , effects from the hand, head, and other regions of a person are avoided to reduce deterioration in the antenna characteristics by placing the built-in antenna  16  in the vicinity of the hinge  8 , which is placed in a position distant from the hand and head. To cause resonance, in general, the first antenna element  40  and second antenna element  60  each have an electrical length of λ/4 to match the frequency band used in communication, forming a dipole antenna that has an electrical length of about λ/2 as the entire device length with the cases open. As illustrated by the arrows in  FIG. 1B , a case current I (high-frequency current) flows in the first antenna element  40  and second antenna element  60 . The larger the case current is, the better the antenna is. 
         [0008]    Although, the antenna elements of the folding-type mobile telephone illustrated in  FIGS. 1A and 1B  are formed with the entire metal members included in the cases,  FIGS. 2A and 2B  illustrate an example in which ground layers on circuit boards in a folding-type mobile telephone are used as antenna elements.  FIG. 2A  illustrates a state in which the cases are open. A first ground layer  44  is formed on a first circuit board  42  in the fixed part  4 . However, the first ground layer  44  is not present in an area, on the first circuit board  42 , that is close to the hinge  8 . Instead, in this area, a built-in antenna  16  is connected through a feeding point  18 . The area is referred to as an antenna area X 1 , as illustrated in  FIG. 2B . In the movable part  6  as well, a second ground layer  64  is formed on a second circuit board  62 . The second ground layer  64  is capacitively coupled to the built-in antenna  16 . A combination of the first ground layer  44  and second ground layer  64  forms an antenna element. 
         [0009]    When the cases are closed as illustrated in  FIG. 2B , however, the antenna area X 1 , in which the built-in antenna  16  is disposed, overlaps part of the second ground layer  64 . Then, the second ground layer  64  shields radio waves directed to the built-in antenna  16 , and the built-in antenna  16  and second ground layer  64  are capacitively coupled to each other. As a result, electric power to be radiated from the antenna flows into ground through the second ground layer  64 . This is problematic in that electric power to be radiated from the antenna is lost and the antenna characteristics are deteriorated. 
       SUMMARY 
       [0010]    According to an aspect of the embodiment, a wireless communication device includes: a first case having an antenna; and a second case connected to the first case, and having a first conductor at a position that is opposite to the antenna when the first case and the second case overlay each other, a second conductor at a position different from the position at which the first conductor is disposed, and a switch that switches an electrical connection state of the first conductor and the second conductor, wherein the switch switches the electrical connection state to disconnect state when the switch detects that the first case and the second case overlay each other. 
         [0011]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0012]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIGS. 1A and 1B  illustrate the principle of operation of an antenna of a general folding-type mobile telephone. 
           [0014]      FIGS. 2A and 2B  illustrate an example in which ground layers on circuit boards in a mobile telephone are used as antenna elements. 
           [0015]      FIGS. 3A and 3B  conceptually illustrate the internal structure of a folding-type mobile telephone to which the technology in this disclosure is applied. 
           [0016]      FIGS. 4A and 4B  also conceptually illustrate the internal structure of a folding-type mobile telephone to which the technology in this disclosure is applied. 
           [0017]      FIGS. 5A and 5B  illustrate an exemplary switch circuit. 
           [0018]      FIGS. 6A and 6B  illustrate a relationship between switch operations and the open and closed states of cases. 
           [0019]      FIGS. 7A and 7B  illustrate a relationship between antenna states and the open and closed states of the cases. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    A preferred embodiment of the technology in this disclosure will be described in detail with reference to the attached drawings. 
         [0021]      FIGS. 3A and 3B  illustrate the structure of a folding-type mobile telephone to which the technology in this disclosure is applied. Specifically,  FIGS. 3A and 3B  conceptually illustrate the internal structure of a folding-type mobile telephone with its cases open. A mobile terminal device  2  is formed by connecting a fixed part (case on a keyboard side)  4  and a movable part (case on a display side)  6  are mutually connected by a hinge  8  so as to be openable and closable. A first circuit board  42  included in the fixed part  4  and a second circuit board  62  included in the movable part  6  are mutually connected by a flexible cable  10  passing through the hinge  8 . The flexible cable  10  transfers control signals and other data between the first circuit board  42  and the second circuit board  62 . The fixed part  4  has a sensor  14  at a position opposite to the movable part  6 . The movable part  6  has a magnet  22  at a position opposite to the sensor  14 . The sensor  14 , which is a magneto-resistive (MR) sensor or another type of sensor that senses magnetism, is used to sense the open and closed states of the cases. The sensor  14  and magnet  22  may be a sensor and magnet that are widely used to control electric power to the display part of a general folding-type mobile telephone. The sensor  14  is disposed at a position at which the distance from the hinge  8  to the sensor  14  is almost the same as the distance from the hinge  8  to the magnet  22 , and the magnetism from the magnet  22  to the sensor  14  changes when the cases are opened and closed. Control signals sent from the sensor  14  are transferred to a switch  12  provided on the second circuit board  62  through the first circuit board  42  in the fixed part  4 , the flexible cable  10 , and the second circuit board  62  in the movable part  6 . The sensor  14  may be disposed on the second circuit board  62  in the movable part  6 , and the magnet  22  may be disposed at a position, opposite to the movable part  6 , on the fixed part  4 . 
         [0022]    A first ground layer  44 , which has a thickness of, for example, about 1 mm or less, is provided on the first circuit board  42  in the fixed part  4 , at a position at which the first ground layer  44  does not structurally interfere with operation keys, a microphone, and other constituent components included in the fixed part  4 . Although, in this embodiment, the first ground layer  44  is disposed on the first circuit board  42 , this is not a limitation. The first ground layer  44  may be a metal pattern or metal foil provided in the first circuit board  42  or may be formed with all metals included in the fixed part  4 , including the cases and the parts. 
         [0023]    The first ground layer  44  is not present in an area, on the first circuit board  42 , that is close to the hinge  8 . Instead, in this area, a built-in antenna  16  is connected through a feeding point  18  on a surface of the first circuit board  42 , the surface being opposite to the surface on which the first ground layer  44  is formed. The built-in antenna  16  is a meandering or linear antenna with an electrical length of λ/4, which is one-fourth of the wavelength λ of a desired frequency f. An end of the feeding point  18  is connected to a wireless signal processing circuit provided on the first circuit board  42  through an impedance matching circuit (not illustrated). This area, which excludes the first ground layer  44  and extends from the built-in antenna  16  to the impedance matching circuit, is referred to as an antenna area  46 . 
         [0024]    A second ground layer (conductor)  64  is formed in an area, distant from the hinge  8 , on the second circuit board  62  in the movable part  6 . A display control circuit, a speaker control circuit, and the like are mounted on a second circuit board  62 , on which the second ground layer  64  is formed. A conductive layer  66 , made of a conductor, is formed in an area, close to the hinge  8 , on the second circuit board  62 . There is no circuit or the like in the area, on the second circuit board  62 , on which the conductive layer  66  is formed. The second ground layer  64  and conductive layer  66 , each having a thickness of, for example, about 1 mm, are disposed in the thin movable part  6  having a thickness of, for example, about 6 mm, at positions at which the second ground layer  64  and conductive layer  66  do not interfere with a speaker, display elements, and other constituent components therein. Alternatively, the second ground layer  64  and conductive layer  66  may be metal patterns provided on or in the second circuit board  62 . 
         [0025]    As illustrated in  FIG. 3B , the electrical length L 1  of the first ground layer  44  is λ/4 with respect to the frequency band used in communication. The total of the electrical length L 2  of the second ground layer  64  and the electrical length L 3  of the conductive layer  66  is λ/4 with respect to the frequency band, which is the same value as the electrical length L 1 . 
         [0026]    The switch  12  is disposed, on the second circuit board  62 , on the boundary between the second ground layer  64  and the conductive layer  66 . A terminal at an end of the switch  12  is connected to the second ground layer  64 , and a terminal at another end is connected to the conductive layer  66 . The switch  12  is structured as a P-intrinsic-N (PIN) diode, a single-pole/double-throw (SPDT) switch, or the like. The switch  12  selectively connects and disconnects the conductive layer  66  to and from the second ground layer  64 . 
         [0027]      FIGS. 4A and 4B  also illustrate the structure of a folding-type mobile telephone to which the technology in this disclosure is applied. Specifically,  FIGS. 4A and 4B  conceptually illustrate the internal structure of a folding-type mobile telephone with its cases closed. As illustrated in  FIGS. 4A and 4B , when the cases are closed, the conductive layer  66  is positioned in the vicinity of the built-in antenna  16  and parallel to it. The total of the length L 3  of the conductive layer  66  and a spacing L 4  between the conductive layer  66  and the second ground layer  64  is equal to the length of the antenna area  46 . 
         [0028]      FIGS. 5A and 5B  illustrate an example of a circuit that forms the switch  12  with a PIN diode. The switch  12  includes a PIN diode  30 , a choke coil  32 , a DC-cut capacitor  34 , and a resistor  36 .  FIG. 5A  illustrates an example in which the PIN diode  30  is oriented so that its anode faces the second ground layer  64  and its cathode faces the conductive layer  66 . An end of the resistor  36  is connected to the anode of the PIN diode  30 . Control signals are input from the sensor  14  to a terminal  38  provided at the other end of the resistor  36 . The cathode of the PIN diode  30  is connected to the conductive layer  66 . When there is no control signal from the sensor  14 , the PIN diode  30  is at a high impedance, preventing a current from flowing between the second ground layer  64  and the conductive layer  66 . When an active ON signal with a positive potential is input from the sensor  14  into the anode through the resistor  36 , the PIN diode  30  is forward biased, causing a current to flow into the second ground layer  64  through the PIN diode  30  and choke coil  32 . The conductive layer  66  and second ground layer  64  are thereby electrically connected to each other. The DC-cut capacitor  34  prevents the current directed to the PIN diode  30  from flowing into the second ground layer  64 . 
         [0029]      FIG. 5B  illustrates an example in which the PIN diode  30  is oriented so that its anode faces the conductive layer  66  and its cathode faces the second ground layer  64 . An end of the resistor  36  is connected to the cathode of the PIN diode  30 . Control signals are input from the sensor  14  to the terminal  38  at the other end of the resistor  36 . The anode is connected to the conductive layer  66 . When there is no control signal from the sensor  14 , the PIN diode  30  is at a high impedance, preventing a current from flowing between the second ground layer  64  and the conductive layer  66 . When an active ON signal with a negative potential is input from the sensor  14  into the cathode through the resistor  36 , the PIN diode  30  is forward biased, causing a current to flow from the second ground layer  64  into the choke coil  32  and PIN diode  30 . The conductive layer  66  and second ground layer  64  are thereby electrically connected to each other. The structure of the switch  12  is not limited to the structure illustrated in  FIGS. 5A and 5B . The switch  12  may be an electronic switch, a mechanical switch, or any other type of switch that is adaptable to high frequencies. 
         [0030]    Next, a switchover of an antenna operation will be described with reference to  FIGS. 6A ,  6 B,  7 A, and  7 B.  FIGS. 6A and 6B  illustrate a relationship between switch operations and the open and closed states of the cases.  FIGS. 7A and 7B  illustrate a relationship between antenna states and the open and closed states of the cases. 
         [0031]      FIG. 6A  is a block diagram illustrating the state of the switch  12  and sensor  14  when the fixed part  4  and movable part  6  of the mobile terminal device  2  are open as illustrated in  FIGS. 3A and 3B . Since, in this state, the sensor  14  and magnet  22  are placed at a distance from each other, the sensor  14  may not sense the magnetism of the magnet  22 . Accordingly, the sensor  14  sends an ON signal by which the switch  12  is placed in a closed state, and the second ground layer  64  and conductive layer  66  are thereby electrically short-circuited. As a result, as illustrated in  FIG. 7A , the second ground layer  64  and conductive layer  66  are capacitively coupled to the built-in antenna  16  and function as a resonator with an electrical length of λ/4, generating a resonant state with an electrical length of λ/2. 
         [0032]      FIG. 6B  is a block diagram illustrating the state of the switch  12  and sensor  14  when the fixed part  4  and movable part  6  of the mobile terminal device  2  are closed as illustrated in  FIGS. 4A and 4B . Since, in this state, the sensor  14  and magnet  22  are placed close to each other, the sensor  14  senses the magnetism of the magnet  22 . Accordingly, the sensor  14  sends an OFF signal by which the switch  12  is placed in an open state, and the second ground layer  64  and conductive layer  66  are thereby insulated from each other. That is, the conductive layer  66  present in the antenna area  46  illustrated in  FIG. 4B  is placed in a floating state. As a result, as illustrated in  FIG. 7B , only the built-in antenna  16  with an electrical length of λ/4, which is connected to the feeding point  18 , functions as an antenna element, forming a monopole antenna with an electrical length of λ/4. 
         [0033]    If, for example, the switch  12  is not provided, even when the fixed part  4  and movable part  6  of the mobile terminal device  2  are closed, the second ground layer  64  and conductive layer  66  remain electrically connected to each other. In this case, not only the second ground layer  64  and conductive layer  66  shield radio waves directed to the built-in antenna  16 , but also the built-in antenna  16  and conductive layer  66  are capacitively coupled to each other. As a result, electric power to be radiated from the antenna flows to the ground side of the second ground layer  64  through the conductive layer  66 . This is problematic in that electric power to be radiated from the antenna is lost and the antenna characteristics are deteriorated. 
         [0034]    In this embodiment, however, the conductive layer  66  is placed in the floating state by the switch  12 . This prevents the conductive layer  66  from being capacitively coupled to the built-in antenna  16  and the power to be radiated from the antenna does not flow into ground through the conductive layer  66 , reducing effects on the antenna characteristics. Although the conductive layer  66  is made of a metal, its electrical length is extremely shorter than λ/2, which is a resonance condition when the cases are closed, so radiation from the built-in antenna  16  is not interfered. 
         [0035]    This completes the detailed description of the preferred embodiment of this disclosure. This disclosure is not limited to a particular embodiment, but various modifications and variations of this disclosure are possible within an outline of this disclosure described in claims. Although, for example, an example of a folding-type mobile telephone has been described in the above embodiment, the structure described above may also be applied to slide mobile telephones, rotary mobile telephones, split-type mobile telephones, and any other types of mobile telephones that have a plurality of cases. 
         [0036]    The wireless communication device is not also limited to a mobile telephone. For example, the wireless communication device may be a PDA, notebook personal computer, or small-sized game machine that has an opening/closing mechanism. 
         [0037]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.