Abstract:
A folding electronic device includes an operation unit, a display unit, a memory unit, a pair of speakers, a detection switch, and a switch. A plurality of information input keys are arranged on the operation unit. The display unit is integrated with the operation unit so as to be foldable, and displays at least image information. Sound source data is stored in the memory unit. A pair of speakers for a left channel and a right channel can be driven in a closed state in which the display unit is folded. The detection switch detects the open state in which the display unit is not folded or the closed state in which the display unit is folded. The switch switches paths through which the sound source data stored in the memory unit is output to the pair of speakers on the basis of an output from the detection switch.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a folding electronic device and, more particularly, to a folding electronic device including left- and right-channel speakers which can be driven independently. 
     For the purpose of improving portability, most types of portable electronic devices (to be also simply referred to as electronic devices hereinafter) such as cellular phones are configured such that a display unit which displays character information or image information and an operation unit on which keys for information input are arranged are integrated into a foldable unit. As disclosed in Japanese Patent Laid-Open No. 2001-177609 (reference 1), some current folding cellular phones have a music function as well as a telephone function. 
     Of cellular phones with a music function, popular cellular phones are those which include left- and right-channel speakers which can be driven independently and are designed to improve acoustic quality by outputting stereo sounds. A folding cellular phone having such an arrangement allows the user to enjoy stereo sounds while watching images on the display unit by driving the left- and right-channel speakers even in the closed state of the cellular phone in which it is folded as well as in the open state in which the cellular phone is not folded. 
     As shown in  FIG. 7 , a conventional folding cellular phone  50  having left- and right-channel speakers which can be driven independently includes a radio transmission/reception unit  52  which transmits/receives radio signals through an extendible transmission/reception antenna  51 , a control unit  53  which forms the main part of the cellular phone  50 , a memory unit  55  which stores external sound source data downloaded through the radio transmission/reception unit  52 , internal sound source data, and the like as sound source data  54 , a detection switch  56  which detects the open or closed state of the cellular phone  50 , and a left (L)-channel speaker  57 L and right (R)-channel speaker  57 R which can be driven independently. 
     The control unit  53  is comprised of a switching control unit  58  formed of a CPU (Central Processing Unit) which controls the switching operation of a switch (to be described later) in accordance with the detection result obtained by the detection switch  56 , a left-channel DA (Digital to Analog) converter  59 L and right-channel DA converter  59 R which convert the sound source data  54  stored in the memory unit  55  into analog data, and a left-channel amplifier  60 L and right-channel amplifier  60 R which respectively amplify outputs from the DA converters  59 L and  59 R. Reference numeral  61  denotes a pull-up resistor connected to a power supply; and  62 L and  62 R, capacitors. 
       FIG. 8  shows another conventional cellular phone having left- and right-channel amplifiers formed of BTL (Balanced Transformerless Amplifier) amplifiers. A folding cellular phone  70  includes a left-channel BTL amplifier  72 L and right-channel BTL amplifier  72 R. The BTL amplifier  72 L is comprised of first and second amplifiers  71 A and  71 B which amplify an output from the left-channel DA converter  59 L. The BTL amplifier  72 R is comprised of third and fourth amplifiers  74 A and  74 B which amplify an output from the right-channel DA converter  59 R. Phase inversion circuits  75 L and  75 R are respectively connected to the input terminals of the amplifier  71 B of the BTL amplifier  72 L and the amplifier  74 B of the BTL amplifier  72 R. Except for this, the arrangement of this cellular phone is almost the same as that shown in  FIG. 7 . Therefore, the same reference numerals as in  FIG. 7  denote the same components in  FIG. 8 , and a description thereof will be omitted. 
     In the conventional folding cellular phones  50  and  70  shown in  FIGS. 7 and 8 , sounds output from the speakers  57 L and  57 R flow in laterally opposite directions in the open state and closed state. This results in unnatural sound reproduction in terms of human hearing sense. More specifically, in the open state, stereo sounds are output from the speakers  57 L and  57 R in synchronism with images on the display unit, and hence natural sounds can be produced in terms of human hearing sense like sounds produced when a car passes by. In the closed state, however, since the positions of the speakers  57 L and  57 R become laterally opposite to those in the open state, output stereo sounds are not synchronized with images. For this reason, the sounds inevitably become unnatural in terms of human hearing sense. 
     An audio set designed to improve such unnaturalness in terms of human hearing sense is disclosed in, for example, Japanese Patent Laid-Open No. 2002-78073 (reference 2). As shown in  FIG. 9A , in the audio set disclosed in reference 2, a main body  100  includes left and right speaker boxes  103  and  102  respectively housing speakers  107  and  106 , which are provided on side surfaces of the main body so as to be pivotal in the back-and-forth direction as indicated by the arrows. This audio set is provided with an angle detection means (not shown) for detecting a state in which the boxes  103  and  102  pivot backward through 90° or more as shown in  FIG. 9B . In such an arrangement, when the angle detection means detects that both the left and right speaker boxes  103  and  102  have pivoted backward through 90° or more, drive signals to the speakers  107  and  106  are interchanged. 
     In the audio set disclosed in reference 2, since control is made to interchange drive signals to the speakers  107  and  106  when the angle detection means mechanically detects that the speakers  107  and  106  have pivoted through a predetermined angle or more, the control becomes complicated. In addition, since this set requires the speaker boxes  103  and  102  housing the speakers  107  and  106 , it is difficult to apply this technique to folding electronic devices like folding cellular phones which are required to satisfy conditions for excellent portability in terms of size, weight, and the like. 
     These problems will be described in detail. In the audio set disclosed in reference 2, the speaker boxes  103  and  102  are configured to pivot backward through 90° or more from the open state to the closed state. For this reason, only when the speaker boxes  103  and  102  have pivoted through 90° or more, drive signals to the speakers  107  and  106  must be interchanged. This complicates the control. 
     The audio set disclosed in reference 2 is directed to an electronic device which is not required to have portability in terms of size, weight, and the like and allowed to include the speaker boxes  103  and  102  housing the speakers  107  and  106 . It is difficult for an electronic device required to satisfy conditions for excellent portability in terms of size, weight, and the like to include the speaker boxes  103  and  102  housing the speakers  107  and  106 . Even if a device includes the speaker boxes  103  and  102 , it is practically impossible to pivot the speaker boxes  103  and  102  to the back side of the main body. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a folding electronic device which can achieve natural sound reproduction in terms of human hearing sense even when left and right speakers are set in the closed state. 
     In order to achieve the above object, according to the present invention, there is provided a folding electronic device comprising an operation unit on which a plurality of information input keys are arranged, a display unit which is integrated with the operation unit so as to be foldable, and displays at least image information, a memory unit in which sound source data is stored, a pair of speakers for a left channel and a right channel which can be driven in a closed state in which the display unit is folded, a detection switch which detects an open state in which the display unit is not folded or the closed state in which the display unit is folded, and a switch which switches paths through which the sound source data stored in the memory unit is output to the pair of speakers on the basis of an output from the detection switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the arrangement of a folding electronic device according to the first embodiment of the present invention; 
         FIG. 2  is a plan view showing the open state of the electronic device shown in  FIG. 1 ; 
         FIG. 3  is a plan view showing the closed state of the electronic device shown in  FIG. 1 ; 
         FIG. 4  is a block diagram showing the arrangement of a folding electronic device according to the second embodiment of the present invention; 
         FIG. 5  is a block diagram showing the arrangement of a folding electronic device according to the third embodiment of the present invention; 
         FIG. 6  is a block diagram showing the arrangement of a folding electronic device according to the fourth embodiment of the present invention; 
         FIG. 7  is a block diagram showing a conventional folding electronic device; 
         FIG. 8  is a block diagram showing another example of a conventional folding electronic device; and 
         FIGS. 9A and 9B  are perspective views respectively showing a state in which the speaker boxes of a conventional folding electronic device are open, and a state in which the speaker boxes are closed. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A folding electronic device according to the first embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . In this embodiment, a cellular phone will be described as an example of the electronic device. 
     As shown in  FIG. 1 , a folding cellular phone  10  according to this embodiment includes a radio transmission/reception unit  2  which transmits/receives radio signals through an extendible transmission/reception antenna  1 , a control unit  3  which forms the main part of the folding cellular phone  10 , a memory unit  5  which stores external sound source data downloaded by the radio transmission/reception unit  2 , internal sound source data, and the like as sound source data  4 , a detection switch  6  which detects the open state or closed state of the cellular phone  10 , and a left (L)-channel speaker  7 L and right (R)-channel speaker  7 R which are provided on the left and right sides of the lower portion of a display unit (to be described later) and can be driven independently. 
     The control unit  3  is comprised of a switching control unit  8  formed of a CPU which controls the switching operation of a switch (to be described later) in accordance with the detection result obtained by the detection switch  6 , a left-channel DA converter  9 L and right-channel DA converter  9 R which convert the sound source data  4  stored in the memory unit  5  into analog data, a left-channel amplifier  11 L and right-channel amplifier  11 R which respectively amplify outputs from the DA converters  9 L and  9 R, and a switch  12  which is controlled by the switching control unit  8  to perform switching operation of selectively connecting the outputs of the amplifiers  11 L and  11 R to the speakers  7 L and  7 R or the speakers  7 R and  7 L. 
     The switch  12  is connected between the amplifiers  11 L and  11 R and the speakers  7 L and  7 R and includes a first movable contact piece  12 A which is normally connected to the speaker  7 L, and a second movable contact piece  12 B which is normally connected to the speaker  7 R. Reference numeral  13  denotes a pull-up resistor connected to a power supply;  14 L, a left-channel capacitor connected between the movable contact piece  12 A and the speaker  7 L; and  14 R, a right-channel capacitor connected between the movable contact piece  12 B and the speaker  7 R. 
     The operation of the folding cellular phone  10  having the above arrangement will be described next. 
     &lt;Open State&gt; 
     As shown in  FIG. 1 , when the detection switch  6  detects the open state of the folding cellular phone  10 , the switching control unit  8  performs control to connect the movable contact pieces  12 A and  12 B of the switch  12  to the amplifiers  11 L and  11 R, respectively. This forms a path through which the output of the DA converter  9 L is connected to the speaker  7 L through the amplifier  11 L and the movable contact piece  12 A of the switch  12 . A path is also formed through which the output of the DA converter  9 R is connected to the speaker  7 R through the amplifier  11 R and the movable contact piece  12 B of the switch  12 . 
     As shown in  FIG. 2 , the folding cellular phone  10  of this embodiment is configured such that a display unit  15  and operation unit  16  are integrated into a foldable unit, and includes the speakers  7 L and  7 R which can be driven independently, as described above. The foldable display unit  15  has two display surfaces  15   a  and  15   b  on the inner surface side (the inner side in the folded state) and the outer surface side (the outer side in the folded state). Identical images are simultaneously displayed or switched/displayed on the display surfaces  15   a  and  15   b . In this case, the images on the display surfaces  15   a  and  15   b  are rightside left. 
     In the folding cellular phone  10  having the above arrangement, sounds are output from the speakers  7 L and  7 R in synchronism with images on the display unit  15 . For this reason, stereo sounds matching images on the display surface  15   a  can be obtained from the speakers  7 L and  7 R, and hence natural sounds can be produced in terms of human hearing sense. 
     &lt;Closed State&gt; 
     When the detection switch  6  detects the closed state of the cellular phone, the switching control unit  8  performs control to connect the movable contact pieces  12 A and  12 B of the switch  12  to the amplifiers  11 R and  11 L, respectively. This forms a path through which the output of the DA converter  9 L is connected to the speaker  7 R through the amplifier  11 L and the movable contact piece  12 B of the switch  12 . A path is also formed through which the output of the DA converter  9 R is connected to the speaker  7 L through the amplifier  11 R and the movable contact piece  12 A of the switch  12 . 
     As shown in  FIG. 3 , therefore, in the folding cellular phone  10 , even if the positions of the speakers  7 L and  7 R become laterally opposite to those in the open state, right- and left-channel sounds are output from the speakers  7 L and  7 R, respectively, in synchronism with images on the display unit  15 . For this reason, stereo sounds matching images on the display surface  15   b  can be obtained from the speakers  7 L and  7 R, and hence natural sounds can be produced in terms of human hearing sense as in the open state. 
     The folding cellular phone of this embodiment is configured such that the display unit and operation unit are integrated into a foldable unit, and includes the left- and right-channel speakers which can be driven independently. According to this embodiment, since outputs from the speakers  7 L and  7 R are laterally switched in the open state and the closed state, stereo sounds synchronized with images are output even in the closed state as in the open state. Therefore, natural sounds can be produced in terms of human hearing sense. 
     A folding electronic device according to the second embodiment of the present invention will be described next with reference to  FIG. 4 . 
     The folding electronic device of this embodiment differs from that of the first embodiment in that a switch is connected between DA converters  9 L and  9 R and amplifiers  11 L and  11 R. In this embodiment as well, a cellular phone will be described as an example of the electronic device. 
     As shown in  FIG. 4 , in a folding cellular phone  20  of this embodiment, a switch  12  is connected to the input stages of the channel amplifiers  11 L and  11 R. That is, the switch  12  switches and connects the DA converters  9 L and  9 R to the amplifiers  11 L and  11 R under the control of the switching control unit  8 . With this operation, outputs from the DA converters  9 L and  9 R are switched and output from speakers  7 L and  7 R through the amplifiers  11 L and  11 R. 
     Except for this, the arrangement of this embodiment is the same as that of the first embodiment. Therefore, the same reference numerals as in  FIG. 1  denote the same parts in  FIG. 4 , and a description thereof will be omitted. 
     A folding electronic device according to the third embodiment of the present invention will be described next with reference to  FIG. 5 . The folding electronic device of this embodiment differs from that of the first embodiment in that amplifiers are formed of BTL amplifiers. 
     As shown in  FIG. 5 , a folding cellular phone  30  according to this embodiment includes a left-channel BTL amplifier  18 L comprised of a pair of parallel-connected amplifiers  17 A and  17 B which amplify an output from a DA converter  9 L, and a right-channel BTL amplifier  18 R comprised of a pair of parallel-connected amplifiers  19 A and  19 B which amplify an output from a DA converter  9 R. Phase inversion circuits  22 L and  22 R are respectively connected to the input stage of the parallel-connected amplifier  17 B of the BTL amplifier  18 L and the input stage of the parallel-connected amplifier  19 B of the BTL amplifier  18 R. 
     A switch  23  controlled by a switching control unit  8  has a first movable contact piece  23 A and second movable contact piece  23 B which are normally connected to a speaker  7 L, and a third movable contact piece  23 C and fourth movable contact piece  23 D which are normally connected to a speaker  7 R. The movable contact pieces  23 A and  23 C are switched to select either the amplifier  17 A of the BTL amplifier  18 L or the amplifier  19 A of the BTL amplifier  18 L. The movable contact pieces  23 B and  23 D are switched to select either the amplifier  17 B of the BTL amplifier  18 L or the amplifier  19 B of the BTL amplifier  18 R. 
     In the BTL amplifiers  18 L and  18 R, voltages applied to the loads are doubled according to the driving scheme for the amplifiers. Therefore, the amplifiers can supply four-fold output power. This makes it possible to obtain a large output with a low power supply voltage. 
     The operation of the folding cellular phone  30  having the above arrangement will be described next. 
     &lt;Open State&gt; 
     As shown in  FIG. 5 , when a detection switch  6  detects the open state of the cellular phone, the switching control unit  8  performs control to connect the movable contact pieces  23 A and  23 B of the switch  23  to the amplifiers  17 A and  17 B of the BTL amplifier  18 L, respectively. The switching control unit  8  also performs control to connect the movable contact pieces  23 C and  23 D to the amplifiers  19 A and  19 B of the BTL amplifier  18 R. This forms a path through which the output of the DA converter  9 L is connected to the speaker  7 L through the BTL amplifier  18 L and the movable contact pieces  23 A and  23 B of the switch  23 . A path is also formed through which the output of the DA converter  9 R is connected to the speaker  7 R through the BTL amplifier  18 R and the movable contact pieces  23 C and  23 D of the switch  23 . 
     As shown in  FIG. 2 , therefore, left- and right-channel sounds are output from the speakers  7 L and  7 R, respectively, in synchronism with images on a display surface  15   a  of a display unit  15 . Since stereo sounds matching images can be obtained from the speakers  7 L and  7 R in this manner, natural sounds can be produced in terms of human hearing sense. 
     &lt;Closed State&gt; 
     When a detection switch  6  detects the closed state of the cellular phone, the switching control unit  8  performs control to connect the movable contact pieces  23 A and  23 B of the switch  23  to the amplifiers  19 A and  19 B of the BTL amplifier  18 R, respectively. The switching control unit  8  also performs control to connect the movable contact pieces  23 C and  23 D to the amplifiers  17 A and  17 B of the BTL amplifier  18 L. This forms a path through which the output of the DA converter  9 L is connected to the speaker  7 R through the BTL amplifier  18 L and the movable contact pieces  23 C and  23 D of the switch  23 . A path is also formed through which the output of the DA converter  9 R is connected to the speaker  7 L through the BTL amplifier  18 R and the movable contact pieces  23 A and  23 B of the switch  23 . 
     As shown in  FIG. 3 , even if the positions of the speakers  7 L and  7 R become laterally opposite to those in the open state, right- and left-channel sounds are output from the speakers  7 L and  7 R in synchronism with images on a display surface  15   b  of the display unit  15 . Since stereo sounds matching images can be obtained from the speakers  7 L and  7 R, natural sounds can be produced in terms of human hearing sense as in the open state. 
     Except for this, the arrangement of this embodiment is the same as that of the first embodiment. Therefore, the same reference numerals as in  FIG. 1  denote the same parts in  FIG. 5 , and a description thereof will be omitted. According to this embodiment, effects similar to those of the first embodiment can be obtained. In addition, according to this embodiment, since BTL amplifiers are used, a large output can be obtained with a low power supply voltage. 
     A folding electronic device according to the fourth embodiment of the present invention will be described next with reference to  FIG. 6 . The folding electronic device according to this embodiment differs from that of the third embodiment in that a switch is connected to the input stage of each amplifier. 
     As shown in  FIG. 6 , in a folding cellular phone  40  according to this embodiment, a switch  12  is connected to the input stages of BTL amplifiers  18 L and  18 R. That is, the switch  12  switches and connects DA converters  9 L and  9 R to the BTL amplifiers  18 L and  18 R under the control of a switching control unit  8 . With this operation, outputs from the DA converters  9 L and  9 R are switched and output to speakers  7 L and  7 R through the BTL amplifiers  18 L and  18 R. 
     Except for this, the arrangement of this embodiment is the same as that of the third embodiment. Therefore, the same reference numerals as in  FIG. 5  denote the same parts in  FIG. 6 , and a description thereof will be omitted. According to this embodiment, effects similar to those of the third embodiment can be obtained. 
     Although the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, specific arrangements are not limited to the embodiments, and the present invention incorporates changes in design and the like within the spirit and scope of the present invention. For example, in each embodiment, the present invention is applied to a cellular phone. However, the present invention is not limited to cellular phones and can be applied to electronic devices in general, e.g., PDAs (Personal Digital Assistants) and portable GPS (Global Positioning Systems). 
     As has been described above, according to the present invention, in an electronic device which is configured such that a display unit and operation unit are integrated into a foldable unit, and includes left- and right-channel speakers which can be driven independently, stereo sounds synchronized with images on a display surface are output even in the closed state in the same manner as in the open state, thereby producing natural sounds in terms of human hearing sense.