Patent Publication Number: US-2003224837-A1

Title: Portable telephone

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a portable telephone, and more particularly to a portable telephone having a rechargeable battery as a power source.  
       [0003] 2. Description of the Prior Art  
       [0004] A conventional portable telephone or cellular phone having a rechargeable battery as a power source will be described with reference to FIG. 1A, FIG. 1B, FIG. 2 and FIG. 3. FIG. 1A is a front view of the conventional portable telephone and FIG. 1B is a rear view thereof. A rechargeable battery  2  having recharging terminals  3  is mounted on a rear surface of the portable telephone  1 .  
       [0005]FIG. 2 is a cross sectional view of the portable telephone  1  shown in FIG. 1A and FIG. 1B. The rechargeable battery  2  is provided in a casing of a body of the portable telephone  1  and supplies electric power to a circuit board  4  such as printed multilayered circuit board, which includes a radio circuit, a receiving circuit, a transmitting circuit and a control circuit, etc., mounted thereon, through a pair of power source pins  6 . Further, an antenna  5  is connected to the radio circuit of the circuit board  4 .  
       [0006] In general, the rechargeable battery is detachably mounted in the body of the portable telephone for the purpose of battery exchange such that the rechargeable battery  2  constitutes a portion of the casing of the portable telephone when mounted therein. FIG. 3 is a plan view of the rechargeable battery  2  on the side of the circuit board of the portable telephone. A pair of power source terminals  7  for supplying power to the circuit board are also provided on the rechargeable battery  2 . A surface area of the rechargeable battery other than the power source terminals is covered by an insulating resin film.  
       [0007] In the conventional portable telephone mentioned above, radio wave is generated by predetermined high frequency current in the antenna  5 . In order to reduce a whole size of the portable telephone, the antenna  5  is made shorter than a half of wavelength at a predetermined frequency. Therefore, high frequency current flows in not only the antenna  5  but also the circuit board  4 . When the rechargeable battery  2  is electrically connected to the circuit board  4  through the power source pins  6 , the rechargeable battery  2  and the circuit board  4  opposing to the rechargeable battery  2  form a parallel flat structure with the power source pins  6  as short-circuiting points. Therefore, high frequency current or antenna current in the circuit board  4  is reflected by the power source pins  6  and the reflected high frequency current is further reflected by an inlet of the high frequency current to the circuit board. Consequently, high frequency current exists in a portion of the circuit board, which is defined between the circuit board and the rechargeable battery as a standing wave, causing high frequency current to be increased substantially. A large amount of high frequency current flowing through the circuit board  4  may be branched to an LSI provided on the circuit board  4  in the area defined between the circuit board  4  and the rechargeable battery  2 , leading to a malfunction of the LSI. For example, there may be a case where a voice quality in talking performed by the telephone is degraded due to pulse noise in a voice signal, which is generated by high frequency current strayed from the circuit board into the LSI constituting the receiving circuit.  
       SUMMARY OF THE INVENTION  
       [0008] An object of the present invention is to provide a portable telephone, which can prevent an LSI provided on a circuit board in the portable telephone from malfunctioning by transmitting high frequency current increased by a rechargeable battery and can provide a good communication performance.  
       [0009] The portable telephone including a rechargeable battery, according to the present invention, is featured by that the rechargeable battery has an electrically conductive outer cover grounded at a plurality of locations to a ground layer of a circuit board provided within a casing of the portable telephone. Particularly, it is preferably that a plurality of grounding terminals are provided on the electrically conductive outer cover of the rechargeable battery and the grounding terminals are arranged in a peripheral portion of the rechargeable battery. Alternatively, the grounding terminals may be arranged at or in the vicinity of four corners of the rechargeable battery.  
       [0010] Further, the rechargeable battery may be detachable from the portable telephone and a plurality of grounding pins connected to the ground layer of the circuit board may be provided such that the grounding pins are in contact with the plurality of the grounding terminals provided on the electrically conductive outer cover of the rechargeable battery.  
       [0011] In the portable telephone according to the present invention in which the electrically conductive outer cover of the rechargeable battery is connected to the ground layer of the circuit board at the plurality of locations, high frequency current of the circuit board flows through the outer cover of the rechargeable battery, so that high frequency current of the circuit board on which the LSI is mounted in an area thereof defined between the circuit board and the rechargeable battery is substantially reduced. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012]FIG. 1A is a front view of a conventional portable telephone;  
     [0013]FIG. 1B is a rear view of the portable telephone shown in FIG. 1A;  
     [0014]FIG. 2 is a cross sectional view of the conventional portable telephone;  
     [0015]FIG. 3 is a plan view of a conventional rechargeable battery;  
     [0016]FIG. 4 is a cross section of a portable telephone according to an embodiment of the present invention;  
     [0017]FIG. 5 is a rear view of the portable telephone of the present invention, showing a plan view of a battery housing with a battery being detached;  
     [0018]FIG. 6A is a plan view of a surface of a rechargeable battery faced opposing to a circuit board; and  
     [0019]FIG. 6B is a cross section taken along a line I-I in FIG. 6A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0020] An embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a cross section of a portable telephone according to an embodiment of the present invention. For simplicity of illustration, a display portion and operation buttons are omitted.  
     [0021] In FIG. 4, the circuit board  4  is a multi-layered printed circuit provided with a ground layer  40  inside. An integrated circuit element  41  such as LSI, etc., is mounted on the circuit board  4 . The circuit board  4  is electrically connected to an antenna  5  and a rechargeable battery  2 . The circuit board  4  and the rechargeable battery  2  are electrically connected to each other through a pair of power source pins  6  and a plurality of grounding pins  8 . Further, a pair of charging terminals  3  are provided on the rechargeable battery.  
     [0022]FIG. 5 is a plan view of a battery receiving portion  120  of the portable telephone  1  with the rechargeable battery being removed. The grounding pins  8  are provided in the vicinity of four corners of a bottom surface of the battery receiving portion, respectively, and the power source pins  6  are provided on the bottom surface of the battery receiving portion. These pins  6  and  8  are electrically connected to the circuit board  4  through holes provided on the bottom surface of the battery receiving portion made of insulating material.  
     [0023] As shown in FIG. 6A and FIG. 6B, the rechargeable battery of the portable telephone of the present invention includes a flat rectangular battery portion  200 , which may be a lithium ion battery, a metal cover  29  of the battery portion  200  and an insulating film  20  covering the metal cover  29 . Four corner portions of the insulating film  20  on the metal cover  29  on the side of the circuit board are removed to expose corresponding portions of the metal cover  29  corresponding in position to the respective grounding pins  8  shown in FIG. 5. Further, the rechargeable battery  2  also has a pair of power source terminals  7 . On the circuit board  4 , a radio circuit electrically connected to the antenna  5 , a receiving circuit, a transmitting circuit and a control circuit, etc., which are well known, are mounted (not shown).  
     [0024] When the rechargeable battery  2  having the recharging terminals  3  is received in the battery receiving portion  120 , the second battery  2  supplies electric power to the circuit board  4  through the power source terminals  7  and the power source pins  6 . Simultaneously therewith, the grounding terminals  9  constituted by the exposed portions of the metal cover  29  of the rechargeable battery portion  200  are connected to the ground layer  40  of the circuit board  4  through the grounding pins  8  provided on the side of the bottom of the battery receiving portion  120  of the portable telephone  1 .  
     [0025] In this construction, high frequency current in the antenna  5  and the circuit board  4  flows to the metal cover  29  of the rechargeable battery  2  through the grounding pins  8  and the grounding terminals  9 , so that such high frequency current does not flow into a portion of the circuit board  4 , which is defined between the circuit board  4  and the rechargeable battery. Therefore, high frequency current in the portion of the circuit board  4 , which is defined between the circuit board and the rechargeable battery, is substantially reduced, compared with the conventional portable telephone in which high frequency current exists in the circuit board as a standing wave. This is because the electrically conductive outer cover  29  of the rechargeable battery  2  connected at the plurality of locations to the ground of the circuit board  4  constitute a shield structure. Therefore, the flow of high frequency current into the LSI provided on the portion of the circuit board  4 , which is defined between the circuit board  4  and the rechargeable battery  2 , is prevented, so that malfunction of the LSI is prevented.  
     [0026] As for the electrically conductive outer cover of the present invention, such kind of metal used for the negative electrode of the battery can be used. In that case, the ground layer of the circuit board can be electrically connected to the electrically conductive outer cover of the battery through the electrical conductive member in a direct current (D.C.) mode.  
     [0027] When the electrically conductive outer cover of the battery is made of the metal common to the positive electrode of the battery, the electrically outer cover of the battery cannot be connected to the ground layer of the circuit board. To avoid the short circuiting between the ground circuit and the outer cover, the metal for the positive electrode can be electrically connected to the ground layer through a dielectric material in a high frequency coupling or radio frequency coupling manner. To this end, the grounding pins  8  shown in FIG. 4 should be removed and the bottom portion of the battery receiving portion which is made of insulating material is used as an dielectric member to achieve the high frequency coupling between the ground layer and the outer cover common to the positive electrode.  
     [0028] According to the present invention, the outer cover of the battery is not necessarily connected to the negative electrode or positive electrode. Typical material for the outer cover of the battery of the present invention is selected from one of such metal as aluminum, iron and stainless steel.  
     [0029] The present invention is not limited to the described embodiment in which the present invention is applied to the portable telephone of one box type. The present invention can be applied to a folding telephone. In the latter case, it is enough that the grounding terminals provided in the peripheral portion of the electrically conducive outer cover of the rechargeable battery provided in one of two body portions of the folding type portable telephone are grounded at a plurality of locations to a ground layer of a circuit board provided within the body portion of the portable telephone, through the grounding pins.  
     [0030] In the above-description, the grounding points are located at four corners. However, according to the present invention, since the suppressing effect for reducing an antenna current running through the ground layer of the circuit board can be achieved by providing at least two grounding points along a longitudinal direction of the circuit board, the scope of the present invention cannot be restricted the embodiments shown in the drawings. When the number of the grounding points are increased, the above-stated suppressing effect can be increased and thus the number of the grounding points may be six or eight in total along the peripheral region. In view of the cost saving, four corner grounding points shown in the embodiment of the present invention is appropriate.  
     [0031] As described above, according to the present invention, a malfunction of an active device such as an LSI provided between a circuit board and a rechargeable battery is prevented, resulting in a good communication performance of the portable telephone. This is because high frequency current in the portion of the circuit board  4  between the circuit board and the rechargeable battery  2  is substantially reduced and, as a result thereof, the flow of high frequency current into the LSI provided on the portion of the circuit board  4  in an area between the circuit board and the rechargeable battery is restricted.