Abstract:
A method for displaying a battery voltage in a Time Division Multiple Access (TDMA) radio terminal is provided. The method includes the steps of detecting the battery voltage. A battery state corresponding to one of a plurality of battery state areas is displayed, when the battery voltage corresponds to one of the plurality of battery state areas. On the other hand, a previous battery state is displayed, when the battery voltage corresponds to one of a plurality of buffer zones. Each of the plurality of buffer zones are disposed between two of the plurality of battery state areas. The battery state being currently displayed is then stored as a previous battery state.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to Time Division Multiple Access (TDMA) radio terminals and, in particular, to a method for stably displaying a battery voltage which temporarily varies during transmission and reception periods in a TDMA radio terminal. 
     2. Description of the Related Art 
     In general, a radio terminal such as a cordless telephone has a battery state displaying function for measuring a current battery voltage and displaying the battery state on a liquid crystal display (LCD). The battery state is generally displayed in the following increments so that a user may recognize the present battery state: a full battery state, a half battery state, a low battery state and an empty battery state. 
     FIGS. 1 and 2 are diagrams respectively illustrating variations of the current consumption and the battery voltage during transmission and reception periods in a TDMA radio terminal. As shown in FIG. 1, in a TDMA radio terminal such as a Digital European Cordless Telephone (DECT), current consumption abruptly increases during transmission (Tx) and reception (Rx). Correspondingly, the battery voltage also abruptly changes during transmission and reception, as shown in FIG.  2 . Accordingly, it is difficult to stably display the battery voltage due to the continual variation of the battery voltage. 
     A conventional method for displaying battery voltage in a TDMA radio terminal will be described with respect to FIGS. 3 and 4. FIG. 3 is a diagram illustrating battery state areas in the conventional TDMA radio terminal, and FIG. 4 is a diagram illustrating a changing battery voltage with respect to a threshold level corresponding to two battery state areas. As shown in FIG. 3, the battery state is divided into four areas: a full battery state area, a half battery state area, a low battery state area and an empty battery state area. Conventionally, when the battery voltage exceeds a first threshold level (for the low battery state), the TDMA radio terminal displays the low battery state on the display, and when the battery voltage is lower than the first threshold level, the TDMA radio terminal displays the empty battery state. However, such a conventional method cannot stably display the battery state due to the continual variation of the battery voltage during the transmission and reception periods. 
     For example, assume that a battery voltage  411  changes during transmission and reception such that voltage  411  swings on (i.e., swings above and below) the first threshold level  412 , as shown in FIG.  4 . In such a case, the TDMA radio terminal displays the low battery state in an idle state and the empty battery state during transmission and reception due to the temporal change of the battery voltage. As a result, as transmission and reception are repeated at intervals, the terminal repeatedly changes the battery state, which decreases reliability of the battery state display function. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method for stably displaying a battery voltage which temporarily varies during transmission and reception periods in a TDMA radio terminal. 
     A method for displaying a battery voltage in a Time Division Multiple Access (TDMA) radio terminal is provided. The method includes the step of detecting the battery voltage. A battery state corresponding to one of a plurality of battery state areas is displayed, when the battery voltage corresponds to one of the plurality of battery state areas. On the other hand, a previous battery state is displayed, when the battery voltage corresponds to one of a plurality of buffer zones. Each of the plurality of buffer zones are disposed between two of the plurality of battery state areas. The battery state being currently displayed is then stored as a previous battery state. 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram illustrating variation of current consumption in a common TDMA radio terminal; 
     FIG. 2 is a diagram illustrating variation of a battery voltage in a common TDMA radio terminal; 
     FIG. 3 is a diagram illustrating threshold levels of the battery states in a conventional TDMA radio terminal; 
     FIG. 4 is a diagram illustrating a changing battery voltage with respect to a threshold level corresponding to two battery state areas; 
     FIG. 5 is a block diagram of a TDMA radio terminal to which the present invention is applied; 
     FIG. 6 is a diagram illustrating threshold levels for the respective battery states according to an embodiment of the present invention; 
     FIG. 7 is a diagram illustrating a state wherein a battery voltage swings on a threshold level during transmission and reception; 
     FIGS. 8A to  8 D are diagrams illustrating icons indicating a full battery state, a half battery state, a low battery state and an empty battery state, respectively; and 
     FIG. 9 is a flowchart illustrating a method for displaying a battery voltage according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well known functions or constructions are not described in detail so as not to obscure the invention in unnecessary detail. In the specification, the term “buffer zone” refers to a zone intervening between (i.e., disposed between) two adjacent battery state areas. 
     FIG. 5 illustrates a block diagram of a TDMA radio terminal to which the present invention is applied. A controller or Central Processing Unit (CPU)  10  is operatively coupled to an RF (Radio Frequency) transceiver  30 , a modem  40 , a voice processor  50 , a memory  20 , a key matrix (or key input unit)  60 , a display  70 , and a battery voltage detector  100 . The RF transceiver  30  is also operatively coupled to an antenna ANT and modem  40 . The voice processor  50  is also operatively coupled to a speaker (or earpiece) SPK, a microphone (or mouthpiece) MIC, and modem  40 . The battery voltage detector  100  is also operatively coupled to a battery  90  and a power supply  80 . 
     The CPU  10  controls the overall operations of the TDMA radio terminal. In particular, CPU  10  measures a battery voltage based upon a battery voltage detection signal output from battery voltage detector  100 , and displays a corresponding battery state on display  70 . The memory  20  includes a ROM (Read Only Memory) for storing a program for controlling the radio terminal and a RAM (Random Access Memory) for temporarily storing data generated during execution of the program. 
     The voice processor  50  converts an analog voice signal input from microphone MIC to Adaptive Differential Pulse Code Modulation (ADPCM) data, and processes a signal input from modem  40  to a voice signal to output the voice signal to speaker SPK. The modem  40  converts the ADPCM data input from voice processor  50  to a baseband signal to output the baseband signal to RF transceiver  30 , and converts a signal input from RF transceiver  30  to digital data to output the digital data to voice processor  50 . The RF transceiver  30  converts the analog baseband signal input from modem  40  to an RF signal to send the RF signal to a fixed part FP (or base unit) through a radio channel, and down-converts an RF signal received through antenna ANT to an analog baseband signal to output the analog baseband signal to modem  40 . 
     The key matrix  60 , which includes a plurality of numeric keys, provides CPU  10  with key data generated by the user&#39;s key manipulation. The display  70  (for example, an LCD), under the control of CPU  10 , displays operating states of the radio terminal (or portable unit). Further, display  70  displays a battery state in response to battery state display data output from CPU  10 . 
     The power supply  80  is provided with a power supply voltage from battery  90  and decreases the power supply voltage to specified levels for the respective parts. The battery  90 , which is normally put on the fixed part FP (not shown), is charged with a charge voltage supplied from the fixed part FP and provides the battery voltage to power supply  80 . The battery voltage detector  100  detects the voltage level of battery  90  and provides a corresponding battery voltage detection signal to CPU  10 . The battery voltage detector  100  includes an analog-to-digital (A/D) convertor for converting an analog voltage level signal from battery  90  to digital data. 
     FIG. 6 is a diagram illustrating threshold levels for the respective battery states according to an embodiment of the present invention. As illustrated, the battery state according to the present invention is divided into a full battery state area, a half battery state area, a low battery state area and an empty battery state area, wherein buffer zones intervene between adjacent battery state areas. Specifically, a first buffer zone intervenes between the full battery state area and the half battery state area, a second buffer zone intervenes between the half battery state area and the low battery state area, and a third buffer zone intervenes between the low battery state area and the empty battery state area. Further, the first to third buffer zones each have upper limits or thresholds ( 660 ,  640  and  620 ) and lower limits or thresholds ( 650 ,  630  and  610 ), respectively. That is, the entire battery state area is divided into four battery state areas and three buffer zones. 
     The CPU  10  determines whether or not the battery voltage detected by battery voltage detector . 100  corresponds to any one of the four battery state areas. If so, CPU  10  displays the corresponding battery state. However, when the detected battery voltage corresponds to any one of the three buffer zones, CPU  10  judges on which limit of a specific buffer zone the detected battery voltage swings. If the battery voltage swings on the upper limit of the specific buffer zone, CPU  10  displays the battery state corresponding to the battery state area situated over the above stated upper limit. However, when the battery voltage swings on the lower limit of the specific buffer zone, CPU  10  displays the battery state corresponding to the battery state area situated below the above stated lower limit. Here, it is preferable that a width of the buffer zones should be wider than a variation width of the battery voltage during transmission and reception. 
     FIG. 7 is a diagram illustrating a state wherein a battery voltage swings on a threshold level during transmission and reception. Referring to FIG. 7, assume that a battery voltage  711  is varied during transmission and reception, swinging on the upper limit  660  of the first buffer zone. That is, the battery voltage corresponds to the first buffer zone during transmission and reception, while it corresponds to the full battery state area during the idle state. In such a case, CPU  10  displays the full battery state, unless the battery voltage drops to the lower limit  650  of the first buffer zone during transmission and reception. 
     FIGS. 8A to  8 D illustrate icons displayed on display  70  for indicating the full battery state, the half battery state, the low battery state and the empty battery state, respectively. 
     FIG. 9 is a flowchart illustrating a method for displaying a battery voltage according to an embodiment of the present invention. The CPU  10  receives the battery voltage detection signal output from battery voltage detector  100  (step  911 ). The CPU  10  then judges whether or not the battery voltage corresponds to the full battery state area (step  912 ). If the battery voltage corresponds to the full battery state area, CPU  10  displays the full battery state (step  930 ) and then proceeds to step  919 . However, if the battery voltage does not correspond to the full battery state area, then CPU  10  judges whether or not the battery voltage corresponds to the first buffer zone (step  913 ). If the battery voltage corresponds to the first buffer zone, then CPU  10  judges whether or not a previous battery state is the full battery state (step  920 ). If the previous battery state is the full battery state, CPU  10  displays the full battery state (step  930 ) and then proceeds to step  919 . However, if the previous battery state is not the full battery state, CPU  10  displays the half battery state on display  70  (step  931 ) and then proceeds to step  919 . 
     However, when the battery voltage does not correspond to the first buffer zone in step  913 , CPU  10  judges whether. or not the battery voltage corresponds to the half battery state area (step  914 ). If the battery voltage corresponds to the half battery state area, CPU  10  displays the half battery state (step  931 ) and then proceeds to step  919 . However, if the battery voltage does not correspond to the half battery state area, CPU  10  judges whether or not the battery voltage corresponds to the second buffer zone (step  915 ). If the battery voltage corresponds to the second buffer zone, then CPU  10  judges whether or not the previous battery state is the half battery state (step  921 ). If the previous battery state is the half battery state, CPU  10  displays the half battery state (step  931 ) and then proceeds to step  919 . However, if the previous battery state is not the half battery state, CPU  10  displays the low battery state on display  70  (step  932 ) and then proceeds to step  919 . 
     However, when the battery voltage does not correspond to the second buffer zone in step  915 , CPU  10  judges whether or not the battery voltage corresponds to the low battery state area (step  916 ). If the battery voltage corresponds to the low battery state area, CPU  10  displays the low battery state (step  932 ) and then proceeds to step  919 . However, if the battery voltage does not correspond to the low battery state area, CPU  10  judges whether or not the battery voltage corresponds to the third buffer zone (step  917 ). If the battery voltage does not corresponds to the third buffer zone, CPU  10  displays the empty battery state (step  918 ). However, if the battery voltage corresponds to the third buffer zone, CPU  10  judges whether or not the previous battery state is the low battery state (step  922 ). If the previous battery state is the low battery state, CPU  10  displays the low battery state (step  932 ) and then proceeds to step  919 . However, if the previous battery state is not the low battery state, CPU  10  displays the empty battery state on display  70  (step  918 ) and then proceeds to step  919 . In step  919 , CPU  10  stores the battery state being currently displayed as a previous battery state and then returns to step  911 . 
     As described above, the TDMA radio terminal of the invention can stably display the battery state, even though the battery voltage temporarily varies during transmission and reception periods. 
     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.