Abstract:
A display device includes a display panel (LCD) applicable to a portable communication device such as a PDA or a web pad. The display device employs at least one photosensitive resistor for the purpose of sensing the variation of the environmental brightness, thereby adjusting the image brightness of the display panel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a display device, and more particularly, to a display device employing photosensitive resistors to adjust the display brightness for images on the display panel according to the variation of environmental brightness.  
           [0003]    2. Description of the Related Art  
           [0004]    A liquid crystal display (LCD) panel provides a planar display that is broadly used in portable electronic equipment such as portable computers, personal digital assistants (PDA), and recently developed web pads. The principal advantage of the LCD panel lies in a substantial reduction of its size and weight and, furthermore, since the LCD panel has no electron accelerator therewithin, the screen thickness are therefore considerably reduced in comparison with traditional CRT display devices.  
           [0005]    Although the numerous advantages described above, LCD panels also have some drawbacks, for example, an inferior display contrast especially as it is operated under relatively high environmental brightness and a narrower angle of view. Regarding some aspects, a LCD device still cannot provide a quality equal to that of the CRT device. Eventually, the display quality is greatly dependent upon the brightness of environment. Although some LCD devices are provided with automatic adjustment of brightness and contrast, these types of adjustment known in the prior art are however in accordance with the displayed frame and further requires a compulsory activation from the user. Therefore, in order to obtain an optimal image display, the user usually has to adjust the display parameters of the LCD device himself. When the brightness of the environment increases, the display contrast or brightness has to be adjusted higher to obtain a better image display. When the environment brightness lowers, the display contrast or brightness has to be lowered for the purpose of better image display and the reduction of the power consumption. For users, manually adjustment no matter via the hardware or software setting is usually cumbersome.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore a principal object of the invention to provide a display device that can automatically adjust the display brightness thereof according to the variation of the environment brightness with the setting of at least one photosensitive resistor.  
           [0007]    It is another object of the invention to provide a display device that can provide an optimal image display in accordance with the variation of the environmental brightness, thereby saving a specific amount of power assumption and protecting the user&#39;s eyes.  
           [0008]    To accomplish the above and other objectives, a display screen device of the invention includes a display panel, at least one photosensitive resistor, and a control circuit having A/D converters and a CPU. The photosensitive resistor is mounted within the display panel. The A/D converter is connected to the photosensitive resistor, the CPU is connected to the display panel. As the environmental brightness increases, the resistance of the photosensitive resistor decreases, and the input voltage of the analog/digital converter increases. Thereafter, the CPU compares the output of the A/D converter with a preset value initially stored to turn the image shown on the display panel to be brighter. If the environmental brightness decreases, the resistance of the photosensitive resistor increases, and the input voltage of the AID converter decreases accordingly. Subsequently, the CPU compares the output of the AID converter with the initially stored preset value to turn image shown on the display panel to be darker. Thereby, this display device may reduce the power consumption thereof significantly and protect the user&#39;s eyes.  
           [0009]    To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being provided only for illustration of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The drawings included herein provide a further understanding of the invention. A brief introduction of the drawings is as follows:  
         [0011]    [0011]FIG. 1 is a perspective view of a first embodiment of the invention according to the present invention;  
         [0012]    [0012]FIG. 2 is a circuit diagram of a display device according to a first embodiment of the invention;  
         [0013]    [0013]FIG. 3 is a perspective view of a second embodiment of the invention according to the present invention; and  
         [0014]    [0014]FIG. 4 is a circuit diagram of a display device according the second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0015]    Wherever possible in the following description, like reference numerals will refer to like elements and parts unless otherwise illustrated.  
         [0016]    [0016]FIG. 1 is a perspective view of a first embodiment  1  according to the present invention. As illustrated, the display device of the invention includes a display panel  10  and is mounted in some portable communication equipment, for example, a PDA or a web pad. In this embodiment, the display device  1  is exemplary illustrated as being used in a web pad. A control circuit  11  is disposed inside the display device  1  (with more details in FIG. 2). The control circuit  11  is electrically connected to the display panel  10  to control the image brightness of the display panel  10 . Proximate to a central region of a front face of the display panel  10  is arranged a groove (not shown) to enable the placement of a photosensitive resistor  12 . Alternatively, the groove can be properly located on the surface facing the user of the display device  1 . The photosensitive resistor  12  is electrically connected to the control circuit  11  and has a resistance that varies according to the environmental brightness variation. Therefore, the brightness of the environmental light with respect to the display device  1  is sensed by the photosensitive resistor  12  and, the resistance thereof changes accordingly. Furthermore, a transparent body (not shown) may additionally cover the photosensitive resistor  12  for the sake of protection.  
         [0017]    Referring to FIG. 2, FIG. 2 is a circuit diagram schematically illustrating an internal circuitry of the first embodiment of the invention. As illustrated, the internal circuitry of the invention principally includes the control circuit  11  having a photosensitive resistor  12  (CDS 1 ), a resistor R 1 , an analog/digital (A/D) converter ADC 1 , and a CPU U 1 . One terminal of the photosensitive resistor CDS 1  is connected to a constant voltage source Vcc. Other terminals of the photosensitive resistor CDS 1  are connected to a ground through the resistor R 1  and to an input terminal of the A/D converter ADC 1  respectively. An output terminal of the ADC 1  is connected to one terminal of the CPU U 1 . The other output terminal of the CPU U 1  is connected to the display panel  10 .  
         [0018]    With such a configuration, variation of the environmental brightness with respect to the display panel  10  can be sensed. When the brightness of the environmental light increases, the resistance of the photosensitive resistor CDS 1  decreases, and accordingly the input voltage of the ADC 1  increases. The CPU U 1  compares the output of the ADC  1  with a preset value to determine how much adjustment should be imposed on the image brightness of the display panel  10 . The CPU U 1  then gradually increases the brightness of the light source inside the display panel  10 . When the brightness of the environmental light decreases, the resistance of the photosensitive resistor CDS 1  increases, and the input voltage of the ADC 1  accordingly decreases. The CPU U 1  compares the ADC  1  output with the preset value to determine the required decrease of the image brightness of the display panel  10 . The CPU U 1  then gradually decreases the brightness of the light source inside the display panel  10 . Thereby, the power consumption is reduced and the user&#39;s eyes are protected.  
         [0019]    The brightness of the light emitted from the display panel  10  is therefore adjusted according to the brightness of the environmental light to favorably achieve an optimal power consumption and a protection of the user&#39;s eyes.  
         [0020]    In the first embodiment of the invention, a single photosensitive resistor  12  is used to detect the change in the environmental brightness. However, more than one photosensitive resistors  12  can be also used to detect the brightness changes at different locations to then obtain an average value of the brightness changes.  
         [0021]    [0021]FIG. 3 is a perspective view of a second embodiment according to the present invention. As illustrated, the display device of this embodiment includes a display panel  10 . A control circuit  11 ′ is disposed inside the display device  1  and electrically connected to the display  10 . Proximate to the end of the front face of display panel  10  is arranged a groove (not shown) to enable the placement of photosensitive resistors  12 ′, which are electrically connected to the control circuit  11 ′. The photosensitive resistors  12 ′ change their corresponding resistance values according to the variation of the environmental light. Therefore, the environmental brightness is sensed by the changes in respective resistance values. Furthermore, a transparent body (not shown) may additionally cover the photosensitive resistors  12 , respectively, for the protection.  
         [0022]    Referring to FIG. 4, a circuit diagram of the second embodiment is schematically illustrated to show an internal circuitry thereof. As illustrated, the internal circuitry of the invention principally includes the control circuit  11 ′ consists of photosensitive resistors  12  (CDS 1 , CDS 2 ), resistors R 1 , R 2 , analog/digital (A/D) converters ADC 1 , ADC 2 , and a CPU U 1 . One terminal of the photosensitive resistor CDS 1  is connected to a constant voltage source Vcc. The other terminal of the photosensitive resistor CDS 1  is connected to a ground via the resistor R 1  and to an input terminal of the A/D converter ADC 1 , respectively. An output terminal of the ADC 1  is connected to one terminal of the CPU U 1 . Meanwhile, one terminal of the photosensitive resistor CDS 2  is connected to a constant voltage source Vcc. Other terminals of the photosensitve resistor CDS 2  are respectively connected to the ground via the resistor R 2  and to an input terminal of the ADC 2 . An output terminal of the ADC 2  is also connected to the CPU U 1 . The other terminal of the CPU U 1  is connected to the display panel  10 .  
         [0023]    With such a configuration, the environmental variation can be sensed. When the brightness of the environmental light increases, the respective resistance values of the photosensitive resistors CDS 1 , CDS 2  decrease, and the input voltages of the ADC 1 , ADC 2  accordingly increase. The CPU U 1  compares the respective outputs of the ADC 1  and ADC 2  to determine how much adjustment of the image brightness should be imposed to the display panel  10 . The CPU U 1  then gradually increases the brightness of the light source inside the display panel  10 . When the brightness of the environmental light decreases, the respective resistance values of the photosensitive resistors CDS 1  and CDS 2  increase, and the input voltages of the ADC 1 , ADC 2  accordingly decrease. The CPU U 1  compares the respective outputs of the ADC 1  and ADC 2  to determine the required decrease for the image brightness of the display panel  10 . The CPU U 1  then gradually decreases the brightness of the light source inside the display panel  10 . Thereby, the power consumption is reduced and the user&#39;s eyes are protected.  
         [0024]    With the use of photosensitive resistors CDS 1  and CDS 2 , the brightness of the light emitted from the display panel  10  can be automatically adjusted according to the environmental brightness to favorably obtain goals of optimizing the power consumption and protecting user&#39;s eyes.  
         [0025]    Furthermore, if the user wants a manual setting of the display device, the CPU U 1  then will not consider the outputs from the ADC 1  and/or ADC 2 .  
         [0026]    It should be apparent to those skilled in the art that the above description is only illustrative of specific embodiments and examples of the invention. The invention should therefore cover various modifications and variations made to the herein-described structure and operations of the invention, provided they fall within the scope of the invention as defined in the following appended claims.