Abstract:
Systems for controlling brightness of displayed images of a display panel are provided. A representative system incorporates a control unit that is operative to adjust brightness of a corresponding display panel based upon at least one of: detected brightness of ambient light and brightness of light emitting elements of the display panel.

Description:
BACKGROUND  
       [0001]     The disclosure relates to image display.  
         [0002]     Display panels of mobile electronic systems are typically user adjustable to compensate for varying levels of environmental brightness. For example, a display panel should be able to generate high brightness to display an image in a bright environment. Conversely, the display of a dark image in a darker environment requires less display panel brightness.  
         [0003]     A conventional method controls brightness of light emitted from a display panel according to voltage generated by a voltage divider.  FIG. 1  is a schematic diagram of a conventional voltage divider. A voltage between two resistors can be adjusted according to the resistance of two resistors. A first maximum gray level provided by voltage divider  10  is 100 nits, a second maximum gray level provided by voltage divider  12  is 150 nits, and a third maximum gray level provided by voltage divider  14  is 200 nits. Therefore, the brightness of light emitted from the display panel can be adjusted by providing different maximum gray levels. Unfortunately, since such a conventional method utilizes numerous voltage dividers to generate multiple voltages for adjusting the brightness of light emitted from the display panel, the cost and size of the display panel can be high.  
       SUMMARY  
       [0004]     Systems for controlling brightness of displayed images are provided. In this regard, a representative embodiment of such a system comprises a signal generator that comprises a control unit, a first processing unit, and a storage unit. The control unit outputs a reference voltage according to the brightness of light emitted from the lamp during a first period and outputs a reference signal during a second period. The first processing unit comprises a first input terminal and a first output terminal. Voltage of the first input terminal is equal to that of the first output terminal during the first period. A logic level of the first output terminal is inverse to a logic level of the first input terminal. The storage unit stores a response voltage according to the reference voltage and the voltage of the first input terminal during the first period and controls the logic level of the first input terminal according to the reference voltage and the response voltage during the second period.  
         [0005]     Another embodiment of such a system comprises a control unit that is operative to adjust brightness of a corresponding display panel based upon at least one of: detected brightness of ambient light and brightness of light emitting elements of the display panel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The invention can be more fully understood by reading the subsequent detailed description and examples with reference made to the accompanying drawings, wherein:  
         [0007]      FIG. 1  is a schematic diagram of a conventional voltage divider;  
         [0008]      FIG. 2   a  is a schematic diagram of an embodiment of a system for controlling brightness of displayed images;  
         [0009]      FIG. 2   b  is a schematic diagram of the embodiment of  FIG. 2   a , showing the signal generator in greater detail:  
         [0010]      FIG. 3  is a timing diagram of the preset signal STV shown in  FIG. 2   b;    
         [0011]      FIG. 4  is a schematic diagram of another exemplary embodiment of a system for controlling brightness of displayed images;  
         [0012]      FIG. 5  is a timing diagram of the preset signal STV shown in  FIG. 2   c;    
         [0013]      FIG. 6  is a schematic diagram of another embodiment of a system for controlling brightness of displayed images:  
         [0014]      FIG. 7  is a schematic diagram of an embodiment of a pixel; and  
         [0015]      FIG. 8  is a schematic diagram of another embodiment of a pixel. 
     
    
     DETAILED DESCRIPTION  
       [0016]     Systems for controlling brightness of displayed images are provided. In this regard, an exemplary embodiment of such a system is depicted schematically in  FIG. 2   a . As shown in  FIG. 2   a , the system incorporates a signal generator  24 . Signal generator  24  comprises a control unit  32 , a first processing unit  34 , and a storage unit  36  connected therebetween.  
         [0017]     During a first period, control unit  32  outputs a reference voltage Vref according to brightness emitted from light-emitting element  30 . During a second period, control unit  32  outputs a reference signal Sp. Control unit  32  comprises a photo-detection device  322  and selection device  324 . Photo-detection device  322  provides reference voltage Vref according to the brightness of light emitted from lamp  30 . Selection device  324  outputs reference voltage Vref or reference signal Sp according to a control signal Sc (not shown). In this embodiment, the logic level of control signal Sc is high during the first period and that of control signal Sc is low during the second period. Therefore, selection device  324  outputs reference voltage Vref during the first period and outputs reference signal Sp during the second period. In this embodiment, reference signal Sp is a triangular signal provided from external.  
         [0018]     The first processing unit  34  comprises an input terminal P 1  and an output terminal P 2 . A voltage of the input terminal P 1  is equal to that of the output terminal P 2  during the first period. Additionally, a logic level of the output terminal P 2  is inverse to a logic level of the input terminal P 1  during the second period.  
         [0019]     Storage unit  36  stores a response voltage Vc according to reference voltage Vref and the voltage of the input terminal P 1  during the first period. Additionally, storage unit  36  controls the logic level of the input terminal P 1  according to reference voltage Vref and the response voltage Vc during the second period. The output terminal P 2  provides preset signal STV according the logic level of the input terminal P 1  during the second period. In this embodiment, storage unit  36  is a capacitor.  
         [0020]      FIG. 2   b  is a schematic diagram of the embodiment of the system for controlling brightness of displayed images of  FIG. 2   a  showing the signal generator  24  in greater detail. In this regard, photo-detection device  322  comprises a photo-sensor  411  and a converter  412  and provides reference voltage Vref according to brightness of light emitted from light-emitting element  30 . Photo-sensor  411  detects the brightness of light emitted from light-emitting element  30  and provides a corresponding current Iref. Converter  412  converts the current Iref to reference voltage Vref. Since a value of the current Iref is small, a current mirror unit (not shown) is utilized to amplify the current Iref. Converter  412  receives the amplified current Iref. Additionally, an amplifier (not shown) can be utilized for amplifying reference voltage Vref. Selection device  324  comprises transistors  413  and  414 . Transistor  413  is a P-type transistor and transistor  414  is an N-type transistor. A source of transistor  413  receives reference signal Sp, a gate thereof receives a control signal Sc, and a drain thereof is coupled to a drain of transistor  414 . A gate of transistor  414  receives the control signal Sc and a source thereof receives reference voltage Vref.  
         [0021]     As the control signal Sc is at high logic level during the first period, transistor  414  is turned on. Therefore, voltage of a node P 3  is approximately equal to reference voltage Vref. As the control signal Sc is at low logic level during the second period, transistor  413  is turned on. Therefore, voltage of a node P 3  is approximately equal to voltage of reference signal Sp.  
         [0022]     The first processing unit  34  comprises a switching device  342  and an inverting device  344  connected in parallel with switching device  342 . During the first period, switching device  342  is turned on such that a voltage of an input terminal P 4  of inverting device  344  is equal to that of an output terminal P 5  of inverting device  344 . During the second period, switching device  342  is turned off such that a logic level of the output terminal P 5  is the inverse of the input terminal P 4 . In some embodiments, inverting device  344  can be an inverter  416  and switching device  342  can be a switch  415 .  
         [0023]     To increase a sensitivity of inverting device  344 , inverting device  344  can include inverters connected in series, with a switch being coupled between an input terminal of a first of the inverters and an output terminal of a last inverters. Additionally, inverting device  344  can comprise a plurality of inverters connected in series, with a plurality of switches, each connected in parallel with one of the inverters. Since inverting device  344  has an inverse function during the second period, the number of inverters should be odd.  
         [0024]     In the embodiment of  FIG. 2   b , photo-sensor  411  detects brightness of light emitted from light-emitting elements of a display panel. Since the light-emitting elements age, the brightness of light emitted from the light-emitting elements typically will decay. Thus, signal generator  24  can compensate for the decaying brightness due to aging of light-emitting elements.  
         [0025]     The operating principle of the system shown in  FIG. 2   b  is described in the following. In this regard,  FIG. 3  is a timing diagram of the preset signal STV of  FIG. 2   b . Assuming the high voltage of inverter  416  is equal to 5V and low voltage thereof is equal to 0V, then during a first period D 1 , switch  415  is turned on such that voltages of nodes P 4  and P 5  are equal to 2.5V. Therefore, preset signal STV 1  approximately equals 2.5V.  
         [0026]     During first period D 1 , control signal Sc is at a high logic level such that transistor  414  is turned on. Therefore, voltage of node P 3  equals reference voltage Vref. If the brightness of light emitted from light-emitting elements of a display panel changes from bright to dark, the reference voltage Vref output from photo-detection device  322  is equal to 1V. When voltage V P4  of node P 4  equals 2.5V and voltage V P3  of node. P 3  equals 1V, the voltage Vc of capacitor  362  equals −1.5V.  
         [0027]     During the second period, control signal Sc is at a low logic level such that transistor  413  is turned on. Therefore, the voltage V P3  is equal to reference signal Sp. Reference signal Sp is a triangular signal in this embodiment having a maximum voltage equal to 5V and a minimum voltage equal to 0V. Since voltage Vc equals to −1.5V, when voltage V P3  is less than 1V, preset signal STV 1  is at a high logic level, and when voltage V P3  is more than 1V, preset signal STV 1  is at a low logic level.  
         [0028]     During the third period D 3 , switch  415  is turned on such that voltages of nodes P 4  and P 5  are equal to 2.5V. Therefore, preset signal STV 1  is equal to 2.5V and voltage Vc will be changed according to reference voltage Vref.  
         [0029]     If the brightness of light emitted from light-emitting elements of a display panel changes from dark to bright, the reference voltage Vref output from photo-detection device  322  is equal to 4V. When voltage V P4  of node P 4  equals 2.5V and voltage V P3  of node P 3  equals to 4V, voltage Vc of capacitor  362  equals 1.5V.  
         [0030]     During the second period, control signal Sc is at a low logic level such that transistor  413  is turned on. Therefore, the voltage V P3  equals reference signal Sp. Since voltage Vc equals 1.5V when voltage V P3  is less than 4V, preset signal STV 2  is at a high logic level, and when voltage V P3  is more than 4V, preset signal STV 2  is at a low logic level.  
         [0031]     During the third period D 3 , switch  415  is turned on such that voltages of nodes P 4  and P 5  are equal to 2.5V. Therefore, preset signal STV 2  is equal to 2.5V and voltage Vc will be changed according to reference voltage Vref.  
         [0032]     As shown in  FIG. 3 , when the brightness emitted from light-emitting elements of a display panel changes, reference voltage Vref output from photo-detection device  322  changes to adjust a duty cycle of preset signal STV.  
         [0033]      FIG. 4  is a schematic diagram of another exemplary embodiment of a system for controlling brightness of displayed images.  FIG. 4  is similar to the embodiment of  FIG. 2   b  except that a second processing unit  38  is coupled to first processing unit  34 . In this embodiment, the first processing unit  38  comprises a switching device  382  and an inverting device  384  connected in parallel with switching device  382 . During the first period, switching device  382  is turned on such that a voltage of an input terminal P 6  of inverting device  384  is equal to that of an output terminal P 7  of inverting device  384 . During the second period, switching device  382  is turned off such that a logic level of the output terminal P 7  is the inverse of the input terminal P 6 . In some embodiments, inverting device  384  can be an inverter  418  and switching device  382  can be a switch  417 .  
         [0034]     To increase a sensitivity of inverting device  384 , inverting device  384  can include inverters connected in series, with a switch coupled between an input terminal of a first of the inverters and an output terminal of a last of the inverters. Additionally, inverting device  384  can comprise a plurality of inverters connected in series, and a plurality switches, each connected in parallel to one of the inverters. Since inverting device  384  has an inverse function during the second period, the number of inverters should be odd. The number of inverters of inverting devices  344  and  384  preferably is even.  
         [0035]     In the embodiment of  FIG. 4 , photo-sensor  411  detects environmental brightness (ambient light). The brightness perceived by a viewer of the display panel that is lower if the environmental brightness is high. Therefore, the brightness of light emitted from the light-emitting elements of a display panel is directly proportional to environmental brightness.  
         [0036]      FIG. 5  is a timing diagram of the preset signal STV of  FIG. 4 . Since signal generator  24  shown in  FIG. 4  detects environmental brightness, preset signals STV 1  and STV 2  are generated accordingly. Preset signal STV 1  is generated when environmental brightness is high. Preset signal STV 2  is generated when environmental brightness is low.  
         [0037]     Additionally, since the signal generator shown in  FIG. 4  comprises second processing unit, the preset signals STV 1  and STV 2  shown in  FIG. 5  are inverse to the preset signals STV 1  and STV 2  shown in  FIG. 3 .  
         [0038]      FIG. 6  is a schematic diagram of another embodiment of a system for controlling brightness of displayed images. In this embodiment, system  20  comprises a display panel  22 , a signal generator  24 , and a driving device  26 . Display panel  22  comprises a plurality of light-emitting elements (not shown). Generally display panel  22  is a liquid crystal display panel although in other embodiments, the panel could be an electroluminescent display panel for example. If display panel  22  is a liquid crystal display panel, the light-emitting elements of display panel  22  are string lamps. If display panel  22  is an electroluminescent display panel, the light-emitting elements of display panel  22  are electroluminescent elements.  
         [0039]     Signal generator  24  generates a preset signal STV according to brightness of light such as environmental light or light from a light-emitting element. Driving device  26  comprises a scan driver  262  and a data driver  264 . Driving device  26  adjusts brightness of light emitted from the light-emitting elements according to preset signal STV.  
         [0040]     If display panel  22  is an electroluminescent display panel, display panel  22  comprises a plurality of pixels. Each pixel comprises an electroluminescent element. In this regard,  FIG. 7  is a schematic diagram of an embodiment of a pixel. For clarity, only one pixel is shown.  
         [0041]     When scan driver  262  asserts scan signal S 1 , a transistor M 1   a  is turned on such that a capacitor Ca is charged according to a data signal D 1  provided from data driver  264 . As the voltage stored in capacitor Ca is sufficient to turn on a transistor M 2   a , high voltage Vdd can be output to a transistor M 3   a.    
         [0042]     If driving signal SC 1  provided by scan driver  262  is at a high logic level, transistor M 3   a  is turned off such that electroluminescent element ELa does not emit light. If driving signal SC 1  is at low logic level, transistor M 3   a  is turned on such that electroluminescent element ELa emits light.  
         [0043]     When the turn-on time of the transistor M 3   a  is longer, luminiferous time of electroluminescent element ELa is longer such that brightness emitted from display panel  22  is brighter. When the turn-on time of transistor M 3   a  is shorter, luminiferous time of electroluminescent element ELa is shorter such that brightness emitted from display panel  22  is less. Therefore, a duty cycle of preset signal STV is utilized to control the turn-on time of transistor M 3   a  for controlling the brightness emitted from display panel  22 .  
         [0044]     For example, referring again to  FIG. 3 , preset signal STV 1  is generated while brightness emitted from light-emitting elements of display panel  22  is changed from bright to dark. Scan driver  262  provides driving signal SC 1  according to preset signal STV 1  shown in  FIG. 3 . In this embodiment, driving signal SC 1  is equal to preset signal STV 1 . When the gate of transistor M 3   a  receives driving signal SC 1 , turn-on time of electroluminescent element ELa is longer than the turn-off time of electroluminescent element ELa. Thus, brightness emitted from display panel  22  is high. Preset signal STV 2  is generated while brightness of light emitted from the light-emitting elements of display panel  22  is changed from dark to bright. Scan driver  262  provides driving signal SC 1  according to preset signal STV 2  shown in  FIG. 3 . In this embodiment, driving signal SC 1  is equal to preset signal STV 2 . When the gate of transistor M 3   a  receives driving signal SC 1 , turn-off time of electroluminescent element ELa is longer than turn-on time of electroluminescent element ELa. Therefore, brightness emitted from display panel  22  is low.  
         [0045]      FIG. 8  is a schematic diagram of another embodiment of a pixel. As transistor M 1   b  is turned on, capacitor Cb can be charged. When voltage stored in capacitor Cb is sufficient to turn on transistor M 2   b , an anode of electroluminescent element ELb receives high voltage Vdd.  
         [0046]     When driving signal SC 1  is at a low logic level, electroluminescent element ELb emits light. When driving signal SC 1  is at a high logic level, electroluminescent element ELb does not emit light.  
         [0047]     For example, reference with  FIG. 5  and  FIG. 8 , preset signal STV 1  is generated as environmental brightness is low. Scan driver  262  provides driving signal SC 1  according to preset signal STV 1  shown in  FIG. 5 . In this embodiment, driving signal SC 1  is equal to preset signal STV 1 . When the anode of electroluminescent element ELb receives STV 1 , turn-off time of electroluminescent element ELb is longer than turn-on time of electroluminescent element ELb. Therefore, brightness emitted from display panel  22  is low when environmental brightness is low. Preset signal STV 2  is generated as brightness emitted from an environment is bright. Scan driver  262  provides driving signal SC 1  according to preset signal STV 2  shown in  FIG. 5 . In this embodiment, driving signal SC 1  is equal to preset signal STV 2 . When the anode of electroluminescent element ELb receives STV 1 , turn-on time of electroluminescent element ELa is longer than turn-off time of electroluminescent element ELb. Therefore, brightness emitted from display panel  22  is high.  
         [0048]     As described previously, signal generator  24  controls a duty cycle of a preset signal according to brightness of environmental light and/or of light of a light-emitting element. When the signal generator  24  is utilized in an electronic system comprising a display panel, if the signal generator  24  detects environmental brightness, brightness of the display panel is changed accordingly. If the signal generator  24  detects brightness of light emitted from the light-emitting element, aging of the light-emitting element can be mitigated.  
         [0049]     While the invention has been described by way of example and in terms of embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.