Patent Publication Number: US-2009225016-A1

Title: Light-sensitive driving circuit, light-sensitive method and display

Description:
This application claims the benefit of Taiwan application Serial No. 97108403, filed Mar. 10, 2008, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a light-sensitive driving circuit, and more particularly to a light-sensitive driving circuit capable of prolonging the lifespan of the light-sensitive apparatus, a light-sensitive driving method and a display. 
     2. Description of the Related Art 
     For the backlight luminance of the display device, most conventional technologies directly apply a fixed voltage to drive the light-sensitive apparatus and adjust the backlight luminance of display device according to a signal outputted by the light-sensitive apparatus. 
     If the thin film transistor of the light-sensitive apparatus is conducted over a long duration, I-V curve drift will occur, and this is called stress effect, which increases the threshold voltage Vth of the thin film transistor and jeopardizes the current driving ability of the thin film transistor. When the threshold voltage Vth of the thin film transistor is larger than a pre-determined value, the thin film transistor cannot be driven, and the lifespan of the light-sensitive apparatus will be reduced. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a light-sensitive driving circuit, a light-sensitive driving method and a display. The light-sensitive driving circuit outputs a pulse width modulation voltage to drive the light-sensitive apparatus, so as to avoid the stress effect, which occurs when a light-sensitive apparatus is driven by a fixed voltage, and prolong the lifespan of the light-sensitive apparatus. 
     According to a first aspect of the present invention, a light-sensitive driving circuit comprising a pulse width modulation (PWM) circuit, a judge unit and a first analog-to-digital converter is provided. The pulse width modulation circuit provides a pulse width modulation voltage to drive the light-sensitive apparatus, so that the light-sensitive apparatus outputs an induced signal according to an external light. The judge unit judges whether a check and burn procedure needs to be operated or not according to an external command. If the check and burn procedure does not need to be operated, the first analog-to-digital converter outputs a digital signal according to the induced signal. 
     According to a second aspect of the present invention, a light-sensitive driving method comprising the following steps is provided. Firstly, a pulse width modulation voltage is provided to drive the light-sensitive apparatus, so that the light-sensitive apparatus outputs an induced signal according to an external light. Next, whether a check and burn procedure needs to be operated or not is judged according to an external command. Lastly, if the check and burn procedure does not need to be operated, the analog-to-digital converter converts the induced voltage to a digital signal and then the digital signal is further outputted. 
     The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a display with the function of dynamically adjusting backlight luminance; 
         FIG. 2  shows a block diagram of a light-sensitive apparatus, a light-sensitive driving circuit and a backlight module; 
         FIG. 3  shows a wave-pattern of a pulse width modulation voltage and an induced voltage; 
         FIG. 4  shows a light-sensitive apparatus and a light-sensitive driving circuit according to a first embodiment of the invention; 
         FIG. 5  shows a light-sensitive apparatus and a light-sensitive driving circuit according to a second embodiment of the invention; and 
         FIG. 6  shows a flowchart of a light-sensitive driving method according to a preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to both  FIG. 1  and  FIG. 2 .  FIG. 1  shows a display with the function of dynamically adjusting backlight luminance.  FIG. 2  shows a block diagram of a light-sensitive apparatus, a light-sensitive driving circuit and a backlight module. The display  10  comprises a display panel  110 , a display driving integrated circuit  120 , a light-sensitive apparatus  130  and a backlight module  140 , wherein the display panel  110  comprises a non-display area  112  (also called “peripheral area”) and a display area  114  (also called “active area”). The display driving integrated circuit  120  and the light-sensitive apparatus  130 , for example, are disposed within the non-display area  112  or on a circuit board (not illustrated). 
     The display driving integrated circuit  120  further comprises a light-sensitive driving circuit  122 , which outputs a pulse width modulation voltage Vpwm to drive the light-sensitive apparatus  130 , so that the light-sensitive apparatus  130  outputs an induced signal S(m) according to an external light. The light-sensitive driving circuit  122  outputs a digital signal D 1 ( m ) according to the induced signal S(m) to dynamically adjust the backlight luminance of the backlight module  140 , wherein symbol m denotes the surrounding luminance of the external light. 
     The abovementioned induced signal S(m) is an induced voltage or an induced current, and the light-sensitive driving circuit  122  and the light-sensitive apparatus  130  can be implemented in many ways. The light-sensitive driving circuit  122  and the light-sensitive apparatus  130  are further elaborated in a first embodiment and a second embodiment below. 
     The light-sensitive apparatus  130  further comprises a light-sensing element  132  and a current-to-voltage element  134 . The light-sensing element  132  generates a current according to an external light, and the current-to-voltage element  134  outputs an induced voltage Vphoto(m) according to the current Iphoto(m). The light-sensitive driving circuit  122  outputs a digital signal D 1 ( m ) according to the induced voltage Vphoto(m) to dynamically adjust the backlight luminance of the backlight module  140 , wherein m denotes the surrounding luminance of the external light. 
     Referring to  FIG. 3 , a wave-pattern of a pulse width modulation voltage and an induced voltage is shown. The light-sensitive apparatus  130 , for example, is constituted by one or more thin film transistors. If the thin film transistor is conducted over a long duration, I-V curve drift will occur, and this is called stress effect, which increases the threshold voltage Vth of the thin film transistor and jeopardizes the current driving ability of the thin film transistor. The thin film transistor cannot be driven when the threshold voltage Vth of the thin film transistor is larger than a pre-determined value. 
     To avoid the thin film transistor being conducted over a long duration, the light-sensitive driving circuit  122  of the present embodiment of the invention does not use a fixed voltage to drive the light-sensitive apparatus  130 , but preferably outputs a pulse width modulation voltage Vpwm to drive the light-sensitive apparatus  130  so as to reduce the stress effect occurring to the thin film transistor. 
     For example, the pulse width modulation voltage Vpwm outputted by the pulse width modulation circuit  1222  has a cycle equaling 
     
       
         
           
             
               s 
               f 
             
             , 
           
         
       
     
     and a working cycle equaling 
     
       
         
           
             
               1 
               
                 4 
                  
                 
                     
                 
                  
                 sf 
               
             
             , 
           
         
       
     
     wherein symbol s denotes the times of pulse width modulation voltage outputted by the pulse width modulation circuit  1222  per second, and symbol f denotes the frame updating rate. 
     The light-sensitive apparatus  130  receives a pulse width modulation voltage Vpwm, and the working cycle of the pulse width modulation voltage Vpwm can be appropriately adjusted according to the properties of the product. Thus, the stress effect occurring to thin film transistor is reduced and the lifespan of the light-sensitive apparatus  130  is prolonged. 
     First Embodiment 
     Referring to  FIG. 4 , a light-sensitive apparatus and a light-sensitive driving circuit according to a first embodiment of the invention is shown. The light-sensitive driving circuit  122  and the light-sensitive apparatus  130  can be implemented in many ways. In the first embodiment, the light-sensitive  5  apparatus  130  comprises a light-sensing element  132  and a current-to-voltage element  134 . The light-sensitive driving circuit  122  comprises a pulse width modulation (PWM) circuit  1222 , an output buffer  1224 , a burning unit  1225 , a judge unit  1226 , an analog-to-digital converter  1227 , an analog-to-digital converter  1228  and a checking unit  1229 . 
     When the induced signal S(m) of  FIG. 2  is an induced voltage, the pulse width modulation circuit  1222  provides a pulse width modulation voltage Vpwm to drive light-sensing element  132  of the light-sensitive apparatus  130 , so that the surrounding luminance m of the external light of the light-sensing element  132  outputs a corresponding induced current Iphoto(m) to the current-to-voltage element  134 . The current-to-voltage element  134  outputs a corresponding induced voltage Vphoto(m) to the buffer  1224  according to the induced current Iphoto(m), and the output buffer  1224  increases the pushing force for outputting the induced voltage Vphoto(m). 
     The judge unit  1226  judges whether to operate a check and burn procedure according to an external command. If the check and burn procedure does not need to be operated, the analog-to-digital converter  1227  converts the induced voltage Vphoto(m) to a digital signal D 1 ( m ) and further outputs the digital signal D 1 ( m ) to dynamically adjust the backlight luminance of the backlight module  140 . 
     To the contrary, if the check and burn procedure needs to be operated, the system end (not shown) designates that the surrounding luminance m of the external light equals ml. Meanwhile, the induced voltage Vphoto(m) outputted by the light-sensitive apparatus  130  equals a first analog value Vphoto(m 1 ), and the analog-to-digital converter  1228  outputs a first digital value D(m 1 ) according to the first analog value Vphoto(m 1 ). Next, the system end indicates that the surrounding luminance m of the external light equals m 2 . Meanwhile, the induced voltage Vphoto(m) outputted by the light-sensitive apparatus  130  equals a second analog value Vphoto(m 2 ), and the analog-to-digital converter  1228  outputs a second digital value D(m 2 ) according to the second analog value Vphoto(m 2 ). 
     The checking unit  1229  checks whether the difference between the first digital value D(m 1 ) and the second digital value D(m 2 ) is larger than a checking value. If the value of [D(m 1 )-D(m 2 )] is not larger than checking value, this implies that the light-sensitive apparatus  130  is a defective product. To the contrary, if the value of [D(m 1 )-D(m 2 )] is larger than checking value, this implies that the light-sensitive apparatus  130  is an accepted product. When the value of [D(m 1 )-D(m 2 )] is larger than checking value, the burning unit  1225  burns the first digital value D(m 1 ) and the second digital value D(m 2 ) to the analog-to-digital converter  1227  to determine an output voltage range of the analog-to-digital converter  1227 . 
     For example, the system end designates that the surrounding luminance m of the external light equals 10000 Lux. Meanwhile, the induced voltage Vphoto (m) outputted by the light-sensitive apparatus  130  equals a first analog value 2.2V, and the analog-to-digital converter  1228  outputs a first digital value D( 10000 ) according to the first analog value 2.2V. Next, the system end designates that the surrounding luminance m of the external light equals 0 Lux. Meanwhile, the induced voltage Vphoto (m) outputted by the light-sensitive apparatus  130  equals a second analog value 1.1V, and the analog-to-digital converter  1228  outputs a second digital value D( 10 ) according to the second analog value 1.1V. 
     When the order of the analog-to-digital converter  1227  is  32  and the precision level is 0.02V, the value of [Vphoto( 10000 )-Vphoto( 10 )] must larger than 0.64V, otherwise the analog-to-digital converter  1227  cannot decode 32-order digital signal. Thus, the checking unit  1229  judges whether the value of [Vphoto( 10000 )-Vphoto( 10 )] is larger than 0.64V according to whether the value of [D( 10000 )-D( 10 )] is larger than a predetermined checking value. When the value of [D( 10000 )-D( 10 )] is larger than the predetermined checking value, the first digital value D( 10000 ) and the second digital value D( 10 ) will be burnt to the analog-to-digital converter  1227 . Meanwhile, the first digital value D( 10000 ) is a maximum output of the analog-to-digital converter  1227  and the second digital value D( 10 ) is a minimum output of the analog-to-digital converter  1227 . 
     The analog-to-digital converter  1227  establishes an output voltage range according to the characteristics of the light-sensitive apparatus  130  of the display panel  110 , hence resolving the problem that given the same luminance, the digital signal outputted by the light-sensitive apparatus  130  disposed on different display panels is different. 
     The embodiment disclosed above can further burn more digital value to the analog-to-digital converter  1227  according to customers&#39; needs to determine other output voltage ranges of the analog-to-digital converter  1227 . For example, given that the surrounding luminance equals 10 Lux, 1000 Lux, 100 Lux and 100 Lux, the induced voltage Vphoto(m) respectively equal a first analog value Vphoto( 10 ), a second analog value Vphoto( 10000 ), a third analog value Vphoto( 100 ) and a fourth analog value Vphoto( 1000 ). The analog-to-digital converter  1228  respectively converts the first analog value Vphoto( 10 ), the second analog value Vphoto( 10000 ), the third analog value Vphoto( 100 ) and the fourth analog value Vphoto( 1000 ) to a first digital value D( 10 ), a second digital value D( 10000 ), a third digital value D( 100 ) and a fourth digital value D( 1000 ). The first digital value D( 10 ), the second digital value D( 10000 ), the third digital value D( 100 ) and the fourth digital value D( 1000 ) are burnt to the analog-to-digital converter  1227  to determine three output voltage ranges of the analog-to-digital converter  1227 .  100311  Within the range between the first digital value D( 10 ) and the third digital value D( 100 ) or the range between the fourth digital value D( 1000 ) and the second digital value D( 10000 ), the digital signal can be flexibly adjusted to have smaller order such as 8 or 16 when corresponding surrounding luminance becomes darker or brighter. The digital signal within the range between the third digital value D( 100 ) and the fourth digital value D( 1000 ) can be flexibly switched to have higher order to fit customers&#39; needs. 
     Second Embodiment 
     Referring to  FIG. 5 , a light-sensitive apparatus and a light-sensitive driving circuit according to a second embodiment of the invention is shown. The light-sensitive driving circuit  122  and the light-sensitive apparatus  130  can be implemented by way of the first embodiment or the second embodiment. In the second embodiment, the light-sensitive apparatus  130  comprises a light-sensing element  132 , and the light-sensitive driving circuit  122  comprises a current-to-voltage element  134 , a pulse width modulation (PWM) circuit  1222 , an output buffer  1224 , a burning unit  1225 , a judge unit  1226 , an analog-to-digital converter  1227 , an analog-to-digital converter  1228  and a checking unit  1229 . 
     When the induced signal S(m) of  FIG. 2  is an induced current, the light-sensitive apparatus  130  of the second embodiment does not comprise the current-to-voltage element  134 , but instead, integrates the current-to-voltage element  134  into the light-sensitive driving circuit  122 . The pulse width modulation circuit  1222  provides a pulse width modulation voltage Vpwm to drive the light-sensing element  132  of the light-sensitive apparatus  130 , so that the surrounding luminance m of the external light of the light-sensing element  132  outputs a corresponding induced current Iphoto(m) to the light-sensitive driving circuit  122 . The light-sensitive driving circuit  122  receives an induced current Iphoto(m), and the current-to-voltage element  134  of the light-sensitive driving circuit  122  converts the induced current Iphoto(m) to an induced voltage Vphoto(m) which is outputted to the output buffer  1224 . 
     Referring to  FIG. 6 , a flowchart of a light-sensitive driving method according to a preferred embodiment of the invention is shown. The light-sensitive driving method is used in the display  10 . The light-sensitive driving method comprises the following steps: 
     Firstly, the method begins at step  510 , the pulse width modulation circuit  1222  provides a pulse width modulation voltage Vpwm to drive the light-sensitive apparatus  130 , so that the light-sensitive apparatus  130  outputs an induced signal S(m) according to an external light. Next, the method proceeds to step  520 , the output buffer  1224  increases the pushing force for outputting the induced signal S(m). Then, the method proceeds to step  530 , the judge unit  1226  judges whether a check and burn procedure needs to be operated or not according to an external command. If the check and burn procedure does not need to be operated, the method proceeds to step  540 , the analog-to-digital converter  1227  outputs a digital signal D 1 ( m ) according to the induced signal S(m). 
     To the contrary, if the check and burn procedure needs to be operated, the method proceeds to step  550 , the analog-to-digital converter  1228  respectively converts the first analog value Vphoto(m 1 ) and the second analog value Vphoto(m 2 ) to a first digital value D 1 ( m   1 ) and a second digital value D 1 ( m   2 ). Then, the method proceeds to step  560 , the checking unit  1229  checks whether the difference between the first digital value D 1 ( m   1 ) and the second digital value D 1 ( m   2 ) is larger than a checking value. If the difference between the first digital value D 1 ( m   1 ) and the second digital value D 1 ( m   2 ) is larger than a checking value, the first digital value D 1 ( m   1 ) and the second digital value D 1 ( m   2 ) are burnt to the analog-to-digital converter  1227  to determine an output voltage range of the analog-to-digital converter  1227 . 
     The light-sensitive driving circuit, the light-sensitive driving method and the display disclosed in the above embodiment of the invention at least have the following advantages. 
     Firstly, the lifespan of the light-sensitive apparatus is prolonged. 
     Secondly, the problem that given the same luminance, the digital signal outputted by the light-sensing element disposed on different display panels is different is resolved. 
     Thirdly, the invention has a checking function to assure that the light-sensitive apparatus functions normally. 
     Fourthly, the invention has a burning function and is capable of determining the output voltage range of the analog-to-digital converter according to the characteristics of the light-sensing element of the display panel. 
     Fifthly, the digital signal can be flexibly switched to different orders according to different output voltage ranges to meets customers&#39; needs 
     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.