Patent Publication Number: US-9905186-B2

Title: Liquid crystal panel and driving method thereof and liquid crystal display

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the technical field of liquid crystal displays, and in particular to a liquid crystal panel and a driving method thereof, and also relates to a liquid crystal display comprising the liquid crystal panel. 
     2. The Related Arts 
     A liquid crystal display (LCD) is a flat and ultra-thin display device, which is composed of a predetermined number of color or monochromic pixels to be placed in front of a light source or a reflection surface. The liquid crystal display has extremely low power consumption and possesses various advantages, such as high image quality, small volume, and light weight, and are thus very favorite by the public, making it the mainstream of display devices. The liquid crystal displays that are currently available are primarily thin-film transistor (TFT) liquid crystal displays. A liquid crystal panel is a major component of the liquid crystal display. 
       FIG. 1  is a schematic view showing the structure of a conventional liquid crystal panel. As shown in  FIG. 1 , the liquid crystal panel comprises a display area  1  comprising an array of pixel units px arranged therein, a source controller  2 , a gate controller  3 , a gamma voltage control section  4 , and a chamfer voltage control section  5 , wherein the chamfer voltage control section  5  supplies a chamfer voltage to the gate controller  4  to allow the gate controller  4  to generate a corresponding scan signal supplied to the pixel units px. The gamma voltage control section  3  supply a gamma voltage to the source controller  2  to allow the source controller  2  to generate a corresponding data signal supplied to the pixel units px. The pixel units px of the liquid crystal panel comprises a thin-film transistor and an equivalent circuit diagram of a pixel unit px is illustrated in  FIG. 2 . As shown in  FIG. 2 , in the drawing, Vgh indicates a turn-on voltage that the gate controller  4  supplies to the thin-film transistor; Vgl indicates a turn-off voltage that the gate controller  4  supplies to the thin-film transistor; Cgs indicates a parasitic capacitor; Cst indicates a storage capacitor; and Ccl indicates a liquid crystal capacitor. Due to the existence of the parasitic capacitor Cgs, repeatedly turning on and off the thin-film transistor leads to the generation of a feed-through voltage ΔV, wherein ΔV=(Vgh−Vgl)Cgs/(Cgs+Ccl+Cst). The existence of ΔV affects the displaying quality of the liquid crystal panel, such as generating a flicker phenomenon. The liquid crystal panel discussed above uses the chamfer voltage control section  5  to generate a chamfer voltage supplied to the gate controller  4  and the scan signal supplied from the gate controller  4  to the thin-film transistor has a waveform illustrated in  FIG. 3 . By decreasing the difference between the turn-on voltage Vgh and the turn-off voltage Vgl, the purpose of reducing ΔV may be achieved. 
     In the liquid crystal panel provided above, the chamfer voltage control section  5  supplies a fixed chamfer voltage. In other words, the difference between the turn-on voltage Vgh and the turn-off voltage Vgl is set constant for image signals of different grey levels. However, for different grey levels, the liquid crystal capacitor Clc is different and ΔV increases with the increase of the grey level. The relationship between ΔV and grey level is illustrated in  FIG. 4 . The greater the difference of ΔV between high and low grey levels is, the more unbalanced the common voltage Vcom of the pixel unit px will be and the worse the displaying performance of the liquid crystal panel will be. 
     SUMMARY OF THE INVENTION 
     In view of the shortcomings of the known techniques, an object of the present invention is to provide a liquid crystal panel and the liquid crystal panel allows for reduction of a feed-through voltage ΔV, while at the same time reducing the difference of ΔV between high and low grey levels and enhancing the displaying quality of the liquid crystal panel. 
     To achieve the above object, the present invention provides the following technical solution: 
     A liquid crystal panel, comprising: 
     a display area, which comprises an array of pixel units formed thereon; 
     a gate controller, which supplies a scan signal to the pixel units; 
     a source controller, which supplies a data signal to the pixel units; 
     a chamfer voltage control section, which comprises n chamfer voltage circuits to supply a chamfer voltage to the gate controller to make the gate controller generating the scan signal corresponding thereto; 
     a gamma voltage control section, which comprises n gamma voltage circuits to supply a gamma voltage to the gate controller to make the gate controller generating the data signal corresponding thereto; 
     the liquid crystal panel further comprising an image inspection section, where the image inspection section, in response to an image signal received thereby, classifies images into n classes according to ranking of grey level of the image signal; 
     wherein when the image inspection section inspects and identifies an image belongs to a mth class, the chamfer voltage control section is operated to have a mth one of the chamfer voltage circuits supplying the chamfer voltage to the gate controller and the gamma voltage control section is operated to have a mth one of the gamma voltage circuits supplying the gamma voltage to the gate controller; 
     where n is an integer greater than 1 and m=1, 2, . . . , n. 
     Wherein, when the grey level of the image signal inspected by the image inspection section is higher, the chamfer voltage supplied from the chamfer voltage control section is smaller. 
     Wherein, the chamfer voltage circuits comprise a 3-step circuit. 
     Wherein, the gamma voltage generated by the mth gamma voltage circuit is obtained through an adjustment made according to the chamfer voltage generated by the mth chamfer voltage circuit. 
     A driving method for the above-described liquid crystal panel comprises: 
     the image inspection section receiving the image signal and classifying images into n classes according to ranking of grey level of the image signal; 
     the chamfer voltage control section being operated according to the classification of an image to control one of the n chamfer voltage circuits to supply the chamfer voltage to the gate controller to make the gate controller generate the scan signal supplied to the pixel units; and 
     the gamma voltage control section being operated according to the classification of the image to control one of the n gamma voltage circuits to supply the gamma voltage to the gate controller to make the gate controller generate the data signal supplied to the pixel units; 
     where n is an integer greater than 1. 
     Wherein, when the grey level of the image signal inspected by the image inspection section is higher, the chamfer voltage supplied from the chamfer voltage control section is smaller. 
     Wherein, the chamfer voltage circuits comprise a 3-step circuit. 
     Wherein, the n gamma voltage circuits are arranged to corresponding to the n chamfer voltage circuits in a one-to-one manner and the gamma voltage generated by each of the gamma voltage circuits is obtained through an adjustment made according to the chamfer voltage generated by the corresponding one of the chamfer voltage circuits. 
     Another aspect of the present invention is to provide a liquid crystal display, which comprises a liquid crystal panel and a backlight module. The liquid crystal panel is arranged opposite to the backlight module. The backlight module supplies displaying light to the liquid crystal panel to allow the liquid crystal panel to display an image. The liquid crystal panel adopted is the liquid crystal panel described above. 
     Compared to the prior art techniques, in the liquid crystal panel provided according to the present invention, classification is made according to ranking of grey level of images based on an inputted image signal and selection of corresponding chamfer voltages and gamma voltages is made according to the classes of the images so that while the feed-through voltage ΔV is reduced, the difference of ΔV between high and low grey levels can also be reduced so as to enhance the displaying quality of the liquid crystal panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing the structure of a conventional liquid crystal panel; 
         FIG. 2  shows an equivalent circuit diagram of a pixel unit px of the liquid crystal panel; 
         FIG. 3  shows a waveform diagram of a scan signal supplied from a gate controller of the prior art; 
         FIG. 4  shows a relationship between a feed-through voltage ΔV and grey level of the prior art; 
         FIG. 5  is a schematic view showing the structure of a liquid crystal display provided according to an embodiment of the present invention; 
         FIG. 6  is a schematic view showing the structure of a liquid crystal panel provided according to an embodiment of the present invention; 
         FIG. 7  is a schematic view illustrating classification of images based on the high-low sequence of grey level according to the present invention; 
         FIG. 8  shows a relationship between a feed-through voltage ΔV and grey level according to the present invention; 
         FIG. 9  is a circuit diagram of a chamfer circuit provided according to an embodiment of the present invention; and 
         FIG. 10  shows a waveform diagram of signals generated during an operation process of the chamfer circuit illustrated in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To make the object, technical solution, and advantages of the present invention more clearly understood, the present invention will be further expounded with reference to embodiments of the present invention, in combination with the attached drawings. 
     As shown in  FIG. 5 , a liquid crystal display provided according to the instant embodiment comprises a liquid crystal panel  100  and a backlight module  200 . The liquid crystal panel  100  is arranged opposite to the backlight module  200 . The backlight module  200  supplies displaying light to the liquid crystal panel  100  to allow the liquid crystal panel  100  to display an image. 
     As shown in  FIG. 6 , the liquid crystal panel  100  according to the instant embodiment comprises a display area  10  that comprises an array of pixel units px (of which only a port is shown in the drawing), a source controller  20 , a gamma voltage control section  30 , a gate controller  40 , and a chamfer voltage control section  50 . The chamfer voltage control section  50  supplies a chamfer voltage to the gate controller  40  to make the gate controller  40  generating a corresponding scan signal supplied to the pixel units px. The gamma voltage control section  30  supplies a gamma voltage to the source controller  20  to make the source controller  20  generating a corresponding data signal supplied to the pixel units px. Referring to  FIG. 6 , the liquid crystal panel  100  according to the instant embodiment further comprises an image inspection section  60 . The chamfer voltage control section  50  comprises n chamfer voltage circuits  51  and the gamma voltage control section  30  comprises n gamma voltage circuits  31 , where n is an integer greater than one (1). 
     A driving method for the above-provided liquid crystal panel comprises the following steps: 
     (a) The image inspection section  60  receiving an image signal and divides images into n classes according to ranking of grey levels of the image signal. As shown in  FIG. 7 , the images are classified, according to the grey level ranking, into class_ 1 , class_ 2 , . . . , class_n- 1 , and class_n, namely n classes in total. For a frame of image contains some pixels of high grey levels and some pixels of low grey levels, if the number of the pixels of high grey levels is greater, then the frame of image is classified as one belonging to a class of high grey level; and if the number of the pixels of low grey levels is greater, then the frame of image is classified as one belonging to a class of low grey level. 
     (b) The chamfer voltage control section  50  is operated according to the class of an image to control one of the n chamfer voltage circuits  51  to supply a chamfer voltage to the gate controller  40  to make the gate controller  40  generating a scan signal supplied to the pixel units px. For example, when the image inspection section  60  inspects and identifies an image belonging to the mth class, the mth chamfer voltage circuit of the chamfer voltage control section  50  supplies a chamfer voltage to the gate controller  40 . 
     (c) The gamma voltage control section  30  is operated according to the class of the image to control one of the n gamma voltage circuits  31  to supply a gamma voltage to the source controller  20  to make the source controller  20  generate a data signal supplied to the pixel units px. For example, when the image inspection section  60  inspects and identifies the image belonging to the mth class, the mth gamma voltage circuit of the gamma voltage control section  30  supplies a gamma voltage to the source controller  20 . 
     In the above, n is an integer greater than one (1) and m=1, 2, . . . , n. 
     When the grey level of an image signal inspected by the image inspection section  60  is higher (namely the image belongs to a class of a higher grey level), the chamber voltage supplied from the chamfer voltage control section  50  gets smaller. As such, when the grey level of an image to be displayed is higher, the chamfer voltage supplied from the chamfer voltage control section  50  is made smaller so that a difference between a turn-on voltage Vgh and a turn-off voltage Vgl is reduced; and when the grey level of an image displayed is lower, the chamfer voltage supplied from the chamfer voltage control section  50  is corresponding larger so that the difference between the turn-on voltage Vgh and the turn-off voltage Vgl is correspondingly enlarged. Through controlling the difference between the turn-on voltage Vgh and the turn-off voltage Vgl for different grey levels, reduction of the difference of ΔV between high and low grey levels within the full grey level range can be achieved and a curve indicating the relationship between ΔV and grey level is shown in  FIG. 8 . 
     In the instant embodiment, the n gamma voltage circuits  31  arranged to correspond to the n chamfer voltage circuits  51  in a one-to-one manner. Controlling of each gamma voltage circuit  31  to generate a gamma voltage is based on the chamfer voltage generated by the corresponding one of the chamfer voltage circuits  51 . 
     The chamfer voltage circuits  51  may be arranged as a 3-step circuit. Specifically, a 3-step circuit provided according to the instant embodiment is shown in  FIG. 9 . The circuit comprises a Zener diode ZD 1 , a first N-type metal oxide semiconductor (MOS) transistor Q 1 , a second N-type MOS transistor Q 2 , and a P-type MOS transistor Q 3 . The first N-type MOS transistor Q 1  has a source terminal electrically connected to ground, a gate terminal connected to a driving signal GVOFF, and a drain terminal connected by a first resistor R 1  and a second resistor R 2  to a source terminal of the P-type MOS transistor Q 3  and receiving a reference voltage signal VGHP. The P-type MOS transistor Q 3  has a drain terminal connected to a connection line A and the P-type MOS transistor Q 3  has a gate terminal connected to a point between the first resistor R 1  and the second resistor R 2 . The second N-type MOS transistor Q 2  has a source terminal electrically connected to ground, a gate terminal connected to a phase-reversed signal GVON of the driving signal, and a drain terminal connected to a positive terminal of the Zener diode ZD 1 . The Zener diode ZD 1  has a negative terminal connected by a third resistor R 3  to the drain terminal of the P-type MOS transistor Q 3 . The connection line A is electrically connected through a capacitor C 1  to ground. In the circuit, a chamfer voltage VGH is outputted through the connection line A. 
     Referring to  FIG. 9 , together with a waveform diagram illustrated in  FIG. 10 , an operation process of the 3-step circuit shown in  FIG. 9  is as follows: 
     (1) When the driving signal GVOFF is of a high level, the first N-type MOS transistor Q 1  is turned on and the P-type MOS transistor Q 3  is turned on; and under this condition, the phase-reversed signal GVON of the driving signal is at a low level so that the second N-type MOS transistor Q 2  is turned off, namely the chamfer voltage outputted is VGH=VGHP and no chamfering is applied. 
     (2) When the driving signal GVOFF is of a low level, the first N-type MOS transistor Q 1  is turned off and the P-type MOS transistor Q 3  is turned off; under this condition, the phase-reversed signal GVON of the driving signal is at a high level so that the second N-type MOS transistor Q 2  is turned on and makes the positive terminal of the Zener diode ZD 1  grounded and voltage accumulated in the capacitor C 1  is discharged through the Zener diode ZD 1  thereby applying chamfering to the outputted chamfer voltage VGH, namely VGH&lt;VGHP. The resistance of the third resistor R 3  is used to control the speed of discharging of the capacitor C 1  and through adjusting parameters of the Zener diode ZD 1 , a bottom line of descending of the chamfer voltage VGH can be limited. Thus, for different ones of the chamfer voltage circuits  51 , through varying the parameters of the Zener diode ZD 1 , different chamfer voltages can be obtained. 
     In summary, compared to the prior art techniques, in the liquid crystal panel provided according to the present invention, classification is made according to ranking of grey level of images based on an inputted image signal and selection of corresponding chamfer voltages and gamma voltages is made according to the classes of the images so that while the feed-through voltage ΔV is reduced, the difference of ΔV between high and low grey levels can also be reduced so as to enhance the displaying quality of the liquid crystal panel. 
     Although the present invention has been described with reference to the preferred embodiments thereof, it is noted that those having ordinary skills may appreciate improvements and modifications without departing from the principle of the present invention and those improvements and modifications are considered within the scope of protection of the present invention.