Driving circuit of LCD panel, LCD device, and method for driving the liquid crystal panel

The present disclosure relates to the field of liquid crystal displays (LCDs), and more particularly to a driving circuit of an LCD panel, an LCD device, and a method for driving the LCD panel.

Over drive (OD) is an important technology and is used to improve dynamic picture quality of a liquid crystal display (LCD) panel. Working principle of the OD is that a signal C is inserted between a signal A and a signal B when the signal A changes to the signal B, and LC molecules are driven to quickly deflect by a voltage difference between the signal A and the signal C. When one frame time of the signal C ends, a deflection angle of the LC molecules exactly accords with an angle requirement of the signal B. In a driving circuit of an LCD, a grey scale corresponds to a voltage of a signal, and the LCD panel automatically looks up a corresponding voltage of the signal C according to grey scale values of the signal A and the signal B. Most LCD panels currently use a color depth of 8-bit, and the signal A and the signal B have 256 grey scales, so capacity of an OD table is 256*256*8-bit (the 8-bit is storage space of the voltage of the signal C). If an OD table of a red pixel, an OD table of a green pixel, and an OD table of a blue pixel are different, the capacity of the OD table is 3*256*256*8-bit.

In most LCD driving circuits, space of a read-only memory (ROM) storing the OD table is not large, thus, an OD table of 17*17*8-bit is used. As shown in FIG. 1 , in the OD table, the corresponding voltage of the signal C is added according to a grey scale value of the signal A and a grey scale value of the signal B, the grey scale values of the signal A is obtained from each of the 16 grey scales of the grey scale values of the signal A, and the grey scale value of the signal B is obtained from each of the 16 grey scales of the grey scale values of the signal B. An OD value of grey scales among each 16 grey scales is calculated by linear interpolation according to surrounding four voltages of the signal C, an equation of calculating the OD value is:

The above-mentioned method solves a problem of the storage of the OD table, but linear interpolation is not accurate, thus the OD table is also not accurate, which causes colored trailing of the dynamic picture.

In view of the above-described problems, the aim of the present disclosure is to provide a driving circuit of a liquid crystal display (LCD) panel, a liquid crystal display (LCD) device, and a method for driving the LCD panel capable of using a small storage space for an over drive (OD) table and avoiding colored trailing of a dynamic picture.

The purpose of the present disclosure is achieved by the following methods:

A method for driving a liquid crystal display (LCD) panel comprises

A: setting an M*M over drive (OD) table by regarding N grey scales as one unit, the M*M OD table comprises a grey scale value XN*a of a previous-frame image, a grey scale value XN*b of a current-frame image, and an OD value (XN*a, XN*b) corresponding to the grey scale value XN*a and the grey scale value XN*b, where a and bε[0, M], N and M are integers, and N>=2;

B: regarding x′ as the grey scale value of the previous-frame image and y′ as the grey scale value of the current-frame image when the LCD panel is driven, and finding out an effective OD value (x′, y′) from the OD table. If x′ is equal to XN*a, and y′ is equal to XN*b, the effective OD value (x′, y′) is directly found out from the OD table; if x′ is not equal to XN*a, and y′ is not equal to XN*b, a three-dimensional coordinate system is set according to coordinate axis of x′, y′, and the OD value (x′, y′); the OD value (x′, y′) is fitted to a continuous two-dimensional surface by reference to the OD value (XN*a, XN*b) in the OD table, and the OD value (x′, y′) is correspondingly calculated according to function of the two-dimensional surface fitted; and

C: outputting the OD value (x′, y′) to the LCD panel after the previous-frame image is output but before the current frame image is output.

Furthermore, the two-dimensional surface in the step B is divided into M*M sub-surfaces, and first derivatives of junctional areas of all sub-surfaces are continuous. The function of the two-dimensional surface fitted in the step B is formed by a sub-surface equation corresponding to each of the sub-surfaces.

The sub-surface equation corresponding to each of the sub-surfaces is:

OD ( x,y )= A+Bx+Cy+Dxy+Ex 2 +Fy 2 +Gx 2 y+Hxy 2 +Ix 3 +Jy 3 , xε[ 0 ,N ), yε[ 0 ,N )  (1)

A boundary condition corresponding to each of the sub-surfaces is:

In the above-mentioned equation:

1) x is a grey scale value of the previous-frame image corresponding to the sub-surface, y is a grey scale value of the current-frame image corresponding to the sub-surface, x′ is a grey scale value of the previous-frame image corresponding to an entire two-dimensional surface, and y′ is a grey scale value of the current-frame image corresponding to the entire two-dimensional surface.

2) A, B, C, D, E, F, G, H, I, and J are constant parameters of each of the surfaces, wherein each of the constant parameters is calculated according to the boundary condition of the corresponding sub-surface.

3) Ch is an OD value corresponding to a left-lower boundary of the sub-surface, Ci is an OD value corresponding to a right-lower boundary of the sub-surface, Cj is an OD value corresponding to a left-upper boundary of the sub-surface, Ck is an OD value corresponding to a right-upper boundary of the sub-surface, Cl is an OD value corresponding to a left-lower boundary of an adjacent sub-surface on the right, Cm is an OD value corresponding to a left-upper boundary of the adjacent sub-surface on the right.

If a grey scale value of a current sub-surface lies in coordinate (x+N*a, y+N*b) of the entire two-dimensional surface, a grey scale value of the adjacent sub-surface on the right lies in coordinate (x+N*(a+1), y+N*b) of the entire two-dimensional surface.

This is a specific function of the two-dimensional surface. The two-dimensional surface is divided into a plurality of sub-surfaces, and the first derivatives of junctional areas of all sub-surfaces is continuous, thus reading the grey scale value x′ of the previous-frame image and the grey scale value y′ of the current-frame image, and after finding out the grey scale coordinate (x, y) of the grey scale value x′ and the grey scale value y′ which correspond to the sub-surface, the OD value (x′, y′) can be calculated according to the equation of the sub-surface and the boundary condition of the sub-surface where the OD value (x′, y′) accurately corresponds to the grey scale value (x′, y′).

Furthermore, the step B comprises:

B1-1: reading the grey scale value x′ of the previous-frame image and the grey scale value y′ of the current-frame image;

B1-2: looking up a grey scale coordinate (x, y) of the grey scale value x′ and the grey scale value y′ that correspond to the sub-surface;

B1-3: reading the OD value Ch corresponding to the left-lower boundary of the sub-surface, the OD value Ci corresponding to the right-lower boundary of the sub-surface, the OD value Cj corresponding to the left-upper boundary of the sub-surface, the OD value Ck corresponding to the right-upper boundary of the sub-surface, the OD value Cl corresponding to the left-lower boundary of the adjacent sub-surface on the right, and the OD value Cm corresponding to the left-upper boundary of the adjacent sub-surface on the right from the OD table; and

B1-4: calculating the OD value (x, y) according to the equations of (1)-(11);

x′=x+N*a, y′=y+N*b , and a and bε[ 0 ,M].

In the method, the driving circuit of the LCD panel only stores the OD table corresponding to the boundary of each of the sub-surfaces and does not store the OD value corresponding to each of the sub-surfaces, which lowers storage space requirements and decreases component costs.

Furthermore, the step B comprises:

B2-1: reading the OD value Ch corresponding to the left-lower boundary of the sub-surface, the OD value Ci corresponding to the right-lower boundary of the sub-surface, the OD value Cj corresponding to the left-upper boundary of the sub-surface, the OD value Ck corresponding to the right-upper boundary of the sub-surface, the OD value Cl corresponding to the left-lower boundary of the adjacent sub-surface on the right, and the OD value Cm corresponding to the left-upper boundary of the adjacent sub-surface on the right from the OD table;

B2-2: calculating the constant parameter of the equation (1) of each of the sub-surfaces by substituting the OD value Ch, Ci, Cj, Ck, Cl, and Cm into the equation (2)-(11) of the boundary condition of each of the sub-surfaces, and storing the constant parameters into a constant parameter table;

B2-3: reading the grey scale value x′ of the previous-frame image and the grey scale value y′ of the current-frame image, and looking up the grey scale coordinate (x, y) of the grey scale value x′ and the grey scale value y′ that correspond to the sub-surface; and

B2-4: calculating the OD value (x, y) according to the equations of (1) of the current sub-surface, wherein the grey scale coordinate (x, y) and the corresponding constant parameter are substituted into the equation (1);

x′=x+N*a, y′=y+N*b , and a and bε[ 0 ,M].

In the method, the constant parameter of the equation of each of the sub-surfaces is calculated in advance and stored in the driving circuit, when the LCD panel is driven, as long as the equation of the sub-surface corresponding to the grey scale value can be determined, the OD value (x′, y′) can be calculated by directly substituting the grey scale coordinate (x, y) into the equation of the sub-surface, which avoids calculation of the constant parameter, thereby improving response speed of the driving circuit and improves display quality of the LCD panel.

Furthermore, M is equal to 17, and N is equal to 16. This is a specific value of M and N, brightness of the display picture is divided into 256 grey scales, and each of the 16 grey scales is regarded as one unit.

A driving circuit of a liquid crystal display (LCD) panel comprises a frame buffer unit storing a previous-frame image, an over drive (OD) table unit storing an M*M OD table set through regarding N grey scales as one unit, and a calculation unit coupled to the OD table unit. The M*M OD table comprises a grey scale value XN*a of the previous-frame image, a grey scale value XN*b of a current-frame image, and an OD value (XN*a, XN*b) corresponding to the grey scale value XN*a and the grey scale value XN*b, where a and bε[0, M], N and M are integers, and N>=2. A grey scale value y′ of the current-frame image and a grey scale value x′ of the previous-frame image stored in the frame buffer unit are sent to the calculation unit, the calculation unit finds out an effective OD value (x′, y′) from the OD table, then the effective OD value (x′, y′) is output to a corresponding data line of the LCD panel.

If x′ is equal to XN*a, and y′ is equal to XN*b, the effective OD value (x′, y′) is directly found out from the OD table.

If x′ is not equal to XN*a, and y′ is not equal to XN*b, a three-dimensional coordinate system is set according to coordinate axis of x′, y′, and the OD value (x′, y′). The OD value (x′, y′) is fitted to a continuous two-dimensional surface by reference to the OD value (XN*a, XN*b) in the OD table, and the OD value (x′, y′) is correspondingly calculated according to function of the two-dimensional surface fitted.

Furthermore, the calculation unit comprises a surface generating unit, a limited unit storing a boundary condition of each of the sub-surfaces, and an arithmetic unit obtaining the OD value (x′, y′) by calculating the equation of each of the sub-surfaces. The surface generating unit divides the two-dimensional surface into M*M sub-surfaces, and allows first derivatives of junctional areas of all sub-surfaces to be continuous.

The sub-surface equation corresponding to each of the sub-surfaces is:

OD ( x,y )= A+Bx+Cy+Dxy+Ex 2 +Fy 2 +Gx 2 y+Hxy 2 +Ix 3 +Jy 3 , xε[ 0 ,N ), yε[ 0 ,N )  (1)

The boundary condition corresponding to each of the sub-surfaces is:

In the above-mentioned equation:

1) x is a grey scale value of the previous-frame image corresponding to the sub-surface, y is a grey scale value of the current-frame image corresponding to the sub-surface, x′ is a grey scale value of the previous-frame image corresponding to an entire two-dimensional surface, and y′ is a grey scale value of the current-frame image corresponding to the entire two-dimensional surface.

2) A, B, C, D, E, F, G, H, I, and J are constant parameters of each of the surfaces, wherein each of the constant parameters is calculated according to the boundary condition of the corresponding sub-surface.

3) Ch is an OD value corresponding to a left-lower boundary of the sub-surface, Ci is an OD value corresponding to a right-lower boundary of the sub-surface, Cj is an OD value corresponding to a left-upper boundary of the sub-surface, Ck is an OD value corresponding to a right-upper boundary of the sub-surface, Cl is an OD value corresponding to a left-lower boundary of an adjacent sub-surface on the right, Cm is an OD value corresponding to a left-upper boundary of the adjacent sub-surface on the right.

If a grey scale value of a current sub-surface lies in coordinate (x+N*a, y+N*b) of the entire two-dimensional surface, a grey scale value of the adjacent sub-surface on the right lies in coordinate (x+N*(a+1), y+N*b) of the entire two-dimensional surface.

This is a specific function of the two-dimensional surface. The two-dimensional surface is divided into a plurality of sub-surfaces, and the first derivatives of junctional areas of all sub-surfaces is continuous, thereby reading the grey scale value x′ of the previous-frame image and the grey scale value y′ of the current-frame image, and finding out the grey scale coordinate (x, y) of the grey scale value x′ and the grey scale value y′ that correspond to the sub-surface, the OD value (x′, y′) can be calculated according to the equation of the sub-surface and the boundary condition of the sub-surface where the OD value (x′, y′) accurately corresponds to the grey scale value (x′, y′). The driving circuit only stores the OD value corresponding to the boundary of each of the sub-surfaces and does not store the OD value corresponding to each of the sub-surfaces, which lowers storage space requirements and decreases component costs.

Furthermore, the driving circuit of the LCD panel further comprises a parameter unit, where the parameter unit is coupled to the calculation unit, and stores a constant parameter table of the equation of each of the sub-surfaces. In the method, the constant parameter of the equation of each of the sub-surfaces is calculated in advance and stored in the driving circuit, when the LCD panel is driven, as long as the equation of the sub-surface corresponding to the grey scale value can be determined, the OD value (x′, y′) can be calculated by directly substituting the grey scale coordinate (x, y) into the equation of the sub-surface, which avoids calculation of the constant parameter, thereby improving response speed of the driving circuit and improves display quality of the LCD panel.

Furthermore, the driving circuit of the LCD panel further comprises a data comparator. The frame buffer unit is coupled to the calculation unit through the data comparator, and the grey scale value x′ of the previous-frame image and the grey scale value y′ of the current-frame image are sent to the calculation unit by the data comparator. In the present disclosure, the data comparator extracts the grey scale values of the previous-frame image and the current-frame image, and sends the grey scale values of the previous-frame image and the current-frame image to the calculation unit, the calculation unit directly reads the grey scale values and substitutes the grey scale values into the equation of the sub-face, which improves calculating speed of the calculation unit.

A liquid crystal display (LCD) device comprises a liquid crystal display (LCD) panel comprising a plurality of data lines, the plurality of data lines are coupled to the above-mentioned driving circuit of the LCD panel.

The present disclosure builds the M*M OD table by regarding N grey scales as one unit, the M*M OD table comprises the grey scale value XN*a of the previous-frame image, the grey scale value XN*b of the current-frame image, and the OD value (XN*a, XN*b) corresponding to the grey scale value XN*a and the grey scale value XN*b, where N>=2. Compared with a method of the OD value corresponding to each of the grey scales, the present disclosure lowers storage space requirements. Additionally, in the present disclosure, the OD value (x′, y′) is fitted to the continuous two-dimensional surface by reference to the OD value (XN*a, XN*b) in the OD table, thus the exact OD value (x′, y′) is calculated by each of the grey scale coordinate (x′, y′) according to the function of the two-dimensional surface fitted, which avoids a colored trailing of dynamic picture.

FIG. 1 is a diagram of a method for calculating an over drive (OD) value of the prior art.

FIG. 2 is a flowchart of a method for driving a liquid crystal display (LCD) panel of the present disclosure.

FIG. 3 is a flowchart of a method for driving a liquid crystal display (LCD) panel of a first example of the present disclosure.

FIG. 4 is a flowchart of a method for driving a liquid crystal display (LCD) of a second example of the present disclosure.

FIG. 5 is a schematic diagram of a driving circuit of a liquid crystal display (LCD) panel excluding a parameter unit of a third example of the present disclosure.

FIG. 6 is a schematic diagram of a driving circuit of a liquid crystal display (LCD) panel including a parameter unit of a third example of the present disclosure.

As shown in FIG. 2 , the present disclosure provides a method for driving a liquid crystal display (LCD) panel, comprising:

A: setting an M*M over drive (OD) table by regarding N grey scales as one unit, the M*M OD table comprises a grey scale value XN*a of a previous-frame image, a grey scale value XN*b of a current-frame image, and an OD value (XN*a, XN*b) corresponding to the grey scale value XN*a and the grey scale value XN*b, where a and bε[0, M], N and M are integers, and N>=2.

B: regarding x′ as the grey scale value of the previous-frame image and y′ as the grey scale value of the current-frame image when the LCD panel is driven, and finding out an effective OD value (x′, y′) from the OD table. If x′ is equal to XN*a, and y′ is equal to XN*b, the effective OD value (x′, y′) is directly found out from the OD table. If x′ is not equal to XN*a, and y′ is not equal to XN*b, a three-dimensional coordinate system is set according to coordinate axis of x′, y′, and the OD value (x′, y′). The OD value (x′, y′) is fitted to a continuous two-dimensional surface by reference to the OD value (XN*a, XN*b) in the OD table, and the OD value (x′, y′) is correspondingly calculated according to function of the two-dimensional surface fitted,

C: outputting the OD value (x′, y′) to the LCD panel after the previous-frame image is output but before the current frame image is output.

The present disclosure sets the M*M OD table by regarding N grey scales as one unit, the M*M OD table comprises the grey scale value XN*a of the previous-frame image, the grey scale value XN*b of the current-frame image, and the OD value (XN*a, XN*b) corresponding to the grey scale value XN*a and the grey scale value XN*b, where N>=2. Compared with a method of the OD value corresponding to each of the grey scales, the present disclosure lowers storage space requirements. Additionally, in the present disclosure, the OD value (x′, y′) is fitted to the continuous two-dimensional surface by reference to the OD value (XN*a, XN*b) in the OD table, thus an exact OD value (x′, y′) is calculated by each of the grey scale coordinate (x′, y′) according to the function of the two-dimensional surface fitted, which avoids colored trailing of a dynamic picture.

The present disclosure is further described in detail in accordance with the figures and the exemplary examples.