1. Field of the Invention
The present invention relates to a liquid crystal display device using an OCB mode liquid crystal and a method of driving the liquid crystal display device.
2. Prior Art of the Invention
A liquid crystal display device is thin and light, and has been used in an increasingly wide range of application as a substitute for a conventional cathode ray tube in recent years. However, a TN (Twisted Nematic) aligned liquid crystal panel which is currently used in a wide range has a narrow view angle, a slow response speed and its image quality is inferior to that of a cathode ray tube, for example, when a moving image is displayed its image appears to linger.
In contrast, a liquid crystal display device using an OCB (Optically Compensated Birefringence) mode featuring high-speed response and a high view angle is available in recent years. This liquid crystal display device is designed to obtain a wide view angle through visual compensation by bend-aligning the liquid crystal and further combining this with an optical phase compensation film.
Nematic liquid crystal, as shown as liquid crystal molecule 52 in
The bent state 54a shown in
Continuously applying a voltage of 2 V or less to the liquid crystal display panel of the liquid crystal display device using the OCB mode causes the liquid crystal display panel to gradually transition from the bent state 54a, 54b to the spray state 53 (hereinafter this transition will be referred to as “counter-transfer”). To prevent such counter-transfer, the liquid crystal display device using the OCB mode performs a drive called a “counter-transfer prevention drive.”
That is, the counter-transfer prevention drive refers to a drive for preventing counter-transfer by periodically applying a voltage corresponding to a black color to each pixel. The counter-transfer prevention drive includes a counter-transfer prevention drive called a “double-speed conversion” which alternately performs an operation of applying a voltage corresponding to a black color to each pixel to prevent counter-transfer and an operation of applying a display voltage. Such a drive allows a high contrast display to be realized. However, the double-speed conversion needs to drive each pixel twice as fast as when no counter-transfer prevention drive is performed, and therefore it is difficult to drive the liquid crystal display device. It is a 1.25-fold speed conversion shown below that solves such a problem.
A 1.25-fold speed conversion which is a kind of counter-transfer prevention drive will be explained using
A source signal line 13 is connected to the source driver 11 through a switch 25 and a gate signal line 15 is connected to a gate driver (not shown). Furthermore, a precharge line 24 is connected to each source signal line 13 through each switch 25. The precharge line 24 is connected to the black insertion voltage generation circuit 101. That is, the switch 25 can select whether the source signal line 13 is connected to the source driver 11 or connected to the black insertion voltage generation circuit 101 through the precharge line 24.
A pixel transistor 18, a pixel electrode 19 and a storage capacitor Cst 20 for adding a compensation potential are formed at the intersection between the source signal line 13 and gate signal line 15 and a liquid crystal layer (not shown) in an OCB mode is sandwiched between the pixel electrode 19 and an opposite electrode 16. Furthermore, one end of the storage capacitor Cst 20 is connected to the pixel electrode 19 and the other end of the storage capacitor Cst 20 is connected to a common electrode 17. Furthermore, the gate of the pixel transistor 18 is connected to the gate signal line 15, the source of the pixel transistor is connected to the source signal line 13 and the drain of the pixel transistor 18 is connected to the pixel electrode 19. Furthermore, a Clc 21 is a capacitor formed of the pixel electrode 19, the opposite electrode 16 and the liquid crystal layer in the OCB mode, a Cgs 23 is a capacitor formed of the gate and source of the pixel transistor 18 and a Cgd 22 is a capacitor formed of the gate and drain of the pixel transistor 18.
The “pixel” in the following descriptions will refer to the part consisting of the pixel electrode 19, pixel transistor 18, storage capacitor Cst 20, portion of the opposite electrode 16 facing the pixel electrode 19 and liquid crystal layer in the OCB mode sandwiched by portion of the opposite electrode 16 facing the pixel electrode 19 and the pixel electrode 19.
The 1.25-fold speed conversion converts an originally 4H video period to a 1.25-fold speed. That is, a 5H video period is provided in the originally 4H video period. Then, a black color is shown during the first 1H video period of the 5H video period and display colors are shown during the remaining 4H video period. Therefore, the 1H video period converted to the 1.25-fold speed is shortened to 0.8 times the original 1H video period. Such a 1.25-fold speed conversion is carried out by a controller circuit 6.
During a 1 horizontal scanning period T1, the black insertion voltage generation circuit 101 writes voltages corresponding to the black color into the four pixels g5, g6, g7, g8 simultaneously. That is, the switches 25 connected to the source signal lines 13 to which these four pixels are connected are switched in such a way that the black insertion voltage generation circuit 101 is connected to the source signal line 13 to which these four pixels are connected. Therefore, voltages corresponding to the black color are applied to these four pixels from the black insertion voltage generation circuit 101.
During the next 1 horizontal scanning period T2, the source driver 11 applies a voltage corresponding to a display color to the pixel g1. That is, the switch 25 connected to the source signal lines 13 to which the pixel g1 is connected is switched in such a way that the source driver 11 is connected to the source signal line 13 to which the pixel g1 is connected. Therefore, the source driver 11 applies the voltage corresponding to the display color to the pixel g1.
Likewise, during a 1 horizontal scanning period T3, a voltage corresponding to the display color is applied to the pixel g2. Then, during a 1 horizontal scanning period T4, a voltage corresponding to the display color is applied to the pixel g3. During a 1 horizontal scanning period T5, a voltage corresponding to the display color is applied to the pixel g4.
Furthermore, during a 1 horizontal scanning period T6, voltages corresponding to the black color are applied to the pixels g9, g10, g11, g12. During 1 horizontal scanning periods T7, T8, T9, T10, voltages corresponding to the display color are applied to the pixel g5, g6, g7, g8 respectively.
By repeating the above described operation, a 1.25-fold speed conversion is performed. Counter-transfer prevention is realized by applying voltages corresponding to the black color to four pixels during 1 horizontal scanning periods T1, T6, etc., through the black insertion voltage generation circuit 101. Thus, by performing a 1.25-fold speed conversion, it is possible to prevent counter-transfer even when a voltage of 2 V or less is applied to pixels.
In a 1.25-fold speed conversion, the speed at which each pixel is displayed becomes 1.25 times the speed when no counter-transfer prevention drive is performed. Thus, the 1.25-fold speed conversion eliminates the necessity to drive each pixel at a high speed as in the case of a double-speed conversion, and therefore it is possible to easily drive the liquid crystal display device and also achieve high contrast as the liquid crystal display device as in the case of the double-speed conversion.
However, when the temperature is as low as 10° C. or below, if each pixel of the liquid crystal display device is displayed, for example, in the same halftone color, streaks which are more blackish than the original display color appear every four lines on the display surface of the liquid crystal display panel as shown in
That is,
When the temperature is low, the capacitance of the liquid crystal increases, and therefore insufficient writing to the source line occurs. That is, even if a voltage corresponding to the black color is applied in order to prevent counter-transfer and then a voltage corresponding to the halftone color is applied to the next pixel, the source signal line 13 does not reach the voltage corresponding to the halftone color due to a parasitic capacitance, etc., of the source signal line 13. When the voltage corresponding to the halftone color is applied to the next pixel, the voltage of the source signal line 13 considerably approximates to the voltage corresponding to the halftone color, and therefore the source signal line 13 becomes the voltage corresponding to the halftone color. Thus, the pixels to which the voltages corresponding to the halftone color are applied immediately after writing the voltage corresponding to the black color for prevention of counter-transfer are displayed in black due to insufficient charge.
This problem that streaks which are more blackish than the original display color appear when the same halftone color is displayed on each pixel is not limited to a 1.25-fold speed conversion whereby the voltage corresponding to the black color is applied to four pixels simultaneously to prevent counter-transfer and then voltages corresponding to the respective display colors are sequentially applied to the four pixels. The same problem also occurs with a counter-transfer prevention drive whereby voltages corresponding to the black color are applied to n pixels simultaneously to prevent counter-transfer and then voltages corresponding to the respective display colors are sequentially applied to the n pixels. Furthermore, the same problem also occurs when each pixel is displayed not only with halftone colors but also with white color.
That is, when a counter-transfer prevention drive is performed through a liquid crystal display device using the OCB mode and the temperature is low, if each pixel is displayed in the same color such as a halftone color or white color, there is a problem that streaks which are more blackish than the original display color are displayed on the display surface of the display panel.
In view of the above described problems, it is an object of the present invention to provide a liquid crystal display device free of streaks which are more blackish than the original display color displayed on the display surface of the display panel even when the temperature is low or when each pixel is displayed in the same color such as a halftone color or white color and a method of driving the liquid crystal display device.
The 1st aspect of the present invention is a liquid crystal display device comprising:
The 2nd aspect of the present invention is the liquid crystal display device according to the 1st aspect of the present invention, wherein said voltage adjusted to a voltage value corresponding to predetermined voltage value means such a voltage that a voltage of said source signal lines becomes a voltage corresponding to a halftone color.
The 3rd aspect of the present invention is the liquid crystal display device according to the 2nd aspect of the present invention, wherein said black insertion voltage generation circuit supplies, as the voltage to be supplied to prevent counter-transfer during said counter-transfer prevention drive period, a voltage according to the voltage corresponding to the gradation of said display data supplied to said source signal lines after the counter-transfer prevention drive period.
The 4th aspect of the present invention is the liquid crystal display device according to the 2nd aspect of the present invention, wherein said black insertion voltage generation circuit supplies, as the voltage supplied to prevent counter-transfer during said counter-transfer prevention drive period, a voltage according to a temperature.
The 5th aspect of the present invention is the liquid crystal display device according to the 2nd aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 6th aspect of the present invention is the liquid crystal display device according to the 5th aspect of the present invention, wherein in case said black insertion voltage generation circuit serves as said source driver, said source driver supplies, as the voltage supplied to prevent counter-transfer during said counter-transfer prevention dive period, a voltage according to the voltage corresponding to gradation of said display data supplied to said source signal lines after the counter-transfer prevention drive period.
The 7th aspect of the present invention is the liquid crystal display device according to the 5th aspect of the present invention, wherein in case said black insertion voltage generation circuit serves as said source driver, said source driver supplies, as the voltage supplied to prevent counter-transfer during said counter-transfer prevention drive period, a voltage according to a temperature.
The 8th aspect of the present invention is the liquid crystal display device according to the 5th aspect of the present invention, wherein in case said black insertion voltage generation circuit serves as said source driver, said source driver supplies such a voltage that a voltage of said source signal lines becomes the voltage corresponding to a halftone color to said source signal lines during a period after said source driver supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period.
The 9th aspect of the present invention is the liquid crystal display device according to the 5th aspect of the present invention, wherein in case said black insertion voltage generation circuit serves as said source driver, said source driver supplies such a voltage that a voltage of said source signal lines becomes the voltage corresponding to a halftone color to said source signal lines during a period after said source driver supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period.
The 10th aspect of the present invention is the liquid crystal display device according to the 1st aspect of the present invention, wherein in case a voltage of source signal lines is supplied with a voltage adjusted to a voltage value corresponding to predetermined voltage value during a period after said black insertion voltage generation circuit supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period,
The 11th aspect of the present invention is the liquid crystal display device according to the 10th aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 12th aspect of the present invention is the liquid crystal display device according to the 1st aspect of the present invention, wherein in case a voltage of source signal lines is supplied with a voltage adjusted to a voltage value corresponding to predetermined voltage value during a period after said black insertion voltage generation circuit supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period,
The 13th aspect of the present invention is the liquid crystal display device according to the 12th aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 14th aspect of the present invention is the liquid crystal display device according to the 1st aspect of the present invention, wherein in case a voltage of source signal lines is supplied with a voltage adjusted to a voltage value corresponding to predetermined voltage value during a period after said black insertion voltage generation circuit supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period,
The 15th aspect of the present invention is the liquid crystal display device according to the 14th aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 16th aspect of the present invention is a method of driving a liquid crystal display device, said liquid crystal display device comprising:
The 17th aspect of the present invention is the method of driving a liquid crystal display device, according to the 16th aspect of the present invention, wherein said voltage adjusted to a voltage value corresponding to predetermined voltage value means such a voltage that said source signal lines becomes a voltage corresponding to a halftone color.
The 18th aspect of the present invention is the method of driving a liquid crystal display device, according to the 17th aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 19th aspect of the present invention is the method of driving a liquid crystal display device, according to the 16th aspect of the present invention, wherein in case a voltage of source signal lines is supplied with a voltage adjusted to a voltage value corresponding to predetermined voltage value during a period after said black insertion voltage generation circuit supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period,
The 20th aspect of the present invention is the method of driving a liquid crystal display device, according to the 19th aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 21st aspect of the present invention is the method of driving a liquid crystal display device, according to the 16th aspect of the present invention, wherein in case a voltage of source signal lines is supplied with a voltage adjusted to a voltage value corresponding to predetermined voltage value during a period after said black insertion voltage generation circuit supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period,
The 22nd aspect of the present invention is the method of driving a liquid crystal display device, according to the 21th aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The 23rd aspect of the present invention is the method of driving a liquid crystal display device, according to the 16th aspect of the present invention, wherein in case a voltage of source signal lines is supplied with a voltage adjusted to a voltage value corresponding to predetermined voltage value during a period after said black insertion voltage generation circuit supplies said voltage to prevent counter-transfer in said counter-transfer prevention drive period,
The 24th aspect of the present invention is the method of driving a liquid crystal display device, according to the 23rd aspect of the present invention, wherein said black insertion voltage generation circuit may serves as said source driver.
The present invention can provide a liquid crystal display device free of streaks which are more blackish than the original display color displayed on the display surface of the display panel even when the temperature is low or when each pixel is displayed in the same color such as a halftone color or white color and a method of driving the liquid crystal display device.
With reference now to the attached drawings, embodiments of the present invention will be explained below.
First, a first embodiment will be explained.
A liquid crystal display device 1 is a liquid crystal play device using OCB mode liquid crystal.
The liquid crystal display device 1 is constructed of a liquid crystal display panel 2, a gate driver 3, a source driver 11, a liquid crystal drive voltage generation circuit 5, a controller circuit 6 and an input power supply 8.
The liquid crystal display panel 2 is a display panel having source signal lines and gate signal lines arranged in matrix form and pixels provided at intersections between the source signal lines and gate signal lines and using OCB mode liquid crystal.
The gate driver 3 is a circuit that supplies a selection scanning signal for carrying out linear sequential scanning of each gate signal line of the liquid crystal display panel 2.
The source driver 11 is a circuit that supplies each source signal line of the liquid crystal display panel 2 with an image signal voltage.
The liquid crystal drive voltage generation circuit 5 is a circuit that supplies a source driver drive voltage to the source driver 11, supplies a gate driver drive voltage to the gate driver 3 and supplies an opposite signal electrode drive voltage to the opposite signal electrode.
The controller circuit 6 is a circuit that controls image signal processing and drive timing. The controller circuit 6 is a circuit that inputs display data, outputs a display signal corresponding to the display data and sends timing control signals to the source driver 11, gate driver 3 and liquid crystal drive voltage generation circuit 5.
The input power supply 8 is means of supplying power for the liquid crystal display device 1 to operate.
A source signal line 13 is connected to the source driver 11 through a switch 25 and a gate signal line 15 is connected to the gate driver 3. Furthermore, a precharge line 24 is connected to each source signal line 13 through each switch 25. The precharge line 24 is connected to the black insertion voltage generation circuit 12.
That is, the switch 25 allows the source signal line 13 to select whether to be connected to the source driver 11 or connected to the black insertion voltage generation circuit 12 through the precharge line 24.
At the intersection between the source signal line 13 and gate signal line 15, a pixel transistor 18, a pixel electrode 19 and a storage capacitor Cst 20 for adding a compensation potential are formed and an OCB mode liquid crystal layer (not shown) is sandwiched between the pixel electrode 19 and opposite electrode 16. Furthermore, one end of the storage capacitor Cst 20 is connected to the pixel electrode 19 and the other end of the storage capacitor Cst 20 is connected to a common electrode 17. Furthermore, the gate of the pixel transistor 18 is connected to the gate signal line 15 and the source of the pixel transistor is connected to the source signal line 13 and the drain of the pixel transistor 18 is connected to the pixel electrode 19.
Furthermore, a Clc 21 is a capacitance formed of the pixel electrode 19, opposite electrode 16 and OCB mode liquid crystal layer, a Cgs 23 is a capacitance formed between the gate and source of the pixel transistor 18 and a Cgd 22 is a capacitance formed between the gate and drain of the pixel transistor 18.
The “pixel” in the following descriptions will refer to the part consisting of the pixel electrode 19, pixel transistor 18, storage capacitor Cst 20, portion of the opposite electrode 16 facing the pixel electrode 19 and liquid crystal layer in the OCB mode sandwiched by portion of the opposite electrode 16 facing the pixel electrode 19 and the pixel electrode 19.
The pixel in this embodiment is an example of the liquid crystal display element of the present invention. Such a voltage that a voltage of said source signal lines becomes a voltage corresponding to a halftone color in this embodiment is an example of the predetermined voltage of the present invention.
Next, the operation of this embodiment will be explained.
The input power supply 8 is supplied to the controller circuit 6 and liquid crystal drive voltage generation circuit 5 and the controller circuit 6 is started first. Then, the controller circuit 6 sends an image display signal and timing control signal to the source driver 11, sends a timing control signal to the gate driver 3 and sends a timing control signal to the liquid crystal drive voltage generation circuit 5.
The liquid crystal drive voltage generation circuit 5 supplies a source driver drive voltage to the source driver 11, supplies a gate driver drive voltage to the gate driver 3 and supplies an opposite signal electrode drive voltage to the opposite signal electrode. A voltage for transfer drive of 20 V to 25 V is applied to each pixel for a predetermined time from the opposite electrode. Thus, the OCB mode liquid crystal of the liquid crystal display panel 2 transitions from a spray state to a bent state, allowing a display operation of the liquid crystal display device.
When a display operation is carried out, the liquid crystal display device using the OCB mode of this embodiment also performs a 1.25-fold speed conversion as a counter-transfer prevention drive as in the case of the liquid crystal display device explained in the conventional technology. Furthermore, suppose the temperature of the liquid crystal display panel 2 is as low as, for example, 10° C. or less.
That is,
As is observed from the source voltage waveform in
Likewise, all voltages of the source signal line 13 during 1 horizontal scanning periods T3, T4, T5, that is, periods during which the halftone color is displayed are set to the voltage corresponding to the halftone color.
Thus, unlike the conventional technology, the black insertion voltage generation circuit 12 of this embodiment supplies a voltage lower by a predetermined value than the voltage corresponding to the black color as the voltage to prevent counter-transfer. That is, since the liquid crystal display device of this embodiment is driven by AC, to be exact, the black insertion voltage generation circuit 12 supplies a voltage whose absolute value is smaller than the absolute value of the voltage corresponding to the black color as the voltage to prevent counter-transfer. Therefore, when a voltage whose absolute value is smaller by a predetermined value than the voltage corresponding to the black color to prevent counter-transfer is applied and then the voltage is written to the next pixel, it is possible to set the voltage of the source signal line 13 to a voltage corresponding to the halftone color.
Thus, streaks which are more blackish than the original display color are no longer displayed on the display surface of the liquid crystal display panel 2 as shown in
As shown above, according to this embodiment, the black insertion voltage generation circuit 12 supplies a voltage whose absolute value is smaller by a predetermined value than the voltage corresponding to the black color, and can thereby compensate for the insufficient charge of the source signal line 13.
This embodiment has been explained assuming that the black insertion voltage generation circuit 12 supplies a voltage whose absolute value is smaller by a predetermined value than the voltage corresponding to the black color, but suppose that as such a predetermined value, a value is used which will prevent streaks which are more blackish than the original display color from being displayed no matter what gradation of the color to be displayed during the 1 horizontal scanning period T2 following the 1 horizontal scanning period T1 may have. Furthermore, it is also possible to determine such a predetermined value depending on the gradation of the color to be displayed during the 1 horizontal scanning period T2 following the 1 horizontal scanning period T1 or depending on the temperature, which case will be explained in more detail in a fourth embodiment which will be described later.
This embodiment has explained the case where the same halftone color is displayed on each pixel when 1.25-fold speed conversion is performed as a counter-transfer prevention drive, but the present invention is not limited to this. A counter-transfer prevention drive which applies a voltage corresponding to the black color to n pixels simultaneously to prevent counter-transfer and then applies voltages corresponding to display colors to n pixels sequentially can also achieve similar effects as those of this embodiment. Furthermore, when each pixel is displayed in not only halftone color but also white color, it is possible to achieve similar effects as those of this embodiment.
Furthermore, this embodiment has been explained assuming that the black insertion voltage generation circuit 12 applies a voltage whose absolute value is smaller by a predetermined value than the voltage corresponding to the black color to prevent counter-transfer, but the present invention is not limited to this. It is also possible not to provide the black insertion voltage generation circuit 12 and to allow the source driver 11 instead of the black insertion voltage generation circuit 12 to apply a voltage lower by a predetermined value than the voltage corresponding to the black color to prevent counter-transfer. The black insertion voltage generation circuit 12 may serve as the source driver 11, and the source driver 11 may serve as the black insertion voltage generation circuit 12.
Next, a second embodiment will be explained.
The configuration of a liquid crystal display device using an OCB mode according to a second embodiment is shown in
The difference between the liquid crystal display device using the OCB mode according to the second embodiment and the liquid crystal display device using the OCB mode according to the first embodiment is that the device in the second embodiment is provided with a black insertion voltage generation circuit 14 shown in
The black insertion voltage generation circuit 14 is a circuit that can have, according to the switch 26, three states; a state in which the source signal line 13 is connected to the supply side of the positive black insertion voltage, a state in which the source signal line 13 is connected to the supply side of the negative black insertion voltage and a state in which the source signal line 13 is connected to both the supply side of the positive black insertion voltage and the supply side of the negative black insertion voltage.
Next, the operation of this embodiment will be explained centered on the difference from the first embodiment.
When the display operation is performed, the liquid crystal display device using the OCB mode in this embodiment as well as the liquid crystal display device explained in the conventional technology carries out a 1.25-fold speed conversion as a counter-transfer prevention drive. Furthermore, suppose that the temperature of the liquid crystal display panel 2 is as low as, for example, 10° C. or less. Furthermore, a case where the same halftone color is displayed on the liquid crystal display panel 2 will be explained.
That is,
The switch 26 is switched so that the supply side of the positive black insertion voltage is electrically continuous with the source signal line 13 and the supply side of the negative black insertion voltage is not electrically continuous with the source signal line 13. Therefore, the positive voltage corresponding to the black color is applied to the source signal line 13 during the 1 horizontal scanning period T1.
Furthermore, in the 1 horizontal scanning period T2 before the source driver 11 supplies the voltage corresponding to a halftone color, the switch 26 is switched so that both the supply side of the positive black insertion voltage and the supply side of the negative black insertion voltage are connected to the source signal line 13. That is, the black insertion voltage generation circuit 14 is short-circuited. For this reason, the voltage resulting from short-circuiting the supply side of the positive black insertion voltage and the supply side of the negative black insertion voltage is supplied to the source signal line 13. Since the voltage resulting from short-circuiting the supply side of the positive black insertion voltage and the supply side of the negative black insertion voltage is a voltage corresponding to a white color, the voltage of the source signal line 13 becomes the voltage responding to the halftone color more quickly during the 1 horizontal scanning period T2. Then, the switch 26 is switched so that neither the supply side of the positive black insertion voltage nor the supply side of the negative black insertion voltage is electrically continuous to the source signal line 13 and the voltage corresponding to the halftone color is supplied from the source driver 11.
As is observed from the source voltage waveform in
Likewise, all the voltages of the source signal line 13 during the 1 horizontal scanning periods T3, T4, T5, that is, periods during which the halftone color is displayed are set to the voltage corresponding to the halftone color.
Thus, the second embodiment short-circuits the black insertion voltage generation circuit 14 during part of the 1 horizontal scanning period T2, and can thereby charge also the pixel, after the voltage corresponding to the black color is applied as the voltage to prevent counter-transfer, to the voltage corresponding to the halftone color.
Thus, according to the second embodiment, by short-circuiting the black insertion voltage generation circuit 14 during a period before the voltage corresponding to the halftone color is supplied to the source signal line 13 out of the display period which is a period next to the counter-transfer prevention drive period, it is possible to supply the source signal line 13 with such a voltage that the voltage of the source signal line 13 becomes the voltage corresponding to the halftone color. Therefore, it is possible to set the source signal line 13 to the voltage corresponding to the halftone color during the 1 horizontal scanning period T2 which is the period next to the counter-transfer prevention drive period.
This embodiment has explained the case where the black insertion voltage generation circuit 14 is short-circuited during the 1 horizontal scanning period T2 which is the display period next to the 1 horizontal scanning period T1, that is, the counter-transfer prevention drive period but the present invention is not limited to this. Even if the black insertion voltage generation circuit 14 is short-circuited during a period after the black insertion voltage generation circuit 14 supplies a voltage to prevent counter-transfer in the counter-transfer prevention drive period, that is, 1 horizontal scanning period T1, it is possible to obtain effects similar to those of this embodiment.
This embodiment has explained the case where the black insertion voltage generation circuit 14 is short-circuited during the counter-transfer prevention drive period, that is, the 1 horizontal scanning period T2 which is the display period next to the 1 horizontal scanning period T1, but the present invention is not limited to this. It is also possible to supply the voltage corresponding to the halftone color from the source driver 11 for the period after the voltage corresponding to the black color is supplied from the black insertion voltage generation circuit 14 to the source signal line 13 in the 1 horizontal scanning period T1.
Furthermore, this embodiment has explained the case where that the black insertion voltage generation circuit 14 is short-circuited for the counter-transfer prevention drive period, that is, 1 horizontal scanning period T2 which is the display period next to the 1 horizontal scanning period T1, but the present invention is not limited to this. It is also possible to supply the voltage corresponding to the halftone color from the black insertion voltage generation circuit 14 for the period after the voltage corresponding to the black color is supplied from the black insertion voltage generation circuit 14 to the source signal line 13 in the 1 horizontal scanning period T1.
Furthermore, this embodiment has explained the case where the same halftone color is displayed on each pixel when a 1.25-fold speed conversion is carried out as a counter-transfer prevention drive, but the present invention is not limited to this. Even a counter-transfer prevention drive which applies the voltage corresponding to the black color to prevent counter-transfer to n pixels simultaneously and then applies voltages corresponding to display colors to n pixels sequentially can obtain effects similar to those of this embodiment. Furthermore when each pixel is displayed in not only a halftone color but also white color, it is possible to obtain effects similar to those of this embodiment.
This embodiment has been explained assuming that the black insertion voltage generation circuit 14 performs a counter-transfer prevention drive, but the present invention is not limited to this. It is also possible not to provide any black insertion voltage generation circuit 14 and to allow the source driver 11 instead of the black insertion voltage generation circuit 14 to perform the counter-transfer prevention drive. In that case, the source driver 11 will assume the function carried out by the black insertion voltage generation circuit 14 instead of the black insertion voltage generation circuit 14. The black insertion voltage generation circuit 14 may serve as the source driver 11, and the source driver 11 may serve as the black insertion voltage generation circuit 14.
Next, a third embodiment will be explained.
The configuration of a liquid crystal display device using an OCB mode according to a third embodiment is shown in
The difference between the liquid crystal display device using the OCB mode according to the third embodiment and the liquid crystal display device using the OCB mode according to the first embodiment is that the source driver 11 carries out a gradation correction.
Next, the operation of this embodiment will be explained centered on the difference from the first embodiment.
When the display operation is performed, the liquid crystal display device using the OCB mode in this embodiment as well as the liquid crystal display device explained in the conventional technology carries out a 1.25-fold speed conversion as a counter-transfer prevention drive. Furthermore, suppose that the temperature of the liquid crystal display panel 2 is as low as, for example, 10° C. or less. Furthermore, a case where the same halftone color is displayed on the liquid crystal display panel 2 will be explained.
That is,
The source driver 11 of this embodiment corrects display gradation when the voltage corresponding to a halftone color is supplied during 1 horizontal scanning periods T3, T4, T5. That is,
For example, when the display gradation is 100, the source driver 11 corrects display gradation so that it is decreased by 7 when the temperature is 0° C. Therefore, in this case, the source driver 11 supplies a voltage corresponding to 93 to the source signal line 13 as display gradation. Furthermore, even when the display gradation is 100, if the temperature is −5° C., the source driver 11 corrects display gradation so that it is decreased by 10. Therefore, in this case, the source driver 11 supplies a voltage corresponding to 90 to the source signal line 13 as display gradation.
Thus, the source driver 11 corrects gradation of the display color according to the temperature and gradation during 1 horizontal scanning periods T3, T4, T5. The amount of gradation correction is a negative value.
That is, the black insertion voltage generation circuit 31 when the temperature is as low as, for example, 10° C. or below, the source driver 11 does not charge the pixel g1 corresponding to the 1 horizontal scanning period T2 up to the voltage corresponding to the halftone color. However, even in such a case, by carrying out gradation correction so that gradation of display colors during 1 horizontal scanning periods T3, T4, T5 becomes smaller, it is possible to prevent streaks which are more blackish than the original display color from appearing.
Therefore, as shown in
This embodiment has been explained assuming that the source driver 11 corrects gradation of the display colors during 1 horizontal scanning periods T3, T4, T5 according to the temperature and gradation, but the present invention is not limited to this. When insufficient charge of the source signal line 13 occurs not only during the 1 horizontal scanning period T2 but also, for example, T3, the source driver 11 corrects gradation according to the insufficient charge during the 1 horizontal scanning period T3 and can correct gradation of the display colors for the 1 horizontal scanning periods T4, T5 according to the temperature and gradation. Thus, the source driver 11 corrects gradation of display colors during 1 horizontal scanning periods after the 1 horizontal scanning period during which the insufficient charge of the source signal line 13 occurs according to the temperature and gradation, and can thereby achieve effects equivalent to those of this embodiment. In short, as the voltage corresponding to the gradation of all said display data after a predetermined number supplied to said source signal lines, any voltage will do as long as such a voltage is supplied that the difference between said voltage to prevent counter-transfer and the voltage corresponding to the gradation of said display data is smaller than the difference between said voltage to prevent counter-transfer and the voltage corresponding to the original display data. Such a voltage is an example of the predetermined voltage of the present invention.
This embodiment has been explained assuming that the source driver 11 corrects gradation of the display colors during the 1 horizontal scanning periods T3, T4, T5 according to the temperature and gradation, but the present invention is not limited to this. It is also possible for the source driver 11 to correct gradation of the display color during the 1 horizontal scanning period T2 according to the temperature and gradation.
In
In this way, the source driver 11 corrects gradation of the display color during the 1 horizontal scanning period T2 according to the temperature and gradation. The amount of gradation correction is a positive value.
That is, when the temperature is as low as, for example, 10° C. or below, the voltage does not become one corresponding to the display color during the 1 horizontal scanning period T2, but even in such a case, the source driver 11 corrects gradation so that the gradation of the display color during the 1 horizontal scanning period T2 becomes greater, and can thereby prevent streaks which are more blackish than the original display color from appearing.
Therefore, as shown in
In
This embodiment has explained the case where the same halftone color is displayed on each pixel when a 1.25-fold speed conversion is performed as a counter-transfer prevention drive, but the present invention is not limited to this. Effects similar to those of this embodiment can be obtained even through a counter-transfer prevention drive whereby the voltage corresponding to the black color is applied to n pixels simultaneously to prevent counter-transfer and then voltages corresponding to display colors are sequentially applied to n pixels. When each pixel is displayed in not only a halftone color but also a white color, effects similar to those of this embodiment can be obtained.
This embodiment has been explained assuming that the black insertion voltage generation circuit 12 carries out a counter-transfer prevention drive, but the present invention is not limited to this. It is also possible not to provide the black insertion voltage generation circuit 12 and to allow the source driver 11 instead of the black insertion voltage generation circuit 12 to carry out a counter-transfer prevention drive. In that case, the source driver 11 will perform the function carried out by the black insertion voltage generation circuit 12 instead of the black insertion voltage generation circuit 12. The black insertion voltage generation circuit 12 may serve as the source driver 11, and the source driver 11 may serve as the black insertion voltage generation circuit 12.
Next, a fourth embodiment will be explained.
The configuration of a liquid crystal display device using an OCB mode according to a fourth embodiment is shown in
Furthermore,
In
Next, this embodiment will be explained centered on the difference from the first embodiment.
When the display operation is performed, the liquid crystal display device using the OCB mode in this embodiment as well as the liquid crystal display device explained in the conventional technology carries out a 1.25-fold speed conversion as a counter-transfer prevention drive. Furthermore, suppose that the temperature of the liquid crystal display panel 2 is as low as, for example, 10° C. or less. Furthermore, a case where the same halftone color is displayed on the liquid crystal display panel 2 will be explained.
That is,
As the voltage to be supplied to each source signal line 13 as the voltage to prevent counter-transfer during a 1 horizontal scanning period T1, the black insertion voltage generation circuit 31 supplies a voltage according to the voltage corresponding to the halftone color to be displayed during T2 which is the 1 horizontal scanning period following the 1 horizontal scanning period T1. In order to determine the voltage to be supplied to each source signal line 13, the black insertion voltage generation circuit 31 calculates an amount of gradation correction from the black gradation first.
For example, when the display gradation to be displayed during T2 which is the 1 horizontal scanning period following the 1 horizontal scanning period T1 is 100, the black insertion voltage generation circuit 31 corrects the black gradation to be displayed during the 1 horizontal scanning period T1 so that it is increased by 7. Therefore, in this case, the black insertion voltage generation circuit 31 supplies the voltage corresponding to 7 as the display gradation to the source signal line 13 as the voltage to be supplied to prevent counter-transfer during the 1 horizontal scanning period T1. Furthermore, even if the display gradation during the 1 horizontal scanning period T2 is 100, if the temperature is −5° C., the black insertion voltage generation circuit 31 corrects the display gradation so that it is increased by 10. Therefore, in this case, the black insertion voltage generation circuit 31 supplies a voltage whose display gradation corresponds to 10 to the source signal line 13 as the voltage to be supplied to prevent counter-transfer during the 1 horizontal scanning period T1. The black insertion voltage generation circuit 31 determines the voltage to prevent counter-transfer for each source signal line 13 as described above and supplies the determined voltage to each source signal line 13.
In this way, the black insertion voltage generation circuit 31 determines the voltage to be supplied to prevent counter-transfer during the 1 horizontal scanning period T1 according to the temperature and also according to the display gradation during T2 which is the 1 horizontal scanning period immediately following the 1 horizontal scanning period T1.
That is, when the temperature is as low as, for example, 10° C. or below, the pixel g1 corresponding to the 1 horizontal scanning period T2 is not charged up to the voltage corresponding to the halftone color. However, even in such a case, by determining the voltage to be supplied during the 1 horizontal scanning period T1 by carrying out a gradation correction from the black gradation, it is possible to prevent streaks which are more blackish than the original display color from appearing.
This embodiment has explained the case where the same halftone color is displayed on each pixel when a 1.25-fold speed conversion is performed as a counter-transfer prevention drive, but the present invention is not limited to this. Effects similar to those of this embodiment can be obtained even through a counter-transfer prevention drive whereby the voltage corresponding to the black color is applied to n pixels simultaneously to prevent counter-transfer and then voltages corresponding to display colors are sequentially applied to n pixels. Furthermore, when each pixel is displayed in not only a halftone color but also a white color, effects similar to those of this embodiment can be obtained.
This embodiment has been explained assuming that the black insertion voltage generation circuit 31 carries out a counter-transfer prevention drive, but the present invention is not limited to this. It is also possible not to provide the black insertion voltage generation circuit 31 and to allow the source driver 11 instead of the black insertion voltage generation circuit 31 to carry out a counter-transfer prevention drive. In that case, the source driver 11 will perform the function carried out by the black insertion voltage generation circuit 31 instead of the black insertion voltage generation circuit 31. The black insertion voltage generation circuit 31 may serve as the source driver 11, and the source driver 11 may serve as the black insertion voltage generation circuit 31.
Next, a fifth embodiment will be explained.
The configuration of a liquid crystal display device using an OCB mode according to a fifth embodiment is shown in
Furthermore,
The difference between the liquid crystal display device using the OCB mode according to the fifth embodiment and the liquid crystal display device using the OCB mode according to the first embodiment is that the controller circuit 6 changes the length of a 1 horizontal scanning period.
Next, the operation of this embodiment will be explained centered on the difference from the first embodiment.
When the display operation is performed, the liquid crystal display device using the OCB mode in this embodiment as well as the liquid crystal display device explained in the conventional technology carries out a 1.25-fold speed conversion as a counter-transfer prevention drive. Furthermore, suppose that the temperature of the liquid crystal display panel 2 is as low as, for example, 10° C. or less. Furthermore, a case where the same halftone color is displayed on the liquid crystal display panel 2 will be explained.
That is,
However, the total length of T1, T2, T3, T4 and T5 remains unchanged. For example, if T2 is multiplied 1.4 times, the lengths of T1, T3, T4 and T5 can be 0.9 times their original lengths.
As is observed from the source voltage waveform in
Likewise, all voltages of the source signal line 13 during 1 horizontal scanning periods T3, T4, T5, that is, a period during which a halftone color is displayed are set to a voltage corresponding to the halftone color.
The 1 horizontal scanning period T2 is set to be longer than the 1 horizontal scanning period T1, T3, T4, T5.
Thus, this embodiment provides the 1 horizontal scanning period T2 longer than the horizontal scanning periods T1, T3, T4, T5, and can thereby set the voltage of the source signal line 13 to the voltage corresponding to the halftone color displayed when the voltage corresponding to the halftone color is written immediately after a counter-transfer prevention drive.
Thus, according to this embodiment, the 1 horizontal scanning period when the voltage corresponding to the halftone color immediately after the voltage corresponding to the black color is applied is set to be longer than the second and subsequent 1 horizontal scanning periods, and it is thereby possible to solve the problem of insufficient charge of the source signal line 13 and set the source signal line 13 to the voltage corresponding to the halftone color. Therefore, it is possible to prevent streaks which are more blackish than the original display color from appearing on the liquid crystal display panel 2.
This embodiment has been explained assuming that the controller circuit 6 makes the 1 horizontal scanning period T2 longer than the 1 horizontal scanning periods T3, T4, T5, but the present invention is not limited to this. When insufficient charge of the source signal line 13 occurs during not only the 1 horizontal scanning period T2 but also, for example, T3, the controller circuit 6 can make the 1 horizontal scanning periods T2 and T3 longer than the 1 horizontal scanning periods T4, T5. Thus, by making the 1 horizontal scanning period during which insufficient charge of the source signal line 13 occurs longer than the 1 horizontal scanning period during which no insufficient charge of the source signal line 13 occurs, the controller circuit 6 can obtain effects equivalent to those of this embodiment.
In short, that wherein said display period corresponding to said display data up to a predetermined number supplied to said source signal lines is longer than said display period corresponding to said display data after said predetermined number is an example of predetermined voltage of the present invention.
This embodiment has explained that the black insertion voltage generation circuit 12 performs a counter-transfer prevention drive, but the present invention is not limited to this. It is also possible not to provide the black insertion voltage generation circuit 12 and to allow the source driver 11 instead of the black insertion voltage generation circuit 12 to carry out a counter-transfer prevention drive. In such a case, the source driver 11 will carry out the function carried out by the black insertion voltage generation circuit 12 instead of the black insertion voltage generation circuit 12.
The black insertion voltage generation circuit 12 may serve as the source driver 11, and the source driver 11 may serve as the black insertion voltage generation circuit 12. The liquid crystal display device and method of driving the liquid crystal display device according to the present invention has the effect of preventing streaks which are more blackish than the original display color from appearing on the display surface of the display panel even when the temperature is low or when each pixel is displayed in the same halftone color or white color and is effectively applicable to a liquid crystal display device using OCB mode liquid crystal and a method of driving the liquid crystal display device, etc.
Number | Date | Country | Kind |
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2004-109273 | Apr 2004 | JP | national |