JPH07119908B2 - LCD panel driving method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a liquid crystal panel having a structure in which a liquid crystal layer is sandwiched between glass substrates having electrodes.

[0002]

2. Description of the Related Art When displaying halftones on a liquid crystal panel, in order to reduce the price of the driver, it is possible to display all gradations with a driver that outputs a number of gradation voltages smaller than the number of gradations to be displayed. As a driving method for driving, there is a frame thinning driving (frame rate control driving (hereinafter abbreviated as FRC driving)). References in this regard to S.
Nishitani et. al. ; "Flicke
rless Multi-Color Display
Method for TFT-LCDs ", Pr
oc. of the 12th IDRC, pp4
71-474, (1992). For example, when performing halftone display of 2n gradations using an n gradation output driver,
The voltage output from the n-gradation output driver is a gradation voltage for every one gradation of black and white and intermediate gradations between them, and as a driving voltage for the other gradations, two of the n-gradation driver outputs are used. By outputting one gray scale voltage every other frame or every two frames, the gray scale between the two gray scale voltages is displayed. Table 1 shows combinations of gray scales and gray scale voltages in FRC driving in which a liquid crystal panel is driven by a driver of 8 gray scale output and 16 gray scales are displayed on the liquid crystal panel.

[0003]

[Table 1] Here, in the normally white mode, the panel displays black at the 0th gradation and displays white at the 15th gradation. Then, in 2 frame driving, 0, 2, 4,
As the gradation voltages for the sixth, eighth, tenth, twelfth and fifteenth gradations, the voltages corresponding to the eight gradations output from the eight gradation output driver are used as they are for each frame.
At the 9th, 11th, 13th, and 14th gradations, the liquid crystal panel is driven with different gradation voltages in the first and second frames. The same applies to four-frame driving. Table 1
The number in indicates the gradation number.

[0004]

The field of the invention, F
In RC driving, if the ON and OFF response speeds are different when the two gradations are switched for every one frame or every two frames, the brightness that is deviated from either of the averages of the two gradations will be displayed. As an example, FIG. 5 shows the waveform applied to the liquid crystal and the luminance waveform of the display pixel when the display of the 14th gradation is performed by driving the 2 frames when the 16 gradation display is performed by the 8 gradation output driver. As shown in the figure, the response time is long when switching from the 15th gradation to the 12th gradation.
Not enough responses. On the other hand, when switching from the 12th gradation to the 15th gradation, the response is completed in one frame. Therefore, the luminance of the 14th gradation is not exactly in the middle of the luminances of the 12th gradation and the 15th gradation, and 1
The luminance becomes higher than that of the fifth gradation, and the difference in luminance between the 14th gradation and the 15th gradation is almost eliminated, and so-called whiteout occurs.

An object of the present invention is to provide a liquid crystal panel driving method in which gradation changes are smooth in FRC driving and white crushing does not occur.

[0006]

[Means for Solving the Problems]

According to the invention of the present application, a driver is provided in a liquid crystal panel having a structure in which a liquid crystal layer is sandwiched between glass substrates having electrodes.
A driving method for displaying 16 gradations on the liquid crystal panel only by applying a voltage corresponding to gradations, wherein two voltages out of the voltages output from the driver are selected and combined every other frame or every two frames. As a result, in the liquid crystal panel driving method by the frame thinning driving for displaying the remaining 8 gradations other than the 8 gradations displayed by the voltage output from the driver, the voltage applied to the liquid crystal at the 0th gradation is the highest. Driving the output voltage of the driver at the 0th, 2nd, 5th, 8th, 11th, 13th, 14th and 15th gradations when the 15th gradation is the lowest gradation and the voltage applied to the liquid crystal is the lowest gradation. There is provided a liquid crystal panel driving method characterized in that, in accordance with the voltage, gradations other than those described above are displayed by outputting voltages of two gradations of the gradations every other frame or every two frames.

[0008]

In the liquid crystal panel driving method of the present invention, FRC driving is adopted for half of the gray scales to be displayed. The combination of gradation setting and gradation voltage in the FRC driving will be described in comparison with that in the conventional FRC driving.

Table 1 shows combinations of set gradations and gradations in the conventional FRC drive when 16 gradation gradation display is performed by the 8 gradation output driver. The gradation-luminance characteristics at this time are shown in FIG. If the gradation-luminance characteristics are taken so that the logarithm of the luminance becomes equal, the human eyes will see the difference in luminance at equal intervals. Therefore, the gradation without FRC drive will have the equal logarithm of luminance. Is set to. In FIG. 2, a large luminance difference occurs between the 12th gradation and the 13th gradation, and 0 to 1 are sequentially displayed on the screen.
When a bar for 16 gradations up to the 5th gradation is displayed, a display having a step is formed at the 12th gradation and the 13th gradation.
This is due to the difference in response time between ON and OFF. 6 and 7 show ON and OFF response times between two gradations. OFF response time when displaying the 13th and 14th gradations (10th to 15th gradations, 12th gradation
24msec and 22msec from the 15th gradation to the 15th gradation)
On the other hand, the response time of ON (from the 15th gradation to 10
It can be seen that the ON response time is extremely long for the gradations of 15th gradation to 12th gradation) of 42 msec and 57 msec. For this reason, as shown in FIG. 5, the OFF response is performed in a state where the ON response is not sufficiently performed, so that the average luminance is increased and white crushing occurs, and at the 12th and 13th gradations. The brightness difference between the two becomes large. This is not limited to 16-gradation display, but is a phenomenon that occurs between gradations with a large difference in ON and OFF response times. For the above-mentioned reason, the FRC is used when the gradation is close to white.
It is unsuitable to use a drive. Therefore, in the first invention, O
The difference in response time between N and OFF is 1.5 times or more 3n / 2
FRC driving is not performed in the gradations from +1 to 2n-1th gradation.

In the case of the 16-gradation display of the second invention, the above gradation corresponds to the 13th to 15th gradations. Since 0th gradation cannot be FRC driven, 8 out of 1st to 12th gradations
FRC drive must be used with individual gradations. FRC
When the luminance shift amount (%) when trying to display the i + kth gradation by using the i + jth gradation and the ith gradation in driving,
Since the gradation is set so that the logarithm of the brightness is equal, a constant x is used with the brightness of the 0th gradation as a, and the brightness a _i of the i-th gradation is a geometric progression. A _i = ax ⁱ (1) can be written. When this is used, the luminance (average luminance) and the i-k when FRC driving is performed using the i-th and i-th gradations
The ratio y of the brightness of the gradation (target brightness) is as follows. y = (a _ij + a _i ) / 2 / a _ik = (x ^−j +1) / 2 / x ^−k (2) Therefore, the amount of luminance deviation is the difference j between the two gradations used for FRC driving and the display gradation ( i−k) and the gradation i of FRC driving are determined by the difference k. Now, in the case of 16 gradation display, since x = 1.3 to 1.4 from the experimental result, assuming that the luminance deviation tolerance from the target set luminance is 10%, | y−1 | ≦
It becomes 0.1, and the value of k becomes only k = 1 or 2. Therefore, since k is 2 at the maximum, it is necessary to set the gradation without FRC at least every two gradations.
If FRC is not used for the first gradation, the gradations that do not use FRC must be set every two gradations from the above condition. However, in this case, the luminance deviation of the second gradation is large and becomes inappropriate. Therefore, FRC must be used for the first gradation. At this time, since the 0th gradation and the 2nd gradation must be used for the 1st gradation, the FRC must not be used for the 2nd gradation. In this way, there are four remaining conditions, but flicker is more noticeable as the flicker luminance amplitude is larger regardless of the average luminance, so it is better to set not to use the FRC for grayscale toward white. The FRC drive gradation setting according to the second aspect is set in this way.

Table 2 shows combinations of set gradations and gradations for FRC driving when 16 gradation gradation display is performed by the 8 gradation output driver according to the first and second inventions.

[0012]

[Table 2] FIG. 1 shows the gradation-luminance characteristics in the case of the combination of gradation 2 according to the table. As compared with the conventional gradation-luminance characteristic shown in FIG. 2, there is no difference in luminance between the 12th gradation and the 13th gradation, and a smooth luminance change is obtained for the entire gradation. In contrast to the target gradation-luminance characteristic that the logarithm of the luminance has an equal difference, conventionally, a maximum luminance deviation of 44% has occurred at the 13th gradation, but in the FRC driving of the present invention, By setting, the maximum luminance deviation is suppressed to 21% at the sixth gradation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the liquid crystal panel driving method according to the present invention, a method of displaying 16 gradations with an 8 gradation output driver will be described below. An example of a liquid crystal display device to which the method of this embodiment is applied is shown in FIG. The input RGB signal is input as an RGB signal of 16 gradations. First, the RGB signals are divided into two, one for each upper and lower line, and are input to the upper driver gate array 1 and the lower driver gate array 2, respectively. The signals of 16 gradations are converted into signals of 8 gradations by the combinations shown in Table 2 in each gate array. As shown in Table 2, in the present invention, 0,
16-gradation display is performed by using eight drive voltages of 2, 5, 8, 11, 13, 14, and 15 gradations. In the case of 2-frame driving, one gradation is displayed in two frames, and in the four-frame driving, one gradation is displayed in four frames. The RGB signals converted into the 8 gradation signals are input to the upper and lower drain drivers 4 and 5, respectively, and 0 and 0 supplied from the gradation voltage power supply circuit 7 to the drain drivers 4 and 5, respectively.
The drain drivers 4 and 5 select voltages of eight gradations of 2, 5, 8, 11, 13, 14, and 15 gradations, respectively.
Output to each drain bus line. At this time,
As shown in the waveform diagrams 4 and 5, the polarity of the waveform voltage applied to the liquid crystal is inverted every frame so that the drain signal voltage is also inverted every frame. Also,
In order to synchronize the gate signal and the drain signal output from the gate driver 3 for turning on the TFT, the horizontal and vertical synchronization clock HSVSCLK is applied to the gate arrays 1 and 2.
Is input to the gate driver 3. Such a TFT
-Smooth gradation as shown in Fig. 1 by LCD module-
We were able to realize a liquid crystal display with brightness characteristics.

[0014]

When the present invention is applied, in the actual display of the FRC drive use gradation with respect to the target set brightness, the brightness deviation of up to 44% has been generated in the past, but 2
It can be suppressed within 1%, and smooth gradation display can be obtained. Therefore, by driving the liquid crystal panel by the method of the present invention, it is possible to prevent the occurrence of so-called whiteout.

[Brief description of drawings]

FIG. 1 is a gradation-luminance characteristic diagram when gradations for FRC driving according to the present invention are set.

FIG. 2 is a gradation-luminance characteristic diagram when gradation is set in a conventional FRC drive.

FIG. 3 is a diagram showing a voltage waveform applied to the liquid crystal and a luminance waveform of a display pixel when the FRC is driven for two frames.

FIG. 4 is a diagram showing a voltage waveform applied to a liquid crystal and a luminance waveform of a display pixel when FRC four-frame driving is performed.

FIG. 5 is a diagram showing a voltage waveform applied to a liquid crystal and a luminance waveform of a display pixel when displaying the 14th gradation using FRC driving at the 12th gradation and the 15th gradation.

FIG. 6 is a diagram showing response time characteristics of ON response of liquid crystal from each gradation.

FIG. 7 is a diagram showing a response time characteristic of OFF response of liquid crystal from each gradation.

FIG. 8 is a configuration diagram of a TFT-LCD module to which a liquid crystal panel driving method according to an embodiment of the present invention is applied.

[Explanation of symbols]

 1 Upper Driver Gate Array 2 Lower Driver Gate Array 3 Gate Driver 4 Upper Drain Driver 5 Lower Drain Driver 6 TFT-LCD Panel 7 Gradation Voltage Power Supply Circuit

Claims (1)

[Claims] 1. A driving method for displaying 16 gradations on a liquid crystal panel by simply applying a voltage for 8 gradations from a driver to a liquid crystal panel having a structure in which a liquid crystal layer is sandwiched between glass substrates having electrodes. By selecting and combining two voltages among the voltages output from the driver for every one frame or every two frames, the remaining eight gradations other than the eight gradations displayed by the voltage output from the driver are selected. In the liquid crystal panel driving method by the frame thinning driving for displaying, when the 0th gradation is the gradation having the highest voltage applied to the liquid crystal and the 15th gradation is the gradation having the lowest voltage applied to the liquid crystal, the driver Output voltage of 0, 2, 5, 8,
According to the drive voltage of the 11, 13, 14, and 15th gradation, the gradations other than the above are displayed by outputting the voltages of two gradations of the gradations every one frame or every two frames. Characteristic liquid crystal panel driving method.