JP2010026281A - Electrooptical apparatus, driving method and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a degradation in display quality due to the effect of a transverse electric field. <P>SOLUTION: A video processing circuit 30 supplies a data signal as follows: on the assumption that a voltage effective value corresponding to a gray scale value assigned to a pixel is applied to a liquid crystal element over a frame period, when a gray scale value at which a threshold falls under a predetermined threshold is assigned to a pixel corresponding to a scanning line selected by a Y driver 130, a data signal of the voltage made higher than the threshold voltage or above and the data signal of the voltage which is the voltage to be made lower than the threshold and which is preset with respect to the gary scale value are alternated for each one frame period and are supplied to the pixel. An X driver 140 supplies the data signal to a data line 114. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for reducing display defects caused by a so-called lateral electric field.

A liquid crystal display device, which is an example of an electro-optical device, has a configuration in which liquid crystal is sandwiched between a pair of substrates that maintain a certain gap. Specifically, pixel electrodes are arranged in a matrix for each pixel on one substrate, and a counter electrode is provided on the other substrate so as to be common to each pixel. A liquid crystal is formed by the pixel electrode and the counter electrode for each pixel. It is the structure which clamped. Then, by maintaining a voltage corresponding to the gradation value between the pixel electrode and the counter electrode, the alignment state of the liquid crystal molecules of both electrodes is defined for each pixel, thereby controlling the transmittance or reflectance. It has a configuration. For this reason, in the electric field acting on the liquid crystal molecules, only the component in the direction from the pixel electrode to the counter electrode, that is, the direction perpendicular to the substrate surface (vertical direction) is the direction that contributes to display control. Can do.

Here, when the pixel pitch is reduced, an electric field generated between adjacent pixel electrodes, that is, an electric field in a direction parallel to the substrate surface (transverse direction) is generated, and the influence cannot be ignored. Specifically, when a horizontal electric field is applied to a liquid crystal that assumes a vertical electric field, such as the TN method or the VA method, liquid crystal alignment failure occurs, and light is lost at the alignment defect portion. This causes a problem that a display defect such as the above occurs.
In order to reduce the influence of such a horizontal electric field, a technique in which a notch portion is provided in a pixel electrode has been proposed (see, for example, Patent Document 1).
JP 2007-199451 A

However, this technique has a problem that the aperture ratio is reduced due to the provision of the notch portion of the pixel electrode.
The present invention has been made in view of the above-described circumstances, and one of its purposes is to provide an electro-optical device and the like in which display defects caused by a lateral electric field are reduced without reducing the aperture ratio. It is in.

In order to achieve the above object, the electro-optical device driving method according to the present invention is provided corresponding to a scanning line, a data line, and an intersection of the scanning line and the data line. A switching element connected to the data line, connected to the pixel electrode at the other end, and applied to the pixel electrode; and a switching element that is in a conductive state between the one end and the other end when the scanning line is selected. And a pixel including an electro-optic element that is in an optical state based on the voltage applied to the counter electrode, and a gradation value designated for the pixel is previously set. When the voltage to be applied between the pixel electrode and the counter electrode according to the gradation value is smaller than a predetermined threshold voltage when it is larger or smaller than a predetermined value, For the pixel, the pixel A data signal for making the gap between the electrode and the counter electrode equal to or higher than the threshold voltage, and a data signal having a voltage lower than the threshold voltage and predetermined for the gradation value. It is characterized in that it is switched through every cycle that is an integral multiple of the frame period and supplied via the data line. According to the present invention, when a gradation value is specified such that the voltage between the pixel electrode and the counter electrode in the electro-optic element is lower than a predetermined threshold voltage, a voltage equal to or higher than the threshold voltage is specified. Since the influence of the transverse electric field is reduced by application,
The degree of orientation failure remaining can be kept small.

In the present invention, in the same frame period, to the pixels in the odd-numbered rows, odd-numbered columns, and even-numbered rows and even-numbered columns, a data signal is supplied to make the gap between the pixel electrode and the counter electrode higher than the threshold voltage. A data signal having a voltage predetermined for the gradation value may be supplied to the pixels in the row odd columns and the odd rows even columns. Thereby, it becomes possible to make it difficult to visually recognize flicker or the like.
In the present invention, when the data signal includes two types of positive polarity that is higher than a predetermined reference voltage and negative polarity that is lower than the predetermined reference voltage, the gap between the pixel electrode and the counter electrode is described above. A voltage to be set to be equal to or higher than the threshold voltage is supplied by either the positive polarity or the negative polarity, and then supplied by either the positive polarity or the negative polarity, and then predetermined for the gradation value. The supplied voltage may be supplied by either the positive polarity or the negative polarity and then supplied by either the positive polarity or the negative polarity, or between the pixel electrode and the counter electrode. A voltage to be set to be equal to or higher than the threshold voltage is supplied by either the positive polarity or the negative polarity, and then supplied by either the positive polarity or the negative polarity, and then predetermined for the gradation value. The positive electrode Or after supplying with either negative, it may be supplied with the other of the positive polarity or negative polarity.
The present invention is not limited to the driving method of the electro-optical device, but can be conceptualized as the electro-optical device itself or as an electronic apparatus having the electro-optical device.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram illustrating the overall configuration of the electro-optical device according to the present embodiment.
As shown in this figure, the electro-optical device 1 includes a control circuit 10 and a liquid crystal display panel 100.
It consists of. Among these, the control circuit 10 is supplied with video data Vd defining the gradation value (luminance) of the pixel in synchronization with the synchronization signal Sync from a host device (not shown). Control circuit 1
0 is composed of a timing control circuit 20 and a video processing circuit 30. Of these, the timing control circuit 20 generates a timing signal, a clock signal, and the like for controlling each unit based on the synchronization signal Sync, and The video processing circuit 30 processes the video data Vd and supplies it to the liquid crystal display panel 10 as a data signal Vid.
Here, for convenience of explanation, it is assumed that the video data Vd is digital data that designates the gradation value of a pixel in eight stages from “0” of the darkest black to “7” of the brightest white.
Details of the contents of the video processing in the video processing circuit 30 will be described later.

In the liquid crystal display panel 100, 1 to m rows of scanning lines 112 extend in the horizontal direction in the figure, while 1 to n columns of data lines 114 extend in the vertical direction. These scanning lines 1
The pixels 110 are arranged so as to correspond to the intersections of the data lines 12 and the data lines 114, respectively. For this reason, in this embodiment, the pixels 110 are arranged in a matrix with m rows × n columns. In addition, one specific pixel among the pixels 110 arranged in a matrix can be specified by the number of rows of the scanning lines 112 and the number of columns of the data lines 114. For example, it can be said that the pixels 110 in the second row and the fourth column correspond to the intersection of the scanning line 112 in the second row and the data line 114 in the fourth column.

For convenience of description, the pixel 110 will be described. FIG. 2 is a diagram illustrating an electrical configuration of the pixel 110.
As shown in FIG. 2, in the pixel 110, the source electrode of the n-channel TFT 116 is connected to the data line 114 and the drain electrode is connected to the pixel electrode 118, while the gate electrode is connected to the scanning line 112. It is connected.
The pixel electrode 118 is provided for each pixel and has a rectangular shape. On the other hand, the counter electrode 108 is provided in common to all the pixels so as to face all of the pixel electrodes 118, and a constant voltage LCcom is applied thereto. Then, the liquid crystal 105 is sandwiched between the counter electrode 108 and the pixel electrode 118, thereby forming the liquid crystal element 120. Therefore, the liquid crystal element 120 including the pixel electrode 118, the counter electrode 108, and the liquid crystal 105 is provided for each pixel.

The liquid crystal element 120 having such a configuration holds a voltage between the pixel electrode 118 and the counter electrode 108, and has a transmittance corresponding to the effective value of the voltage if it is a transmission type. Therefore, when a selection voltage is applied to the scanning line 112 and a data signal having a voltage corresponding to the designated gradation value is supplied to the data line 114 for the pixel corresponding to the selected scanning line 112, the selective scanning is performed. The TFT 116 of the pixel 110 in the line is turned on, and the data signal is
Since the voltage is applied to the pixel electrode 118 through the TFT 116 in the on state, a voltage corresponding to the gradation value is applied to and held in the liquid crystal element 120 so that the transmittance corresponds to the target gradation. It should be possible.
Note that even if a non-selection voltage is applied to the scanning line and the TFT 116 is turned off, the TFT 1
The voltage written in the liquid crystal element 120 when 16 is in the on state is held by its capacitance.

In this embodiment, if the voltage effective value held in the liquid crystal element 120 is close to zero for convenience,
It is assumed that the normally white mode in which the light transmittance is maximized and white display is performed while the amount of transmitted light decreases as the effective voltage value increases.
Further, in order to prevent a direct current component from being applied to the liquid crystal 105, the liquid crystal element 120 has a high-side positive voltage and a low-side negative voltage with respect to the same reference voltage Vc as the voltage LCcom of the counter electrode 108. Applied alternately (AC drive).

Returning to FIG. 1, the Y driver 130 supplies scanning signals Y1, Y2, Y3,..., Ym to the scanning lines 112 in the 1, 2, 3,. It functions as. Specifically, as shown in FIG. 3, the Y driver 130 moves the scanning lines 112 in the order of the first, second, third,..., Mth rows in the vertical scanning period Fa in one frame period, and While selecting exclusively, the scanning signal to the selected scanning line is selected as the selection voltage Vdd.
Further, a scanning signal to other non-selected scanning lines is set as a non-selection voltage Vss.
The X driver 140 is supplied from the video processing circuit 30 and adjusts the data signal Vid corresponding to the 1 to n columns of pixels corresponding to the selected scanning line so that the scanning signal to the selected scanning line becomes the selection voltage Vdd. The data signals X1 to X1 are sampled on the data lines 114 in the first to nth columns.
It is supplied as Xn.
Therefore, a data signal supply circuit that supplies a data signal having a voltage corresponding to a gradation value designated for a pixel is configured by the video processing circuit 30 and the X driver 140.

In the present embodiment, the non-selection voltage Vss will be described with reference to the voltage zero except for the voltage held by the liquid crystal element 120. In the liquid crystal element 120, the voltage L of the counter electrode 108
This is because the difference between the voltage of Ccom and the voltage of the pixel electrode 118 is maintained, so that it is necessary to separate the reference from other signals.

By the way, the relationship between the effective voltage value held in the liquid crystal element and the transmittance in the normally white mode is expressed by a VT characteristic as shown in FIG. For this reason, the video data Vd
If the gradation value of the pixel designated by 8 is designated in 8 levels from “0” to “7”, the effective value of the voltage held in the liquid crystal element becomes V0 to V7 according to the gradation value. By controlling in this way, the actual transmittance (optical state) of the liquid crystal element with respect to the gradation value designated for the pixel can be set to a characteristic indicated by C in FIG.

The effective value of the voltage held in the liquid crystal element is a value based on the voltage of the counter electrode voltage LCcom and the data signal applied to the pixel electrode, and is a value with one frame period as a reference unit. For this reason, the gradation value of the data signal in the case of the voltage amplitude method is “0” to “7”.
So that the effective values V0 to V7 are applied to the liquid crystal element, the voltage V0 (+) is positive.
~ V7 (+), and if negative, it should be specified to voltages V0 (-) to V7 (-), respectively (see FIG. 6).
However, if the data signal is defined only in accordance with the gradation and polarity specified by the video data Vd as described above, a display defect due to the horizontal electric field occurs.

Then, next, the problem on the display by this horizontal electric field is considered. FIG. 11 is a diagram showing an example of a display defect which is a problem in the present invention.
First, such deterioration in display quality is, for example, as shown in FIG. 11, in which a moving image that slowly moves to the right with a white area as a background in a slightly dark gray window area A is displayed on the screen. In this case, a region B that should become white after the gray region A has moved is a phenomenon in which the gray and white are in an intermediate gradation (slightly dark white). This phenomenon is also called a tailing phenomenon because a slightly dark white region B is visually perceived after the movement of the gray region A, and tends to disappear over time.
In FIG. 11, light and dark are expressed by the density of oblique lines. The same applies to the following FIG. 12 and FIG.

Here, the cause of the deterioration in display quality will be described with reference to FIGS.
For example, in the surface inversion method, in the same frame, the pixel electrodes 118 in the white region have the same potential, and the pixel electrodes 118 in the gray region have the same potential. However, in the case of positive polarity, the pixel electrode 118 in the gray region is higher than the pixel electrode 118 in the white region.
For this reason, focusing on the pixels located at the boundary between the white region and the gray region in a certain frame period, if the polarity is positive, the pixel electrode in the gray region is changed from the pixel electrode in the white region as indicated by the arrow shown in FIG. A transverse electric field is generated in the direction of heading. In the case of negative polarity, only the direction of the arrow is reversed, and a transverse electric field is generated similarly.

On the other hand, the voltage held in the liquid crystal element is higher in the gray area than in the white area in the normally white mode, so when compared between the pixels in the white area and the gray area, The gray area is stronger than the white area.
When the pixels located at the boundary between the white region and the gray region are compared with each other, the horizontal electric field is generated in the same manner. However, the relatively strong vertical electric field is dominant in the pixels in the gray region. The effect is negligible, and it turns gray almost correctly. On the other hand, since the vertical electric field is weak in the pixels in the white region, the influence of the horizontal electric field cannot be ignored. This effect becomes larger as the gray pixel is closer. In the normally white mode, the alignment failure works in the direction of darkening the pixel. Therefore, as shown in FIG. 12, in the white pixel located at the boundary with the gray region,
The closer to the gray pixel, the darker part.

Since the gap between pixels is shielded by a black matrix (not shown),
The alignment failure caused by the gap is not a problem here.
In addition, in FIG. 12, the alignment failure occurring in the white pixel in the boundary between white and gray is
Since the boundary is only blurred, it is hard to be seen as a display defect.

However, when the gray region moves in the next frame period, the deterioration of display quality due to poor alignment becomes obvious.
To explain this point, first, the gray pixel located at the boundary between the white region and the gray region in FIG. 12 changes to white as shown in FIG. The pixel maintains its white color. Even when the same gradation is maintained between adjacent frames, the potential of the pixel electrode in the liquid crystal element changes due to polarity inversion accompanying AC driving, but the voltage effective value held in the liquid crystal element. There is no change when seen.

It is known that the voltage responsiveness of the liquid crystal decreases in the direction in which the voltage held in the liquid crystal element is decreased and the effective value after the change decreases. When a pixel that was gray in the previous frame changed to white in the next frame, the liquid crystal responsiveness was lowered, and alignment failure due to the horizontal electric field remained. Therefore, even if an orientation defect remains when the color changes to white, the degree is small enough not to cause a problem.
On the other hand, in the pixel that was white in the previous frame, the influence of the horizontal electric field was large, and in the next frame, it remained white and the voltage of the liquid crystal element did not change. Remains at a degree. Since there is no change in the white color even after the next frame, an orientation defect due to a lateral electric field remains.
For this reason, as shown in FIG. 13, the white pixel that was once affected by the lateral electric field because it was located at the boundary with the gray area does not become white even after the movement of the gray area.
A state in which part of the image becomes dark continues. Therefore, some of the pixels that should become white after the gray area has moved have pixels that have partially darkened according to the movement interval of the gray area A, so that they appear dark on average. Will be visually recognized.

The alignment defect due to the transverse electric field is directed to the direction of elimination with time, but the alignment defect once generated in the white region, strictly speaking, the region where the effective value of the voltage held by the liquid crystal element is small is
It can be said that there is a strong tendency to remain for a relatively long time.
Such an orientation failure occurs in a pixel having a weak vertical electric field, such as a white pixel in a normally white mode. However, for pixels where the vertical electric field is strong and the influence of the horizontal electric field is small just before the change, such as a pixel that changes from gray to white at the boundary, the effect of orientation failure is affected even if the vertical electric field is weakened. Is small.

Therefore, in the present embodiment, first, for a pixel for which a gradation value that is likely to be affected by a lateral electric field, that is, a gradation value that is brighter than a predetermined value, is specified, a voltage for increasing the vertical electric field is set. This is expressed as an average transmittance between a frame period forcibly applied and a frame period for applying a voltage determined in advance according to the gradation value. As a result, when a voltage for increasing the vertical electric field is applied, the horizontal electric field becomes small enough to be ignored, and thereafter, the influence of the horizontal electric field can be prevented from remaining.
Note that for pixels for which a gradation value that can ignore the influence of the transverse electric field is specified,
A voltage corresponding to the gradation value is applied to and held in the liquid crystal element.
Further, the vertical electric field in the liquid crystal element is proportional to the effective value of the voltage between the pixel electrode and the counter electrode in the liquid crystal element. For this reason, the vertical electric field can be discussed by the effective voltage value held in the liquid crystal element in one frame period.

Next, if a voltage for increasing the vertical electric field is applied to the pixels for which the bright gradation value is likely to be affected by the horizontal electric field at the same frame period, It becomes dark during the frame period, causing flicker.
Therefore, in the present embodiment, secondly, in a certain frame period, among the pixels for which such a bright gradation value is designated, the vertical electric field is strongly applied to the pixels in the odd-numbered row odd-numbered column and the even-numbered row even-numbered column. Voltage is applied to the even-numbered rows, the odd-numbered rows, and the odd-numbered rows and even-numbered columns, and a voltage predetermined according to the gradation is applied, while the voltage applied to the pixels is switched in the next frame period. The configuration.

Subsequently, the liquid crystal element must be AC driven, but the polarity inversion period is 1 as in the prior art.
If the frame period is set, in the present embodiment, a direct current component is applied to a pixel for which a bright gradation value that is likely to be affected by a lateral electric field is specified, in view of applying two types of voltages. There is a possibility that. Therefore, in order to avoid this, in the present embodiment, thirdly, the polarity inversion period is, for example, two frame periods.
When the polarity inversion cycle is set to a two-frame period, in order to distinguish each frame, the two-frame period, which is positive for convenience, is set as the first and second frames in order, and is negative. The period of 2 frames is assumed to be the third and fourth frames in order.

In the present embodiment, the video processing circuit 30 executes the first to third processes. FIG. 5 shows, for each of the first to fourth frames, for each pixel position, when the video processing circuit 30 converts the gradation value specified by the video data Vd into the data signal Vid. It is a table.
Specifically, the video processing circuit 30 determines that the video data Vd is in accordance with the upper table of FIG. 5 if the pixels having the gradation values specified by the video data Vd are odd rows and odd columns and even rows and even columns.
If d is converted into a data signal Vid and if it is an even-numbered row and an odd-numbered column and an odd-numbered row and an even-numbered column, the video data Vd is converted into a data signal Vid according to the lower table of FIG.

Here, in FIG. 5, the positive voltage Vth (+) generates a vertical electric field that can be ignored by the liquid crystal element when it is supplied as a data signal and applied to the pixel electrode 118. This is the lower limit value of the voltage range to be caused. The negative voltage Vth (−) is an upper limit value of a voltage range that generates a vertical electric field that can be ignored by the liquid crystal element when supplied as a data signal.
Actually, the voltages Vth (+) and Vth (−) are actually obtained experimentally through experiments and display evaluation. In addition, when the voltage Vth (+) and Vth (−) are applied to the pixel electrode 118 and the effective voltage applied to the liquid crystal element is Vth, for example, as shown in FIG. It is assumed that the rate corresponds to the gradation values “4” and “5”. In other words, in the present embodiment, the threshold voltage of the liquid crystal element that starts to be affected by the horizontal electric field is Vth, and if the gradation value is “5” or more, the normal voltage amplitude method is affected by the horizontal electric field. It is assumed that it will occur.

In this assumption, the video processing circuit 30 according to the present embodiment has the gradation value specified for the pixel when the pixel corresponding to the video data Vd is an odd row and an odd column and an even row and an even column.
When “5”, “6”, and “7” are 5 or more, the first frame is converted into the data signal Vid of the voltage Vth (+) regardless of these gradation values. At this time, if the video processing circuit 30 is the second frame, the voltage Vb (+), which is predetermined according to these gradation values,
In Va (+) and V7 (+), in the third frame, the voltage Vth (-) is set regardless of the gradation values, and in the fourth frame, the voltage Vb ( -), Va (-), and V7 (-), respectively.
On the other hand, when the pixels corresponding to the video data Vd are an even-numbered row and an odd-numbered column and an odd-numbered row and an even-numbered column, the gradation values designated for the pixel are “5”, “6”, and “7”. When
The voltages of the first and second frames in the odd and odd columns and the even and even columns are interchanged, and the voltages of the third and fourth frames in the odd and odd columns and the even and even columns are interchanged.
Here, the voltage effective value of the liquid crystal element when the voltages Va (+) and Va (−) are applied to the pixel electrode 118 is Va, and similarly, the voltages Vb (+) and Vb (−) are applied to the pixel electrode 118. The voltage effective value of the liquid crystal element when applied is Vb. Here, the effective voltage values Va and Vb of the liquid crystal element have a relationship of V7 <Va <Vb <Vth as shown in FIG.
Note that the video processing circuit 30 uses the data signal Vid for the gradation values “0” to “4”.
Depending on the gradation value, the voltages V0 (+) to V4 (+) are applied to the first and second frames, and the voltages V0 (−) to V4 (−) are applied to the third and fourth frames. Convert each one.

In the configuration in which the video data Vd is converted into the data signal Vid by the video processing circuit 30, for example, when a plurality of pixels for which the gradation value “7” is specified are adjacent to each other in the vertical and horizontal directions, as shown in FIG. In the first frame, since the data signal of the voltage Vth (+) is supplied to the pixels 110 in the odd-numbered rows, odd-numbered columns and even-numbered rows and even-numbered columns in the adjacent region, the gradation value “7”.
The pixel 1 of the even-numbered odd-numbered column and the odd-numbered even-numbered column is smaller than the transmittance corresponding to
Since the data signal of voltage V7 (+) is supplied to 10, the transmittance corresponds to the gradation value “7”.
On the other hand, when the gradation value “7” is maintained in the adjacent region, in the second frame, the data of the voltage V7 (+) is applied to the pixels 110 in the odd-numbered row / odd-numbered column and even-numbered row / even-numbered column in the adjacent region. Since the signal is supplied, the transmittance corresponding to the gradation value “7” is obtained, whereas the data signal of the voltage Vth (+) is supplied to the pixels 110 in the even-numbered odd-numbered columns and the odd-numbered even-numbered columns. So
It becomes smaller than the transmittance corresponding to the gradation value “7”.
Then, when the gradation value “7” is continuously maintained in the adjacent area, in the third frame, the pixels 110 in the odd-numbered and odd-numbered columns and the even-numbered and even-numbered columns in the adjacent area have the gradation value “7”.
The pixel 110 in the even-numbered odd-numbered column and the odd-numbered even-numbered column has a transmittance corresponding to the gradation value “7”. In the fourth frame, The pixels 110 in the odd-numbered and odd-numbered columns and the even-numbered and even-numbered columns have the transmittance corresponding to the gradation value “7”, whereas the pixels 110 in the even-numbered and odd-numbered columns and the odd-numbered and even-numbered columns have the gradation value “7”. It becomes smaller than the transmittance corresponding to.

As described above, when the pixel having the gradation value “7” is viewed in two consecutive frame periods,
The transmittance corresponds to the gradation value “7” in one frame period, and the transmittance corresponds to the gradation value “4” and “5” in the other one frame period. Therefore, the gradation value “
A pixel designated with “7” is an average value of the two transmittances when viewed with reference to the two-frame period, and is smaller than the transmittance corresponding to the gradation value “7”. Will be.
However, in the present embodiment, by applying the data signal Vid having the voltages Vth (+) and Vth (−) to the pixel electrode 118, the influence of the horizontal electric field of the liquid crystal element, that is, the remaining alignment failure is prevented. Therefore, it is possible to suppress a reduction in display quality, and it is not necessary to provide a notch or the like in the pixel electrode and the shape does not need to be changed, so that a reduction in aperture ratio can also be prevented.
Further, even if pixels having the same gradation value “7” are designated, a pixel to which a data signal of voltage Vth (+) or Vth (−) is supplied and a voltage V7 (+) or V7 (−) of Since the pixels to which the data signal is supplied are alternately arranged for each pixel in the vertical and horizontal directions in the same frame period,
Flicker is inconspicuous.
Further, when the effective voltage value of the liquid crystal element is alternately set to Vth and V7 for each frame period, if the polarity inversion period is set to one frame period, a direct current component is applied to the liquid crystal. However, since it is set to 2 frame periods, no direct current component is applied to the liquid crystal when the 4 frame periods are taken as a unit.
Here, the polarity inversion period is a two-frame period, but it may be a frame period corresponding to an even number of 4 or more.

A pixel for which the gradation value “6” is designated has a transmittance corresponding to the voltage effective value Va in one frame period when viewed in two consecutive frame periods, and the voltage effective value in the other one frame period. Since the transmittance corresponds to Vth, when the two frame periods are taken as a reference, the average value of the two transmittances is obtained.
A pixel for which the gradation value “5” is designated has a transmittance corresponding to the voltage time value Vb in one frame period when viewed in two consecutive frame periods, and the effective voltage value in the other one frame period. Since the transmittance corresponds to Vth, when the two frame periods are taken as a reference, the average value of the two transmittances is obtained.
Note that the pixels for which the gradation values “4” to “0” are designated can be viewed in two consecutive frame periods.
Even in any one frame period, the transmittance corresponds to the voltage effective values V4 to V0.

Here, the transmittance with respect to the effective voltage values V7, Va, Vb, Vth, and V4 decreases in this order as shown in FIG. For this reason, the average value of the transmittance by the voltage effective values V7 and Vth when the gradation value “7” is designated, and the transmittance by the voltage effective values Va and Vth when the gradation value “6” is designated. , The average transmittance of the voltage effective values Vb and Vth when the gradation value “5” is designated, and the transmittance of the voltage effective value V4 when the gradation value “4” is designated. As for and, it becomes smaller in this order.
Therefore, in the present embodiment, as indicated by the solid thick line D in FIG.
Although the actual (average) transmittance corresponding to “5”, “6”, and “7” is slightly lower than the initial transmittance, continuity of gradation is ensured.

However, as shown by a solid thin line E in FIG. 8, the actual transmittance corresponding to the maximum gradation value “7” is assumed to be the maximum value, and the transmittance for each gradation value is re-defined, whereby It is also possible to smoothly connect the transmittance characteristics in the gradation values “5” to “7” from the gradation values “0” to “4”. At this time, so as to have a so-called gamma characteristic according to the human visual sensitivity,
The transmittance of the liquid crystal element for each gradation value may be redefined.

In the above-described embodiment, the cycle of polarity inversion in AC driving is set to 2 frame periods.
As shown in FIG. 9, it is also possible to make one frame period by supplying a data signal having the same voltage effective value of the liquid crystal element over the positive polarity and the negative polarity. Note that the first, second, third, and fourth frames in FIG. 9 are the first, third, and third frames, respectively, in FIG.
, Corresponding to the second and fourth frames. As described above, by supplying the data signal, it is possible to prevent the display quality from being deteriorated due to the residual horizontal electric field while avoiding application of a DC component to the liquid crystal.

Further, in the present embodiment, the frame period is considered as a period period in which scanning lines are selected in the order of the 1st to 1st rows, and is a period in which one frame of video data is supplied (usually 1 of 60 Hz).
(Period) may be the same or different. When the frame period is shorter than the period during which one frame of video data is supplied, for example, when the frame period is half (double speed), when attention is paid to a certain pixel, the same gradation value is designated over two frame periods. It will be
When the gradation values are “5”, “6”, and “7”, the voltage effective values of the liquid crystal elements are different with the conversion contents shown in FIG.
It may be driven not only at 2 × speed but also at 3 × speed, 4 × speed,.

In the above-described example, for the gradation value “5”, for example, in addition to one frame period in which the voltage effective value of the liquid crystal element is Vth, the period in which the voltage effective value Vb is only one frame period,
Although these average transmissivities are expressed, voltages other than the effective voltage value Vth may be expressed by the average transmissivities by making them the same or different over a period of two frame periods or more.
Further, in the above-described embodiment, Vth (+) is supplied for the positive polarity and Vth (-) is supplied for the negative polarity as a voltage that generates a vertical electric field that does not leave alignment defects due to the horizontal electric field in the liquid crystal element. However, a voltage of Vth (+) or more may be used for the positive polarity, and Vth (+) for the negative polarity.
-) The following voltages may be used.

In the example described above, plane inversion is described in which all the polarities of pixels written over one frame period are the same. However, in scanning line inversion in which the polarity is changed for each scanning line, adjacent pixels in the vertical direction The polarities are different from each other. Further, in column inversion in which the polarity is changed for each data line, the adjacent pixels in the horizontal direction have different polarities, and thus are easily affected by the horizontal electric field. In the dot inversion in which the polarity of the pixel is replaced for every pixel adjacent in the vertical and horizontal directions, the pixels adjacent to each other in both the vertical and horizontal directions have different polarities, so that they are most susceptible to the influence of the horizontal electric field. Therefore, the present invention can be applied to any of these methods.

Furthermore, although the liquid crystal element 120 is in the normally white mode, it may be in a normally black mode in which the liquid crystal element 120 becomes dark when no voltage is applied. When the liquid crystal element 120 is in a normally black mode, it is affected by a lateral electric field when expressing a dark gradation,
When a gradation value equal to or lower than a predetermined value is designated, a data signal that causes the liquid crystal element to exceed the threshold voltage and a data signal that has a predetermined voltage with respect to the gradation value are switched and supplied. It ’s fine. Further, the liquid crystal element 120 is not limited to a transmissive type, and may be a reflective type.
In the above description, the reference voltage Vc having the writing polarity is applied to the counter electrode 108 which is the other end of the pixel capacitor.
This is a case where the TFT 116 in the pixel 110 functions as an ideal switch, and in practice, due to the parasitic capacitance between the gate and the drain of the TFT 116, the TFT 116 in the pixel 110 functions as an ideal switch. When the state changes, the drain electrode (pixel electrode 118
) Occurs (called push-down, punch-through, field-through, etc.). For this reason, when the reference voltage Vc of the writing polarity matches the voltage LCcom, the effective voltage value of the liquid crystal element 120 by the negative polarity writing is slightly larger than the effective value by the positive polarity writing when viewed in one frame period. (When TFT 116 is n-channel). Therefore,
The reference voltage Vc of the write polarity may be set by being offset higher than the voltage LCcom so that the influence of pushdown is offset.

<Electronic equipment>
Next, a projector using the electro-optical device as a light valve will be described as an example of an electronic apparatus using the electro-optical device according to the above-described embodiment. FIG. 10 is a plan view showing the configuration of the projector.
As shown in this figure, a projector 2100 is provided with a lamp unit 2102 composed of a white light source such as a halogen lamp. The projection light emitted from the lamp unit 2102 is separated into three primary colors of R (red), G (green), and B (blue) by three mirrors 2106 and two dichroic mirrors 2108 arranged inside. Are guided to the light valves 100R, 100G and 100B corresponding to the respective primary colors. Note that B light has a long optical path compared to other R and G colors.
The light is guided through a relay lens system 2121 including an entrance lens 2122, a relay lens 2123, and an exit lens 2124.

In the projector 2100, the electro-optical device 1 including the liquid crystal display panel 100 is R,
Three sets are provided corresponding to each color of G and B. The video data corresponding to each color of R, G, and B is supplied from an external host device. Light valve 100R,
The configurations of 100G and 100B are the same as those of the liquid crystal display panel 100 in the above-described embodiment, and are driven by data signals corresponding to R, G, and B, respectively.
The lights modulated by the light valves 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, the R and B light beams are refracted at 90 degrees, while the G light beam travels straight.
Therefore, after the images of the respective colors are combined, the projection lens 2114 is displayed on the screen 2120.
As a result, a color image is projected.

The light valves 100R, 100G, and 100B include a dichroic mirror 2
Since light corresponding to the primary colors of R, G, and B is incident by 108, there is no need to provide a color filter. In addition, the transmission images of the light valves 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmission image of the light valve 100G is projected as it is, so the horizontal scanning direction by the light valves 100R and 100B is The image is reversed in the horizontal scanning direction by the light valve 100G and displayed in an inverted image.

In addition to the electronic device described with reference to FIG. 10, the electronic device includes a television, a viewfinder type / monitor direct view type video tape recorder, a car navigation device, a pager, an electronic notebook, a calculator, a word processor, a workstation, a television. Examples include a telephone, a POS terminal, a digital still camera, a mobile phone, and a device equipped with a touch panel. Needless to say, the electro-optical device according to the present invention is applicable to these various electronic devices.

1 is a block diagram illustrating a configuration of an electro-optical device according to an embodiment of the invention. FIG. FIG. 3 is a diagram illustrating an example of a pixel in the electro-optical device. It is a figure which shows operation | movement of the Y driver in the same electro-optical apparatus. It is a figure which shows the voltage-transmission characteristic in the same electro-optical apparatus. It is a figure which shows operation | movement of the video processing circuit in the same electro-optical apparatus. It is a figure which shows the relationship of the voltage in the same electro-optical apparatus. FIG. 3 is a diagram illustrating a writing state in the same electro-optical device. It is a figure which shows the relationship between the gradation value and the actual transmittance | permeability in the same electro-optical apparatus. It is a figure which shows another operation | movement of the video processing circuit. 1 is a diagram illustrating a configuration of a projector using an electro-optical device according to an embodiment. It is a figure which shows the malfunction on the display resulting from a horizontal electric field. It is a figure for demonstrating the cause of the malfunction on a display. It is a figure for demonstrating the cause of the malfunction on a display.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Control circuit, 20 ... Timing control circuit, 30 ... Video processing circuit, 100 ... Liquid crystal display panel, 108 ... Counter electrode, 110 ... Pixel, 112 ... Scan line, 114 ... Data line, 116
... TFT, 118 ... Pixel electrode, 120 ... Liquid crystal element, 130 ... Y driver, 140 ... X driver, 2100 ... Projector

Claims (6)

Scanning lines;
Data lines,
Provided corresponding to the intersection of the scan line and the data line, one end connected to the data line, the other end connected to a pixel electrode, and when the scan line is selected, the one end and the data line A pixel including a switching element that is conductive between the other ends, and an electro-optical element that is in an optical state based on a voltage applied to the pixel electrode and a voltage applied to the counter electrode;
An electro-optical device driving method comprising:
When the gradation value designated for the pixel is larger or smaller than a predetermined value, a voltage to be applied between the pixel electrode and the counter electrode is determined according to the gradation value. When the threshold voltage is smaller than
A data signal for making the gap between the pixel electrode and the counter electrode equal to or higher than the threshold voltage;
A data signal having a voltage lower than the threshold voltage and having a predetermined voltage with respect to the gradation value is switched every cycle that is an integral multiple of a frame period and supplied via the data line. A method for driving an electro-optical device. In the same frame period
For odd-numbered and odd-numbered columns and even-numbered and even-numbered columns of pixels, a data signal for supplying a voltage between the pixel electrode and the counter electrode equal to or higher than the threshold voltage is supplied.
2. The electro-optical device drive according to claim 1, wherein a data signal having a voltage predetermined with respect to the gradation value is supplied to pixels in even rows and odd columns and odd rows and even columns. Method. The data signal has two types of positive polarity that is higher than a predetermined reference voltage and negative polarity that is lower.
A voltage that makes the gap between the pixel electrode and the counter electrode equal to or higher than the threshold voltage and a voltage that is predetermined for the gradation value are either positive or negative in this order or in the reverse order. On the other hand, after supplying
A voltage that makes the gap between the pixel electrode and the counter electrode equal to or higher than the threshold voltage and a voltage that is predetermined for the gradation value are either positive or negative in this order or in the reverse order. The method of driving an electro-optical device according to claim 2, wherein the electro-optical device is supplied from the other. The data signal has two types of positive polarity that is higher than a predetermined reference voltage and negative polarity that is lower.
A voltage that causes the pixel electrode and the counter electrode to be equal to or higher than the threshold voltage is supplied by either the positive polarity or the negative polarity, and then supplied by either the positive polarity or the negative polarity,
Subsequently, a predetermined voltage with respect to the gradation value is supplied by either the positive polarity or the negative polarity, and then supplied by either the positive polarity or the negative polarity. The driving method of the electro-optical device according to claim 2. Scanning lines;
Data lines,
Provided corresponding to the intersection of the scan line and the data line, one end connected to the data line, the other end connected to a pixel electrode, and when the scan line is selected, the one end and the data line A pixel including a switching element that is conductive between the other ends, and an electro-optical element that is in an optical state based on a voltage applied to the pixel electrode and a voltage applied to the counter electrode;
A scanning line driving circuit for supplying a scanning signal for selecting the scanning line;
The gradation value specified for the pixel is larger or smaller than a predetermined value, and a voltage to be applied between the pixel electrode and the counter electrode according to the gradation value is a threshold value. When the voltage is smaller than the voltage,
A data signal for making the gap between the pixel electrode and the counter electrode equal to or higher than the threshold voltage;
Data that is lower than the threshold voltage and is supplied via the data line by switching a data signal having a voltage that is predetermined with respect to the gradation value every cycle that is an integral multiple of a frame period An electro-optical device comprising: a signal supply circuit.   An electronic apparatus comprising the electro-optical device according to claim 5.

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