JP5682243B2 - Electro-optical device, driving method of electro-optical device, and electronic apparatus - Google Patents

Description

The present invention relates to a technique for driving a pixel either on or off in each of a plurality of subfields obtained by dividing one frame.

For example, in an electro-optical device having a liquid crystal element in a pixel, the following technique has been proposed for gradation display. That is, for each of a plurality of subfields obtained by dividing one frame (one field), the pixel (display element) is driven either on or off, and the proportion of time for driving on (or off) is changed. A technique for displaying an intermediate gradation as a temporal integration value has been proposed (see Patent Document 1).

JP 2007-148417 A (FIG. 6, paragraph 0099)

By the way, if the liquid crystal element is in a normally black mode, for example, when the gradation level is changed, the period sum of the subfields to be turned on is changed from the low gradation side (dark) to the high gradation side (bright). It is necessary to increase sequentially. In order to express a large number of gradations with a small number of subfields, subfields may be set to different periods with weights instead of equal periods. In this case, however, the gradation level changes particularly on the high gradation side. When this is done, it is necessary to turn on a subfield having a large weight (long period). At this time, if the position of the center of gravity of the subfield that is turned on moves greatly, there is a problem that the pseudo contour is easily visually recognized at the boundary between adjacent gradations.
The present invention has been made in view of the above-described circumstances, and one of its purposes is that when weighting the period length of a subfield, a subfield having a relatively large weight when viewed from adjacent gradations is used. It is an object of the present invention to provide a technique capable of suppressing the generation of a pseudo contour even when turned on (or off).

In order to achieve the above object, in the electro-optical device driving method according to the present invention, one frame is divided into at least two blocks having the same period length and continuous in time. A driving method of an electro-optical device in which each is divided into subfields having different period lengths, and gradation display is performed by controlling pixels on or off for each subfield. At the key level, one subfield is turned on in any one of the at least two blocks, and the sum of periods of subfields turned on over the one block is turned on over the other block. When the total period is less than or equal to the field period, the gradation level changes by “1” from the one gradation level. When the subfield that is on in the one block is the closest in duration and the subfield that is adjacent in time is turned on, the subfield that is turned on over the one block The gradation levels that are set so that the variation of the period sum is smaller than the period sum of the subfield that is turned on over the other block are included in the gradation levels that can be expressed by the pixels. And According to this driving method, when the gradation level changes by “1”, even if the center of gravity shifts by turning on one subfield in one block, the period sum of the subfield turned on in the other block Since is more dominant, the influence of the movement of the center of gravity can be ignored when viewed with two blocks. For this reason, generation | occurrence | production of a pseudo contour can be suppressed. In the above driving method, it may be considered that subfield on is replaced with subfield off.

In the driving method, when the gradation level changes by “1” from the one gradation level, the one subfield may be turned off in the one block. In this way, since the change in brightness in one block is smaller than in the case where it is kept on, the change in gradation is small even when viewed with two blocks. In other words,
This is suitable for the case where the actual gradation change can be reduced with respect to the gradation level change. further,
If the on / off state of each subfield is not changed in the other block, the influence of the center of gravity movement in one block can be further reduced.
In the above driving method, the pixel includes a liquid crystal element, and the number of blocks included in the one frame is a multiple of 4, and the same on-off pattern is used in two blocks and the other two blocks. The drive may be driven with the polarity reversed. In this way, it is possible to prevent a DC component from being applied to the liquid crystal element included in the pixel when viewed in one frame.
The present invention can be conceptualized not only as a method for driving an electro-optical device, but also as an electro-optical device, and further, an electronic apparatus including the electro-optical device. Examples of such an electronic device include a projector that magnifies and projects an image light-modulated by the electro-optical device.

It is a figure which shows the whole structure of the display apparatus with which the drive method which concerns on embodiment is applied. It is a figure which shows the structure of the pixel in a display apparatus. It is a figure which shows the structure of the flame | frame and subfield in a display apparatus. It is a figure which shows the conversion content of the SF code conversion part in a display apparatus. It is a figure which shows the conversion content of the SF code conversion part in a display apparatus. It is a figure which shows the transmittance | permeability change with respect to a frame by comparing between adjacent gradations. It is a figure which shows the transmittance | permeability change with respect to a frame by comparing between adjacent gradations. It is a figure which shows the ON voltage and OFF voltage in embodiment. It is a figure which shows the structure of the projector to which a display apparatus is applied.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram illustrating an overall configuration of an electro-optical device 1 according to the embodiment. As shown in this figure, the electro-optical device 1 is roughly divided into a control circuit 10, a memory 20, a conversion unit 30, a display circuit 100, a scanning line driving circuit 130, and a data line driving circuit 140.
Among these, the control circuit 10 includes a vertical scanning signal Vs supplied from a host device (not shown).
Each unit is controlled in synchronization with the horizontal scanning signal Hs and the dot clock signal Clk.
In the display circuit 100, the pixels 110 are arranged in a matrix. Specifically, in the display circuit 100, 1080 rows of scanning lines 112 extend in the X (horizontal) direction in the figure, while 1920 columns of data lines 114 are electrically insulated from the scanning lines 112, while , Extending in the Y (vertical) direction. Pixels 110 are provided so as to correspond to the intersections of the scanning lines 112 and the data lines 114.
Therefore, in the present embodiment, the pixel 110 is vertically 1080 in the display circuit 100.
They are arranged in a matrix of rows x 1920 columns. However, the present invention is not intended to be limited to this arrangement.

The memory 20 has storage areas corresponding to pixels arranged in vertical 1080 rows × horizontal 1920 columns, and each storage area stores a video signal Vid corresponding to each pixel 110. Video signal V
id specifies the brightness (gradation level) of the pixel 110 in increments of “1” from “0” to “255” in this embodiment.
The video signal Vid is supplied from a host device (not shown) and is stored in the storage area corresponding to the pixel by the control circuit 10, while the display circuit 100 corresponding to the pixel to be written is the memory 20. Is read as display data Da.
The conversion unit 30 converts the read display data Da into a pixel 110 (liquid crystal element) according to the gradation level specified by the display data Da and the subfield indicated by the data sfn.
Is converted into a display bit Db indicating whether to turn on or off. Details of this conversion will be described later.

For convenience of description, the configuration of the pixel 110 will be described with reference to FIG. FIG. 2 shows the pixel 11
FIG. 4 is a diagram showing an equivalent circuit of 0, and a configuration of 4 × 2 pixels corresponding to an intersection of i row and (i + 1) row adjacent thereto, j column and (j + 1) column adjacent thereto is formed. It is shown.
Here, i and (i + 1) are symbols for generally indicating the row in which the pixels 110 are arranged. In this embodiment, i and (i + 1) are integers of 1 to 1080, and j and (j + 1) are pixels. 110
Is a symbol for generally indicating a column to be arranged, and is an integer of 1 or more and 1920 or less.

As shown in FIG. 2, each pixel 110 includes an n-channel TFT (Thin Film Transistor).
or: a thin film transistor) 116, a liquid crystal element 120, and an auxiliary capacitor 125.
Here, since each pixel 110 has the same configuration, a description will be given taking an example where the pixel 110 is located in i row and j column. The gate electrode of the TFT 116 in the pixel 110 in the i row and j column is i.
While connected to the scanning line 112 in the row, its source electrode is connected to the data line 114 in the j-th column, and its drain electrode is connected to the pixel electrode 118 that is one end of the liquid crystal element 120 and one end of the auxiliary capacitor 125. Yes. The other end of the liquid crystal element 120 is a common electrode 108. The common electrode 108 is common to all the pixels 110, and in this embodiment, the voltage L
Kept at Ccom. The other end of the auxiliary capacitor 125 is a capacitor line 115, which is common to all the pixels 110 and is kept at the same voltage LCcom as the common electrode 108. For this reason, the auxiliary capacitor 125 is configured to be connected in parallel to the liquid crystal element 120 for each pixel 110.

The display circuit 100 includes a scanning line 112, a data line 114, a TFT 116, and a pixel electrode 118.
The element substrate on which the auxiliary capacitor 125 and the like are formed and the counter substrate on which the common electrode 108 is formed are bonded so that the electrode formation surfaces face each other while maintaining a certain gap. Is sealed. Therefore, the liquid crystal element 120 is
The pixel electrode 118 and the common electrode 108 are configured to sandwich the liquid crystal 105.
In the present embodiment, a transparent substrate such as glass is used for the element substrate and the counter substrate, and the scanning line driving circuit 130 and the data line driving circuit 140 are formed on the counter surface of the element substrate together with the TFT 116 by the high-temperature polysilicon process. Is done.
Note that a silicon substrate is used as the element substrate, so-called LCOS (Liquid Crystal on Silicon).
con), the control circuit 10, the memory 20, and the conversion unit 30 may all be formed. In the case of the LCOS type, the liquid crystal element 120 is a reflection type.

By the way, when the liquid crystal element 120 is in a normally black mode, the liquid crystal element 1
The transmittance of 20 (reflectance in the case of a reflective type) is lowest (black) when the voltage applied to the liquid crystal element 120, that is, the potential difference between the pixel electrode 118 and the common electrode 108 is zero, It increases (lightens) as the effective value of the voltage increases.
In general, when gradation is expressed by the liquid crystal element 120, the scanning line 112 is selected and the TFT is selected.
A voltage modulation method (analog driving) is employed in which the analog voltage corresponding to the target gradation is applied to the liquid crystal element 120 via the data line 114 by turning on the data line 116. On the other hand, in this embodiment, only the on voltage or the off voltage is applied to the pixel electrode 118, and gradation display is performed as follows. Specifically, in the present embodiment, gradation display is performed by dividing one frame into a plurality of subfields and applying a turn-on voltage to the pixel electrode 118 to turn on the liquid crystal element 120 and a turn-off voltage. The period during which the liquid crystal element 120 is turned off by applying the voltage is controlled by digital driving in which time is distributed and controlled in units of subfields.

In the normally black mode, when the transmittance in the darkest state is 0% relative transmittance and the transmittance in the brightest state is 100% relative transmittance, the relative transmittance among the voltages applied to the liquid crystal element 120 is The voltage at 10% is called the optical threshold voltage, and the relative transmittance is 90%.
This voltage is called optical saturation voltage. The on-voltage used in this embodiment refers to a voltage that brings the liquid crystal element 120 to the saturation voltage or higher and turns it on when it is applied to the pixel electrode 118. The off voltage refers to a voltage that brings the liquid crystal element 120 to an optical threshold voltage or less and turns it off when it is applied to the pixel electrode 118.

Thus, in this embodiment, the period during which the liquid crystal element 120 is turned on or off is
It is executed by distributing and controlling subfields as units. Then, the structure of the subfield in this embodiment is demonstrated next.

FIG. 3 is a diagram showing a configuration of subfields in the present embodiment.
In this figure, one frame means a period during which the video signal Vid for one cut (frame) is supplied from the host device or a period required for the display circuit 100 to form an image for one cut. When the frequency of the vertical scanning signal Vs is 60 Hz, 16.67 for one cycle thereof.
Milliseconds.
As shown in this figure, in this embodiment, the period of one frame is equally divided into four blocks A, B, C, and D, and each block is further divided into eight subfields. For this reason, since one frame is divided into a total of 32 subfields, for convenience, each subfield is sf1, sf2, sf3,.
, Sf32.

Here, the period length of each block is 4.17 milliseconds. The period lengths of the subfields sf1, sf2, sf3, sf4, sf5, sf6, sf7, and sf8 in the block A are 1.72 milliseconds, 0.80 milliseconds, 0.60 milliseconds, 0.40 milliseconds,
It is set to 0.30 milliseconds, 0.20 milliseconds, 0.10 milliseconds, and 0.05 milliseconds.
In other words, when the period length of the subfield sf8 is weighted by setting the period length of the shortest subfield sf8 to “1”, the subfields sf1, sf2, sf3, sf4,
The weights of the period lengths of sf5, sf6, and sf7 are “34.4”, “16”, and “12”, respectively.
, “8”, “6”, “4”, “2”.
Subfields sf9 to sf16 in block B, subfields sf17 to sf24 in block C, and subfields sf25 to sf3 in block D
2 is set to the same period length as the subfields sf1 to sf8 in the block A.

Next, how on / off is assigned to the subfields sf1 to sf32 constituting the frame for each gradation level will be described.

4 and 5 are diagrams showing the on / off patterns assigned to the subfields sf1 to sf16 among the subfields sf1 to sf32 with respect to the grayscale level. FIG. 4 is a diagram illustrating conversion contents of a conversion unit 30. In this figure, the subfields sf17 to sf32 are omitted for the following reason. That is, in this embodiment, since the liquid crystal element 120 is included in the pixel 110, the liquid crystal element 120 needs to be AC driven. Therefore, in this embodiment, the blocks A and B located in the first half of one frame are each driven with positive polarity, and the block C located in the second half is driven.
, D are driven with a negative polarity, and the first half and the second half are driven with the same on / off pattern. For this reason, for the blocks C and D in the latter half, the first block A,
Since it is the same on / off pattern as B, illustration is omitted. The gradation level is “78”.
”To“ 255 ”are also omitted.

As shown in FIGS. 4 and 5, in this embodiment, for each gradation level, whether to turn on or off the subfields sf1 to sf16 (sf17 to sf32) is defined. For example, in FIG. 4, when the gradation level is “11”, the subfield s
Since it is “0” in f4 (sf20), it is defined that it should be turned off. For example, in FIG. 5, when the gradation level is “45”, the subfield sf13 (sf
29) “1”, it is specified that it should be turned on.

In the present embodiment, since the liquid crystal element 120 is in the normally black mode, it is defined that the liquid crystal element 120 is turned off over all subfields when the gradation level is the lowest “0”.
When the gradation level is “1”, it is defined that only the subfield sf8 is turned on among the subfields sf8 and sf16 having the shortest period length. Next, when the gradation level is “2”, it is specified that the subfield sf16 is turned on in addition to the subfield sf8.
Subsequently, when the gradation level is “3”, the subfield sf7 whose period length is the second shortest,
It is specified that only the subfield sf7 is turned on in sf15. Here, the sum of the weights of the period lengths of the subfields to be turned on when the gradation level is “2” is “2”.
It is. On the other hand, the sum of the weights of the period lengths of the subfields that are turned on when the gradation level is “3” is also “2”, which is the same as when the gradation level is “2”. For this reason,
It seems that there is no difference in the gradation actually expressed between the case where the gradation level is “2” and the case where it is “3”. However, the liquid crystal element 120 used in the present embodiment has a relatively slow optical response to voltage changes. That is, the transmittance changes slowly with respect to the application of the on-voltage (or off-voltage) to the pixel electrode 118. For this reason, the subfields sf8 and sf1
6 and when the sub-field sf7 is continuously turned on for the same period, even if the on-drive period sum is the same, the actual transmittance is continuous. When the on-drive is activated, the power is larger (brighter) than when the on-drive is discretely performed.
In FIG. 4 and FIG. 5, ON or OFF in each subfield is defined using such characteristics. As a result, in this embodiment, it is possible to express the gradation more than the difference in the sum of periods of the subfields to be turned on.

When the gradation level is “4”, in addition to the subfield sf7, it is specified to turn on the subfield sf16 having the smallest period weight and temporally separated from the subfield sf7. Note that the subfield sf is not the subfield sf8.
The reason why 16 is turned on is as follows. That is, when the subfield sf8 is turned on, the on-period continues to be on with the subfield sf7 that is already turned on, and the actual gradation greatly fluctuates with respect to the change in gradation level. This is because it is not suitable for fine gradation changes on the key side.
In this case, the subfield sf7 with the weight “2” is turned on in the block A, and the subfield sf16 with the weight “1” is turned on in the block B. The sum of periods of subfields to be turned on is the block A
It is less than or equal to the sum of periods of subfields that are turned on.

When the gradation level is “5”, the subfields sf1 to sf8 of the block A are not changed as compared with the case of the gradation level “4”. However, for the block B, the subfield sf16 is changed from on to off, and the subfield sf16
Subfield sf15 whose weight is larger than 16 by one rank and temporally adjacent
Has been changed from off to on.
Note that the gradation level is “53” for the effect of changing the subfield having the largest weight among the subfields that have been turned on in the block B when the gradation level has changed. As an example, the case of changing from “54” to “54” will be described later.

When the gradation level is “6”, the subfield sf8 of the block A is changed to ON as compared with the case of the gradation level “5”.
When the gradation level is “7”, the subfield sf16 of the block B is changed to ON as compared with the case of the gradation level “6”.
In this case, since the subfields sf7 and sf8 are turned on in the block A, and the subfields sf15 and sf16 having the same weight are turned on in the block B, the subfields that are turned on over the block A when compared between the blocks. The sum of periods is block B
It is the same as the period sum of the subfields that are turned on. Even in this case, the period sum of the subfields that are turned on over the block A is equal to or less than the period sum of the subfields that are turned on over the block B.

When the gradation level is “8”, the subfields sf9 to sf16 of the block B are not changed as compared with the gradation level “7”. However, for the block A, the subfields sf7 and sf8 are changed to OFF, and among them, the subfield sf6 whose weight is larger by one rank than the subfield sf7 having the largest weight and temporally adjacent. Has been changed from off to on.
Note that the gradation level is “64” for the effect of changing the subfield having the largest weight among the subfields that have been turned on in the block A when the gradation level has changed. As an example, the case of changing from “65” to “65” will be described later.
In this manner, the subfields sf1 to sf16 are similarly applied to the subsequent gradation levels.
On / off of (sf17 to sf32) is determined.

Returning to FIG. 1 again, the scanning line driving circuit 130 sequentially shifts the start pulse Dy supplied from the control circuit 10 in accordance with the clock signal Cly, and the scanning signals G1, G2, G3,
..., G1080 is supplied to the scanning lines 112 in the 1, 2, 3,. In the present embodiment, the scanning line 112 is set to 1 in each of the subfields sf1 to sf32.
The second, third,..., And 1080th rows are selected in order, and the liquid crystal element 120 is turned on or off corresponding to each subfield.
Therefore, as shown in FIG. 3, the control circuit 10 outputs the start pulse Dy at the timing corresponding to the period length of each subfield from the beginning of one frame and generates the clock signal Cly to generate the scanning line driving circuit. 130.
In this configuration, the subfield sf8 (sf16, sf24,
It is necessary to complete selection of all scanning lines within the period of sf32).
Using the technique described in Japanese Patent Application Laid-Open No. 004-177930, the scanning lines are not in the order of 1, 2, 3, 4,..., But in the order of 1, (n + 1), 2, (n + 2), 3, (n + 3). 4, (n +
4),... May be selected in the order of skipping n rows, such as row.

The data line driving circuit 140 sequentially samples the display bit Db converted by the conversion unit 30 with the clock signal Clx, converts the display bit Db into a voltage having a polarity specified by the signal Frp, and supplies the voltage to the data line 114 as a data signal. To do.
More specifically, the data line driving circuit 140 has a case where the display bit Db is “1” indicating ON, and if the positive polarity writing is designated, the negative polarity writing is performed at the voltage Von (+). If it is specified, it is converted to voltage Von (-), while it is "0" indicating OFF, and if positive writing is specified, it is converted to voltage Voff (+). If voltage is included, voltage Voff (-)
Respectively.
Therefore, as shown in FIG. 3, the control circuit 10 sets the signal Frp to H level in the blocks A and B to specify positive polarity, and sets the signal Frp to L level in the blocks C and D to specify negative polarity. Further, the control circuit 10 generates a clock signal Clx in synchronization with reading from the memory 20 (conversion to the display bit Db), and supplies the clock signal Clx to the data line driving circuit 140, although not particularly shown.
The data signals supplied to the data lines 114 in the 1, 2, 3,..., 1920 columns are represented as data signals d1, d2, d3,.

The voltages Von (+) and Von (−) are on-voltages with respect to the liquid crystal element 120 and have a symmetrical positional relationship with respect to the voltage Vc as shown in FIG. As described above, in the present embodiment, since the voltage LCcom is applied to the common electrode 108, the voltage Von (+) is applied to the pixel electrode 1.
18, a voltage difference between the voltage Von (+) and the voltage LCcom is applied to the liquid crystal element 120, and a voltage Von (−) is applied to the pixel electrode 118 when the voltage Von (−) is applied to the pixel electrode 118. The difference voltage between (−) and the voltage LCcom is written and turned on.
On the other hand, the voltages Voff (+) and Voff (−) are off voltages with respect to the liquid crystal element 120, and FIG.
As shown in FIG. 6, the positional relationship is symmetrical with respect to the voltage Vc. When the voltage Voff (+) is applied to the pixel electrode 118, the liquid crystal element 120 has a voltage difference between the voltage Voff (+ and the voltage LCcom, and when the voltage Vb (−) is applied to the pixel electrode 118, the liquid crystal element. In 120, the difference voltage between the voltage Voff (−) and the voltage LCcom is written, and is turned off.

The applied voltage LCcom to the common electrode 108 is the reference voltage Vc as shown in FIG.
Is set to the lower side. This is because, in the n-channel TFT 116, due to the parasitic capacitance between the gate and drain electrodes, a pushdown occurs in which the potential of the drain electrode (pixel electrode 118) decreases when the state changes from on to off. It is to do. If the voltage LCcom is matched with the reference voltage Vc, the effective voltage value of the liquid crystal element 120 by negative polarity writing is slightly larger than the effective voltage value by positive polarity writing due to pushdown. For this reason, the voltage LCcom is offset to a lower side than the reference voltage Vc so that the influence of pushdown is offset. However, if the influence of pushdown can be ignored, the voltage LCcom and the reference voltage Vc may be set to coincide with each other. In this case, the off voltage may be the voltage LCcom regardless of the polarity.
Regarding the voltage, in this embodiment, for example, a non-selection voltage (L
Level), that is, ground potential Gnd. Note that the selection voltage (H level) to the scanning line 112 is higher than the voltage Von (+).

The scanning line driving circuit 130 applies a selection voltage to one scanning line 112 to turn on the TFT 116, and the data line driving circuit 140 connects the pixel electrode 118 to the data line 1.
14 and the on-state TFT 116 are supplied with an on-voltage or off-voltage data signal. The liquid crystal element 120 corresponding to the intersection of the scanning line 112 to which the selection voltage is applied and the data line 114 to which the data signal is supplied corresponds to the difference between the voltage of the data signal and the voltage LCcom applied to the common electrode 108. A voltage is applied. When the scanning line 112 becomes a non-selection voltage, the TFT 116 is turned off (non-conducting). However, in the liquid crystal element 120, the voltage applied when the TFT 116 is turned on is self-capacitance and auxiliary capacitance 125. Held by.
Therefore, the pixel 110 is scanned by the scanning line driving circuit 130 and the data line driving circuit 140.
A driving circuit for driving the liquid crystal element 120 on or off according to the display bit for each subfield is configured.

Next, the operation of the electro-optical device 1 according to the embodiment will be described.
As shown in FIG. 3, when the vertical scanning signal Vs is supplied, the control circuit 10 transmits the start pulse Dy in one vertical scanning period (frame) defined by the vertical scanning signal Vs.
The data is output for each period divided according to the weights of the subfields sf1 to sf32. Further, the control circuit 10 designates the signal Frp as H level in the first half of one frame and designates the negative polarity as L level in the second half of one frame. Further, the control circuit 10 counts the number of times that the start pulse Dy is output from the start of one frame, and uses the counted number as the data sfn indicating the subfield of the display circuit 100 at the present time.
Supply to zero.

The control circuit 10 temporarily stores in the memory 20 the video signal Vid supplied in synchronization with the vertical scanning signal Vs, the horizontal scanning signal Hs, and the dot clock signal Clk.
After storing in the memory 20, the control circuit 10 reads out display data Da corresponding to the pixels in the corresponding row in the 1st to 1920th columns from the memory 40 before selecting a scanning line in a given row in each sub-feed. The conversion unit 30 converts the read display data Da into display bits Db for each pixel according to the gradation level and the subfield indicated by the data sfn.

The scanning line driving circuit 130 transfers the start pulse Dy according to the clock signal Cly, thereby sequentially setting the scanning signals G1 to G1080 to the H level in each subfield. Here, before the scanning line of a certain row is selected by the scanning line driving circuit 130, the display data Da of the row is read from the memory 20 and converted into the display bit Db by the conversion unit 30. Before the selection of the scanning line, the data line driving circuit 140 is supplied with the display bit Db corresponding to the pixels in the 1st to 1920th columns corresponding to the scanning line and corresponding to the subfield to be written in the selection. Will be.
The data line driving circuit 140 converts the display bit Db for one row into an on voltage or an off voltage, respectively, into a data signal having the polarity specified by the signal Frp, and when the scanning line of the row is selected. In addition, a data signal is supplied to the data lines 114 of 1 to 1920 columns.
When the scanning line of the row is selected, the data signal supplied to the data line 114 is supplied from the pixel electrode 118 of the liquid crystal element 120 when the TFT 116 corresponding to the row is turned on.
As a result, the liquid crystal element 120 is turned on or off with a specified polarity.
Note that when the selection of the scanning line is completed, the TFT 116 is turned off, but the liquid crystal element 120 holds the voltage applied to the pixel electrode 118 when the TFT 116 is turned on because of the capacitance. The on or off drive is maintained until the next scanning line is selected again.

Such an operation is sequentially executed for the 1st to 1080th rows in one subfield. Furthermore, the operation of this one subfield is the subfield s in one frame.
It is executed in the order of f1 to sf32.
As a result, each pixel is turned on or off in accordance with the display bit Db in each of the subfields sf1 to sf32, so that the average transmittance when one frame is regarded as a unit period is the gradation level. As a result, the gradation is expressed, and the AC drive of the liquid crystal element 120 is completed in one frame.

According to the present embodiment, for example, when the gradation level is “53”, as shown in FIGS. 5 and 6, the display bit Db is displayed in the subfields sf1 to sf8 (sf17 to sf24) of the block A (C). Are converted into “00111100”, respectively. The time when the periods of the subfields sf3 to sf6 (sf19 to sf20) turned on at this time are totaled is “1.50 msec”, and “30” in terms of weight. In this case, block B
In the subfields sf9 to sf16 (sf25 to sf32) of (D), the display bit Db is converted to “00011011”, respectively. The time when the periods of the subfields sf12, sf13, sf15, and sf16 that are turned on at this time are totaled is “0.85 msec”, and the weight is “17”.
Next, when the gradation level increases from “53” to “54” by “1”, the block A (
There is no change for C), but for block B, the subfield sf11 adjacent to subfield sf12 is one rank higher in weight than subfield sf12 having the largest weight among the subfields that have been turned on so far. Is on. On the other hand, if the subfield sf11 is only turned on, the amount of change in the period sum becomes too large, so that the subfields sf12, sf15, and sf16 are changed to off in order to cancel. The time when the periods of the subfields sf11 and sf13 that are turned on at this time are totaled is “0.90 msec”, which is “18” in terms of weight.

In the case where the gradation level is “54”, compared with the case where the gradation level is “53”, the subfields sf1 to sf8 of the block A are not changed. On the other hand, for the block B, the subfields sf12, sf15, and sf16 are changed to off, and among the subfields that have been turned on so far, the weight is larger by one rank than the subfield sf12 that has the largest weight, and , The temporally adjacent subfield sf11 is changed from OFF to ON.
When the gradation level changes from “53” to “54”, the variation of the period sum that is turned on in block B is “1” because it is a change from “17” to “18” in terms of weight. Yes,
It is smaller than “30”, which is the sum of periods in block A. Therefore, in the block B, the subfields sf12, sf15, and sf16 are turned off, and the subfield sf11
Is changed to ON, and even if the centroid position of the subfield to be turned on moves, the sum of the periods of the subfields already turned on in block A is dominant and the centroid does not move in block A. When the blocks A and B are taken as a unit, the movement of the center of gravity in the block B can be ignored.
As shown in FIG. 6, even if the optical response waveforms when the gradation level is “53” and “54” are compared over a plurality of frames, as shown in FIG. Since the optical response due to ON / OFF in block A becomes dominant with respect to the optical response, when the blocks A and B are taken as a unit, and when the blocks C and D are added and taken as a unit of one frame The movement of the center of gravity can be reduced. For this reason, even if a pixel with a gradation level of “53” and a pixel with a gradation level of “54” are adjacent on the display circuit 100, it is possible to suppress the occurrence of a pseudo contour at the boundary between the adjacent portions. Become.

Further, when the gradation level is “64”, the block A as shown in FIGS.
In the subfields sf1 to sf8 (sf17 to sf24) of (C), the display bit D
Each b is converted to “00111011”. The time when the subfield periods to be turned on at this time are totaled is “1.35 ms”, and the weight is “27”. In this case, the subfields sf9 to sf16 (sf25 to sf3) of the block B (D)
In 2), the display bit Db is converted to “00111110”. The total time of the subfields turned on at this time is “1.60 msec”, and “32” in terms of weight.
Next, when the gradation level is increased by “1” from “64” to “65”, the block B (
D) is not changed, but for block A, subfield sf2 whose weight is one rank higher than subfield sf3 having the largest weight among subfields that have been turned on so far and that is adjacent to subfield sf3. Is on. On the other hand,
If only the subfield sf2 is turned on, the amount of change in the period sum becomes too large, so that the subfields sf3 and sf7 are changed to off in order to cancel. The time when the subfield periods to be turned on at this time are totaled is “1.45 ms”, and the weight is “19”.

In the case where the gradation level is “65”, the block B is not changed as compared with the case where the gradation level is “64”. On the other hand, for the block A, the subfields sf3 and sf7 are changed to off, and the weight of the subfield sf3 having the largest weight among the subfields that have been turned on so far is larger by one rank, and the time The adjacent subfield sf2 is changed from off to on.
When the gradation level changes from “64” to “65”, the variation of the sum of periods turned on in block A is “2” because it is a change from “27” to “29” in terms of weight. Yes,
It is smaller than “32”, which is the sum of periods in the block A. For this reason, even if the subfields sf3 and sf7 are changed to OFF and the subfield sf2 is changed to ON in the block A, and the centroid position of the ON subfield is moved, the subfield that is already ON in the block B Block A is dominant and does not move, so block A
, B as a unit, the movement of the center of gravity in the block A can be ignored.
Even if the optical response waveforms when the gradation level is “64” and “65” are compared over a plurality of frames, as shown in FIG. Since the optical response by ON / OFF in the block B becomes dominant with respect to the optical response, when the blocks A and B are taken as a unit, and when the blocks C and D are added and taken as a unit of one frame The movement of the center of gravity can be reduced. For this reason, even if a pixel with a gradation level of “64” and a pixel with a gradation level of “65” are adjacent on the display circuit 100, it is possible to suppress the occurrence of a pseudo contour at the boundary between the adjacent portions. Become.

In this description, when the gradation level is “53” and “54”, the gradation level is “6”.
4 ”and“ 65 ”, but as can be seen from FIG. 4 and FIG. 5, it is assumed that the block B becomes dominant with respect to the movement of the center of gravity of the block A.
When the gradation level is “7” and “8”
When the gradation level is “14” and “15”,
When the gradation level is “26” and “27”,
When the gradation level is “41” and “42”,
In some cases, the gradation levels are “64” and “65”.
In addition, assuming that block A becomes dominant with respect to the movement of the center of gravity of block B,
When the gradation level is “4” and “5”,
When the gradation level is “10” and “11”,
When the gradation level is “21” and “22”,
When the gradation level is “33” and “34”,
When the gradation level is “53” and “54”,
In some cases, the gradation levels are “73” and “74”.
Then, as the gradation level increases, the block B becomes dominant with respect to the movement of the center of gravity of the block A and the block A becomes dominant with respect to the movement of the center of gravity of the block B alternately. It will be.

In the above-described embodiment, the liquid crystal element 120 has been described in the normally black mode, but may be in a normally white mode. Further, one frame is divided into four blocks A to D, but is divided into multiples of 4, for example, divided into eight, and the first, second, fifth, and sixth blocks are positive (or negative). ), The third, fourth, seventh and eighth blocks may be driven with negative polarity (or positive polarity), respectively.
Further, in the case where an element that does not need to be driven by alternating current, such as an organic or inorganic EL element or an electrophoretic element, is used for the pixel 110 instead of the liquid crystal element 120, instead of four frames, the block A, It is only necessary to divide it into two.

In the embodiment, the arrangement of the subfields for each block is arranged in order from the longest period to the shortest period. Conversely, the subfields may be arranged in order from the shortest period to the longest period. Long (short) subfields may be alternately arranged with respect to a field (or a long subfield) in the order of time and after.

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 1 described above. FIG. 9 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 made of a white light source such as a halogen lamp. This lamp unit 2102
The projection light emitted from the light 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. The light valves 100R, 100G, and 100B corresponding to the respective primary colors are respectively guided. Note that B light has a longer optical path than other R and G colors, and therefore, in order to prevent the loss, B light passes through a relay lens system 2121 including an incident lens 2122, a relay lens 2123, and an exit lens 2124. Led.

In the projector 2100, three sets of electro-optical devices including the display circuit 100 are provided corresponding to each of the R color, the G color, and the B color. The video signals corresponding to each of the R, G, and B colors are supplied from the upper circuit and converted into display bits corresponding to the gradation level and the subfield. The configuration of the light valves 100R, 100G, and 100B is the same as that of the display circuit 100 described above, and is driven on or off for each subfield according to the display bits corresponding to the R, G, and B colors. Is done.
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 each of the R color, G color, and B color is incident by 108, there is no need to provide a color filter. Further, the transmission images of the light valves 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the light valve 100 is projected.
Since the G transmission image is projected as it is, the horizontal scanning direction by the light valves 100R and 100B is opposite to the horizontal scanning direction by the light valve 100G, and an image obtained by inverting the left and right is displayed.

In addition to the projector described with reference to FIG. 9, examples of the electronic device include an electronic viewfinder, a rear projection type television, a head mounted display, and the like.

DESCRIPTION OF SYMBOLS 1 ... Electro-optical device, 10 ... Control circuit, 20 ... Memory, 30 ... Conversion part, 100 ... Display circuit, 105 ... Liquid crystal, 108 ... Common electrode, 116 ... TFT, 118 ... Pixel electrode, 120 ... Liquid crystal element, 130 ... Scanning line drive circuit, 140 ... data line drive circuit, 1100 ... projector

Claims (5)

A frame is divided into at least two blocks having a period length equal to each other and continuous in time,
Each of the blocks is divided into subfields having different period lengths,
A driving method of an electro-optical device that performs gradation display by controlling pixels on or off for each subfield,
At one gradation level, one subfield is turned on in one of the at least two blocks, and the sum of periods of subfields turned on in the one block is turned on in the other block. If it is less than or equal to the field period sum,
When the gradation level changes from the one gradation level by “1”,
In the other block, when a subfield having a longer period than the subfield that was turned on before the change is newly turned on in the one block without changing the on and off of the subfield,
The newly turned on subfield is a subfield whose period length is closest to the subfield turned on before the change and is adjacent in time . The subfield turned on before the change Is turned off. A method for driving an electro-optical device. When the gradation level changes from the one gradation level by “1”,
The driving method of the electro-optical device according to claim 1, wherein on / off of each subfield does not change in the other block. The pixel includes a liquid crystal element,
The number of blocks included in one frame is a multiple of four;
The method of driving an electro-optical device according to claim 1, wherein the two blocks and the other two blocks are driven with the same on / off pattern and polarity inversion. Having a plurality of pixels,
A frame is divided into at least two blocks having a period length equal to each other and continuous in time,
Each of the blocks is divided into subfields having different period lengths,
An electro-optical device that controls pixels on or off for each subfield,
A conversion unit that converts display data designating a gradation level of the pixel into display bits designating either on or off in accordance with the subfield;
A driving circuit for driving the pixel on or off according to a display bit for each subfield;
Comprising
The converter is
At one gradation level, one subfield is turned on in one of the at least two blocks, and the sum of periods of subfields turned on in the one block is turned on in the other block. If it is less than or equal to the field period sum,
When the gradation level changes from the one gradation level by “1”,
In the other block, when a subfield having a longer period than the subfield that was turned on before the change is newly turned on in the one block without changing the on and off of the subfield,
The newly turned on subfield is a subfield whose period length is closest to the subfield turned on before the change and is adjacent in time . The subfield turned on before the change Is an electro-optical device that is turned off.   An electronic apparatus comprising the electro-optical device according to claim 4.