JP2007121690A - Electrooptical device, method for driving the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve the reduction of a contrast ratio due to a temperature drop by simple constitution. <P>SOLUTION: A pixel 120 of the i-th row and j-th column has a TFT to be turned on when a scanning signal Yi supplied to a scanning line 311 of the i-th row is turned to a H level and obtains a gradation corresponding to the voltage of a data signal Xj supplied to a data line 211 of the j-th column. A temperature sensor 50 outputs a temperature signal Tmp indicating a detected surrounding temperature. A scanning line driving circuit 350 selects scanning lines 311 in fixed order and applies H-level selection voltage to each selected scanning line 311 only for a prescribed period. In this case, the scanning line driving circuit 350 extends the period for applying the selection voltage in accordance with the reduction of the surrounding temperature indicated by the temperature signal Tmp. A data line driving circuit 250 supplies a data signal of voltage corresponding to the gradation of the pixel corresponding to the scanning line 311 to which the selection voltage is applied through a data line during the period in which the selection voltage is applied to the scanning line 311. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a technique for preventing a reduction in contrast ratio at a low temperature when display is performed using an electro-optical change of an electro-optical material.

An electro-optical device that performs display by electro-optical change of an electro-optical material such as liquid crystal has a switching element such as a thin film transistor for each pixel, and applies a selection voltage to the switching element via a scanning line. The voltage effective value applied to the pixel is controlled by applying a voltage corresponding to the gradation to the pixel electrode via the data line, thereby performing gradation display. It has a configuration. Here, in a thin film transistor, particularly in a type using amorphous silicon as a semiconductor layer, when the ambient temperature decreases,
It has a characteristic that the on-characteristics deteriorate due to a decrease in carrier mobility. When the on-characteristics deteriorate, the target voltage cannot be sufficiently written, so that the contrast ratio of the display screen is lowered.
Therefore, the deterioration of the on-characteristics of the thin film transistor is compensated by increasing the selection voltage (gate voltage) according to the decrease in the ambient temperature or by displacing the amplitude center of the voltage according to the gradation with respect to the gate voltage. The technique to do is proposed (refer patent document 1).
Japanese Patent Laid-Open No. 6-138843 (see FIGS. 3 and 5)

However, in order to increase the gate voltage or displace the amplitude center of the voltage according to the gradation with respect to the gate voltage, means for changing the setting of the voltage, such as a D / A converter circuit, a variable resistor, etc. This causes a problem that the circuit configuration is complicated and power consumption is increased.
Further, in order to supply a high gate voltage when the temperature is lowered, it is necessary to increase the breakdown voltage of the circuit, which makes it difficult to reduce the size and cost.
The present invention has been made in view of such circumstances, and the object of the present invention is to increase the power consumption and the like in a circuit configuration, and in the display screen even if the ambient temperature changes. It is an object of the present invention to provide an electro-optical device, a driving method thereof, and an electronic apparatus which prevent a reduction in contrast ratio.

According to the experiment and research of the present inventor, the mobility of carriers in the thin film transistor is μ, the gate voltage is Vg, the application period of the gate voltage is t, the constant determined by the thin film transistor is C,
When μt (Vg−C) is constant, it was found that the writing ability when the thin film transistor is on is constant. That is, when the temperature is lowered, the mobility μ is lowered, but the application period t of the gate voltage Vg may be increased without changing the gate voltage Vg.

Therefore, in the present invention, a plurality of pixels provided corresponding to the intersections of the plurality of scanning lines and the plurality of data lines, the conductive state when the selection voltage is applied to the scanning lines. A plurality of scanning lines in a predetermined order, and a pixel having a gradation corresponding to a voltage of a data signal supplied to the data line when the switching element becomes conductive In addition, the selection voltage is applied to the selected scanning line, and the application period of the selection voltage to the selection scanning line is increased as the ambient temperature indicated by the temperature signal decreases, and the scanning line is applied to the scanning line. A data line driving circuit for supplying a data signal corresponding to the gradation of the pixel corresponding to the scanning line to which the selection voltage is applied through the data line in a period during which the selection voltage is applied. It is characterized in that.
According to the present invention, since the voltage is not changed, the circuit configuration is prevented from being complicated and the power consumption is increased, and the deterioration of the on-characteristic is compensated by the longer period for applying the selection voltage. The

Note that the deterioration of the writing ability due to the temperature drop occurs remarkably in the amorphous thin film transistor. Therefore, the present invention is suitable when an amorphous thin film transistor is used as the switching element.
In the present invention, as the ambient temperature decreases, the selection voltage application period for bringing the switching element into a conductive state is lengthened. However, when the selection voltage application period is lengthened, the frame frequency is decreased. For this reason, when a liquid crystal whose response characteristic is lowered as the temperature is lowered is used as a pixel, the occurrence of flicker can be suppressed even if the frame frequency is lowered.

In the present invention, it is determined whether the ambient temperature indicated by the temperature signal belongs to any of the first, second,..., M-th (m is a natural number) ranges that are preliminarily divided in the direction of decreasing temperature. The scanning line drive circuit further includes a determination circuit that applies the selection voltage over a predetermined reference period when the determination circuit determines that the ambient temperature belongs to the first range. When all the scanning lines are selected in the frame period and the ambient temperature is determined to belong to the nth range (n is an integer not smaller than 1 and not larger than m) by the determination circuit, the selection voltage is set to a predetermined reference period. On the other hand, the selection voltage may be applied over a period n times the reference period, and all the scanning lines may be selected in the n frame period.
In this configuration, the determination circuit changes when the ambient temperature changes in a decreasing direction.
A hysteresis characteristic may be provided by changing a threshold value for dividing a temperature range depending on a case where the ambient temperature changes in a rising direction.
In the present invention, a temperature sensor that detects the ambient temperature and outputs a temperature signal indicating the detected ambient temperature may be further provided, or a temperature signal indicating the ambient temperature may be supplied from an external host device. It is good also as a structure to receive.
The present invention is not limited to the electro-optical device, the driving method of the electro-optical device,
It can also be conceptualized as an electronic device having the electro-optical device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
First, the electro-optical device according to the first embodiment of the invention will be described. FIG. 1 is a block diagram showing a configuration of the electro-optical device 10.
As shown in this figure, the electro-optical device 10 includes a temperature sensor 50, a display area 100,
A data line driving circuit 250, a scanning line driving circuit 350, and a scanning control circuit 400 are included. Among these, in the display region 100, 320 scanning lines 311 extend in the row (X) direction, while 2
Forty data lines 211 are provided so as to extend in the column (Y) direction. The pixels 120 are arranged corresponding to the intersections of the scanning lines 311 of 320 rows and the data lines 211 of 240 columns, respectively. Therefore, in this embodiment, the pixels 120 are 320 rows long ×
They are arranged in a matrix with 240 horizontal rows. However, this arrangement is not intended to limit the present invention.

Here, a detailed configuration of the pixel 120 will be described. FIG. 2 is a diagram illustrating a configuration of the pixel 120, i rows and (i + 1) rows adjacent thereto, j columns and (j + 1) adjacent thereto.
A configuration of a total of 4 pixels of 2 × 2 corresponding to the intersections with the columns is shown. I, (i + 1)
Is a symbol for generally indicating a row in which the pixels 120 are arranged, and is an integer of 1 to 320, and j and (j + 1) are symbols for generally indicating the column in which the pixels 120 are arranged. And an integer of 1 to 240.

As shown in FIG. 2, each pixel 120 includes a pixel capacitor 130 and an n-channel thin film transistor (hereinafter simply referred to as “TFT”) that functions as a switching element.
241). Since each pixel 120 has the same configuration, i row j
The description will be made representatively of those located in the column. In the pixel 120 in the i row and j column, the TFT 2
The gate 41 is connected to the i-th scanning line 311, the source is connected to the j-th column data line 211, and the drain is connected to the pixel electrode 231 that is one end of the pixel capacitor 130.
The other end of the pixel capacitor 130 is connected to the common electrode 110. This common electrode 1
10 is common to all the pixels 120 as shown in FIG. 1, and a voltage LCcom constant in time is applied.

The pixel capacitor 130 has a configuration in which the voltage difference between the pixel electrode 231 and the common electrode 110 is held, and the transmitted (or reflected) light amount of the pixel capacitor 130 changes according to the effective value of the held voltage. .
Although it is considered that such a configuration does not need to be described in detail, a method in which the liquid crystal is sandwiched between the pixel electrode and the common electrode and the electric field direction applied to the liquid crystal is the substrate surface vertical direction, the pixel electrode, Examples include a method in which an insulating layer and a common electrode are stacked so that the direction of the electric field applied to the liquid crystal is the horizontal direction of the substrate surface.
In the present embodiment, for convenience of description, if the effective voltage value held in the pixel capacitor 130 is close to zero, the light transmittance is maximized to display white, while the effective voltage value is increased. The normally white mode in which the amount of light decreases and finally the black display with the minimum transmittance is achieved.

Returning to FIG. 1 again, the temperature sensor 50 is provided in the vicinity of the display region 100, detects the ambient temperature, and outputs a temperature signal Tmp indicating the detected ambient temperature. The temperature sensor 50 may be incorporated in either an electro-optical device or an electronic device.
The scanning control circuit 400 generates a transfer start pulse D according to the ambient temperature indicated by the temperature signal Tmp.
By outputting y and the clock signal Cy, the vertical scanning of the display area 100 by the scanning line driving circuit 350 is controlled, and by outputting the control signal CntX, the horizontal scanning of the display area 100 by the data line driving circuit 250 is performed. It is something to control. Specifically, the scan control circuit 400 reduces the frequency of the clock signal Cy as the ambient temperature indicated by the temperature signal Tmp decreases, and the data line driving circuit within the horizontal scanning period defined by the clock signal Cy. The horizontal scanning by 250 is controlled.
The scan control circuit 400 also outputs a polarity instruction signal Pol that specifies the writing polarity of the pixel capacitor 130.
Is supplied to the data line driving circuit 250. Here, if the polarity instruction signal Pol is at the H level, it designates the positive polarity writing with the pixel electrode 231 on the higher side for the pixel capacitor 130, and if it is at the L level, the pixel electrode 231 is on the lower side. As shown in FIG. 3, in the same frame period (1F), the polarity is inverted every period (1H) and between adjacent one frame period (1F), as shown in FIG. Even if attention is paid to the same horizontal scanning period, the polarity is reversed. For this reason, in this embodiment, scanning line inversion (row inversion) is performed in which the writing polarity is inverted for each scanning line, but the present invention is not limited to this. The reason why the polarity is inverted in this way is to prevent deterioration due to application of a direct current component to the liquid crystal.

The scanning line driving circuit 350 has a shift register therein and sequentially transfers the transfer start pulse Dy supplied at the beginning of one frame period (1F) according to the clock signal Cy.
,..., 320 are supplied as scanning signals Y1, Y2, Y3,. For this reason, the scanning signals Y1, Y2, Y3,..., Y320 are each at the H level in this order.
Here, for convenience, when the scanning signal is generally described without specifying a particular row, Yi
Is written. The H level of the scanning signal corresponds to the selection voltage Vdd, and the L level corresponds to the voltage-referenced ground potential Gnd. The voltage LCcom of the common electrode 110 is generated by a power supply circuit (not shown) so as to have an intermediate value between the selection voltage Vdd and the ground potential Gnd.

Next, in this embodiment, the data line driving circuit 250 has storage areas (not shown) corresponding to a matrix arrangement of 320 vertical rows × 240 horizontal columns, and each storage area has a corresponding level of the pixel 120. Key data Da is stored. The gradation data Da is data that designates the gradation value (brightness) of the pixel 120. The gradation data Da is supplied from an external host device (not shown), and when the display content is changed, the write address Ad is used. The gradation data Da stored in the designated storage area is rewritten.
Further, when one scanning line 311 is selected by the scanning line driving circuit 350, the data line driving circuit 250 performs one row of the gradation data Da of the pixel located on the scanning line according to the control signal CntX. Minutes are read in advance, and one row of the gradation data Da is read out by the polarity instruction signal P
.., X240 are simultaneously output corresponding to the data lines 211 of 1, 2, 3,..., 240 columns, respectively, as data signals X1, X2, X3,.
Here, when the data signals X1, X2, X3,..., X240 are generally described as Xj when not particularly specifying a column, the data signal Xj supplied to the data line 211 of the jth column is When the i-th scanning line 311 is selected, the voltage LCcom applied to the common electrode 110 if the polarity instruction signal Pol becomes H level and positive writing is designated.
If the polarity instruction signal Pol becomes L level and negative writing is designated while the voltage corresponding to the gradation data of i row and j column is higher than the voltage LCcom, It is generated by the data line driving circuit 250 so that the voltage corresponding to the grayscale data of i rows and j columns becomes a lower voltage.

Next, of the operations of the electro-optical device 10 according to the first embodiment, a case at normal temperature that is a reference for the operation will be described.
First, when the ambient temperature detected by the temperature sensor 50 is normal temperature (about 25 ° C.),
As shown in FIG. 4A, the scan control circuit 400 outputs a transfer start pulse Dy and a clock signal Cy. Note that the transfer start pulse Dy and the clock signal Cy shown in FIG. 4A are the same as those in FIG.

As shown in FIG. 3 or FIG. 4A, the scanning signals Y1, Y2, Y3,..., Y320 become H level in this order. Here, a period in which the scanning signal Yi is at the H level at room temperature is defined as a reference period (1H).
On the other hand, before the scanning signal Y1 becomes H level, in the data line driving circuit 250, one row and one column,
The gradation data Da of 1 row, 2 columns, 1 row, 3 columns,..., 1 row and 240 columns is read from each storage area. Then, in the period (1H) when the scanning signal Y1 is at the H level, each is changed to the analog voltage as described above and applied to the data line 211 of the corresponding column.
For this reason, the data signal Xj supplied to the data line 211 in the j-th column will be described as one row j
Only the voltage Va specified by the gradation data Da corresponding to the pixels in the column is equal to the voltage L of the common electrode 110.
The voltage is higher than Ccom (see FIG. 4).
Here, if the scanning signal Y1 is at the H level, the TFT 241 is turned on in all the pixels 120 located in the first row.
A voltage corresponding to the gradation value of the pixel in the row 1 column is applied until the end of the horizontal scanning period, whereby the voltage of the target gradation value is written in the pixel capacitor 130. The same applies to the other pixels from the second column to the 240th column.

Next, the scanning signal Y2 becomes H level. The operation at this time is the same as that when the scanning signal Y2 becomes H level, and 2 rows, 1 column, 2 rows, 2 columns, 2 rows, 3 columns,... The voltage of the gradation value defined by the gradation data Da in the row 240 column is written into the pixel capacitor 130 of the corresponding pixel. Similarly, the scanning signals Y3, Y4,..., Y320 sequentially become H level, and the pixel capacitance 130
A voltage corresponding to the gradation value defined by the corresponding gradation data Da is written into the.
Thereby, each pixel maintains a gradation corresponding to the written voltage until the next writing.

Also in the next frame, the scanning signals Y1, Y2, Y3,..., Y320 become H level in this order, and corresponding to the gradation value designated by the gradation data Da for each pixel capacitor 130 in the same manner. Voltage is written. However, since the writing polarity is reversed from that of the previous frame, each pixel capacitor 130 is AC driven.
For example, regarding the pixel in the above-mentioned 1 row and j column, the data signal Xj when the scanning signal Y1 becomes H level is the voltage LCcom specified by the corresponding gradation data Da in the previous frame. In the next frame, if the gradation value does not change, only the voltage Va is applied to the pixel electrode 231 as a lower voltage with respect to the voltage LCcom in the next frame. It will be.

Next, the operation when the ambient temperature decreases from room temperature will be described. When the temperature sensor 50 detects a decrease in the ambient temperature, the scanning control circuit 400 increases the frequency of the clock signal Cy by the amount corresponding to the decrease from the normal temperature. As described above, if μt (Vg−C) is constant, the writing ability of the thin film transistor is constant. For this reason, the temperature signal T
When the ambient temperature indicated by mp is Td (° C.), the scanning control circuit 400 sets one cycle of the clock signal Cy corresponding to the period t for applying the selection voltage to μ (
25 ° C) / μ (Tmp) times longer. Here, μ (25 ° C.) and μ (Tmp) are each 25 ° C.
The temperature dependence of the mobility can be known by measuring the electrical characteristics of the transistor alone while varying the ambient temperature in advance. This varies depending on the manufacturing conditions of the transistor. For example, in a certain transistor measured by the authors, the mobility at 25 ° C. is 0.2 cm ^ 2 / (Volt Sec) and the temperature coefficient is 0.0035 [cm ^ 2 / (Volt Sec)] / d
It was eg. Therefore, for example, when the ambient temperature is −5 ° C., the scanning control circuit 400 determines that one cycle of the clock signal Cy is 2.1 (= 0.2 / (0.2−3) of 1H period at normal temperature.
0deg × 0.0035)) times.
The scan control circuit 400 changes the transfer start pulse Dy, the cycle of the polarity signal Pol, and the output timing in accordance with the cycle change of the clock signal Cy. Thereby, as shown in FIG. 4B, the selection period of the scanning line 311, that is, the scanning signals Y1, Y2, Y3,.
The period during which the signal is at the H level is extended. Further, the scanning control circuit 400 has a scanning signal of H
Along with the extension of the level period, the control signal CntX to the data line driving circuit 250 is also changed. Thereby, the supply timing of the data signal to the pixel corresponding to the selected scanning line 311 does not shift with the extension of the selection period.

As described above, in this embodiment, even when the ambient temperature Td is lowered, the selection period, which is a period during which the TFT 241 is turned on, is extended by the amount lowered from 25 ° C., which is normal temperature. There is no shortage of voltage writing. For this reason, according to the electro-optical device 10 according to the present embodiment, the contrast ratio is lowered due to insufficient voltage writing. Specifically, since the present embodiment is in the normally white mode, a high voltage cannot be maintained. As a result, it is possible to prevent the phenomenon that the pixel does not become sufficiently black.
Note that when the selection period is extended, the frame period required to select all the scanning lines (
1F) becomes longer, so that it is visually recognized as flicker at room temperature. However, in this embodiment, since the selection period is extended at low temperatures when the response time of the liquid crystal is lowered, it is not visually recognized as flicker.

Second Embodiment
In the first embodiment described above, the data line driving circuit 250 has a storage area corresponding to the pixel array, and each storage area stores the gradation data Da of the corresponding pixel 120. In order to simplify the configuration, there is a configuration that does not have a storage area. In a configuration having no storage area, the gradation data Da is supplied from an external host device in synchronization with a vertical scanning signal or a horizontal scanning signal.
Here, when the length of the selection period is changed according to the ambient temperature, the frame period is changed as described above. For this reason, the external host device needs to supply gradation data in accordance with the changed frame period, resulting in a complicated circuit configuration.
Therefore, next, even if the ambient temperature is lowered and the frame period is changed, the external higher-level device side does not have to supply the gradation data Da without changing it to the normal temperature. The optical device will be described.

FIG. 5 is a block diagram illustrating a configuration of the electro-optical device 10 according to the second embodiment. The configuration shown in FIG. 5 differs from the configuration shown in FIG. 1 mainly in that first, the gradation data Da that defines the gradation of the pixel is a vertical scanning signal, a horizontal scanning signal, a dot clock. A point of being supplied as shown in FIG. 6 in synchronism with signals (collectively referred to as “Sync”), and secondly, a determination circuit 60 for inputting a temperature signal Tmp is provided. 60 is a temperature range (a), (b), (c) according to the ambient temperature Td indicated by the temperature signal Tmp and the change direction of the ambient temperature.
) And third, the scanning line driving circuit 350 and the data line driving circuit 250 operate according to the determined temperature range.
In the display area 100 of the second embodiment, for the sake of explanation, the arrangement of the pixels 120 is simplified to 9 rows × 12 columns.

Among the differences from the first embodiment, the first point will be described. The gradation data Da is
As shown in FIG. 6, first, the portion corresponding to the pixels in the 1st row and the 1st column to the 1st row and the 12th column is supplied in the period of 1H, and then the 2nd row and the 1st column to the 2nd row and the 12th column, the 3rd row and the 1st column to 3 rows and 12 columns, ..., 9 rows and 1 column to 9 rows and 1
Two columns of pixels are supplied in each row for a period of 1H. Through the subsequent 2H blank period, the pixels of the first, second, third,..., 9 rows are supplied again.
Note that the numbers in FIG. 6 indicate periods in which the gradation data Da for one row of pixels in the row indicated by the numbers is supplied. For example, “2” indicates a period in which one row of pixels from 2 rows and 1 column to 2 rows and 12 columns is supplied.

Next, the second point will be described. As shown in FIG. 8, the determination circuit 60 sets the ambient temperature Td to a temperature range (a) in the normal temperature range, a temperature range (b) lower than that, and a lower temperature range (b). It is determined whether it belongs to one of the temperature ranges (c). In this determination, when the ambient temperature Td changes in the increasing direction, the determination circuit 60 determines that the ambient temperature Td is within the temperature range (c) when the ambient temperature Td is equal to or higher than the threshold value Tc-b. When the temperature range (b) is determined and the ambient temperature is equal to or higher than the threshold value Tb-a, the ambient temperature Td is changed from the temperature range (b) to the temperature range (
While it is determined that the process has shifted to a), when the ambient temperature Td is changing in the downward direction, and the ambient temperature Td falls below the threshold Ta-b, the ambient temperature Td is changed from the temperature range (a) to the temperature range. When the transition to the range (b) is determined and the ambient temperature Td falls below the threshold value Tb-c, the ambient temperature T
d It is determined that the temperature range (b) has shifted to the temperature range (c). In the present embodiment, the threshold values have a relationship of Tb-c <Tc-b and Ta-b <Tb-a.

Further, the third point will be described. The scanning control circuit 400 changes the scanning line driving circuit 350 and the data line driving circuit 250 in accordance with the control signals CntYa and CntXa according to the temperature range determined by the determination circuit 60 as follows. To control.
First, the scanning line driving circuit 350 determines that the ambient temperature Td is within the temperature range (a) by the determination circuit 60.
.., The scanning lines 311 in the first, second, third,..., And ninth rows are selected in order, and scanning corresponding to the selected scanning line 311 is performed as shown in FIG. The signal is set to H level only for a period of 1H. This point is the same as the operation at normal temperature in the first embodiment.
However, after the scanning signal Y9 in the last nine rows returns from the H level to the L level, the next scanning signal Y1 becomes the H level after a period of 2H.

Next, when it is determined that the ambient temperature Td is in the temperature range (b), the scanning line driving circuit 350 sets the scanning line 311 to the odd number 1, the odd number frame, as shown in FIG. 7B. 3, 5
, 7 and 9 in order, and in the even frame, the scanning line 311 is selected as an even number 2, 4, 6, 8
The scanning signals corresponding to the selected scanning line 311 are set to the H level only for the period of 2H.
Here, when an odd number is n, (n + 2), (n + 4),...
+1), (n + 3), (n + 5),...
In the odd-numbered frame, the scanning signals Y1, Y3, Y5, Y7, Y9 in the odd-numbered rows change from the L level to the H level, and in the even-numbered frames, the scanning signals Y2, Y in the even-numbered rows
The timing when 4, Y6, and Y8 change from the L level to the H level is the timing when the scanning signal in the same frame and the same row changes from the L level to the H level when it is determined that they are in the temperature range (a). Are the same. Therefore, the scan signal Y9 is H in the odd frame.
After returning from the level to the L level, a period of 2H passes until the scanning signal Y2 becomes the H level in the next even frame. Similarly, after the scanning signal Y8 returns from the H level to the L level in the even frame, a period of 2H passes from the scanning signal Y1 to the H level in the next odd frame (not shown).

Further, when it is determined that the ambient temperature is in the temperature range (c), the scanning line driving circuit 350 has the scanning lines 311 of the 1st to 9th rows in the n frame as shown in FIG. 7C. 3
In the order of the 1st, 4th and 7th rows, the remainder becomes “1” when divided by 1, and in the (n + 1) frame, the remainder becomes “2” when the scanning line 311 is divided by 3. 2 In the order of the 5th and 8th rows, in the (n + 2) frame, the scanning line 311 whose remainder is “2” when divided by 3 is
Selection is made in the order of the third, sixth, and ninth rows, and the scanning signal corresponding to the selected scanning line 311 is set to the H level only for the period of 3H.
Note that the (n + 3) frame returns to selection in the same manner as the n frame.
Timing when scanning signals Y1, Y4, Y7 change from L level to H level in n frame, timing when scanning signals Y2, Y5, Y8 change from L level to H level in (n + 1) frame, and scanning in (n + 2) frame The timing at which the signals Y3, Y6, and Y9 change from the L level to the H level is determined in the temperature range (a), respectively.
It is the same as the timing when the scanning signal in the same frame and the same row changes from L level to H level.
Therefore, after the scanning signal Y7 returns from the H level to the L level in the n frame, a period of 3H passes until the scanning signal Y2 becomes the H level in the next (n + 1) frame.
After the scanning signal Y8 returns from the H level to the L level in the (n + 1) frame, the next (
In the n + 2) frame, a period of 3H is passed until the scanning signal Y3 becomes H level. (N
+2) Immediately after the scanning signal Y9 returns from the H level to the L level in the frame, the next (
In the n + 3) frame, the scanning signal Y1 becomes H level.

On the other hand, when the discrimination circuit 60 determines that the ambient temperature is in the temperature range (a), the data line driving circuit 250 receives the grayscale data Da supplied from the external host device as shown in FIG. 6A. After the accumulated amount, the accumulated gradation data for one row is converted into data signals X1 to X12,
The data is supplied to the corresponding data line 211 over a period 1H in which the next one row is supplied.
Therefore, in the case of the temperature range (a), 1, 2, 3,...
The ninth row is selected in order, and in each pixel, the TFT 241 is turned on for a period of 1H. Therefore, the operation of writing the data signal voltage similar to that at room temperature in the first embodiment is executed.
Since the data line driving circuit 250 accumulates one row of gradation data Da supplied from the external host device as described above, the supply period of the data signal obtained by converting the gradation data Da is the gradation. The relationship is delayed with respect to the supply period of the data Da. In the second embodiment, when the frame period is in the temperature range (a), the scanning signal Y1 becomes the H level again after the scanning signal Y1 becomes the H level with respect to the display region 100. The period is up to.

If the data line driving circuit 250 determines that the ambient temperature is in the temperature range (b), the data line driving circuit 250 may
As shown in (b), in the odd-numbered frame, only one odd-numbered row is accumulated in the grayscale data Da, and the accumulated grayscale data in the odd-numbered row is converted into data signals X1 to X12. In the frame, after storing even-numbered rows of grayscale data Da for one row, the accumulated grayscale data of even-numbered rows is converted into data signals X1 to X12, and the converted data signals are handled over a period of 2H. The operation of supplying to the data line 211 is repeated.
For this reason, in the temperature range (b), in the odd-numbered frame, each pixel in the odd-numbered row has T
Although the FT 241 is turned on for a period of 2H and the operation of writing the voltage of the data signal is executed, the writing operation is not executed in each pixel in the even-numbered row. On the other hand, in the even frame, the TFT 241 is turned on for 2H in each pixel in the even row and the operation of writing the voltage of the data signal is executed. However, the write operation is not executed in each pixel in the odd row. As described above, in the second embodiment, in the temperature range (b), all the scanning lines 311 are selected over two frame periods, and in each pixel, the TFT 241 is used.
Is turned on for a period of 2H.

When the data line driving circuit 250 determines that the ambient temperature is in the temperature range (c), the data line driving circuit 250 performs FIG.
As shown in (c), in the n frame, after 1, 4, and 7 rows in which the remainder when divided by 3 becomes “1” are accumulated for one row in the gradation data Da of each row, The accumulated row gradation data is converted into data signals X1 to X12, and in the (n + 1) frame, the remainder when dividing by 3 in the gradation data Da of each row is “2,” 2, 5, 8 After accumulating only one row, the accumulated gradation data of the row is converted into data signals X1 to X12, and in the (n + 2) frame, the remainder when dividing by 3 in the gradation data Da of each row. After accumulating only one row of 3, 6 and 9 that becomes “0”, the gradation data of the accumulated row is converted into data signals X1 to X12, and the converted data signals are corresponding data over a period of 3H. The operation of supplying the line 211 is repeated.
For this reason, in the temperature range (c), in the n frame, the TFT 241 is turned on in each pixel in the first, fourth, and seventh rows for a period of 3H, and the operation of writing the voltage of the data signal is executed. The writing operation is not executed for each pixel in the other row. Similarly, (n
+1) For each pixel in the 2nd, 5th, and 8th rows in the frame, in the (n + 2) frame, 3, 6,
In each pixel in the ninth row, the TFT 241 is turned on for a period of 3H, and the operation of writing the voltage of the data signal is executed. However, the writing operation is not executed in each pixel of the other row. As described above, in the third embodiment, in the temperature range (c), all the scanning lines 311 are selected over three frame periods, and in each pixel, the TFT 24
1 is turned on over a period of 3H.

As described above, according to the second embodiment, the period during which the selection voltage for bringing the TFT 241 into a conductive state is extended stepwise as the ambient temperature decreases. There will be no shortage of voltage writing due to deterioration in the writing capability. For this reason,
Also in the second embodiment, it is possible to prevent a reduction in contrast ratio.
Furthermore, in the second embodiment, since the external host device may supply the gradation data Da at the same supply timing regardless of the ambient temperature, the configuration of the external host device is avoided.

By the way, in the second embodiment, all the pixels 1 in the temperature ranges (a), (b), and (c).
The period required to rewrite 20 is 1F when the ambient temperature is in the temperature range (a), 2F when the temperature is in the temperature range (b), and 3F when the temperature is in the temperature range (c). Therefore, a difference occurs in display quality. For this reason, if the transition to the temperature range frequently occurs, the display quality also changes, and the difference is easily visually recognized. In the present embodiment, since the threshold value for determining the temperature range is different between the upward direction and the downward direction, it has hysteresis characteristics. For this reason, even if the ambient temperature slightly changes in the vicinity of the threshold value, frequent transition of the temperature range is prevented, so that it is possible to suppress a change in display quality associated with the transition.

In the second embodiment, the temperature range is divided into three parts, but may be divided into two parts.
Of course, it may be divided into more than one. For example, when dividing into m (m is a natural number), when it is determined that the ambient temperature is in the temperature range of n (n is an integer satisfying 1 ≦ n ≦ m) from the top, the selection voltage is set to the reference period. A configuration may be adopted in which application is performed over a period n times (1H) and all scanning lines are selected in an n frame period.

In the first and second embodiments, the voltage LCcom applied to the common electrode 110 is used as a reference for polarity inversion. However, due to the parasitic capacitance between the gate and drain of the TFT 241, the drain (pixel electrode) is turned on from off. 231) occurs in which the potential decreases (called push-down, punch-through, field-through, etc.). In order to prevent the deterioration of the liquid crystal, AC driving is a principle for the pixel capacitor 130, but the voltage LCcom is used as a reference for polarity inversion.
When the alternate writing is performed, the effective voltage value of the pixel capacitor 130 is slightly larger in the negative polarity writing than in the positive polarity writing because of the push-down. Therefore, the polarity inversion reference voltage and the voltage LCcom of the common electrode 110 are made different from each other, and the polarities of the pixel capacitors 130 are made equal to each other even if positive polarity / negative polarity writing is performed at the same gradation. The voltage LCcom may be set slightly higher than the reference voltage for inversion.

In the above-described embodiment, the row inversion is performed to invert the writing polarity for each scanning line, because the reason is only to prevent application of a DC component in the pixel capacitor 130, and the inversion method is Surface inversion, column inversion, dot inversion, etc. are optional.
Furthermore, in the embodiment, a normally white mode in which white is displayed in a state in which no voltage is applied is used. However, a normally black mode in which black is displayed in a state in which no voltage is applied may be used.
For example, color display may be performed by forming one dot with three pixels of R (red), G (green), and B (blue).

Next, an electronic apparatus having the electro-optical device 10 according to the above-described embodiment as a display device will be described. FIG. 9 is a perspective view showing a configuration of a mobile phone 1200 using the electro-optical device 10 according to the first or second embodiment.
As shown in this figure, the mobile phone 1200 includes the electro-optical device 10 described above in addition to the plurality of operation buttons 1202, the earpiece 1204, and the mouthpiece 1206. Since the components other than the display area 100 are built in the telephone, they do not appear as appearances.

As an electronic apparatus to which the electro-optical device 10 is applied, in addition to the mobile phone shown in FIG. 9, a digital still camera, a notebook personal computer, a liquid crystal television, a viewfinder type (or monitor direct view type) video recorder. , Car navigation device, pager, electronic notebook,
Examples include calculators, word processors, workstations, videophones, POS terminals, devices with touch panels, and the like. Needless to say, the electro-optical device 10 described above can be applied as a display device of these various electronic devices. In any electronic device, a display that suppresses a decrease in contrast ratio due to a decrease in temperature is realized with a simple configuration.

1 is a diagram illustrating a configuration of an electro-optical device according to a first embodiment of the invention. FIG. It is a figure which shows the structure of the pixel of the same electro-optical apparatus. It is a figure which shows operation | movement of the same electro-optical apparatus. It is a figure which shows operation | movement of the same electro-optical apparatus. FIG. 6 is a diagram illustrating a configuration of an electro-optical device according to a second embodiment of the invention. It is a figure which shows operation | movement of the same electro-optical apparatus. It is a figure which shows operation | movement of the same electro-optical apparatus. It is a figure which shows operation | movement of the same electro-optical apparatus. 1 is a diagram illustrating a configuration of an electronic apparatus to which an electro-optical device according to an embodiment is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electro-optical apparatus, 50 ... Temperature sensor, 60 ... Discrimination circuit, 110 ... Common electrode, 12
DESCRIPTION OF SYMBOLS 0 ... Pixel, 211 ... Data line, 231 ... Pixel electrode, 241 ... TFT, 250 ... Data line drive circuit, 311 ... Scan line, 350 ... Scan line drive circuit, 400 ... Scan control circuit

Claims (6)

A plurality of pixels provided corresponding to intersections of a plurality of scanning lines and a plurality of data lines, the switching elements including a switching element that is rendered conductive when a selection voltage is applied to the scanning lines; A pixel having a gradation according to the voltage of the data signal supplied to the data line when
The plurality of scanning lines are selected in a predetermined order, and the selection voltage is applied to the selected scanning lines. As the ambient temperature indicated by the temperature signal becomes lower, the selection voltage application period for the selected scanning lines is lengthened. A scanning line driving circuit to
A data line driving circuit for supplying a data signal corresponding to the gray level of the pixel corresponding to the scanning line to which the selection voltage is applied through the data line in a period in which the selection voltage is applied to the scanning line;
An electro-optical device comprising: The ambient temperature indicated by the temperature signal is preliminarily partitioned in a direction in which the temperature decreases.
, Second,..., Further comprising a determination circuit for determining whether it belongs to any of the m-th (m is a natural number) ranges,
The scanning line driving circuit includes:
When the determination circuit determines that the ambient temperature belongs to the first range, the selection voltage is applied over a predetermined reference period, and all scanning lines are selected in one frame period,
When the determination circuit determines that the ambient temperature belongs to the n-th range (n is an integer not less than 1 and not more than m), the selection voltage is set to the reference period with respect to a predetermined reference period. 2. The electro-optical device according to claim 1, wherein the scanning is applied over a period of n times and all scanning lines are selected in an n frame period. 3. The determination circuit according to claim 2, wherein the threshold value for dividing the temperature range is different between a case where the ambient temperature changes in a decreasing direction and a case where the ambient temperature changes in a rising direction. The electro-optical device described. A temperature sensor that detects the ambient temperature and outputs it as a temperature signal indicating the ambient temperature.
The electro-optical device according to claim 1, further comprising: A plurality of pixels provided corresponding to intersections of a plurality of scanning lines and a plurality of data lines, the switching elements including a switching element that is rendered conductive when a selection voltage is applied to the scanning lines; A driving method of an electro-optical device having a pixel having a gradation corresponding to a voltage of a data signal supplied to the data line when
The plurality of scanning lines are selected in a predetermined order, the selection voltage is applied to the selected scanning lines, and the selection voltage is applied to the selection scanning lines as the ambient temperature indicated by the temperature signal decreases. Lengthen and
In the period when the selection voltage is applied to the scanning line, a data signal corresponding to the gradation of the pixel corresponding to the scanning line to which the selection voltage is applied is supplied via the data line. Driving method of optical device.   An electronic apparatus comprising the electro-optical device according to claim 1.

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