JPH10222130A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device whose power consumption is reduced without accompanied by remarkable increase of a circuit scale and a mounting area. SOLUTION: A picture signal is written to column electrodes 12 by a column electrode driving circuit 19. After this writing, the column electrodes 12 are switchingly connected to capacitors 24, 25 for holding electric charges. Power consumption is reduced by moving electric charges accumulated on the column electrodes 12 to the capacitors 24, 25, moving electric charges of an opposite polarity accumulated on the capacitors 24, 25 to the column electrodes 12 and making electric charge supplying quantities small at the time of writing of the next picture signal of an opposite polarity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device having reduced power consumption.

[0002]

2. Description of the Related Art In general, a liquid crystal display device is lightweight and thin.
Because of its low power consumption, it is used as a display element such as a television, a portable information terminal, or a graphic display. In particular, a matrix type liquid crystal display device using thin film transistors (TFTs) as switching elements has excellent high-speed response, is suitable for high definition, and has high image quality, large size and color image of a display screen. It is attracting attention as a realization.

Conventionally, as this type of liquid crystal display device, for example, a liquid crystal display device shown in FIG. 8 is known.

The liquid crystal display device shown in FIG. 8 has a scanning row electrode 11 and an image signal column electrode 12 wired in a matrix. Each is provided with a thin film transistor 13 as a switching element. Each of these thin film transistors
The pixel electrodes 14 are connected to the pixel electrodes 13, and the pixel electrodes 14 face the counter electrodes 16 via the liquid crystal layer 15.

Each row electrode 11 is connected to a row electrode drive circuit 18, each column electrode 12 is connected to a column electrode drive circuit 19, and each counter electrode
Reference numerals 16 are connected to the counter electrode drive circuit 20, respectively.
Then, a selection signal corresponding to the horizontal scanning cycle is sequentially applied to each row electrode 11 from above by the row electrode drive circuit 18. Each column electrode 12 has a column electrode driving circuit.
From 19, a voltage corresponding to the image signal is applied. For this reason, the thin film transistor 13 is turned on at the timing when the selection signal from the row electrode 11 is applied, and samples a voltage corresponding to an image signal from the column electrode 12 to sample the pixel electrode.
Give to 14. Therefore, the liquid crystal layer 15 is charged with the difference between the voltage applied to the pixel electrode 14 and the voltage applied to the counter electrode 16 from the counter electrode drive circuit 20, and is displayed in an optical response.

FIG. 9 shows such a liquid crystal display device.
Voltage waveform a corresponding to an image signal applied to each column electrode 12
And a current waveform b corresponding to the voltage waveform a.

In general, the liquid crystal must be driven by an alternating current, and the voltage waveform a applied to the column electrode 12 is inverted at a predetermined period as shown in the figure. In addition, the column electrode 12
Has inevitably a capacitance component such as an intersection with the row electrode 11 and a parasitic capacitance of the pixel transistor. In order to drive the column electrode 12 with alternating current, such a capacitance component is charged and discharged. Therefore, as shown in FIG. 9, the current waveform b corresponds to the polarity inversion of the voltage waveform a. Electric current flows.

At this time, for example, at the time of writing an image signal having a positive voltage, the positive charges used to charge the pixel electrode capacitance and the column electrode capacitance are changed at the time of writing the image signal having the negative voltage. Discharge, ie, discard, via the column electrode drive circuit 19. Then, at the time of writing the next positive polarity voltage,
Positive charges are supplied again from the column electrode drive circuit 19.

Conversely, the negative charge used to charge the pixel electrode capacitance and the column electrode capacitance during the writing of the image signal having a negative polarity voltage becomes smaller when the image signal having a positive polarity voltage is written. It is discarded via the electrode drive circuit 19, and at the time of writing the next negative voltage, a negative charge is supplied again from the column electrode drive circuit 19.

As described above, since the column electrode driving circuit 19 frequently supplies and discards electric charges, the power consumption of the liquid crystal display device increases.

As a method of reducing power consumption when driving such a capacitive load, a method of storing and reusing electric charges is described in Mark Hahm: Modest Power Savings for Appli.
cations Dominated by Switching of Large Capacitive
Loads, 1994 IEEE Symposium on Low Power Electroni
cs, pp. 60-61.

In this description, a charge storage capacitor is provided at the output of a digital circuit having a capacitive load via a switch, and the charge accumulated in the load capacitor when the output is at the H level is transferred from H to Instead of being discarded to the ground at the time of the change to the L level, the charge storage capacitor is once charged and reused at the time of the next change from L to H. As a result, the amount of charge that must be supplied by the power supply can be saved, and power consumption can be reduced. In an ideal case, power consumption can be reduced to 50%.

However, it is difficult to directly apply this technique to reduce the power consumption of a liquid crystal display device.
For example, a liquid crystal display device for a computer has thousands of column electrodes which are capacitive loads. When the above technology is directly applied to such a liquid crystal display device, a charge storage capacitor must be provided for each of these thousands of column electrodes. It is impractical because the area is enlarged. Further, a complicated logic circuit is required to control the switch, which also increases the circuit scale and the mounting area, and hinders application to a liquid crystal display device.

[0014]

As described above, in the conventional liquid crystal display device, supply and disposal of charges to and from a capacitive load such as a column electrode are frequently repeated. I have.

[0015] The present invention has been made in view of the above problems, and does not involve a significant increase in circuit scale or mounting area.
An object of the present invention is to provide a liquid crystal display device in which power consumption is reduced by effectively utilizing a charge charged in a capacitive load.

[0016]

SUMMARY OF THE INVENTION The present invention relates to a scanning row electrode and an image signal column electrode arranged in a matrix, and switching elements provided at each intersection of the row electrode and the column electrode. A matrix array substrate having a pixel electrode connected to the switching element,
A counter substrate provided opposite to the matrix array substrate and having a counter electrode; and a liquid crystal layer sandwiched between the matrix array substrate and the counter substrate. An image from the column electrode is provided by a scanning signal from the row electrode. Supplying a signal to the pixel electrode connected to the switching element;
In a liquid crystal display device that performs display in addition to the liquid crystal layer between the counter electrodes, a column electrode driving circuit that applies an image signal whose polarity is inverted at a predetermined cycle to each of the column electrodes; The column electrodes are connected to a column electrode driving circuit each time the polarity of the image signal is inverted, and an image signal is written, and the connection destination of each column electrode is switched between the column electrode driving circuit and the capacitance element. Switching means. Then, after writing the image signal, the switching means switches and connects the column electrode to the capacitor element for holding electric charge, and the electric charge stored in the column electrode is moved to the capacitor element, whereby the opposite polarity stored in the capacitor element is transferred. The electric charges are transferred to the column electrodes, and the amount of electric charges supplied is reduced when the next image signal of the opposite polarity is written, thereby reducing power consumption.

The switching element has two types, one for the positive polarity and the other for the negative polarity. The switching means writes the image signal of one polarity to each column electrode and then switches the capacitance for the polarity corresponding to the image signal. Element, and after this switching, it switches to the capacitive element for the opposite polarity. Then, after writing the image signal of one polarity, the column electrode is switched to and connected to the capacitance element for the polarity corresponding to this image signal, and the electric charge accumulated in the column electrode is moved. To the column electrodes, and the charges of the opposite polarity stored in the capacitors are moved to the column electrodes, and the amount of charge supplied during the next writing of the image signals of the opposite polarity is reduced to reduce power consumption. Reduce.

Further, the switching means switches the connection destination of each column electrode to both adjacent column electrodes after writing the image signal. Then, the charges accumulated in each column electrode can be transferred to the column electrode of the opposite polarity, and the amount of charge supply at the time of writing the image signal after the polarity inversion is reduced, thereby reducing power consumption.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the liquid crystal display device of the present invention will be described below with reference to the drawings. The parts corresponding to those in the conventional example shown in FIG.

As shown in FIG. 1, a scanning row electrode 11 and an image signal column electrode 12 are arranged in a matrix. Each intersection of the row electrode 11 and the column electrode 12 has A thin film transistor 13 is provided as a switching element, and each thin film transistor 13 is connected to a pixel electrode 14 to form a matrix array substrate. The pixel electrodes 14 face the counter electrodes 16 of the counter substrate facing the matrix array substrate, and a liquid crystal layer 15 is sandwiched between the pixel electrodes 14 of the matrix array substrate and the counter electrodes 16 of the counter substrate. I have. Further, a predetermined voltage is applied to the counter electrode 16 from the counter electrode drive circuit 20.

Each row electrode 11 is connected to a row electrode driving circuit 18.
To control the switching of the thin film transistor 13 sequentially from above. Further, for each column electrode 12, a column electrode drive circuit 19 for applying an image signal, whose polarity is inverted at a predetermined cycle, is provided, and between these column electrodes 12 and the column electrode drive circuit 19. An analog switch 23, which is a three-point switching type switching means, is provided.

The central terminal of the analog switch 23 is connected to the column electrode driving circuit 19, and an image signal whose polarity is inverted at a predetermined cycle is applied to the central terminal. Further, the left and right terminals are respectively connected to a capacitor 24 as a capacitance element for storing positive charges for positive polarity, and connected to a capacitor 25 as a capacitance element for storing negative charges for negative polarity, respectively. . Then, the analog switch 23 selects and connects each of the column electrodes 12 to the column electrode drive circuit 19, the capacitor 24 for positive polarity, or the capacitor 25 for negative polarity.

The switching of the analog switch 23 is controlled by an analog switch control circuit 26.
The switching control of the analog switch 23 will be described with reference to FIG.

First, the analog switch 23 is controlled by three digital signals A, B and C. That is, according to these three digital signals A, B, and C, the connection destination of each column electrode 12 is selected from the column electrode drive circuit 19, the positive polarity capacitor 24, or the negative polarity capacitor 25 as shown in Table 1.

[0025]

[Table 1] As is apparent from Table 1, when the signal A is at the H (1) level, each column electrode 12 is connected to the column electrode drive circuit 19 regardless of the signals B and C. When the signal A is at the L (0) level and the signal B is also at the L level, the column electrode 12 is connected to the capacitor 25 for the negative polarity when the signal C is at the L level, and to the positive electrode when the signal C is at the H level. It becomes a capacitor 24 for sex.
When the signal A is at the L level and the signal B is at the H level, the column electrode 12 is connected to the capacitor 24 for the positive polarity when the signal C is at the L level and for the negative polarity when the signal C is at the H level. It becomes the capacitor 25.

FIG. 2 shows a change in the potential waveform of the column electrode 12 when the analog switch 23 is controlled by the signals A, B, and C as described above. For comparison, the potential waveform of the column electrode when black is written in the conventional example is also shown.

Next, the operation will be described with reference to FIG.

First, in the operation a1, positive polarity writing is performed, and the signals A, B, C are in the period of 1,0,0 and 1,0,1.
The analog switch 23 is switched to the center terminal in the figure,
Each column electrode 12 is connected to a column electrode drive circuit 19. Therefore, the column electrode driving circuit 19 writes a positive potential for an image signal to each column electrode 12.

Then, in operation b1, a positive charge is stored. When the positive polarity writing is completed, the signals A, B, and C are in the state of 0, 1, 0, the analog switch 23 is switched to the right terminal, and each column electrode 12 is connected to the positive polarity capacitor 24, respectively. You. As a result, a charge sharing effect occurs between the capacity of the column electrode 12 and the positive capacitor 24, and the potential of each column electrode 12 and the positive capacitor 24 becomes equal. That is, since the potential of each column electrode 12 at the end of the positive polarity writing was higher than the potential of the positive polarity capacitor 24, the positive charges accumulated in each column electrode 12 moved to the positive polarity capacitor 24. Then, the potential of the column electrode 12 decreases.

In operation c1, the negative charge is reused. The signals A, B, and C become 0, 1, and 1, the analog switch 23 is switched to the terminal on the left side in the figure, and each column electrode 12 is connected to the capacitor 25 for negative polarity.
Here also, a charge sharing effect occurs between the capacity of the column electrode 12 and the capacitor 25 for negative polarity. That is, at the time of the above-described operation b1, the potential of the negative polarity capacitor 25 is lower than the potential of the column electrode 12, so that the negative charge stored in the negative polarity capacitor 25 immediately after the previous negative polarity writing is stored in the column. It moves to the electrode 12, and the potential of the column electrode 12 decreases.

Further, in operation d1, a negative polarity write is performed. In the period in which the signals A, B, and C are in the states of 1, 1, 0 and 1, 1, 1, the analog switch 23 is switched again to the center terminal in the figure, and each column electrode 12 is connected to the column electrode drive circuit 19. I do. Therefore, each column electrode 12 has a column electrode drive circuit 19
As a result, a negative potential for an image signal is written.

Further, in operation e1, a negative charge is stored. When the writing of the negative polarity is completed, the signals A, B, and C become 0, 0, 0, the analog switch 23 is switched to the left terminal, and each column electrode 12 is connected to the capacitor 25 for the negative polarity. You. As a result, a charge sharing effect occurs between the capacitance of the column electrode 12 and the capacitor 25 for negative polarity, and the potential of each column electrode 12 and the capacitor 25 for negative polarity become equal. That is, since the potential of each column electrode 12 at the end of the negative polarity writing was lower than the potential of the negative polarity capacitor 25, the negative charges accumulated in each column electrode 12 moved to the negative polarity capacitor 25. , The potential of the column electrode 12 increases.

In operation f1, the positive charge is reused. The signals A, B, and C become 0, 0, and 1, the analog switch 23 is switched to the terminal on the right side in the figure, and each column electrode 12 is connected to the capacitor 24 for positive polarity.
Here, a charge sharing effect occurs between the capacity of the column electrode 12 and the capacitor 24 for positive polarity. That is, at the time of the above-described operation e1, the potential of the capacitor 24 for positive polarity is higher than the potential of the column electrode 12, so that the positive charges stored in the capacitor 24 for positive polarity immediately after the previous writing of positive polarity are stored in the column. It moves to the electrode 12, and the potential of the column electrode 12 rises.

The display is made by repeating the above-mentioned operations a1 to f1. Next, the fact that the power consumption is reduced by the operations a1 to f1 will be described.

First, at the end of the positive polarity writing in the operation a1 described above, positive charges corresponding to the respective image signals are accumulated in the capacitance of the column electrode 12. In the conventional example, this positive charge is discarded via the drive circuit at the time of the next writing of the negative polarity.

However, when the writing of the positive polarity is completed,
All column electrodes 12 are connected to a capacitor 24 for positive polarity by an analog switch 23.
Since the potential of 12 is higher than that of the capacitor 24 for positive polarity, the positive charges accumulated in the column electrode 12 move to the capacitor 24 for positive polarity due to the charge sharing effect (operation b1). Then, the positive polarity capacitor 24 is connected to all the column electrodes 12 by the analog switch 23 immediately before the next positive polarity writing. At this time, the potential of the capacitor 24 for positive polarity is higher than that of the column electrode 12, that is, the column electrode 12 is stored in the capacitor 24 for positive polarity due to the charge sharing effect because the column electrode 12 has been written to negative polarity. The positive charge moves to the column electrode 12 (operation f1).

As a result, the amount of positive charges that must be supplied by the drive circuit at the time of the next positive polarity write can be reduced, and the power consumed by the drive circuit can be reduced.

The same applies to the case of negative polarity. That is, the negative charge accumulated in the column electrode 12 during the negative polarity writing (operation d1) is accumulated in the negative polarity capacitor 25 (operation e1), and this negative charge is stored immediately before the next negative polarity writing. Then, it is returned to the column electrode 12 and reused (operation c1). With this series of operations, the amount of negative charge supplied by the drive circuit at the time of writing of negative polarity can be reduced, and the power consumed by the drive circuit can be reduced.

What is important here is that only two types of capacitors 24 and 25, one for positive polarity and the other for negative polarity, need to be provided as capacitance means for storing electric charges necessary for the above-mentioned operation. In the digital integrated circuit described in the conventional paper,
Since there is no regularity in which direction each terminal changes, the storage capacity is required by the number of capacitive loads. In contrast, in the case of a liquid crystal display device, the potential of the column electrode, which is a capacitive load, changes in the same direction almost simultaneously, so when storing and reusing the charges, all the column electrodes are collectively used for positive polarity or negative polarity. It can be connected to capacitors 24 and 25 for sex. As a result, the number of capacitors 24, 25
The number can be reduced to a very small number as compared with the number of 12, and increase in the circuit scale and the mounting area can be suppressed.

As described above, in the liquid crystal display device of the above-described embodiment, by using a smaller number of charge storage capacitors as compared with the column electrodes, the conventional driving method is discarded while suppressing an increase in circuit scale and mounting area. The stored charge can be effectively reused, and low power consumption can be realized.

As a countermeasure against flicker, a so-called V-line inversion drive in which drive voltages of column electrodes 12 adjacent to each other are made to have opposite polarities is known. In the case of using this driving method, the driving voltages of the odd-numbered columns and the even-numbered columns of the column electrodes 12 have opposite polarities. Therefore, two capacitors 24 and 25 are provided for the even-numbered columns and the odd-numbered columns. Operated by capacitors 24 and 25 and analog switch 23 a
The operations 1 to f1 may be executed with their phases shifted from each other.

Further, the polarity of the signal of the adjacent column electrode may be inverted in the same phase, and the signal may be driven to have the opposite polarity in the adjacent row.

Next, another embodiment will be described with reference to FIG.

The liquid crystal display device of the embodiment shown in FIG. 3 is basically the same as the liquid crystal display device shown in FIG. 1, but uses one capacitor element for holding electric charges. In this configuration, positive charges and negative charges are stored and reused. With this configuration, it is possible to further suppress an increase in circuit scale and mounting area as compared with the embodiment shown in FIG.

As shown in FIG. 3, a matrix array substrate has scanning row electrodes 11 and image signal column electrodes 12 wired in a matrix, and each of these row electrodes 11 and column electrodes 12 The thin film transistors 13 are provided at the intersections, and the thin film transistors 13 are connected to the pixel electrodes 14, respectively. The pixel electrodes 14 face the counter electrode 16 of the counter substrate via the liquid crystal layer 15, respectively, and a predetermined voltage is applied to the counter electrode 16 from the counter electrode drive circuit 20.

Each row electrode 11 is sequentially driven from above by a row electrode driving circuit 18 to form a thin film transistor.
Controls 13 switching. In addition, for each column electrode 12, a column electrode drive circuit 19 for applying an image signal, whose polarity is inverted at a predetermined cycle, is provided.

Between these column electrodes 12 and the column electrode driving circuit 19, a two-point switching type analog switch as switching means is provided.
33 are provided.

The left terminal of the two-point switching type analog switch 33 is connected to a column electrode drive circuit 19 to which an image signal whose polarity is inverted at a predetermined cycle is applied. The right terminals are respectively connected to capacitors 34 as capacitance elements for holding electric charges. This analog switch 33 connects each column electrode 12 to the column electrode drive circuit 19.
And the capacitor 34.

The switching of the analog switch 33 is controlled by an analog switch control circuit 36. The switching of the analog switch 33 is controlled by the column electrodes shown in FIG.
A description will be given in connection with the potential change of 12. The switching of the analog switch 33 is performed by one digital control signal A1, and the connection destination of the column electrode 12 is determined by the signal level of the digital control signal A1.
Can be switched between 34 and. That is, when the digital control signal A1 is at the H level, the column electrode 12
When the digital control signal A1 is at L level,
The column electrode 12 is connected to a charge holding capacitor.

The operation will be described below with reference to FIG.

First, in operation a2, positive polarity writing is performed. When the digital control signal A1 is at the H level, the analog switch 33 is switched to the right terminal, and the column electrode 12 is connected to the column electrode drive circuit 19. For this reason, a positive potential for an image signal is written into each column electrode 12 by the column electrode drive circuit 19.

In operation b2, positive charge storage and negative charge reuse are performed. When the positive polarity write is completed, the digital control signal A1 goes to L level, and the analog switch
33 is switched to the terminal on the left, and each column electrode 12 is connected to a capacitor 34, respectively. As a result, a charge sharing effect occurs between the capacitance of the column electrode 12 and the capacitor 34,
The potentials of each column electrode 12 and the capacitor 34 become equal. That is, since the potential of each column electrode 12 at the end of the positive polarity writing is higher than the potential of the capacitor 34, the positive charges accumulated in each column electrode 12 move to the capacitor 34, and the potential of the column electrode 12 decreases.

Here, the movement of the positive charge from the column electrode 12 to the capacitor 34 is equivalent to the movement of the negative charge from the capacitor 34 to the column electrode 12. Therefore, simultaneously with storing the positive charge in the capacitor 34, the negative charge stored in the capacitor 34 is moved to the column electrode 12 immediately after the previous writing of the negative polarity, and the potential of the column electrode 12 decreases.

In operation c2, a negative polarity write is performed. Since the digital control signal A1 becomes H level, the analog switch 23 is switched to the left terminal again, and each column electrode 12 is connected to the column electrode drive circuit 19. Therefore, the column electrode driving circuit 19 writes a negative potential for an image signal to each column electrode 12.

Next, in operation d2, negative charge storage and positive charge reuse are performed. When the negative polarity writing is completed, the digital control signal A1 goes to L level, and the analog switch
33 is switched to the right terminal, and each column electrode 12 is connected to a capacitor 34, respectively. As a result, a charge sharing effect occurs between the capacitance of the column electrode 12 and the capacitor 34,
The potentials of each column electrode 12 and the capacitor 34 become equal. That is, the potential of each column electrode 12 at the end of the negative polarity writing is
Since the potential is lower than the potential of the capacitor 34, the negative charges accumulated in each column electrode 12 move to the capacitor 34, and the potential of the column electrode 12 rises.

Here, the movement of the negative charge from the column electrode 12 to the capacitor 34 is equivalent to the movement of the positive charge from the capacitor 34 to the column electrode 12. Therefore, the negative charge is stored in the capacitor 34, and at the same time, the positive charge stored in the capacitor 34 is moved to the column electrode 12 immediately after the previous positive polarity write, and the potential of the column electrode 12 rises.

In this embodiment, the operations a2 to d described above are performed.
This is displayed by repeating step 2, and power consumption is reduced.

That is, at the end of the positive polarity writing (operation a2), a positive charge corresponding to each image signal is accumulated in the capacitance of the column electrode 12. In the conventional example, this positive charge was discarded at the time of the next writing of the negative polarity. However, in this embodiment, when the writing of the positive polarity is completed, all the column electrodes 12 are set to the capacitor by the analog switch 33. Connected to 34. In addition, since the potential of the column electrode 12 is higher than that of the capacitor 34 just before the connection, the positive charges accumulated in the column electrode 12 move to the capacitor 34 due to the charge sharing effect. Also, equivalently, the negative charge stored in the capacitor 34 immediately after the previous negative polarity write moves to the column electrode 12, and the potential of the column electrode 12 decreases (operation b2).
).

As a result, the amount of negative charge that must be supplied by the drive circuit during the writing of the negative polarity (operation c2) can be reduced, and the power consumed by the drive circuit can be reduced.

In operation d2, as in operation b2,
At the same time as storing the negative charge, the positive charge stored in the capacitor 34 moves to the column electrode 12 immediately after the previous positive polarity writing, so that the potential of the column electrode 12 is improved. At the time of writing with positive polarity (operation a2), the amount of positive charge that must be supplied by the drive circuit can be reduced, and the power consumed by the drive circuit can be reduced.

In this embodiment, one capacitor 34
By using only the element, power consumption can be reduced.
Also, since the analog switch 33 may be of a two-point switching type, power consumption can be reduced while further suppressing an increase in circuit scale and mounting area as compared with the configuration of FIG.

When the above-described V-line inversion driving method is used, since the driving voltages of the odd columns and the even columns of the column electrodes 12 have opposite polarities, the capacitors 34 are used for the even columns and the odd columns. In each case, that is, two sets are provided and operated by these capacitors 34 and analog switches 33.
2 to d2 may be executed with their phases shifted from each other.

As shown in FIG. 5, in addition to the above-described embodiments, the capacitance element of the column electrode 12 is additionally used as a capacitance element for retaining electric charge, and the electric charge can be stored and reused. Good.

As shown in FIG. 5, a scanning row electrode 11 and an image signal column electrode 12 wired in a matrix on a matrix array substrate are provided. The thin film transistors 13 are provided at the intersections, and the thin film transistors 13 are connected to the pixel electrodes 14, respectively. These pixel electrodes 14 face the counter electrode 16 of the counter substrate via the liquid crystal layer 15, respectively, and a predetermined voltage is applied to the counter electrode 16 from the counter electrode drive circuit 20.
Each row electrode 11 is sequentially driven from above by a row electrode driving circuit 18 to control the switching of the thin film transistor 13.

A voltage waveform as an image signal whose polarity is inverted at a predetermined cycle is applied to each column electrode 12 from the column electrode driving circuit 39. The column electrode driving circuit 39 applies a voltage of the image signal to the column electrode 12. Are applied so that the even and odd rows of each column electrode 12 have opposite polarities.

A switching type analog switch 43 as switching means is provided between the column electrode 12 and the column electrode driving circuit 39. The analog switch 43 selectively connects the column electrode 12 to one of the column electrode drive circuit 39 and one of the adjacent column electrodes.

The switching of the analog switch 43 is controlled by an analog switch control circuit 46. The switching control of the analog switch 43 will be described with reference to FIG. The switching of the analog switch 43 is performed by one digital control signal A2, and the connection destination of the column electrode 12 is switched between the column electrode driving circuit 39 and one of the adjacent column electrodes 12 according to the signal level of the digital control signal A2. Can be That is, when the digital control signal A2 is at the H level, the column electrode 12 is connected to the column electrode drive circuit 39, and when the digital control signal A2 is at the L level, the column electrode 12 is connected to one of the adjacent column electrodes 12.

The operation will be described below with reference to FIG.

First, in operation a3, writing is performed. When the digital control signal A2 is at the H level, each column electrode 12 is connected to the column electrode drive circuit 39 by the analog switch 43. Therefore, a potential for an image signal is written to each column electrode 12 by the column electrode drive circuit 19. Here, the potentials of the image signals written to the adjacent column electrodes 12 have opposite polarities.

Next, in operation b3, charge storage and charge reuse are performed. When the writing is completed, the digital control signal A2 becomes L level, and the analog switch 33
Each column electrode 12 is connected to one adjacent column electrode 12. By this write operation, a signal of the opposite polarity is written to the adjacent column electrode 12. For this reason, a charge sharing effect occurs between adjacent column electrodes 12 connected to each other, and positive charges move from the column electrodes 12 on which positive polarity has been written to the column electrodes 12 on which negative polarity has been written, or the negative charges have been written. The negative charges move from the column electrode 12 to the column electrode 12 on which the positive polarity has been written, and the potentials of the adjacent column electrodes 12 become equal.

In operation c3, writing is performed. Since the digital control signal A2 becomes H level, each column electrode 12 is again connected to the column electrode drive circuit 39 by the analog switch 43. Therefore, a potential for an image signal is written to each column electrode 12 by the column electrode drive circuit 19. At this time, the potentials of the image signals written to the adjacent column electrodes 12 have the opposite polarities to each other, and also to the operation a3.

Further, in operation d3, charge storage and charge reuse are performed. When the operation c3 is completed, the digital control signal A2 goes to L level, and the analog switch 33 causes each column electrode 12 to return to one of the adjacent column electrodes 12 again.
Connected to Since the signal of the opposite polarity is written to the adjacent column electrode 12 by the operation c3, a charge sharing effect occurs between the connected adjacent column electrodes 12, and the positive polarity write is performed similarly to the operation b3. The positive charge moves from the written column electrode 12 to the column electrode 12 on which the negative polarity is written, or the negative charge moves from the column electrode 12 on which the negative polarity is written to the column electrode 12 on which the positive polarity is written. The potentials of the column electrodes 12, 12 become equal. However, the moving direction of the electric charge is opposite to that in the operation b3.

In this embodiment, the operations a3 to d
3 is displayed repeatedly to reduce power consumption.

That is, at the end of the operation a3, a positive charge corresponding to the image signal is stored in the capacity of the column electrode 12 written in the positive polarity, and a capacity in the column electrode 12 written in the negative polarity is set in the capacity.
Negative charges corresponding to the image signals are respectively stored. Conventionally, these charges have been discarded during the next writing. In this embodiment, when the writing of the operation a3 is completed, all the column electrodes 12 are connected to the adjacent column electrodes 12 by the analog switch 43. Signals of opposite polarities are written to these adjacent column electrodes 12 by operation a3. Therefore, due to the charge sharing effect, the column electrode 12 written to the positive polarity changes from the column electrode 12 written to the negative polarity.
The positive charge moves to 12. In addition, negative charges move from the column electrode 12 written to the negative polarity to the column electrode 12 written to the positive polarity equivalently (operation b3).

As described above, the potential of the column electrode 12 written to the positive polarity decreases, and the column electrode 12 written to the negative polarity decreases.
Potential rises. Therefore, the next write (operation c)
In the case of 3), the amount of charges supplied from the column electrode drive circuit 39 to each column electrode 12 can be small. That is, power consumption is reduced.

The operation for the next save and reuse (operation d 3) and writing (operation a 3) is the same as the operation b
3 and the operation c3, the polarities are inverted but the same, and the description is omitted.

In this embodiment, the electric charge is stored and reused by utilizing the capacitance of the adjacent column electrode 12, and the power consumption can be reduced.

In the above embodiment, when the electric charge is stored and reused, as shown in FIG. 5, the analog switch 43 is used to connect to only one of the adjacent column electrodes 12, but FIG. As shown in the figure, the analog switch 53
May be connected to both adjacent column electrodes 12. In this case, when storing and reusing the charges (operation b
3 and operation d3), all column electrodes 12 are connected.

[0079]

According to the present invention, after the image signal is written, the column electrode is switched and connected to the charge holding capacitance element by the switching means, while suppressing the increase in the circuit scale and the mounting area, and is stored in the column electrode. The transferred charge is transferred to the capacitor element, the charge of the opposite polarity stored in the capacitor element is transferred to the column electrode, and the amount of charge supplied at the time of writing the next opposite polarity image signal is reduced, thereby reducing power consumption. This saves and reuses the electric charge that has been discarded in the related art, so that the power consumption required for display driving can be reduced.

Further, the present invention can be applied to a so-called V-line inversion driving method in which driving voltages of adjacent column electrodes used for measures against flicker are reversed in polarity.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing one embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a waveform chart for explaining the above operation.

FIG. 3 is an equivalent circuit diagram showing a liquid crystal display device according to another embodiment of the present invention.

FIG. 4 is a waveform chart for explaining the above operation.

FIG. 5 is an equivalent circuit diagram showing a liquid crystal display device according to another embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the above operation.

FIG. 7 is an equivalent circuit diagram showing a liquid crystal display device according to still another embodiment of the present invention.

FIG. 8 is an equivalent circuit diagram of a conventional liquid crystal display device.

FIG. 9 is a waveform diagram showing a voltage waveform for an image signal and a corresponding current waveform in a conventional example.

[Explanation of symbols]

 11 Row electrodes 12 Column electrodes also functioning as capacitance elements 13 Thin film transistors as switching elements 14 Pixel electrodes 15 Liquid crystal layer 16 Counter electrodes 19 Column electrode driving circuits 23, 33, 43 Analog switches 24, 25, 34 as switching means Capacitor as capacitance element

Claims (4)

[Claims] 1. A scanning row electrode and an image signal column electrode arranged in a matrix, switching elements provided at respective intersections of the row electrodes and column electrodes, and connected to the switching elements. A matrix array substrate having pixel electrodes, a counter substrate having a counter electrode provided to face the matrix array substrate, and a liquid crystal layer sandwiched between the matrix array substrate and the counter substrate; In a liquid crystal display device that supplies an image signal from the column electrode to the pixel electrode connected to the switching element by a scanning signal and displays the image in addition to the liquid crystal layer between the counter electrode, A column electrode driving circuit for applying an image signal whose polarity is inverted at a predetermined cycle; a capacitor element for holding electric charges; Switching means for connecting the column electrodes to the column electrode drive circuit and writing the image signal every time the polarity is inverted, and switching the connection destination of each column electrode between the column electrode drive circuit and the capacitor element. Liquid crystal display device. 2. The capacitor element has two types, one for a positive polarity and the other for a negative polarity. After switching each column electrode to an image signal of one polarity, the switching means switches a capacitor for a polarity corresponding to the image signal. 2. The liquid crystal display device according to claim 1, wherein the element is switched to an element, and after the switching, the element is switched to a capacitor element for the opposite polarity. 3. The column electrode drive circuit according to claim 1, wherein the voltage of the image signal is reversed in the even-numbered column and the odd-numbered column of each column electrode, and a capacitor element and switching means are provided for each of the even-numbered column and the odd-numbered column. The liquid crystal display device according to claim 1 or 2, wherein: 4. The liquid crystal display device according to claim 1, wherein the switching unit switches the connection destination of each of the column electrodes to both adjacent column electrodes after writing the image signal.