WO2006123532A1

WO2006123532A1 - Display apparatus driving circuit and driving method

Info

Publication number: WO2006123532A1
Application number: PCT/JP2006/308947
Authority: WO
Inventors: Toshihiko Miyashita
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2005-05-20
Filing date: 2006-04-28
Publication date: 2006-11-23

Abstract

To reduce the power consumption in an opposed AC drive and suppress the degradation of the display quality caused by switching the opposed voltages or the like. In a common electrode driving part using a CC bias circuit to perform an opposed AC drive, if opposed voltages are to be switched such that the center voltage is varied from Vc1 to Vc2 (where Vc1 > Vc2), the bias voltage is varied such that the target value of the center voltage at a time point (t1) of starting the switching is a value Vc3 that is smaller than the value Vc2 as varied (where Vc2 > Vc3), and then the bias voltage is varied such that the target value of the center voltage is Vc2 at a predetermined later time point (t2). In this way, the bias voltage is controlled such that the variation of the bias voltage used for varying the center voltage (DC component) of the opposed voltage is transiently magnified, whereby the time period in which to switch the opposed voltages can be shortened. The present invention is suitable for a liquid crystal display apparatus of opposed AC driving system in which the opposed voltages are changed in accordance with the switching of the display modes or the like.

Description

Specification

Display device drive circuit and drive method

Technical field

TECHNICAL FIELD [0001] The present invention relates to a display device such as a liquid crystal display device that displays an image by applying a voltage between a plurality of pixel electrodes and a common electrode opposed to the plurality of pixel electrodes. Display configured so that the value of the counter voltage to be applied to the electrode switches alternately between two voltage values in a predetermined cycle, and the counter voltage (the center voltage) is changed according to the change of the display mode, etc. The present invention relates to a driving circuit of the device.

Background art

At present, as a flat display device, an active matrix liquid crystal display device (hereinafter referred to as “TFT-LCD device”) using a thin film transistor (TFT) is widely used.

A liquid crystal panel (hereinafter referred to as “TFT—LCD panel”) in a TFT-LCD device has a pair of substrates (hereinafter referred to as “first and second substrates”) facing each other. These substrates are fixed by being separated by a predetermined distance, and a liquid crystal material is filled between these substrates to form a liquid crystal layer. At least one of these substrates is transparent, and when performing transmissive display, both substrates must be transparent. In the TFT-LCD device, a plurality of scanning signal lines parallel to each other and a plurality of data signal lines intersecting at right angles to the scanning signal lines are provided on the first substrate! / At each intersection of the scanning signal line and the data signal line, a pixel electrode and a pixel TFT which is a switching element for electrically connecting the pixel electrode to the data signal line are provided. The gate terminal of the pixel TFT is connected to the scanning signal line, the source terminal is connected to the data signal line, and the drain terminal is connected to the pixel electrode.

[0004] On the second substrate facing the first substrate, a common electrode as a counter electrode is provided on the entire surface. An appropriate voltage is applied to the common electrode by the common electrode driving unit. Therefore, a voltage corresponding to the potential difference between the pixel electrode and the common electrode is applied to the liquid crystal layer. Since the light transmittance of the liquid crystal layer can be controlled by this applied voltage, the data signal is transmitted. Line force A desired pixel display can be performed by applying an appropriate voltage to each pixel electrode.

In a liquid crystal display device, it is necessary to drive the liquid crystal panel so that the voltage applied to the liquid crystal is AC in order to prevent deterioration of the liquid crystal material. TFT— As a method of alternating current drive for liquid crystal panels such as LCD panels, the polarity of the voltage applied to the liquid crystal is reversed every frame period in order to prevent deterioration of display quality due to flickering force, etc. There is known a driving method called a line inversion driving method in which the polarity is inverted every one or a predetermined number of scanning lines.

In the liquid crystal display device of the line inversion driving method, in order to suppress the amplitude of the voltage of the data signal line, the potential of the common electrode, that is, the value of the counter voltage is changed according to the AC driving (hereinafter referred to as “ It is common to use the “opposite AC drive system”. In a line inversion drive type liquid crystal display device that inverts the polarity of the voltage applied to the liquid crystal for each horizontal scanning line in each frame, the polarity of the data signal applied to each data signal line (based on the relative voltage) In order to perform opposite AC drive every 1 horizontal period, the opposite voltage value is 1 between a predetermined high voltage value and low voltage value in conjunction with the polarity inversion of each data signal. It is switched every horizontal period.

[0007] By the way, depending on the liquid crystal display device, there are a plurality of types of optimal counter voltages, and it may be necessary to switch the counter voltages to be applied to the common electrode between the plurality of types of optimal counter voltages. . For example, as described in the following Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-206089), in a liquid crystal display device having a plurality of reflective regions and a plurality of transmissive regions, the voltage applied to the liquid crystal is the same. Even so, the saturation in the display differs between the transmissive region and the reflective region. In order to cope with such a problem, for example, in the case of a liquid crystal display device capable of both transmissive display and reflective display, it is necessary to change the counter voltage between the reflective display and the transmissive display. Specifically, as shown in FIG. 13, in a certain operation mode (eg, reflective display mode), a value between a predetermined first high voltage value VHil and a first low voltage value VLol is obtained. Is applied to the common electrode as the optimum counter voltage, which is switched every horizontal period.In another operation mode (e.g., transmissive display mode), the predetermined second high voltage value is applied. 1 value between VHi2 and second low voltage value VLo2 It is necessary to apply the second type of counter voltage Vcom2, which switches every flat period, to the common electrode as the optimal counter voltage. Normally, the amplitude of the first type counter voltage Vcoml (difference between the first high voltage and the first low voltage VHil -VLol) and the amplitude of the second type counter voltage Vcom2 (second high voltage and The difference from the second low voltage (VHi2-VLo2) can be the same, so by changing the center voltage corresponding to the DC component of the counter voltage, the counter voltage becomes the first type counter voltage Vcoml and the second type. Is switched between the opposite voltage Vcom2.

[0008] As described above, for example, an operational amplifier (operational amplifier) 53 and a counter voltage waveform generation circuit 51 are used in order to switch the counter voltage to be applied to the common electrode between a plurality of types of optimal counter voltages. A circuit as shown in (A) is used. According to such a circuit using the operational amplifier 53, the rectangular wave voltage VCOMin applied to the non-inverting input terminal of the operational amplifier 53 is switched as shown by the dotted line in FIG. Counter voltage VCOMout can be changed.

[0009] In addition, in order to switch the counter voltage to be applied to the common electrode between a plurality of types of optimum counter voltages, a bias voltage generation circuit 61, a rectangular wave voltage generation circuit 63, a coupling capacitor C1, A circuit (hereinafter referred to as “CC bias circuit”) configured by combining the first and second resistance elements Rl and R2 as shown in FIG. 15A is also used. In this CC bias circuit, a rectangular wave voltage Vpp as shown in FIG. 15 (B) is applied to the connection point Nout between the first resistance element R1 and the second resistance element via the coupling capacitor C1, and the first The bias voltage Vba from the bias voltage generating circuit 61 is applied to one end of the resistance element R1, and the voltage at the connection point Nout is output as the counter voltage VCOMout. In such a CC bias circuit, by changing the bias voltage Vba so that the center voltage Vc (corresponding to the direct current component) of the counter voltage changes as shown by the one-dot chain line in FIG. The optimum counter voltage to be applied to the common electrode can be switched.

Patent Document 1: Japanese Unexamined Patent Publication No. 2005-3962

Patent Document 2: Japanese Unexamined Patent Publication No. 10-268258

Patent Document 3: Japanese Patent Laid-Open No. 10-214066

Disclosure of the invention

Problems to be solved by the invention [0010] As described above, when the counter voltage to be applied to the common electrode is switched between a plurality of types of optimum counter voltages, the period from the start of the switching of the optimum counter voltage to the completion of the switching (hereinafter referred to as " The switching period “t ヽぅ) is given to the common electrode! / The opposing voltage is not optimal. Therefore, if this switching period is long, the display quality is degraded due to the generation of flick force and the like.

On the other hand, when a circuit such as that shown in FIG. 14A using an operational amplifier is used, the optimum counter voltage to be applied to the common electrode is directly output from the operational amplifier force. The period is almost negligible, and the deterioration of display quality due to switching of the optimum counter voltage is not a problem. However, the circuit shown in FIG. 14 (A) is not suitable for a liquid crystal display device used in portable information devices, etc., where the power consumption due to the operational current of the operational amplifier is large and there is a strong demand for low power consumption.

On the other hand, when the CC bias circuit shown in FIG. 15A is used, the resistance value of the resistance elements Rl and R2 to which the bias voltage Vba is applied is large and the power consumption is small. However, the above switching period is determined by the product of the capacitance value of the coupling capacitor C1 and the resistance values of the resistance elements Rl and R2, and the conventional CC bias circuit requires a switching period of about 0.5 seconds, for example. (Refer to the dotted circle in Fig. 15 (C)). Therefore, during this time, a non-optimal counter voltage is applied to the common electrode, and there is a problem that the deterioration of display quality during the switching period is visually recognized.

[0013] Therefore, the present invention provides a drive circuit and a drive method for a display device that can suppress a decrease in display quality due to a change in bias voltage for switching the opposite voltage while keeping power consumption in the opposed AC drive low. The purpose is to do.

Means for solving the problem

[0014] In a first aspect of the present invention, the plurality of individual electrodes respectively corresponding to the unit images constituting the image to be displayed and the common electrode provided to face the plurality of individual electrodes. A driving circuit of a display device that displays the image by applying a voltage according to the image,

An individual electrode driver that applies a voltage corresponding to the image to the plurality of individual electrodes; and outputs a counter voltage to be applied to the common electrode, and sets the value of the counter voltage to a predetermined high voltage A common electrode driver that alternately switches between a pressure value and a predetermined low voltage value at a predetermined cycle,

The common electrode driving unit includes:

A resistor string including two resistive elements connected in series with each other;

A DC voltage generating circuit for applying a DC voltage between both ends of the resistor string;

With a given capacitor,

A rectangular wave voltage generating circuit connected to a connection point between the two resistance elements via the capacitor and outputting a rectangular wave voltage corresponding to the waveform of the counter voltage;

A bias control unit that changes a DC component of the voltage at the connection point by changing a value of the DC voltage,

The common electrode driving unit applies the voltage at the connection point to the common electrode as the counter voltage;

The bias control unit is characterized in that when changing the DC component of the counter voltage, the value of the DC voltage is changed transiently larger than the change necessary for changing the DC component.

[0015] A second aspect of the present invention is the first aspect of the present invention,

When changing the DC component of the counter voltage, the bias control unit changes the value of the DC voltage to be larger than the change necessary for changing the DC component for a predetermined period immediately after the change of the DC component. It is characterized by that.

[0016] A third aspect of the present invention is the first aspect of the present invention,

The bias control unit causes the value of the DC voltage to be included in the voltage at the connection point when the display device starts the display, and the DC voltage that the counter voltage should have for display on the display device. It is characterized by a change that is transiently larger than the change required for

[0017] A fourth aspect of the present invention is the first aspect of the present invention,

A voltage detector for detecting a voltage at the connection point;

The bias controller is configured to determine a voltage value at the connection point determined based on a set value determined in advance as a value after the change of the direct current component of the counter voltage and a detection result of the voltage detector. The value of the DC voltage is determined so that the difference from the detected value, which is the value of the DC component, is canceled out.

[0018] According to a fifth aspect of the present invention, in a fourth aspect of the present invention,

The bias control unit includes:

When the difference is larger than a predetermined allowable value and the set value is larger than the detected value, a predetermined maximum value is determined as the value of the DC voltage;

When the difference is larger than the allowable value and the set value is smaller than the detected value, a predetermined minimum value is determined as the value of the DC voltage,

When the difference is less than or equal to the allowable value, the set value is determined as the value of the DC voltage.

[0019] In a sixth aspect of the present invention, a plurality of individual electrodes respectively corresponding to unit images constituting an image to be displayed are provided between the common electrode provided so as to face the plurality of individual electrodes. A driving circuit of a display device that displays the image by applying a voltage according to the image,

An individual electrode driving unit that applies a voltage according to the image to the plurality of individual electrodes, and outputs a counter voltage to be applied to the common electrode, and the value of the counter voltage is set to a predetermined high voltage value and a predetermined low voltage value. A common electrode driving unit that alternately switches between and with a predetermined cycle,

The common electrode driving unit includes:

A DC voltage is applied across the resistor string including two resistance elements connected in series with each other,

A rectangular wave voltage corresponding to the waveform of the counter voltage is applied to a connection point between the two resistance elements through a predetermined capacitor,

Applying the voltage at the connection point to the common electrode as the counter voltage;

When changing the DC component of the counter voltage, the value of the DC voltage is changed transiently to be larger than the change necessary for changing the DC component.

[0020] A seventh aspect of the present invention is a display device,

A drive circuit according to any one of the first to sixth aspects of the present invention is provided. To do.

[0021] In an eighth aspect of the present invention, the plurality of individual electrodes respectively corresponding to the unit images constituting the image to be displayed and the common electrode provided so as to face the plurality of individual electrodes. A method of driving a display device that displays the image by applying a voltage according to the image,

An individual electrode driving step for applying a voltage corresponding to the image to the plurality of individual electrodes; and a counter voltage to be applied to the common electrode is output, and the value of the counter voltage is set to a predetermined high voltage value and a predetermined low voltage value. A common electrode driving step that alternately switches between and with a predetermined cycle,

The common electrode driving step includes:

A DC voltage applying step for applying a DC voltage between both ends of a resistor string including two resistance elements connected in series;

A rectangular wave voltage applying step of applying a rectangular wave voltage corresponding to the waveform of the counter voltage to a connection point between the two resistance elements via a predetermined capacitor;

An output step of applying the voltage at the connection point to the common electrode as the counter voltage, and when changing the DC component of the counter voltage, the value of the DC voltage is more transient than the change necessary for the change of the DC component. And a bias control step that changes greatly.

[0022] A ninth aspect of the present invention is the eighth aspect of the present invention,

In the bias control unit step, at the start of display on the display device, the DC voltage causes the voltage at the connection point to have a DC component that the counter voltage should have for display on the display device. It is characterized by a change that is transiently larger than the change required for this.

[0023] A tenth aspect of the present invention is the eighth aspect of the present invention,

A detection step of detecting a voltage at the connection point;

In the bias control step, a setting value predetermined as a value after the change of the DC component of the counter voltage and a value of the DC component of the voltage at the connection point determined based on the detection result in the detection step So that the difference from the detected value is cancelled. The pressure value is determined.

The invention's effect

[0024] According to the first aspect of the present invention, the DC component of the counter voltage is changed in the common electrode drive unit using the CC bias circuit including the resistor string having the first and second resistance element forces and the capacitor. When this occurs, the value of the DC voltage applied to the resistor string changes transiently larger than the change necessary to change the DC component. As a result, the counter voltage switching period and the bias start-up period are shortened compared to the conventional case. Therefore, in a liquid crystal display device or the like that performs counter AC drive, the power consumption for driving the common electrode is kept low while the counter voltage is reduced. It is possible to suppress deterioration in display quality associated with switching and bias activation at the start of display.

[0025] According to the second aspect of the present invention, when the DC component of the counter voltage is changed, the resistor string constituting the CC bias circuit as the common electrode drive unit only for a predetermined period immediately after the change of the DC component. When the value of the DC voltage applied to is changed more greatly than the change necessary to change the DC component, the switching period of the counter voltage is shortened compared to the conventional case.

[0026] According to the third aspect of the present invention, the direct current applied to the resistor string composed of the first and second resistance elements at the start of display on the display device including the CC bias circuit as the common electrode driving unit. The voltage value changes transiently larger than the change necessary to obtain the DC component that the counter voltage should have for display on the display device. As a result, the bias start-up period at the start of display is shortened compared to the conventional case, so that it is possible to suppress deterioration in display quality when the bias voltage is raised at the start of display.

According to the fourth aspect of the present invention, when the DC component of the counter voltage is changed, the first and second resistance element forces in the CC bias circuit as the common electrode driving unit are also applied to the resistor string. In addition to the DC voltage value obtained being transiently larger than the change necessary for changing the DC component of the counter voltage, a set value that is predetermined as the changed value of the DC component and the voltage The DC voltage is adjusted so that the difference between the detected value, which is the DC component value of the voltage at the connection point between the first resistance element and the second resistance element, determined based on the detection result of the detector is canceled out. The value of is determined. Therefore, it is possible to shorten the counter voltage switching period and the bias start-up period without determining in advance the period in which the change in the value of the DC voltage is to be increased transiently. [0028] According to the fifth aspect of the present invention, the set value predetermined as the value after the change of the DC component of the counter voltage, the first resistance element determined based on the detection result of the voltage detector, When the difference between the detected value, which is the DC component value of the voltage at the connection point with the second resistance element, is larger than the allowable value, the first and second resistance element forces are also given to the resistance string. The value of the DC voltage is a predetermined maximum value or minimum value. Therefore, it is substantially unnecessary to determine how much the DC voltage value should be increased transiently in order to shorten the counter voltage switching period and the bias starting period.

Brief Description of Drawings

FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of the liquid crystal panel in the first embodiment.

FIG. 3 is a block diagram functionally showing the configuration of a common electrode driving section in the first embodiment.

FIG. 4 is a circuit diagram showing a configuration example of a bias voltage generating circuit constituting the common electrode driving unit in the first embodiment.

FIG. 5 is a voltage waveform diagram (A, B) showing the operation of the common electrode driving section in the first embodiment.

FIG. 6 is a voltage waveform diagram for explaining the effect of the first embodiment.

FIG. 7 is a circuit diagram showing a circuit model used for the simulation of the common electrode driving unit in the first embodiment.

[FIG. 8] A voltage waveform diagram (A) showing the change of the first example of the bias voltage in which the variable voltage source force is also applied to one end of the first resistance element in the simulation, and the second example of the bias voltage. It is a voltage waveform diagram (B) showing a change.

[FIG. 9] Waveform diagram showing the bias voltage of the first example and the second example in the simulation (A), the counter voltage obtained at the output point when the bias voltage of the first example is given, and the corresponding second voltage FIG. 4 is a waveform diagram (B) schematically showing a counter voltage obtained at an output point when an example bias voltage is applied, and a waveform diagram (C) showing the counter voltage in detail.

FIG. 10 is a waveform diagram showing a change in bias voltage at the start of display of the common electrode driver in the first embodiment (A). The waveform diagram (B) showing the change of the first voltage and the waveform diagram showing the change of the high voltage value in the counter voltage due to the change of the bias voltage at the start of the display of the first embodiment and the conventional common electrode drive unit (C).

FIG. 11 is a block diagram functionally showing the configuration of the common electrode driving unit in the second embodiment of the present invention.

FIG. 12 is a flowchart showing an operation of a control calculation unit constituting the common electrode driving unit in the second embodiment.

13] A voltage waveform diagram for explaining switching of the counter voltage in the liquid crystal display device.

FIG. 14 is a block diagram (A) showing a configuration of a first conventional example of a common electrode driving unit in a liquid crystal display device, and a voltage waveform diagram (B) showing an operation of the first conventional example.

FIG. 15 is a block diagram (A) showing a configuration of a second conventional example of a common electrode driving unit in a liquid crystal display device, and voltage waveform diagrams (B, C) showing the operation of the second conventional example. .

Explanation of symbols

10 • · -TFT (switching element)

11… Bias voltage generator

13 ... Square wave voltage generator

15 • · 'Bias voltage controller (bias controller)

17… Voltage detection circuit

19 • · · Arithmetic control unit (bias control unit)

21… Voltage setting register

100 ... LCD panel

102-TFT substrate

104… Counter substrate

120 • "Source Driver (Individual Electrode Driver)

130… Gate driver (Individual electrode driver)

200… Controller

210 —DZA conversion circuit 300 ••• DCZDC Converter

410, 420… Common electrode drive

CI… coupling capacitor

Rl ... 1st resistance element

R2 ... Second resistance element

Nout… Output point

Ec ... Common electrode

Vcom… Opposite voltage

VHi: High voltage value that is the maximum value in each cycle of the counter voltage

VLi: Low voltage value that is the minimum value in each cycle of the counter voltage

Va ... Amplitude of counter voltage

Vc: Center voltage (opposite voltage)

Vt ... Center voltage target value

Vba… Noise voltage

Vpp… rectangular wave voltage

BEST MODE FOR CARRYING OUT THE INVENTION

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

<1. First Embodiment>

<1.1 Overall configuration and operation>

FIG. 1 is a block diagram showing the configuration of the liquid crystal display device according to the first embodiment of the present invention. This liquid crystal display device is a TFT-LCD device that adopts a line inversion driving method and performs opposed AC driving, and includes a liquid crystal panel 100 and a source driver 120 as a data signal line driving circuit mounted on the liquid crystal panel 100. And a gate driver 130 as a scanning signal line drive circuit, a controller 200 as a display control circuit, a DCZDC converter 300 as a power supply circuit, and a first resistance element R1 as a component of the common electrode drive unit And a second resistance element R2 and a capacitor C1.

[0032] The liquid crystal panel 100 according to the present embodiment includes a pair of substrates 102 and 104 that sandwich a liquid crystal layer, and a polarizing plate is attached to the outer surface of each substrate. One of this pair of substrates 102 is called a TFT substrate. In the TFT substrate 102, a plurality of source lines Ls as data signal lines and a plurality of gate lines Lg as scanning signal lines cross each other on an insulating substrate such as glass. A plurality of pixel circuits are formed in a matrix form corresponding to the intersections of the plurality of source lines Ls and the plurality of gate lines Lg (hereinafter, formed in a matrix form in this manner). The plurality of pixel circuits thus formed is referred to as a “pixel array” and denoted by reference numeral “110”). As shown in FIG. 2, each pixel circuit includes a pixel capacitor Cp having a liquid crystal capacitive force formed by a pixel electrode as an individual electrode formed on the TFT substrate 102 and a counter electrode Ec described later, and a switching element. Includes TFT10. The gate terminal and the source terminal of the TFT 10 are respectively connected to the gate line Lg and the source line Ls passing through the intersection corresponding to the pixel circuit, and the drain terminal of the TFT 10 is connected to the pixel electrode.

[0033] On the other hand, the other substrate 104 of the pair of substrates is called a counter substrate, and a common electrode Ec and an alignment film as a counter electrode are sequentially stacked over a transparent insulating substrate such as glass. ing. There is a liquid crystal layer sandwiched between the counter substrate 104 and the TFT substrate 102 so as to be sandwiched between the liquid crystal layer and each pixel electrode disposed so as to sandwich the liquid crystal layer. The liquid crystal capacitance is formed as the pixel capacitance Cp by the common electrode Ec. Usually, an auxiliary capacitor is provided in parallel with the liquid crystal capacitor that should surely hold the voltage in the pixel capacitor Cp. However, since the auxiliary capacitor is not directly related to the present invention, its description and illustration are omitted.

In the liquid crystal panel as described above, as will be described later, the common electrode Ec as the counter electrode is supplied with the counter voltage Vcom by the common electrode driving unit, and each pixel electrode has a voltage corresponding to the image to be displayed. The voltage is provided by the source driver 120 and the gate driver 130. As a result, a voltage corresponding to the potential difference between the electrodes is applied to the liquid crystal layer sandwiched between each pixel electrode and the common electrode Ec. Thus, image display is realized by optically modulating each part of the liquid crystal layer. The source driver 120 and the gate driver 130 constitute a drive unit that applies a voltage corresponding to the image to a pixel electrode as an individual electrode corresponding to a unit image constituting an image to be displayed, that is, an individual electrode drive unit. The controller 200 is a drive control signal (a voltage corresponding to a pixel value is applied to each pixel electrode) for operating the source driver 120 based on an image signal and a control signal to which an external signal source (not shown) is also applied. Ssdv) and a drive control signal Sgdv for operating the gate driver 130 are generated. The controller 200 also includes a DZA conversion circuit 210 as a bias voltage generation circuit that outputs a bias voltage Vba for driving the common electrode Ec.

[0036] The DCZDC converter 300 is based on a control signal Sig from the controller 200 and is supplied by another power source (for example, a power source (not shown) of an electronic device such as a mobile phone including the liquid crystal display device). From this, a DC voltage V01 is generated as a power supply voltage for the controller 200, the source driver 120, and the like. In addition to this, the DCZDC converter 300 outputs a rectangular wave voltage Vpp and a reference voltage V00, which will be described later, for driving the common electrode Ec.

[0037] The bias voltage Vba output from the DZA conversion circuit 210 in the controller 200 is applied to one end of the first resistance element R1, and the other end of the first resistance element R1 is connected to the second resistance element R2. Connected to one end. The other end of the second resistance element R2 is supplied with the reference voltage V00 output from the DCZDC comparator 300, whereby the other end of the second resistance element R2 is grounded, and the first and first resistance elements R2 are grounded. A bias voltage Vba as a direct current voltage is applied between both ends of the resistor string composed of the two resistance elements Rl and R2. In addition, one end of a capacitor C1 is connected to a connection point Nout between the first resistor element R1 and the second resistor element R2, and a rectangular wave output from the DCZDC converter 300 is connected to the other end of the capacitor C1. The voltage Vpp is given. Thus, the first resistor element R1 and the second resistor element R2 form a resistor string for dividing the noise voltage Vba, and the capacitor C1 generates a rectangular wave voltage Vpp within the resistor string. It functions as a coupling capacitor to give to the connection point Nout.

[0038] The DZA conversion circuit 210 in the controller 200, the DCZDC converter 300, the first and second resistance elements Rl and R2, and the capacitor C1 constitute a common electrode drive unit, and the first resistance The connection point between the element R1 and the second resistance element R2 (hereinafter referred to as “output point” t) is applied to the common electrode Ec of the liquid crystal panel 100 as the counter voltage Vcom.

[0039] The source driver 120 is connected to each source line Ls in the liquid crystal panel 100. In order to display an image on the liquid crystal panel 100, a data signal to be applied to each source line Ls is generated based on the drive control signal Ssdv from the controller 200. The gate driver 130 is connected to each gate line Lg in the liquid crystal panel 100, and generates a scanning signal to be applied to each gate line Lg. The gate driver 130 displays an image by applying a scanning signal to each gate line Lg in order to write a data signal applied from the source driver 120 to each source line Ls to each pixel forming portion (pixel capacitance Cp). In each frame period (each vertical scanning period), the gate line Lg in the liquid crystal panel 100 is sequentially selected by approximately one horizontal period. In this embodiment, the source driver 120 and the gate driver 130 are mounted on the TFT substrate 102. However, the present invention is not limited to this mounting mode. For example, the source driver 120 and the TFT substrate 102 are connected via a flexible substrate. The upper wiring (source line or the like) may be connected. Further, a so-called driver monolithic liquid crystal display device or a partial driver monolithic liquid crystal display device in which one or both of the source driver 120 and the gate driver 130 are integrally formed with a pixel circuit on a glass substrate may be used.

In the present embodiment, since the line inversion driving method is adopted as described above, the polarity of the data signal applied to each source line Ls from the source driver 120 (as the potential of the common electrode Ec) The polarity of the counter voltage (Vcom) is reversed every horizontal period. Further, in the present embodiment, the value of the counter voltage Vcom output from the common electrode driving unit configured as described above that performs counter AC driving is set so that the amplitude of the data signal is reduced. Interlocking with the polarity inversion of the data signal, it switches between two predetermined voltage values every horizontal period (details will be described later).

[0041] <1. 2 Configuration and operation of common electrode drive unit>

FIG. 3 is a block diagram functionally showing the configuration of the common electrode driving unit in the present embodiment. Functionally, the common electrode drive unit 410 in the present embodiment functionally includes the bias voltage generation circuit 11, the rectangular wave voltage generation circuit 13, and the bias voltage control unit 15, which are connected as described above. It consists of two resistive elements Rl, R2 and a capacitor C1, and is configured as a CC bias circuit. In the following, the symbol “C1” also represents the capacitance value of the capacitor C1, and the symbols “R1” and “R2” respectively represent the resistance values of the first and second resistance elements Rl and R2. It shall represent.

Here, the bias voltage generation circuit 11 is realized as the above-described DZA conversion circuit 210 in the controller 200. FIG. 4 is a circuit diagram showing a configuration example of the DZA conversion circuit 210. The DZA conversion circuit 210 according to this configuration example includes a resistor string composed of five resistor elements Ral to Ra5 connected in series, a ground voltage and a voltage Vref of a predetermined reference power supply (hereinafter referred to as “reference voltage Vref”). Switching switches SW1 to SW4 that can be selected between these switching switches SW1 to SW4 and each of the two resistance elements Raj, Raj + 1 (j = 1, 2, 3, 4) The resistor elements Rbl to Rb4, the voltage setting register 21, and the voltage hollow 23 are connected to each other, and both ends of the resistor string are grounded, and the connection point between the resistor elements Ra4 and Ra5 is The voltage holo 23 is connected to the non-inverting input terminal of the operational amplifier. The switching switches SW1 to SW4 are controlled by data Dba as a voltage setting value written in the voltage setting register 21. The data Dba is written to the voltage setting register 21 based on the function of the controller 200. The part of the controller 200 that writes the data Dba to the voltage setting register 21 is The bias voltage control unit 15 is configured.

[0043] According to the above configuration, when the bias voltage control unit 15 realized in the controller 200 writes the data Dba (voltage setting value) to the voltage setting register 21, the voltage corresponding to the voltage setting register 21 is changed to the voltage hologram. It is input to 23, converted to voltage and impedance, and output as a bias voltage Vba. In this manner, by writing the data Dba as a digital value in the voltage setting register 21, an analog voltage corresponding to the data Dba can be output as the bias voltage Vba.

The rectangular wave voltage generation circuit 13 generates a rectangular wave voltage Vpp having the same amplitude, period and phase as the counter voltage Vcom to be applied to the common electrode Ec. In the present embodiment, the counter voltage Vcom to be applied to the common electrode Ec is 1 between a predetermined high voltage value and a low voltage value in conjunction with the polarity inversion of the data signal applied to each source line Ls. This is a voltage whose value changes every horizontal period (1H). Here, when the difference between the high voltage value and the low voltage value, that is, the amplitude is Va, the rectangular wave voltage Vpp is a rectangular wave (pulse waveform with a duty ratio of 1Z2) as shown in Fig. 5 (A). Voltage. Such a rectangular wave voltage Vpp is output via the coupling capacitor C1. Force point (connection point between the first resistance element Rl and the second resistance element R2) is given to Nout. Here, the capacitance value of the coupling capacitor C1 and the resistance values of the first and second resistance elements Rl and R2 are determined by the time constant (C1 X R1 -R2 / (Rl + R2)) is a rectangular wave voltage Vpp Is set to be sufficiently larger than one horizontal period (1H) corresponding to the pulse width (1Z2 of the pulse repetition period) (see Fig. 7). Therefore, the rectangular wave voltage Vpp is applied to the output point Nout after the DC component is cut off by the coupling capacitor C1, and the output point Nout has the same amplitude, phase, and cycle as the rectangular wave voltage Vpp. A rectangular wave voltage in which the component, that is, the center voltage (average value of the maximum value and the minimum value of the rectangular wave) is changed, is obtained as the counter voltage Vcom. The center voltage Vc of the counter voltage Vcom is given by the following equation based on the bias voltage Vba and the resistance values of the first and second resistance elements R 1 and R2.

Vc = {R2 / (R1 + R2)} X Vba

Incidentally, for example, in a liquid crystal display device capable of both reflective display and transmissive display, it may be necessary to switch the counter voltage Vcom as in the case of switching to the reflective display mode force transmissive display mode. When a CC noise circuit is employed as the common electrode drive unit as in the present embodiment, it is possible to switch to a counter voltage Vcom having a different DC component, that is, a center voltage Vc, by changing the noise voltage Vba. In this embodiment, in this case, the bias voltage Vba is controlled so that the change in the noise voltage Vba becomes transiently (temporarily) larger than the change necessary to change the center voltage Vc to the value after switching. Is done. That is, the bias voltage Vba is controlled so that the change in the noise voltage Vba for changing the center voltage Vc to the value after switching is transiently (temporarily) expanded.

[0046] For example, when the counter voltage Vcom is switched so that the center voltage Vc is changed from the first center voltage value Vcl to the second center voltage value Vc2, and Vcl> Vc2, The bias voltage Vba is controlled so that the center voltage target value Vt obtained changes as shown by the one-dot chain line in FIG.

Vt = {R2 / (Rl + R2)} X Vba…

That is, the value of the noise voltage Vba is changed as follows.

First, at the switching start time tl of the counter voltage Vcom, the center voltage value after the change is The bias voltage Vba is changed so that the center voltage Vc changes toward the third center voltage value Vc3 smaller than the center voltage value Vc2 of 2. That is, from the above equation (1), the bias voltage Vba is

Vba3 = {(Rl + R2) / R2} X Vc3 · '· (2)

Changed to Specifically, the bias voltage control unit 15 writes the voltage setting value Dba3 corresponding to the bias voltage Vba3 given by the above equation (2) into the voltage setting register 21 in the DZA conversion circuit 210. This means that the center voltage target value Vt is changed from the first center voltage value Vcl to the third center voltage value Vc3.

[0048] After that, at a time point t2 when a predetermined time has elapsed, the bias voltage Vba is changed so that the center voltage Vc is directed to the second center voltage value Vc2. That is, the voltage setting value Dba2 corresponding to the bias voltage value Vba2 given by the following equation is written in the voltage setting register 21 of the noise voltage control unit 15 DZA conversion circuit 210. This means that the center voltage target value Vt is changed from the third center voltage value Vc3 to the second center voltage value Vc2.

Vba2 = {(Rl + R2) / R2} X Vc2 · '· (3)

[0049] By changing the bias voltage Vba for determining the center voltage Vc as described above, the counter voltage Vcom changes as indicated by a solid line in FIG. That is, the counter voltage V com is switched every horizontal period (1H) between the first high voltage value VHil and the first low voltage value VLol in the period before the switching start time tl. It is a rectangular wave voltage, and the voltage value switches between the second high voltage value VHi2 and the second low voltage value VLo2 every horizontal period (1H) at a predetermined time near the time t2 after the time t2. It becomes a square wave voltage. However,

Va = VHil -VLol = VHi2-VLo2 '(4)

Vcl = (VHil + VLol) / 2 '' (5)

Vc2 = (VHi2 + VLo2) / 2

It is.

[0050] For convenience of explanation (in order to make the rectangular wave easier to see), in Fig. 5 (Α) and Fig. 5 (Β), the period (or pulse width) of the pulse waveform indicating the rectangular wave voltage Vpp and the counter voltage Vcom is shown. The period of the actual pulse waveform is much longer than the switching period. This is a short period (see Figure 9 (C)).

In the present embodiment, as described above, the change of the center voltage target value Vt for switching the counter voltage Vcom is transiently expanded, that is, the bias voltage Vba is a direct current of the counter voltage Vcom. The bias voltage Vba is changed so that it changes transiently and larger than the change necessary to change the center voltage Vc as a component (the value of the bias voltage Vba is Vba3 only during the period up to t2). Be controlled. As a result, the time required for switching the counter voltage Vcom (switching period) can be shortened compared to the conventional case. This point will be described below with reference to FIG.

[0052] As shown by the one-dot chain line in FIG. 6, the bias voltage Vba changes to the first bias voltage value Vbal force to the third bias voltage value Vba3 (formula (2)) at time tl, and at time t2. The third bias voltage value Vba3 changes to the second negative voltage value Vba2 (Equation (3)) (hereinafter, the change of the bias voltage Vba is expressed as “Vbal → Vba3 → Vba2”). When the value of the noise voltage Vba changes in this way from Vbal → Vba3 → Vba2, the high voltage value VHi that is the maximum value in each cycle of the counter voltage Vcom as a rectangular wave voltage is as shown by the solid line in FIG. Change. That is, the high voltage value VHi is substantially equal to the changed high voltage value (second high voltage value) VHi2 at the time ta in the vicinity of the time t2 after the time t2 (the changed high voltage value VHi2 The length of the switching period is Tl = ta-tl. In contrast, when the value of the bias voltage Vba is changed from the first Roh Iasu voltage value Vbal to the second bias voltage value _V ba2 (the conventional case) at the time tl, the high voltage VHi, the In FIG. 6, it changes as indicated by the dotted line with the symbol “VHi (Vbal → Vba2)”, and at the time tb when a considerable amount of time has elapsed from the time t2, the changed high voltage value (second (High voltage value) VH12 is approximately equal, and the length of the switching period is T2 = tb 1 (Tl << T 2). In FIG. 6, the dotted line with the symbol “VHi (Vbal → Vba3)” indicates that the value of the bias voltage Vba changes from the first bias voltage value Vbal to the third bias voltage value Vba3 at time tl. After that, the high voltage value when the third noise voltage value Vba3 is maintained is shown.

Thus, according to this embodiment, when the common electrode Ec is driven using the CC bias circuit, switching of the counter voltage Vcom (change of the center voltage Vc as a DC component) is performed. Further, the time required for the switching, that is, the switching period can be greatly shortened. Here, how much the switching period can be shortened depends on the third noise voltage value Vba3 and the time from time tl to time t2. That is, the force that transiently expands the change in the bias voltage Vba compared to the change necessary to change the center voltage Vc of the counter voltage Vcom and the change in the noisy voltage Vba to the center voltage Vc. Depends on how long it takes to expand beyond the change needed to make the change. These specific values are determined based on simulations and experiments. In general, the transient change of the bias voltage Vba (change from Vbal to Vba3 above) for changing the DC component (center voltage Vc) at the counter voltage Vcom is increased as much as possible. It is preferable that the time point t2 of this time be close to the time point tl.

[0054] In the above description, the counter voltage Vcom is switched so that the center voltage Vc is low.

(When Vcl> Vc2, VHil> VHi2, VLol> VLo2)! /, Explained (see Fig. 5 (B), Fig. 6), switch the counter voltage Vcom so that its center voltage Vc is higher (Vcl <Vc2, VHil <Hi2, VLol <VLo2) [But, even in the controller 200 [In this case, the bias voltage control unit 15 sets the data Dba to the voltage setting register 21 to oppose The change in the bias voltage Vba due to the change in the DC component (center voltage Vc) at the voltage Vcom is expanded transiently. That is, in this case, the bias voltage Vba is controlled from the time point tl to the time point t2 so that the center voltage Vc changes toward a value Vc4 that is larger than the center voltage value Vc2 after switching, and the time point t2 Thereafter, the bias voltage Vba is controlled so that the center voltage Vc changes toward the center voltage value Vc2 after switching. This means that the center voltage target value Vt is also changed to Vc4 (> Vc2) at time tl and Vc4 is also changed to Vc2 at time t2. Thus, according to the present embodiment, the switching period can be shortened even when the counter voltage Vcom is switched so that the center voltage Vc becomes high.

[0055] <1. 3 Common electrode driver simulation>

As described above, according to the present embodiment, the bias voltage Vba is controlled so that the change in the bias voltage Vba for switching the counter voltage Vcom (the center voltage Vc) is transiently expanded, and thus the switching period is changed. Is shortened. The inventor of the present application uses this In order to confirm the effect of shortening the switching period as described above, the operation of the common electrode driver 410 was simulated by numerical calculation. Hereinafter, this simulation will be described with reference to FIGS.

FIG. 7 is a circuit diagram showing a circuit model used for simulation of the CC bias circuit as the common electrode driving unit 410 in the liquid crystal display device. In this circuit model, the common electrode driver controls the power supply corresponding to the rectangular wave voltage generation circuit 13 (hereinafter referred to as “rectangular wave voltage source” V) and the voltage value corresponding to the bias voltage generation circuit 11. A possible DC voltage source (hereinafter referred to as “variable voltage source”) E2 and a 180 kΩ resistance element corresponding to the first resistance element R1 (also referred to as “first resistance element”) ) Rls, 120 kΩ resistance element corresponding to the second resistance element R2 (also referred to as “second resistance element”) R2s, and a capacitor Cls corresponding to the coupling capacitor C1 . One end of the first resistance element Rls is connected to the positive electrode of the variable voltage source E2, and the other end of the first resistance element R1 is connected to one end of the second resistance element R2s. The other end is grounded, and the output terminal of the rectangular wave voltage source E1 is connected to an output point Nout, which is a connection point between the first resistance element Rls and the second resistance element R2, via the capacitor Cls. The negative electrode of variable voltage source E2 is grounded.

FIG. 8A shows a change in the first example of the bias voltage Vba applied from the variable voltage source E2 to one end of the first resistance element Rls in the above simulation (corresponding to the change in the bias voltage Vba in this embodiment). 8 (B) shows the change in the second example of the noise voltage V ba given to one end of the first resistance element Rls from the variable voltage source E2 in the above simulation (conventional bias). FIG. 6 is a voltage waveform diagram showing a change in voltage Vba). In the first example, the bias voltage Vba is 4 V at the start of the simulation (hereinafter simply referred to as “start time”), and changes from 4 V to −12 V when 0.03 seconds have elapsed from the start time. When 0.04 seconds have elapsed from the start, it changes from 12V to 0V, and then remains at 0V. On the other hand, in the second example, the bias voltage Vba is 4V at the start time, and when 0.03 seconds have elapsed from the start time, the 4V force also changes to 0V, and thereafter is maintained at 0V.

[0058] FIGS. 9 (A) to 9 (C) show the simulation results of the bias voltage of the first example and the second example. It is a voltage wave form diagram shown with pressure Vba. Fig. 9 (A) shows the bias voltage Vba of the first and second examples together, and Fig. 9 (B) shows the output point Nout when the bias voltage Vba of the first example is given. The waveform of the counter voltage Vcom obtained is shown by a solid line, and the waveform of the counter voltage Vcom obtained at the output point Nout when the bias voltage Vba of the second example is given is shown by a dotted line. However, the counter voltage Vcom is a rectangular wave voltage with a very short period compared to the switching period (or compared to the time constant determined by the capacitor Cls and the resistance elements Rls and R2s), as shown in FIG. 9 (C). Therefore, Fig. 9 (B) shows the change of the counter voltage Vcom between the high voltage value VHi which is the maximum value in each cycle of the counter voltage Vcom as a rectangular wave voltage and the low voltage value VLo which is the minimum value. . That is, in FIG. 9B, the change of the rectangular wave is represented by the upper envelope CHi and the lower envelope CLo of the rectangular wave indicating the counter voltage Vcom (see FIG. 9C).

[0059] As shown in FIG. 9B, according to the simulation result, when the bias voltage Vba of the first example corresponding to this embodiment is given, about 0.05 seconds have passed since the start time. At that time, the waveform of the counter voltage Vcom has settled to the waveform after switching, and the length of the switching period is about 0.02 seconds. On the other hand, when the bias voltage Vba of the second example corresponding to the conventional case is given, the waveform of the counter voltage Vcom is settled to the waveform after switching after about 0.13 seconds from the start time. The length of the period is about 0.1 second. Thus, according to the present embodiment, it can be confirmed by the above simulation that the switching period when switching the counter voltage Vcom can be significantly shortened compared to the conventional case.

[0060] <1.4 Operation of common electrode driver at start of display>

Next, the operation at the start of display of the common electrode driving unit 410 in this embodiment will be described. In general, a liquid crystal display device requires a plurality of power supplies, and most of these power supplies are activated before the display is started. However, the noise voltage generation circuit 11 that outputs the bias voltage Vba, which is a voltage related to display, is activated at the start of display. For this reason, the period until the time when the square wave voltage having the center voltage V c (DC component) determined by the display start time force counter voltage Vcom force bias voltage Vba is reached corresponds to the switching period described above. Therefore, the counter voltage Vcom is not optimal during the relevant period at the start of display (hereinafter referred to as “bias start-up period”). I can't.

However, in the present embodiment, the bias activation period as the switching period at the start of display can be shortened in the same manner as described above. That is, at the start of display, the counter voltage V com has a center voltage value Vc 1 corresponding to the optimum bias voltage value Vba 1 from a rectangular wave voltage having a center voltage Vc corresponding to the bias voltage Vba = 0. Switching to a square wave voltage is difficult. Therefore, in the present embodiment, as shown in FIG. 10A, the bias voltage Vba changes, that is, the changing voltage of the bias voltage Vba, and the center voltage Vc as the DC component of the counter voltage Vcom is changed from 0 to Vcl. The noise voltage control unit 15 writes the data Dba to the voltage setting register 21 so that it becomes transiently larger at the display start time than the change necessary for this. As a result, the bias activation period at the start of display is shortened compared to the conventional case. Specifically, the bias voltage Vba is a predetermined bias voltage value Vba 1 that gives the center voltage value Vc 1 of the optimum counter voltage Vcom from 0 at the display start time tOl, that is, a predetermined value that is larger than the original bias voltage value Vbal. The bias voltage value is changed to VbaO, and then at the time t02, the voltage value VbaO is changed to the original bias voltage value Vbal.

[0062] At the start of display, by controlling the bias voltage Vba of the common electrode driver 410 as described above, a change in the high voltage value VHi of the rectangular wave indicating the counter voltage Vcom (the upper envelope of the rectangular wave) ) Is shown as a solid line in Fig. 10 (C). On the other hand, when the bias voltage Vba is changed from 0 to the optimum bias voltage value Vbal at the display start time tOl as in the past (refer to the waveform indicated by the dotted line in FIG. 10B), the counter voltage The change in the high voltage value VHi of the rectangular wave indicating Vcom (upper envelope of the rectangular wave) is shown by the dotted line in Fig. 10 (C). FIG. 10 (C) shows that according to the present embodiment, the bias activation period at the start of display is greatly shortened compared to the conventional case.

[0063] <1.5 Effect>

In the switching period and the bias starting period, the display voltage is deteriorated because the counter voltage Vcom (the center voltage Vc) is not the original value, that is, the optimum state. When a CC bias circuit is used as the common electrode driver, power consumption can be kept low, but the switching period and bias start-up period described above are The period is relatively long depending on the time constant determined by the first and second resistance elements Rl and R2 having a large resistance value. Therefore, in the conventional common electrode driving unit using the CC bias circuit, there has been a problem of t しまう that the deterioration of display quality during the switching period and the bias starting period is perceived by humans.

However, according to the present embodiment, in the liquid crystal display device that performs counter AC driving by the common electrode driving unit (FIG. 3) using the CC bias circuit, the counter voltage Vcom (the center voltage Vc) is switched. The bias voltage is controlled so that the change in the bias voltage Vba is transiently expanded, which greatly shortens the switching period compared to the conventional method (Fig. 6). In addition, when the noise voltage Vba for generating the counter voltage Vcom is raised at the start of the display, the bias voltage Vba for raising the center voltage Vc of the counter voltage Vcom to the original center voltage value Vc 1 is set. The bias voltage Vba is controlled so that the change is expanded transiently, which significantly shortens the bias start-up period compared to the conventional method (Fig. 10 (C)). Therefore, according to the present embodiment, in the liquid crystal display device that performs counter AC driving, the switching of the counter voltage Vcom (switching of the center voltage Vc) and the power consumption for driving the common electrode are kept low. It is possible to suppress the deterioration of display quality when the bias voltage is raised at the start of display.

[0065] <2. Second embodiment>

Next, a liquid crystal display device according to a second embodiment of the present invention will be described. Since this liquid crystal display device has the same overall configuration as that of the first embodiment and is as shown in FIG. 1 and FIG. 2, the same parts are denoted by the same reference numerals and detailed description thereof is omitted. To do. Further, the overall operation of the liquid crystal display device is the same as that of the first embodiment, and thus the description thereof is omitted. Below, it demonstrates centering around the structure and operation | movement of a common electrode drive part in this embodiment. In the following description, the same reference numerals are assigned to the same constituent elements as those in the first embodiment among the constituent elements of the common electrode driving unit in the present embodiment.

FIG. 11 is a block diagram functionally showing the configuration of the common electrode driving unit in the present embodiment. As in the first embodiment, the common electrode driver 420 in the present embodiment includes a bias voltage generation circuit 11, a rectangular wave voltage generation circuit 13, and first and second resistance elements R1, R2. R2 and a capacitor CI are provided, and these components are connected in the same manner as in the first embodiment to constitute a CC bias circuit. The common electrode driving unit 420 further includes a voltage detection circuit 17 for detecting the voltage at the output point (connection point between the first resistance element R1 and the second resistance element R2) Nout, and bias control means. As an alternative, a control calculation unit 19 is provided instead of the bias voltage control unit. The control calculation unit 19 controls the bias voltage Vba by writing data Dba to the voltage setting register 21 (see FIG. 4) in the bias voltage generation circuit 11 based on the processing described later shown in FIG. This is realized based on the functions of the controller 200.

[0067] In the above configuration, the voltage detection circuit 17 detects the maximum value Vdmax and the minimum value Vdmin of the voltage at the output point Nout (this voltage is applied to the common electrode Ec as the counter voltage Vcom) and controls these. This is given to the arithmetic unit 19. Based on the maximum value Vdmax and the minimum value Vdmin, the control calculation unit 19 writes the data D ba into the voltage setting register 21 in the bias voltage generation circuit 11 according to the process shown in the flowchart of FIG. That is, the control calculation unit 19 operates as follows.

First, whether or not there is a change in the value of the center voltage Vc of the counter voltage Vcom to be generated as the voltage at the output point Nout (hereinafter referred to as “center voltage setting value Vst”), that is, (for example, the reflection display mode) In step S12, it is determined whether or not the counter voltage Vcom is to be switched. If there is no change in the center voltage set value Vst as a result of this determination, the bias voltage value Dst corresponding to the center voltage set value Vst, that is, the bias voltage value Dst for applying the center voltage Vc of the set value Vst is set to the voltage. As the set value Dba (step S26), the process proceeds to step S28.

[0069] If the result of determination in step S12 is that the center voltage set value Vst has changed, the center voltage set value Vst is updated to the changed value (step S14). Next, based on the maximum value Vdmax and the minimum value Vdmin of the voltage at the output point Nout given from the voltage detection circuit 17, the DC component of the voltage at the output point Nout is calculated as the center voltage detection value Vd by the following equation: (Step S16).

Vd = (Vdmax + Vdmin) / 2 (7)

[0070] After that, can the center voltage detection value Vd be considered practically equal to the center voltage setting value Vst? In order to check whether or not, the difference I Vt−Vd I between the center voltage setting value Vst and the center voltage detection value Vd is determined whether it is smaller than a predetermined small positive value ε (step S18). As a result of this determination, if the difference I Vt—Vd I is smaller than the positive value ε, the center voltage detection value Vd can be regarded as practically equivalent to the center voltage setting value Vst, and corresponds to the center voltage setting value Vst. The bias voltage value Dst is set to the voltage setting value Dba (step S26), and the process proceeds to step S28.

[0071] If the difference I Vt−Vd I is greater than or equal to the positive value ε as a result of the determination in step S18, it is determined whether or not the center voltage set value Vst is greater than the center voltage detection value Vd ( Step S20). As a result of this determination, if the center voltage setting value Vst is larger than the center voltage detection value Vd, the maximum value that can be set in the voltage setting register 21 (hereinafter, “maximum value that can be set”) Dmax is set. Set to the voltage setting value Dba (step S22), and proceed to step S28. On the other hand, if the result of determination in step S20 is that the center voltage setting value Vst is smaller than the center voltage detection value Vd, a predetermined value (hereinafter “setting”) is set as the minimum value that can be set in the voltage setting register 21. Minimum possible value ”) Set Dmin to the voltage setting value Dba (step S24), and proceed to step S28.

In step S28, the voltage setting value Dba determined as described above is written into the voltage setting register 21 in the bias voltage generating circuit 11. Thereafter, the process returns to step S12, and the subsequent steps are repeatedly executed.

As in the first embodiment, the noise voltage generation circuit 11 generates an analog voltage corresponding to the voltage setting value Dba, which is data written in the internal voltage setting register 21, as the bias voltage Vba. To do. This bias voltage Vba is applied to one end of the first resistance element R1, and the center voltage Vc corresponding to the DC component of the counter voltage Vcom obtained at the output point Nout is as follows based on this bias voltage Vba. .

Vc = {R2 / (R1 + R2)} X Vba

However, even if the bias voltage Vba is changed, the change is not immediately reflected in the center voltage Vc of the counter voltage Vcom. This is because when the CC bias circuit is used as in the present embodiment, the time constant determined by the capacitance value of the capacitor C1 and the resistance values of the first and second resistance elements is large. .

Therefore, in the present embodiment, when the counter voltage Vcom is switched by changing the center voltage Vc, as shown in FIG. 12, the control calculation unit 19 in the controller 200 The center voltage detection value Vd (this is calculated from the maximum value Vdmax and minimum value Vdmin of the output point Nout detected by the voltage detection circuit 17 is determined that the cardiac voltage set value Vst has been changed (Step SI 2). The voltage setting to be written next to the voltage setting register 21 in the bias voltage generation circuit 11 according to the difference between the counter voltage Vcom and the current center voltage Vc) and the changed center voltage setting value Vst Determine the value Dba. In other words, if the difference between the center voltage detection value Vd and the center voltage setting value Vst is a problem in practice (if it is determined No in step S18), the maximum value that can be set if Vst> Vd The value Dmax is set as the voltage setting value Dba, and if Vst is Vd, the minimum setting value Dmin is written as the voltage setting value Dba in the voltage setting register 21 (steps S20 to S24). This is because the difference between the center voltage setting value Vst corresponding to the DC component that the counter voltage Vcom after switching should have and the detected value Vd of the DC component of the voltage actually obtained as the counter voltage Vcom at the output point Nout. This means that the voltage setting value Dba is determined so that it is turned off. Since Dmax> Dst and Dmin in Dst, this means that the change in the bias voltage Vba is the change necessary to change the center voltage Vc of the counter voltage Vcom (the value of the center voltage Vc is the center voltage). This means that the voltage setting value Dba is determined so as to change more than the setting value Vst).

[0075] As described above, while there is a practical difference between the center voltage setting value Vst and the center voltage detection value Vd, the value of the center voltage Vc is changed to the center voltage setting value Vst. The maximum settable value Dmax or the minimum settable value Dmin is set according to the magnitude relationship between the center voltage setting value Vst and the center voltage detection value Vd so that the change in the bias voltage Vba It is written to the voltage setting register 21 as the value Dba. By controlling the bias voltage Vba in this way, when the center voltage detection value Vd can be regarded as practically equal to the center voltage setting value Vst (when it is determined Yes in step S18), The bias voltage value Dst corresponding to the center voltage setting value Vst is written to the voltage setting register 21 as the voltage setting value Dba.

[0076] As described above, according to the present embodiment, as in the first embodiment, the common electrode drive unit 420 using the CC bias circuit is connected to the common voltage drive unit 420! /, And the counter voltage Vcom (the center voltage Vc). The change of the bias voltage Vba for switching The switching period and the bias activation period are shortened. For this reason, in a liquid crystal display device that is driven by opposed AC, the power consumption for driving the common electrode Ec is kept low, while switching of the opposed voltage Vcom (change of the center voltage Vc) and the rise of the bias voltage at the start of display. It is possible to suppress the deterioration of display quality due to the increase. According to the present embodiment, when the center voltage detection value Vd can be regarded as practically equal to the center voltage setting value Vst, the bias voltage value Dst corresponding to the center voltage setting value Vst becomes the voltage setting value. It is written to the voltage setting register 21 as Dba. That is, feedback control is performed on the center voltage Vc of the counter voltage Vcom. For this reason, it is not necessary to determine in advance how long the change of the bias voltage value Vba is to be transiently expanded in order to shorten the switching period or the like. If there is a practical problem between the center voltage setting value Vst and the center voltage detection value Vd, the bias voltage Vba is the difference between the center voltage Vc setting value Vst and the detection value Vd. The maximum outputable value (bias voltage value corresponding to the maximum settable value Dmax) or output is possible so that the difference is canceled out and the change of the bias voltage Vba for changing the center voltage Vc is expanded Minimum value (bias voltage value corresponding to the minimum value Dmin that can be set). For this reason, it is substantially unnecessary to determine how much the change in the bias voltage value Vba is to be temporarily expanded in order to shorten the switching period.

In the present embodiment, when there is a practically problematic difference between the center voltage setting value Vst and the center voltage detection value Vd, the voltage is applied as in steps S20 to S24 above. Force that determines the set value Dba It is not limited to such a determination method. To determine the voltage set value D ba so that the change of the bias voltage value Vba for changing the center voltage Vc is expanded. Any other method may be used as long as it is a determination method. For example, the voltage setting value Dba is set so that the change of the bias voltage Vba after switching with respect to the bias voltage Vba before switching of the counter voltage Vcom is adjusted according to the difference between the center voltage setting value Vst and the center voltage detection value Vd. You can decide ヽ.

[0078] <3.Modification>

In the first and second embodiments, the negative voltage generation circuit 11 that generates the bias voltage Vba in the common electrode driving units 410 and 420 is realized as the DZA conversion circuit 210 as shown in FIG. Force bias voltage generator circuit 11 The configuration is not limited, and any configuration that can control the value of the noise voltage Vba may be used, and the configuration may be provided outside the controller 200.

[0079] In the first and second embodiments, the force described by taking the liquid crystal panel in which the pixel electrode and the common electrode are formed on different substrates as an example. These electrode structures are not limited, for example. A pixel electrode and a common electrode may be formed on the same substrate as in the IPS (In Plane Switching) method.

In the first and second embodiments, the liquid crystal display device of the line inversion driving method in which the polarity of the voltage applied to the liquid crystal is inverted for each horizontal scanning line has been described as an example. The present invention is not limited to this, and can be applied to other inversion drive type display devices in which opposed AC drive is performed. For example, the present invention can be applied to an n-line inversion driving type liquid crystal display device (n≥2) or a frame inversion driving type liquid crystal display device in which the polar force of the voltage applied to the liquid crystal is inverted for each horizontal scanning line. Furthermore, the same technique as that of the present invention can be applied to a liquid crystal display device that does not perform opposed AC drive, that is, a liquid crystal display device that performs opposed DC drive. That is, when switching the counter voltage as a DC voltage, by controlling the bias voltage so that the change in the bias voltage for switching is transiently expanded, that is, the bias voltage is necessary for switching the counter voltage. The switching period can be shortened by controlling the bias voltage so that it changes more greatly than the change. In this case, the coupling capacitor C1 in the configuration of FIG. 3 does not exist, but the connection point of the first resistance element R1 and the second resistance element R2, that is, the output point, is a liquid crystal panel as a capacitive load. A common electrode is connected.

[0081] As can be seen from the description of the first and second embodiments, the present invention is applicable regardless of whether the liquid crystal panel is driven in a line-sequential manner. For example, the present invention can be applied to a liquid crystal display device in which a plurality of data signal lines are driven in a time division manner within each horizontal period by providing a switching switch between the output terminal of the source driver and the source line of the liquid crystal panel.

[0082] As can be seen from the description of the operation at the start of display of the common electrode driving unit 410 in the first embodiment, the present invention is also effective in shortening the noise activation period at the start of display. Therefore, the present invention can be applied to a liquid crystal display device having only a single optimum counter voltage. Industrial applicability

The present invention provides a display device that displays an image by applying a voltage between a plurality of pixel electrodes and a common electrode facing the pixel electrode, and the value of the counter voltage to be applied to the common electrode is two in a predetermined cycle. This is applied to a so-called counter AC drive type display device that alternately switches between voltage values, and is suitable for a counter AC drive type liquid crystal display device in which the counter voltage is changed according to switching of the display mode or the like.

Claims

The scope of the claims

[1] A voltage is applied according to the image between a plurality of individual electrodes corresponding to unit images constituting an image to be displayed and a common electrode provided to face the plurality of individual electrodes. A display device driving circuit for displaying the image, wherein an individual electrode driving unit that applies a voltage corresponding to the image to the plurality of individual electrodes; and a counter voltage to be applied to the common electrode; A common electrode driver that alternately switches a voltage value between a predetermined high voltage value and a predetermined low voltage value at a predetermined cycle,

The common electrode driving unit includes:

With a given capacitor,

The bias control unit, when changing the DC component of the counter voltage, changes the value of the DC voltage transiently larger than the change necessary for changing the DC component.

[2] When the bias control unit changes the DC component of the counter voltage, the value of the DC voltage is changed from the change necessary for the change of the DC component only for a predetermined period immediately after the change of the DC component. 2. The driving circuit according to claim 1, wherein the driving circuit is largely changed.

[3] The bias control unit converts the DC voltage value at the start of display on the display device into the DC component that the counter voltage should have for display on the display device. The drive circuit according to claim 1, wherein the drive circuit is changed in a transitionally larger manner than the change necessary for holding.

[4] It further comprises a voltage detector for detecting the voltage at the connection point,

The bias control unit includes a set value predetermined as a value after the change of the DC component of the counter voltage and a value of the DC component of the voltage at the connection point determined based on the detection result of the voltage detector. 2. The drive circuit according to claim 1, wherein the value of the DC voltage is determined so that a difference from a certain detection value is canceled out.

[5] The bias control unit includes:

5. The drive circuit according to claim 4, wherein when the difference is equal to or less than the allowable value, the set value is determined as a value of the DC voltage.

[6] A voltage is applied according to the image between a plurality of individual electrodes corresponding to unit images constituting an image to be displayed and a common electrode provided to face the plurality of individual electrodes. A display device driving circuit for displaying the image, wherein an individual electrode driving unit that applies a voltage corresponding to the image to the plurality of individual electrodes; and a counter voltage to be applied to the common electrode; A common electrode driver that alternately switches a voltage value between a predetermined high voltage value and a predetermined low voltage value at a predetermined cycle,

The common electrode driving unit includes:

When changing the direct current component of the counter voltage, the drive circuit is characterized in that the value of the direct current voltage is changed transiently larger than the change necessary for changing the direct current component.

[7] A display device comprising the drive circuit according to any one of [1] to [6].

[8] A voltage is applied according to the image between a plurality of individual electrodes respectively corresponding to unit images constituting an image to be displayed and a common electrode provided to face the plurality of individual electrodes. A display device driving method for displaying the image by:

The common electrode driving step includes:

An output step of applying the voltage at the connection point to the common electrode as the counter voltage, and when changing the DC component of the counter voltage, the value of the DC voltage is more transient than the change necessary for the change of the DC component. And a bias control step for greatly changing the driving method.

[9] In the bias control unit step, at the start of display on the display device, the DC voltage changes the DC component that the counter voltage should have for display on the display device to the voltage at the connection point. 9. The driving method according to claim 8, wherein the driving method changes transiently and greatly than the change necessary for holding.

[10] The method further comprises a detection step of detecting a voltage at the connection point,

In the bias control step, a setting value predetermined as a value after the change of the DC component of the counter voltage and a value of the DC component of the voltage at the connection point determined based on the detection result in the detection step 9. The driving method according to claim 8, wherein the value of the DC voltage is determined so that a difference from the detected value is cancelled.