JPH05150747A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make a display uniform which has no crosstalk. CONSTITUTION:The driving device for a liquid crystal panel 10 has plural scanning lines and plural signal lines and a liquid crystal layer arranged between those lines. When multiplex driving is performed by inverting the polarity of a voltage impressed to the liquid crystal panel 10 to generate an AC voltage in each period wherein the scanning lines are scanned, the potential outputted from a signal line driving circuit 12 is held as high as the nonselection potential of a scanning line driving circuit 11 temporarily before the polarity of the voltage impressed to the panel is inverted and then charges accumulated in the panel are nearly eliminated; and then the polarity is inverted and the voltage having a selection potential and the nonselection potential is impressed to the panel from the signal line driving circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex drive liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display element is generally driven by an AC voltage wave type in order to prevent deterioration of liquid crystal, and a large liquid crystal display element has conventionally been operated by alternating voltage (driving voltage is changed every frame). Polarity inversion) is used. However, the occurrence of display unevenness called crosstalk depending on the display content was unavoidable. It is already known that this is due to factors such as the drive frequency being different depending on the displayed contents.

Therefore, in the conventional liquid crystal display element, it has been attempted to reduce the crosstalk by performing the polarity reversal in a relatively short period. This is to forcibly invert the drive wave type polarity every N scanning lines regardless of the display content (N line inversion method). For example, 200 scan lines
In the liquid crystal display element having 640 signal lines and 640 signal lines, for example, the polarity of the drive voltage is inverted every time 13 scanning lines are addressed.

The period of polarity inversion is relatively short, for example,
In principle, if the polarity of the driving voltage is inverted every time three scanning lines are addressed, it is difficult for crosstalk depending on the display content to occur. However, as will be described below, the influence of the occurrence of the wave-shaped dullness of the driving voltage cannot be ignored inside the liquid crystal display element, and the voltage fluctuation by this amount causes new crosstalk. In addition to this, shortening the cycle of polarity reversal naturally leads to an increase in power consumption, so the cycle cannot be shortened too much.

By the way, since a liquid crystal display device generally has a structure in which a liquid crystal layer is sandwiched between electrodes formed by scanning lines and signal lines, it can be regarded as a capacitor in terms of an equivalent circuit, and a conventional driving method. In the case of (1), the charge is always accumulated in the liquid crystal display element or the charge is moving during the driving. If the polarity of the drive voltage is reversed in such a state, the polarity is normally reversed at the same time over all display pixels, so that the charge stored in the electrostatic capacitance corresponding to the entire liquid crystal display element is moved or reversed. Happens. Therefore, a large current must be momentarily supplied to all display pixels.

Nevertheless, a driver IC, which is a drive circuit used to drive a liquid crystal display element, has input and output impedances of a magnitude that hinders supply of a sufficient current, and a liquid crystal display pixel The transparent electrodes forming the scanning lines and the signal lines that are formed have impedances equivalent to those. Therefore, on the output terminal of the driver IC or on the transparent electrode, a voltage wave type delay generated from the charge amount and polarity charged in the liquid crystal and the impedance of the driver IC and the transparent electrode, a so-called voltage wave type delay is generated. Distortion occurs. This wavy distortion causes a decrease or increase in the voltage-type effective value voltage applied to the liquid crystal layer, and as a result, the difference in light transmittance depending on the location of the liquid crystal display element,
It appears as uneven display called so-called crosstalk.

Further, the electrostatic capacity of the liquid crystal capacitor is characterized in that it changes depending on the applied voltage due to the property of liquid crystal (dielectric anisotropy). For example, regarding one scanning line of the liquid crystal display element, the larger the number of pixels showing the liquid crystal on state, the larger the capacitance of this scanning line. Here, if the driving capability (output resistance) of the scanning line driver IC that drives the scanning line is constant, the rounding of the selection potential wave type output from the scanning line driver IC depending on the content displayed on the scanning line. It will be different. The characteristic of the liquid crystal peculiar capacitor as described above increases the magnitude of the above-mentioned wavy distortion.

Conventionally, as an attempt to reduce crosstalk, a method of canceling the voltage fluctuation at the output terminal of the driver IC by changing the voltage level applied to the driver IC by a minute voltage based on the display data has been studied. (See page 413 of SID'90 Digst). This method does not focus on the state of charge at the time of polarity reversal,
This is a method of canceling out the voltage distortion that may occur in the drive electrode as needed, and the above-mentioned essential effect of reducing crosstalk cannot be obtained. Furthermore, since this method is intended to cancel the voltage distortion that is induced in the driving electrode for a very short time, it is necessary to control the compensation voltage in a very minute and precise manner. Configuration is difficult.

[0009]

As described above, it is difficult for the conventional matrix type liquid crystal display device to obtain a uniform display without crosstalk.

The present invention has been made in view of the above, and an object thereof is to improve the driving voltage applied to a liquid crystal display element to eliminate crosstalk and easily obtain a uniform display.

[0011]

According to the present invention, there is provided a liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, and a liquid crystal layer disposed between the lines, and a liquid crystal display element connected to the scanning lines. A scanning line drive circuit capable of outputting a selection potential and a non-selection potential, a signal line drive circuit connected to the signal line and capable of outputting at least a selection potential and a non-selection potential, and supplying these potentials And a power supply circuit for controlling the potential of the voltage output from the scanning line driving circuit and the voltage output from the signal line driving circuit for each scanning period of a plurality of scanning lines. In the liquid crystal display device that reverses the polarity of the voltage applied to the liquid crystal display element and converts it to alternating current to perform multiplex drive, outputs the signal line drive circuit before reversing the polarity of the voltage applied to the liquid crystal display element. Potential Once the potential is set to the same as the non-selection potential of the scanning line drive circuit, the electric charge accumulated in the liquid crystal display element is reduced or made substantially 0, and then the polarity is inverted, and then the potential output from the signal line drive circuit. Provides a liquid crystal display device characterized in that a selected potential and a non-selected potential are again applied to the liquid crystal display element.

Further, a liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, and a liquid crystal layer disposed between the lines, and a selection potential and a non-selection potential connected to the scanning lines are output. And a signal line drive circuit that is connected to the signal line and can output at least a selection potential and a non-selection potential, and a power supply circuit for supplying these potentials. And a voltage output from the scanning line driving circuit for each period of scanning a plurality of scanning lines,
In the liquid crystal display device in which the relationship of the potential with the voltage output from the signal line drive circuit is inverted to invert the polarity of the voltage applied to the liquid crystal display element to be alternating current and the multiplex drive is performed, Before inverting the polarity of the applied voltage, the selection potential output from the scanning line drive circuit is once set to the same potential as the non-selection potential of the scanning line drive circuit, and output from the signal line drive circuit. The electric potential is once set to the same potential as the non-selection electric potential of the scanning line driving circuit to reduce or almost eliminate the electric charge stored in the liquid crystal display element to reverse the polarity, and then the scanning line driving circuit and the signal line driving The liquid crystal display device is characterized in that the potential outputted from the circuit is selected again from the selection potential and the non-selection potential.

[0013]

When the polarity of the drive voltage of the liquid crystal display element is reversed, the charge accumulated in the pixel causes distortion in the liquid crystal applied voltage waveform. Therefore, according to the present invention, before the polarity reversal, the electric charge accumulated in the liquid crystal display element in advance is made substantially zero and the polarity is reversed. This state is shown in FIG. That is, when the polarity inversion signal FR is inverted, the voltage of the drive circuit is set so that the liquid crystal drive voltage v before the inversion is 0.
As a result, the electric charge stored in the liquid crystal display element becomes zero.
In this way, by performing the polarity reversal in the state where the electric charge is 0, the distortion in the voltage waveform does not occur. By the same action, it is possible to prevent the distortion of the selection voltage wave type caused by the dielectric anisotropy of the liquid crystal. In this way, the drive voltage wave type distortion that has specifically occurred at the time of polarity reversal is eliminated, crosstalk can be reduced, and uniform image display can be realized.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 The liquid crystal display device of this example is
A super twist type liquid crystal display element is used. FIG. 1 shows the configuration of this super twist type liquid crystal display device. The liquid crystal panel 10 is of A4 size and has 640 and 400 signal lines X1 to XM and scanning lines Y1 to YN, respectively.
It is a 0-dot super twist type liquid crystal display device.

The cell thickness (thickness of the liquid crystal layer) is about 7 μm, a polyimide alignment layer subjected to rubbing alignment treatment is provided, and liquid crystal molecules are twisted by 240 ° in the liquid crystal panel.
In this embodiment, in order to obtain a super twist type liquid crystal display device for monochrome display, a phase compensating liquid crystal cell was overlaid on the driving panel. As the liquid crystal, ZLI-2293 manufactured by Merck was used. The transparent electrode is made of ITO. LCD panel 1
A scan line driver IC 11 as a scan line drive circuit and a signal line driver IC 12 as a signal line drive circuit are connected to 0. The scan line driver IC (Toshiba T9822) has 100 outputs, and the signal line driver IC (Toshiba T9
821A) has 160 outputs and both are connected to the liquid crystal panel 10 by the TAB method. The liquid crystal display device of this embodiment uses four scanning line driver ICs and eight signal line driver ICs. In FIG. 1, the driver I
The liquid crystal drive voltage input to C is V for the scanning line drive circuit.
0, V1, V4, V5 and for signal line drive circuit are shown as V0 ', V2, V3, V5'. Here, the scanning line driving voltage is the selection potential V0, the selection potential V5 when the polarity is inverted, the non-selection potential V4, and the non-selection potential V1 when the polarity is inverted. Regarding the signal line driving voltage, the selection potential V5 ', the selection potential V0' when the polarity is inverted,
The non-selection potential V3 and the non-selection potential V2 when the polarity is inverted.

Scan line drive circuit 11 and signal line drive circuit 12
Is a control signal (SC
The control unit 13 supplies P, LP) and a display data signal (DATA). LP is a latch signal which gives a time for one scanning line, SCP is a pulse for transferring display data by a clock, and DATA is display data or scanning data. The driving duty ratio is 1/400 and the frame frequency is 70 Hz. In this example, a normally black transmissive display device having a fluorescent lamp on the back surface was used.

The liquid crystal drive voltages V0, V1, V2, V3, V4, V5 are obtained by dividing the liquid crystal drive voltage input Vcc by the resistors R1, R2 of the power supply circuit 14, and the relationship of each potential is V0>V1> V2. >V3>V4> V5. The bias ratio is given as R1 / (4xR1 + R2), and in this embodiment, the bias ratio was set to 1/17. A voltage follower of the operational amplifier 14a is inserted into each output for current amplification.

The liquid crystal driving voltages V0, V1, V2, V3, V4, V5
Enters the switch unit 15 and the signal line driving voltages V0 ′, V2, V
3, V5 'is made. The switch section receives the switch signal S from the timing generating section 16 and switches between the A side and the B side, that is, V0, V1, V2, V3, V4, V5 to switch the signal line driving voltages V0 ', V2. , V3, V5 'are output.

FIG. 2 shows a timing chart at this time. In the present embodiment, since the polarity of the liquid crystal drive voltage is inverted for every 13 scanning lines, the latch pulse LP for determining the address time of one scanning line in the timing generator 16.
And the polarity inversion signal S
Is getting In this embodiment, the signal line driving voltage V0 ′, for one scanning period before and after the liquid crystal driving voltage is inverted by the inversion signal FR,
By setting V2, V3, and V5 'to the non-selection potentials V1 and V4 of the scanning line drive voltage, the liquid crystal application voltage is set to approximately 0 only during this period.

By constructing the liquid crystal display device as described above, it is possible to perform polarity reversal in a state where no charge is accumulated in the liquid crystal display element.

After the liquid crystal display element is driven in this way to display the entire screen in white, first, a black block of 200 dots vertically and 10 dots horizontally is displayed near the center,
Subsequently, the number of horizontal dots was gradually increased to 500 dots, but a uniform display without crosstalk could be maintained. Also, when displaying Kanji and alphabet characters, the original effect of polarity reversal was obtained, so a display with very little crosstalk was obtained.

(Comparative Example 1) In the first embodiment, the switch signal S from the timing generating section 16 is removed from the circuit of the switch section 15, and the circuit of the switch section always outputs V0.
I set it so that V5 and V5 'are output to V0' and V5 '. That is, the liquid crystal display element was driven by the conventional driving method in which this voltage is constantly applied to the liquid crystal panel regardless of the polarity inversion.

The liquid crystal display device is driven in this way, and the entire screen is displayed in white as in the case of the first embodiment. First, a black block of 200 dots vertically and 10 dots horizontally is displayed near the center. Then, the number of horizontal dots was gradually increased to 500 dots. When a black block with 200 dots in the vertical direction and 10 dots in the horizontal direction is displayed, white crosstalk occurs more vertically than the surrounding white in the vertical direction of the block. It changed from talk to black crosstalk. Also, when displaying kanji or alphabetic characters, the original effect of polarity reversal was not obtained, resulting in a display with a lot of crosstalk.

[Second Embodiment] FIG. 3 shows the present embodiment. A super twist type liquid crystal display element panel 20 was used. The cell thickness is about 5 μm. The same reference numerals as in FIG. 1 indicate the same parts.

This super twist type liquid crystal display device is
The response speed is much faster than that of the first embodiment, which is about 60 ms. When the response speed of the liquid crystal display element is high as described above, it is necessary to further devise the circuit of the first embodiment. In the first embodiment, at the time of polarity inversion, the liquid crystal applied voltage is 0 when the output voltage of the scanning line driving circuit is the non-selection potential, but when the output voltage of the scanning line driving circuit is the selection voltage, scanning is performed for that one scanning line. A selection potential is applied. The existence of this electric charge is 1 / frame (400 scanning lines) when viewed from the entire display screen, and it has a property of almost negligible value and has no effect. However, when the response of the liquid crystal display panel is fast. This instantaneously applied scanning selection voltage appears as an optical response on the liquid crystal display panel. Then, at this moment, it is visually recognized as a white horizontal line (stripe-shaped unevenness of density) from the surroundings. Since this appears in the cycle of polarity reversal, it is seen as a flicker as a result,
It deteriorates the display quality.

Therefore, as shown in FIG. 3, a second switch section 21 is newly added to the configuration of the first embodiment. The second switch section 21 receives the switch signal S from the timing generation section 16, switches between V0, V1, V4, and V5 and outputs a scanning line driving voltage. That is, the second switch unit 2
In 1, the switch receives the switch signal S and falls to the B side for one scanning period before and after the liquid crystal drive voltage is inverted by the inversion signal FR. Therefore, the selection voltage is not output from the scanning line drive circuit.

Other than that, the operations of the switch section 15, the timing generation section 16 and the like are the same as in the first embodiment. in this way,
In this embodiment, the applied voltage to all liquid crystal panels is set to 0 for one scanning period before and after the liquid crystal drive voltage is inverted by the inversion signal FR.

By configuring the liquid crystal display device as described above, it is possible to perform polarity reversal in a state where no charge is stored in the liquid crystal display element.

After the liquid crystal display element is driven in this manner to display the entire screen in white, first, a black block of 200 dots vertically and 10 dots horizontally is displayed near the center,
Subsequently, the number of horizontal dots was gradually increased to 500 dots, but a uniform display without crosstalk could be maintained. Also, when displaying Kanji and alphabet characters, the original effect of polarity reversal was obtained, so a display with very little crosstalk was obtained.

(Comparative Example 2) In Example 2, the switch signal S from the timing generating section 16 is removed from the second switch section 21, and the circuit of the second switch section 21 always outputs V0 and V5. Moreover, the circuit of the switch unit 15 is set so that V0 and V5 are always output to V0 ′ and V5 ′. That is, the liquid crystal display element was driven by the conventional driving method in which the voltage is constantly applied to the liquid crystal panel regardless of the polarity inversion.

The liquid crystal display device was driven in this way, and the entire screen was displayed in white as in the case of Example 2. First, a black block of 200 dots vertically and 10 dots horizontally was displayed near the center, Then, the number of horizontal dots was gradually increased to 500 dots. First, when the entire screen was displayed in white, stripe-shaped light and shade unevenness appeared in a cycle of polarity reversal, and the screen flickered. Next, 200 dots vertically,
When a black block of 10 dots wide is displayed, in addition to the flicker described above, whiter crosstalk than the surrounding white occurs in the vertical direction of the block.
Subsequently, as the number of horizontal dots was increased, the white crosstalk changed to black crosstalk. Also, when displaying kanji or alphabetic characters, the original effect of polarity reversal was not obtained, resulting in a display with a lot of crosstalk.

[Third Embodiment] In the configuration of the first embodiment, when the control unit is changed to the 16-gradation display by the frame thinning method and 16-gradation display is performed, crosstalk is very small and liquid crystal display is performed. Since the panel can be displayed uniformly, it was possible to distinguish 14 gradations.

As described in the first to third embodiments, the effect can be obtained by simply adding a simple circuit to the conventionally used liquid crystal display device. However, as described below, Various functions can be incorporated in the driver IC.

FIGS. 4 (a) and 4 (b) are block diagrams of driver ICs which can be driven according to the present invention. (a) is a configuration of a signal line driver IC, in which the number of output potentials of a conventional driver circuit is increased by 2 potentials to 6 potentials. v1, V
Reference numeral 4 is a potential for making the applied voltage to the liquid crystal display element 0, and these potentials are selected by the decoder 41 based on the signals input to the input terminals S and FR. Also, V0, V2, V
As in the conventional case, the display data of 3, V5 is input to the DATA terminal and stored in the shift register 43 by the transfer clock SCP. This data is latched by the data latch 42
It is input to the decoder 41 at once by the LP signal, and V0, V2, V
3, V5 is selected. In this embodiment, the shift register 4
3 and the data latch 42 have 160 bits each, the decoder 41 has 160 circuits, and the driver 40 has 160 channels.

(B) is a structure of the scanning line driver IC, in which the S terminal is added to the conventional driver, and when the signal is input to the S terminal, the output of the driver is forcibly set to the non-selection potential. .. The display data (scan pulse) is input to the DATA terminal, and the shift register 46 is driven by the transfer clock SCP.
It is stored inside. This data is input to the AND gate, but the input to the decoder is limited by the signal of the S terminal connected to the other input of the AND gate. Decoder 4
In step 5, the output of the AND gate and the signal input to FR are received to select one of V0, V1, V4 and V5. In this embodiment, each shift register has 100 bits and AND
100 gates, 100 decoders, 4 drivers
4 made a 100-channel driver IC. In addition,
Both the driver ICs (a) and (b) are provided with enable terminals so that cascade connection of a plurality of stages is possible.

FIG. 5 shows the structure of a liquid crystal module 50 using the driver IC shown in FIG. 51 is a liquid crystal panel, 52
Is a timing circuit, and 53 is a power supply circuit. When display was performed under the same drive conditions as in Example 2 for this module, display with very little crosstalk was obtained for all display patterns.

In the embodiment described above, the period during which the voltage of the liquid crystal display element is set to approximately 0 at the time of polarity reversal is set to the scanning line 1 address time. However, from the viewpoint of taking a large effective value of the drive voltage, the liquid crystal display element is It is preferable to set the minimum time necessary for discharging the accumulated charge.

Further, in the embodiment, a square wave waveform is used as the waveform means for setting the voltage of the liquid crystal display element to 0 at the time of polarity reversal, but in the sense that charges are moved slowly,
Waveforms with a delay in rising and falling of the waveform, for example, 1-
It goes without saying that the same effect can be obtained by using e ^{-t / CR} and e ^{-t / CR} (where CR is a constant).

[0040]

As described above, the liquid crystal display device of this patent can achieve uniform display without crosstalk.

The liquid crystal display device of the present invention includes not only an ST (super twist) type liquid crystal display element but also a TN (twisted nematic) type liquid crystal display element, a GH (guest host) type liquid crystal display element, and a polymer dispersion type liquid crystal. It goes without saying that a display element (PDLCD) or the like can be used. The present invention can also be applied to an active matrix type liquid crystal display device.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a drive timing chart of an embodiment of the liquid crystal display device of the present invention.

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

FIG. 4 is a circuit diagram showing a configuration of a drive circuit of an embodiment of the liquid crystal display device of the present invention.

5 is a block diagram showing a module of a liquid crystal display device using the drive circuit of FIG.

FIG. 6 is a diagram illustrating a driving method of the liquid crystal display device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Liquid crystal panel, 11 ... Scan line drive circuit, 12 ... Signal line drive circuit, 13 ... Control part, 1
4 ... Power supply circuit, 15 ... Switch part, 16
... Timing generator

Claims (2)

[Claims] 1. A liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, and a liquid crystal layer disposed between the lines, and a selection potential and a non-selection potential connected to the scanning lines. And a signal line drive circuit that is connected to the signal line and can output at least a selection potential and a non-selection potential, and a power supply circuit for supplying these potentials. Then, the potential relationship between the voltage output from the scanning line driving circuit and the voltage output from the signal line driving circuit is inverted and applied to the liquid crystal display element for each scanning period of a plurality of scanning lines. In the liquid crystal display device that inverts the polarity of the voltage and converts the voltage to alternating current and multiplex-drives the voltage output from the signal line driving circuit before the polarity of the voltage applied to the liquid crystal display element is reversed. Drive times The electric potential accumulated in the liquid crystal display element is reduced to approximately the same potential as the non-selection potential of the path or the polarity is inverted to approximately 0, and then the potential output from the signal line drive circuit is changed to the selection potential again. A liquid crystal display device, wherein a non-selection potential is selected and applied to the liquid crystal display element. 2. A liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, and a liquid crystal layer disposed between the lines, and a selection potential and a non-selection potential connected to the scanning lines. And a signal line drive circuit that is connected to the signal line and can output at least a selection potential and a non-selection potential, and a power supply circuit for supplying these potentials. Then, the potential relationship between the voltage output from the scanning line driving circuit and the voltage output from the signal line driving circuit is inverted and applied to the liquid crystal display element for each period of scanning a plurality of scanning lines. In a liquid crystal display device in which the polarity of a voltage applied to the liquid crystal display device is inverted and converted into an alternating current, the selection potential output from the scanning line drive circuit is temporarily changed before the polarity of the voltage applied to the liquid crystal display element is inverted. The scan line The electric potential stored in the liquid crystal display element is reduced by setting the same potential as the non-selection potential of the drive circuit and the potential output from the signal line drive circuit once to the same potential as the non-selection potential of the scanning line drive circuit. Or almost 0
The liquid crystal display device is characterized in that the polarity is inverted, and then the potential output from the scanning line drive circuit and the signal line drive circuit is selected between a selection potential and a non-selection potential again.