JPH04265991A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the picture quality of a liquid crystal display element by eliminating the problem of the rounding of a driving voltage waveform applied to the liquid crystal display element at the time of polarity inversion and reducing a display irregularity. CONSTITUTION:A liquid crystal applied voltage is not inverted abruptly before or after the polarity inversion of the liquid crystal display element 1 and a voltage (S1) having a waveform which is delayed before or after the polarity inversion in synchronism with a polarity inversion signal (FR) is generated by additional voltage generating circuit 9 and added to liquid crystal driving voltages outputted from segment drivers IC 11 and a common driver IC 12 to generate a liquid crystal applied voltage (S2) before or after the polarity inversion which has a gentle waveform having a specific gradient, thereby moving charges in the liquid crystal display element before and after the polarity inversion. Consequently, the problem of the rounding of the liquid crystal applied voltage at the time of the polarity inversion can be eliminated to reduce the display irregularity and a uniform image display of high picture quality is realized.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention reduces display unevenness caused by polarity reversal, and can be used not only for general binary display but also for general binary display.
In particular, the present invention relates to a liquid crystal display device that embodies a high-quality screen display with excellent gradation expression.

0003

2. Description of the Related Art Generally, in order to prevent deterioration of the liquid crystal, the polarity of the applied driving voltage is reversed, like an alternating current voltage, in a liquid crystal display element.

However, in so-called large liquid crystal display devices, if this polarity reversal is performed every frame, display unevenness will occur depending on the display content.

It is already known that this is due to factors such as the drive frequency being different depending on the content of the display.

For this reason, in conventional liquid crystal display elements, display unevenness is reduced by performing the above-mentioned polarity reversal in a relatively short period.

For example, in a liquid crystal display element having 200×2 common electrodes and 640 segment electrodes, the polarity of the driving voltage is reversed every 13 common electrodes.

[0008]

[Problem to be Solved by the Invention] However, if the polarity reversal described above is made relatively short, the display unevenness depending on the display content is reduced, but on the other hand, the polarity reversal becomes shorter and becomes steeper in time. The delay in the voltage change inside the liquid crystal display element cannot be ignored with respect to the voltage change, and display unevenness occurs due to this influence.

[0009] Furthermore, shortening the period of polarity reversal means that
It cannot be made too short as this will lead to an increase in power consumption.

[0010] Normally, this polarity reversal is performed over all display pixels, so if the entire liquid crystal display element is considered as one capacitor, it can be assumed that a corresponding amount of charge is accumulated and discharged. Can be done.

[0011] When polarity reversal occurs, a rapid movement of charges occurs, so that a large current must be instantaneously supplied across all display pixels.

[0012] However, the driver IC for driving the liquid crystal display element, the transparent electrodes constituting the liquid crystal display element and display pixels, etc., have an output impedance that is large enough to prevent the supply of sufficient current. , the applied voltage waveform becomes rounded due to the above-mentioned steep voltage change.

For this reason, it is thought that display unevenness occurs due to the rounding of the waveform as described above.

The present invention has been made in view of the above problems.

The present invention includes an additional voltage circuit to add an additional voltage to the voltage applied to the liquid crystal, thereby changing the waveform of the voltage applied to the liquid crystal before and after polarity reversal into a gentle waveform, thereby changing the voltage applied to the liquid crystal display element. It is an object of the present invention to provide a liquid crystal display element that eliminates the problem of waveform rounding, reduces display unevenness, and realizes uniform image display.

[Configuration of the invention]

[0017]

[Means for Solving the Problems] The device of the present invention includes a matrix type liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, a common driver circuit connected to the scanning line, and a common driver circuit connected to the signal line. A segment driver circuit to be connected,
A voltage having a waveform that smoothly rises or falls before and after the polarity inversion of the polarity inversion signal is inverted, via the common driver circuit and the segment driver circuit,
The method is characterized in that it includes means for applying voltage to the matrix type liquid crystal display element.

[0018]

[Operation] When the polarity of the drive voltage of the liquid crystal display element is sharply reversed, the waveform of the voltage applied to the liquid crystal becomes rounded due to the charges accumulated in the pixels.

Therefore, in synchronization with the polarity reversal signal, an additional voltage circuit generates a waveform voltage at a predetermined time before and after the polarity reversal, and the liquid crystal drive voltage output from the common driver IC and the segment driver IC is is applied to the liquid crystal in a gentle waveform with a predetermined slope before and after the polarity reversal, and the charges in the liquid crystal display element are gradually moved before and after the polarity reversal.

[0020] This eliminates the problem of rounding of the voltage waveform applied to the liquid crystal during polarity reversal, reduces display unevenness, and realizes homogeneous, high-quality image display.

[0021]

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing the configuration of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing a polarity inversion signal.
FIG. 3 is a waveform chart showing the applied voltage, and FIG. 4 is a waveform chart showing an example of the voltage applied to the liquid crystal.

(Embodiment 1) The liquid crystal display device shown in FIG. 4 common driver ICs 12, address counter 4 and data RO
Additional voltage circuit 9 (modulation circuit) consisting of M5, D/A converter 6, amplifier 7, and variable resistor 8, and voltage dividing resistor circuit 1
0.

[0024] This STN type liquid crystal display element panel 1 has a
It has 4 sizes and a pixel count of 640 x 400 dots.

[0025] The cell thickness is approximately 7 μm, and it has a polyimide alignment layer that has been subjected to rubbing alignment treatment, and the liquid crystal molecules are aligned within the cell.
It uses an STN type liquid crystal that is twisted 240 degrees. For this liquid crystal, ZLI-2293 manufactured by Merck & Co., Ltd. was used.

The transparent electrodes of the signal line 2 and the scanning line 3 are made of ITO with a sheet resistance of 70Ω/□, and are connected to the segment driver IC 11 and the common driver IC 1, respectively.
2, and is driven in a matrix as a display pixel electrode.

The capacitance of the entire liquid crystal display element is approximately 200
nF.

Segment driver IC11 for driving liquid crystal
and common driver IC12 are Toshiba T982 respectively.
1, T9822 was used.

[0029] Of all the outputs of the segment driver IC 11 (
The (parallel) equivalent resistance value and the (parallel) equivalent resistance value of all outputs of the common driver IC 12 are each about 50Ω.

These ICs have TA on the substrate of the liquid crystal display element.
It is implemented using method B.

This liquid crystal display element 1 has a duty ratio of 1/200, a bias ratio of 1/13, and a frame frequency of 70 Hz according to a general voltage averaging method using a signal control circuit (not shown), a segment driver IC 11, a common driver IC 12, etc. is driven by.

The additional voltage circuit 9 includes an address counter 4,
It consists of a data ROM 5, a D/A converter 6, an amplifier 7, and a variable resistor 8.

This additional voltage circuit 9 generates an additional voltage (
S1) is generated.

The address counter 4 counts the input latch pulse (LP) 13 times and generates a polarity inversion signal (F
R) as well as a clock pulse (SCP)
By counting and applying this to the data ROM 5, the data written in the ROM is read out.

Data for generating the additional voltage (S1) is stored in advance in the data ROM 5, and this data is output to the D/A converter 6 in synchronization with the polarity inversion signal (FR).

Note that the data stored in the data ROM 5 is rewritable.

The D/A converter 6 and the amplifier 7 convert the data outputted from the data ROM 5 into analog and amplify them to generate an additional voltage (S1).

In this embodiment, two
An additional voltage (S1) having a crest-like waveform that fluctuates between 0V and -20V during 0μs is generated.

The waveform of this additional voltage (S1) is shown in FIG.

The variable resistor 8 is provided for adjusting the absolute value of the added voltage.

The resistance value of the voltage dividing resistor circuit 10 is set so that the bias ratio of the drive voltage is 1/13.

The voltage dividing resistor circuit 10 divides the additional voltage (S1) generated by the additional voltage circuit 9 described above, and applies the voltage to the segment driver IC 11 and the common driver I described above.
Input to C12.

The segment driver IC 11 and the common driver IC 12 receive the aforementioned divided additional voltage, polarity inversion signal (FR), image signal (DATA) and line pulse (LP) input from a signal control circuit (not shown).
), etc., a liquid crystal drive voltage (S2) is applied to the liquid crystal display element 1 in response to the input signal.

Next, the operation of this embodiment will be explained.

When the polarity is inverted, the additional voltage circuit 9 generates an additional voltage (S1) having a crest-like waveform that fluctuates between predetermined voltages for 20 μs before and after the polarity inversion.

In this embodiment, this additional voltage is set to vary between -20V and 0V.

The generated additional voltage (S1) is divided by the voltage dividing resistor circuit 10 and inputted to the segment driver IC11 and the common driver IC12.

When the divided additional voltage is input to the segment driver IC 11 and the common driver IC 12, this is added to the normal drive voltage (not shown) with polarity inversion, and the voltage applied to the liquid crystal is (S2) A waveform (hereinafter referred to as liquid crystal applied voltage) is formed.

An example of the liquid crystal applied voltage waveform formed in this manner is shown in FIG.

For example, at the time when the drive voltage waveform rises at the time of polarity reversal, the voltage applied to the liquid crystal gradually decreases with time from before that point, and reaches the minimum (approximately 0 V) at the time of polarity reversal, and after a predetermined delay time has elapsed. The waveform has a maximum value.

In this way, by applying an additional voltage with a crest-like waveform for 20 μs before and after the rise or fall of the drive voltage at the time of polarity reversal, the charges accumulated in the display pixels can be rapidly removed. instead of moving it to
Move the voltage gradually to solve the problem of rounding of the voltage waveform. As a result, display unevenness is significantly reduced.

By the way, it has been found in the present invention that the aforementioned predetermined delay time can be set to the conditions shown below.

That is, (time constant of predetermined delay time)≧(capacitance corresponding to liquid crystal display element)×(common driver I
Equivalent resistance value of all parallel outputs of C + segment driver IC
(equivalent resistance value of all outputs in parallel).

The liquid crystal display device driven in this manner had very little display unevenness depending on the displayed content and was able to display high-quality images.

Further, the apparatus of the present invention arranged as described above was inputted with a 16-gradation signal using the frame thinning method to perform display, and the gradation reproducibility was verified.

As a result, 13 gradations could be distinguished.

(Comparative Example 1) The additional voltage circuit 9 and voltage dividing resistor circuit 10 of the device of Example 1 were separated, and a drive voltage based on a general polarity inversion signal was applied to the voltage dividing resistor circuit 10. and convert it into a device with a normal drive system.

In other words, a conventional drive voltage waveform using a polarity inversion signal without adding a crest-like additional voltage waveform was used, and other conditions such as the liquid crystal display element were set to the same conditions as in Example 1. Prepare equipment using this technology.

[0059] In devices using such a normal driving method, many display irregularities depending on the display contents occur, and it is not possible to display high-quality images.

In addition, a 16-gradation signal using the frame thinning method as in Example 1 was input and displayed, and the gradation reproducibility was verified.

[0061] As a result, many display irregularities depending on the display contents occurred, and because of these display irregularities, only up to 10 gradations could be distinguished.

(Example 2) The device of Example 1 was used to perform display using the pulse width modulation method, and its gradation reproducibility was verified.

However, in this case, the image data signal system, common driver IC, segment driver IC, etc.
Changed to one compatible with pulse width modulation method. In particular, the driver ICs are Toshiba T9822 and Oki Electric MSM.
5300 is used.

Under the same conditions as in Example 1, a 16-gradation signal based on the pulse width modulation method was input to perform display.

As a result, 10 gradations could be distinguished.

(Comparative Example 2) The additional voltage circuit 9 was removed from the device of Example 2, and the voltage waveform applied to the liquid crystal was changed to a normal voltage waveform without adding the crest-like additional voltage waveform, and other liquid crystal display elements, etc. An apparatus was prepared in which the conditions were the same as in Example 2.

Then, a 16-gradation signal using the pulse width modulation method as in Example 2 described above was input and displayed, and the gradation reproducibility was verified.

[0068] As a result, many display irregularities depending on the display contents occurred, and because of these display irregularities, only up to eight gradations could be distinguished.

As described above, it has been confirmed that the device of the present invention can realize a high-quality screen display with less display unevenness and excellent gradation expression than conventional liquid crystal display devices.

[0070] In this example, S is used as the liquid crystal display element.
Although a TN type liquid crystal display element was used, the present invention is not limited to this.
(Twisted Nematic) type, GH (Guest Host) type, and PDLCD (Polymer Dispersion) type liquid crystal display elements can also be used in the same manner.

Regarding the waveform of the additional voltage, we have experimentally generated a crest-like waveform using a data ROM, a D/A converter, etc., but a circuit that realizes a similar function,
For example, a time constant circuit that combines a resistor and a capacitor can be used to make it more practical.

Further, the functions that determine the time constants of the rising and falling points are 1-exp (-t/CR) and exp
It is not necessarily limited to only (-t/CR).

A similar effect can be obtained by using a linear increasing or decreasing function with a delay as defined by this time constant, or an increasing and decreasing portion of a SIN function.

[0074]

[Effects of the Invention] As explained above, the liquid crystal display device of the present invention can significantly eliminate display unevenness depending on display content, and can display a homogeneous display screen. It is a liquid crystal display device that embodies a high-quality screen display with excellent gradation expression.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing a drive circuit of a device of the present invention.

FIG. 2 is a waveform diagram showing a polarity inversion signal of the device of the present invention.

FIG. 3 is a waveform diagram showing the applied voltage waveform of the device of the present invention.

FIG. 4 is a waveform diagram showing an example of a liquid crystal applied voltage waveform of the device of the present invention.

[Explanation of symbols]

1 Liquid crystal display element 2 Signal line 2 3 Scanning line 3 4 Address counter 5 Data ROM 6 D/A converter 7 Amplifier 8 Variable resistor 9 Additional voltage circuit 10 Voltage dividing resistor circuit 11 Segment driver IC 12 Common driver IC

Claims (1)

[Claims] 1. A matrix liquid crystal display element having a plurality of scanning lines and a plurality of signal lines, a common driver circuit connected to the scanning line, a segment driver circuit connected to the signal line, and a polarity reversal element. A liquid crystal display device comprising means for applying a voltage having a waveform that smoothly rises or falls before and after the polarity of a signal is reversed to the matrix type liquid crystal display element via the common driver circuit and the segment driver circuit. .