JPH09113873A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high definition display by the disolving of display unevenness and to simplify a scanning driver circuit. SOLUTION: A liquid crystal display element 6 provided with plural lines of scanning electrodes 1 and plural lines of signal clectrodes 2 and in which liquid crystal is held by allowing these electrodes to be confronted is driven by a scanning driver circuit 7 and a signal driver circuit 8. A liquid crystal driving voltage generating circuit 9 supplying plural DC potentials to these drivers 7, 8 generates six potentials Y0, V1, Y2, V3, V4, V5 in the order of increasing potentials. The selection voltage and the non-selection voltage of the outputs of the scanning driver 7 are constituted of two potentials of the potential V1 and the potential V4. Outputs of the signal driver 8 are constituted of the selection voltage and four potentials of non-selection voltages V0, V2, V3, V5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a scan driver for supplying a driving voltage to a liquid crystal display element and a signal driver.

[0002]

2. Description of the Related Art A liquid crystal display device has features such as thinness, light weight, and low power consumption. Therefore, it is used as a display device of a device suitable for the liquid crystal display device, and a high-definition, high-quality display is provided in a TV or a computer. Is required.
In response to such a demand, in recent years, the number of pixels of a simple matrix type liquid crystal display element represented by an STN (Super Twisted Nematic) type liquid crystal display element (the number of scanning electrodes x
The number of signal electrodes) has increased remarkably.

Along with this, the driving frequency of the liquid crystal display element (frequency of driving voltage pulse) is also increasing. For example, the scanning time (minimum pulse width) for one scan electrode of a liquid crystal display device with 240 scan electrodes and 640 signal electrodes is 60 to 70 μs.
It is short to the extent.

Generally, an equivalent circuit of a liquid crystal display element can be represented as a capacitor C (electrostatic capacity). Further, there is an output impedance in the driver IC for driving the liquid crystal display element, and this equivalent circuit can be generally represented by an electric resistance R. Since the simple matrix type liquid crystal display element is driven by a square wave pulse, distortion or dullness due to the time constant CR occurs in the drive voltage type applied to the liquid crystal display element at this time. The distortion or dullness of the driving voltage waveform causes a decrease or increase in the voltage applied to the liquid crystal layer, which results in a positional variation in light transmittance within the screen of the liquid crystal display element. This is display unevenness called crosstalk.

It can be said that the fluctuation of the liquid crystal applied voltage caused by the voltage distortion generated in the scanning electrodes is most involved in the generation of the crosstalk in the simple matrix type liquid crystal display element.

In order to solve the problem of display unevenness due to such distortion voltage, for example, as a technique for STN type liquid crystal display elements, the signal electrode driver disclosed in SID'90 Digest p.413 is used. A method of converting display data into a voltage applied to the scan electrode driver and minutely changing the voltage to cancel the voltage fluctuation at the output terminal of the scan electrode driver has been studied. However, the method of adding such a control circuit has a problem that the structure of the liquid crystal drive circuit becomes very complicated, the manufacturing cost is increased, and the circuit must be adjusted.

Further, a method of reducing the output resistance of the driver IC and the electrode resistance of the liquid crystal display element can be considered, but the size of the driver IC chip must be increased or metal electrodes must be provided on the electrodes of the liquid crystal display element. Therefore, there is a problem such as an increase in manufacturing cost.

In the conventional liquid crystal display device, the scan driver and the signal driver are connected to the scan electrode and the signal electrode of the liquid crystal display element, respectively. The voltage generated by the liquid crystal drive voltage generation circuit is supplied to the scan driver and the signal driver. In general, this circuit receives a voltage from a power source to generate a DC voltage potential required to drive a liquid crystal display element. FIG. 3 shows a general circuit. In this circuit, the input power supply voltage is divided by resistors R3 and R4, and these voltages are passed through a buffer by an operational amplifier to generate six potential DC voltage potentials (V0, V1, V2, V3, V4, V5). It has gained. Of these DC voltage potentials, V0, V1, V4, V5 are supplied to the scan driver, and V0, V2, V3, V5 are supplied to the signal driver.

FIG. 7A shows a scanning drive waveform. The selection potential V0 (voltage V5 at the time of polarity reversal for AC drive) for selection data, and the non-selection potential V4 for non-selection data.
(At the time of polarity reversal for AC driving, voltage V1) is selected and output to each scanning line.

FIG. 7 (b) shows a signal drive waveform. In the case of selected (on) data, the selected potential V5 (voltage V0 at the time of polarity inversion for AC drive) is selected, and in the case of non-selected data (off). Non-selection potential V3 (voltage V2 is selected at the time of polarity inversion for AC drive and output to each signal line. FIG. 7C shows the voltage drive waveform applied to the liquid crystal. Here, V0y, V
5y is a voltage value according to the scanning waveform.

Since the scan driver circuit used in the conventional liquid crystal display device is driven by four potentials V0, V1, V4 and V5 as shown in FIG. 6, its circuit scale is large and complicated.
The data DATA is transferred to the shift register 20, and this output and the FR signal decoder (2 to 4 decoder) 21 are input,
The four decoded signals control the four transistor switches 23 via the voltage level shift circuit 22 to obtain an output according to the truth table shown in the figure.

[0012]

As described above, in the conventional liquid crystal display device, this occurs due to the output resistance of the driver IC, the electrode resistance value of the liquid crystal display element, and the capacitance of the liquid crystal layer. There is a problem that the waveform of the voltage applied to the liquid crystal changes due to the drive waveform distortion, and display unevenness (crosstalk) occurs on the screen.

On the other hand, the known technique proposed for this has a problem that the device becomes complicated and becomes expensive.

The present invention has been made to solve such a problem, and an object thereof is to provide a liquid crystal display device,
It is an object of the present invention to provide a liquid crystal display device that solves the problem of display unevenness (crosstalk) on the screen by a simple and inexpensive means and realizes high-quality image display.

[0015]

According to the present invention, there are provided a liquid crystal display element having a plurality of scanning electrodes and a plurality of signal electrodes, and a liquid crystal sandwiching the electrodes so as to sandwich the liquid crystal, and the plurality of scanning electrodes. A scan driver for driving, a signal driver for driving the plurality of signal electrodes, a liquid crystal drive voltage generating circuit for supplying a plurality of DC potentials to the scan driver and the signal driver, and scan data for the scan driver. In the liquid crystal display device, which comprises a data generating circuit which supplies the signal data to the signal driver, the liquid crystal display device is driven by a driving waveform in which the polarity is inverted, V0, V
A liquid crystal drive voltage generating circuit for outputting six potentials of 1, V2, V3, V4, V5, and a selection voltage based on the input scan data.
V1 or the non-selection voltage V4 is output, and when the polarity is inverted, the selection driver outputs the selection voltage V4 or the non-selection voltage V1 based on the input scan data, and the input signal data to the output driver. And a signal driver that outputs a selection voltage V5 or a non-selection voltage V3 based on the signal data and outputs a selection voltage V0 or a non-selection voltage V2 based on the input signal data when the polarity is inverted. A display device is obtained.

Thus, a TN (Twisted Nematic) type liquid crystal display element, an STN (Super Twisted Nematic) type liquid crystal display element, a GH (Guest Host) type liquid crystal display element, a polymer dispersion type liquid crystal display element, a ferroelectric liquid crystal display element. It is suitable for an XY matrix type liquid crystal display device using an element or the like, and can exert a great effect in removing crosstalk caused by waveform distortion of a scanning voltage in driving thereof.

The potential output from the scan driver of the liquid crystal display device of the present invention is 2 of the 6 potentials (V0, V1, V2, V3, V4, V5) created by the liquid crystal drive voltage generating circuit. There are only two potentials (V1, V4), and this is a feature.

The scan driver outputs the selection voltage V1 or the non-selection voltage V4 based on the input data, and operates to output the selection voltage V4 or the non-selection voltage V1 at the time of polarity inversion. As described above, since the configuration is such that only two potentials are switched, the circuit configuration of the driver can be greatly simplified.
In particular, since the number of final-stage transistors in the driver circuit can be reduced to half that of the conventional one, the final-stage transistors of the scan driver of the liquid crystal display device of the present invention can be made sufficiently large. As a result, the output resistance of the scan driver of the liquid crystal display device of the present invention can be remarkably reduced, and the distortion of the scan drive waveform can be suppressed.

In such a liquid crystal display device of the present invention, since it is only necessary to reduce the number of output voltages of the scan driver of the conventional liquid crystal display device to two, it is very simple and inexpensive, and the scan electrodes on the scan electrodes are provided. The voltage waveform distortion can be reduced, and high-quality image display can be realized.

[0020]

1 to 5 show a liquid crystal display device according to an embodiment of the present invention.

As shown in FIG. 2, the scanning electrodes 1 and the signal electrodes 2 made of transparent electrodes are formed on the substrates 3 and 4 and are arranged so as to face each other in a matrix, and the gaps (cell gaps) therebetween.
A liquid crystal display element 6 in which a liquid crystal 5 is sandwiched, a scan driver 7 and a signal driver 8 connected to the electrodes 1 and 2 of the element 6 for driving, and a liquid crystal drive voltage generating circuit 9 for supplying a liquid crystal drive voltage. Have and.

As the liquid crystal display element 6, an STN type liquid crystal display element is used. The screen size is A4 size, and the display capacity (number of pixels) is 640 x 480 dots. The cell gap of this STN type liquid crystal display device is about 7 μm, and the alignment film made of polyimide subjected to rubbing alignment treatment is provided on each electrode so that the liquid crystal molecules are twisted by 240 ° in the cell of the liquid crystal display device. There is. As the liquid crystal, nematic liquid crystal having positive dielectric anisotropy (ZLI-2293 manufactured by Merck & Co., Inc.) was used. The transparent electrodes of the scan electrode 1 and the signal electrode 2 are I
It consists of TO.

In the liquid crystal display device of this embodiment, an optical phase compensation cell 11 is attached on the liquid crystal display element 6 for displaying black and white, and black display is made when no voltage is applied and white display is made when voltage is applied. I got it.

Next, the structure and drive waveform of the liquid crystal display device will be described with reference to FIG.

A scan driver 7 and a signal driver 8 each composed of an IC are connected to the scan electrode 1 and the signal electrode 2 of the liquid crystal display element 6, respectively. The voltage generated by the liquid crystal drive voltage generation circuit 9 is supplied to the scan driver 7 and the signal driver 8. In general, this circuit receives a voltage from a power source to generate a DC voltage potential required to drive a liquid crystal display element. As shown in FIG. 3, the liquid crystal drive voltage generation circuit 9 divides the input power supply voltage by resistors R3 and R4,
These voltages are passed through an operational amplifier buffer and
Two potentials DC voltage potentials (V0, V1, V2, V3, V4, V5) are obtained. Where V0>V1>V2>V3>V4> V5
It is. Of these DC voltage potentials, V1 and V4 are supplied to the scan driver, and V0, V2, V3 and V5 are supplied to the signal driver.

The output of the scan driver 7 receives the signal from the scan data generating circuit and selects and sets one of the potentials V1 and V4. Specifically, as shown in FIG. 1, the scan driver includes a shift register (polarity control) 71 for sequentially transferring scan data and a scan potential (V1, V4) or non-selection at the time of scan selection by this data. And a switch section 72 for selecting the scanning potential (V4, V1) at the time of scanning selection.

The shift register 71 receives a frame pulse which determines one frame time as scanning data, and outputs Y1 to Y by LP (latch pulse) which determines one scanning time.
Up to 240 data is transferred.

The switch unit 72 transfers these transferred data.
Based on the data, if the data is selected data, the selection potential V1 (voltage V4 at the time of polarity reversal for AC drive) is selected, and if the data is not selected, the non-selection potential V4 (polarity reversal for AC drive). Sometimes voltage V1) is selected and output to each scan line. Thus, for example, a general scan drive waveform as shown in FIG. 5A is obtained.

In the signal driver 8, the data generation circuit 10
In response to the signal from, one of the potentials V0, V2, V3 and V5 is selected and output. Specifically, as shown in FIG. 1, the signal driver uses a shift register 81 for sequentially transferring signal data, a data latch (polarity control) 82 for temporarily storing this data, and this data. A switch section 83 for selecting a signal selection potential (V0, V5) for designating ON display or a signal non-selection potential (V2, V3) for designating OFF display
Consists of The shift register 81 receives the display data DATA and receives a clock pulse CP for transferring this data.
The data is transferred from the output X1 to X640 by. Date
The data latch receives LP (latch pulse) and accumulates the data from the outputs X1 to X640. On the basis of these accumulated data, the switch unit 8 3 supplies the selection potential V5 (the voltage V0 at the time of polarity inversion for AC drive) to the unselected data (if the data is selected (on) data). If it is off, the non-selection potential V3 (voltage V2 is selected at the time of polarity reversal for AC drive and output to each signal line. Thus, for example, a signal drive waveform as shown in FIG. 5B is obtained.

In this way, the drive waveforms are applied to the scanning electrode 1 and the signal electrode 2, respectively, and the voltage waveform as shown in FIG. 5C is applied to the liquid crystal. For example, the drive is such that the polarity of the waveform is inverted every frame, and the amplitude of the selection pulse changes according to the display content (ON or OFF).

As is well known, the polarity inversion drive is a method for alternating current to avoid deterioration due to application of a DC voltage component of liquid crystal, and the polarities of the scan driver and the signal driver described above are inverted at a constant cycle. A function for performing the scanning is added, which is controlled by the FR (polarity inversion) signal from the scanning and signal data generating circuit 10.

As described above, in the liquid crystal display device according to the embodiment of the present invention, V1, V4 are scan drivers, and V0, V2, V3, V.
5 is supplied to the signal driver, and in particular, the potential output from the scan driver is only two potentials (V1, V4).

FIG. 4 shows the scan driver circuit of this embodiment. Receiving the input data DATA and FR signal, outputs V1 and V4 according to the truth table shown in the figure are obtained. The data is transferred to the shift register 71, and this output and FR signal
EX-OR is taken by the exclusive OR circuit 720, and the result is controlled by the voltage level shift circuit 721 to the two transistor switches 722. As described above, since the configuration is such that only two potentials (V1 and V4) are switched, the circuit configuration of the driver is much simpler than that of the scan driver circuit used in the conventional liquid crystal display device shown in FIG. Has become.

As described above, according to the present invention, the circuit of the scan driver 7 is extremely simplified, and in particular, the number of output transistor switches is half, which is half of the conventional one. For this reason, the size of the transistor can be made sufficiently larger than in the conventional case, and a sufficient current can be supplied to drive the liquid crystal. That is, the scanning waveform was not distorted, and the crosstalk could be reduced.

The liquid crystal display device according to the present invention as described above is driven by a duty ratio of 1/240, a bias ratio of 1/13 and a frame frequency of 80 Hz so as to invert the polarity of 13 lines. The display quality was visually verified.

First, after displaying the entire screen in white, a horizontal stripe pattern of white and black is displayed in the area of 150 dots × 10 dots in the center of the screen, and the number of dots next to this area is continuously set.
The difference was gradually increased up to 500 dots, but in any case, a uniform display without crosstalk could be maintained. In addition, Chinese characters and alphabets were displayed continuously, but the generation of strain voltage at the scan electrodes was suppressed and
It was possible to maintain a uniform display with no cracks.

On the other hand, in the conventional liquid crystal display device, crosstalk in the vertical and horizontal directions was conspicuous, and the display quality was degraded.

Since the scanning driver used for the liquid crystal display of the present invention has a greatly simplified circuit as compared with the conventional scanning driver, it can be easily manufactured and provided at low cost.

[0039]

According to the liquid crystal display device of the present invention, it is possible to eliminate the display unevenness due to the waveform rounding of the liquid crystal applied voltage, and to realize a uniform and good display without crosstalk.
Further, the scanning triber can be simply constructed.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a structure of a liquid crystal display element according to an embodiment of the present invention.

FIG. 3 is a diagram showing a liquid crystal drive voltage generating circuit used in this embodiment.

FIG. 4 is a diagram showing a scan driver circuit used in an embodiment of the present invention.

FIG. 5 is a diagram showing a liquid crystal drive waveform of the liquid crystal display device of the present invention.

FIG. 6 is a diagram showing a scan driver circuit of a conventional liquid crystal display device.

FIG. 7 is a diagram showing a liquid crystal drive waveform of a conventional liquid crystal display device.

[Explanation of symbols]

 1: Scanning electrode 2: Signal electrode 5: Liquid crystal 6: Liquid crystal display element 7: Scan driver 8: Signal driver 9: Liquid crystal drive voltage generation circuit 10: Data generation circuit

Claims (1)

[Claims] 1. A liquid crystal display element comprising a plurality of scanning electrodes and a plurality of signal electrodes, the electrodes being opposed to each other to sandwich a liquid crystal, a scan driver for driving the plurality of scanning electrodes, and the plurality of the plurality of scanning electrodes. A signal driver for driving the signal electrodes of the book, a liquid crystal drive voltage generating circuit for supplying a plurality of DC potentials to the scan driver and the signal driver, and a scan data for supplying a scan data to the scan driver. −
In the liquid crystal display device, which comprises a data generating circuit for supplying data, and in which the liquid crystal display element is driven by a driving waveform in which the polarity is inverted, six liquid crystal display devices of V0, V1, V2, V3, V4, V5 are arranged in descending order of potential. A liquid crystal drive voltage generation circuit that outputs a potential, and a selection voltage V1 based on the input scan data, or
The non-selection voltage V4 is output, and when the polarity is inverted, the selection voltage V4 or the non-selection voltage V1 is input based on the input scan data.
An output driver that outputs a selection voltage V5 based on the input signal data, or
The non-selection voltage V3 is output, and when the polarity is inverted, the selection voltage V0 or the non-selection voltage V2 is output based on the input signal data.
A liquid crystal display device comprising: a signal driver for outputting the signal.