JP2000010078A - Liquid crystal device driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a liquid crystal display device driving circuit simple in configuration, low in cost and capable of performing the assigning gradation display of liquid crystal by applying a digital gradation signal expressed by frequency instead of an analog gradation signal onto a data line. SOLUTION: In a liquid crystal display device having transparent electrodes which are arranged with the liquid crystal between corresponding to every pixel of the liquid crystal and a common electrode and thin film transistors which select pixels and also apply gradations on them, scanning signals Vyj for selecting pixels are applied to gates of thin film transistors in a fixed cycle and also digital gradation data V1, V2, V3, V4 for applying gradations on pixels of the liquid crystal are applied to the transparent electrodes via either one of sources or drains of the thin film transistors with a fixed amplitude and with frequencies corresponding to gradations.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device, and more particularly to a method of supplying a driving signal for displaying a gradation in an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, high-performance liquid crystal display devices have been developed for personal computers and workstations in place of conventional CRT display devices, and have come into practical use. As this type of liquid crystal display device, an active matrix type liquid crystal display device called a TFT (thin film transistor) type is predominant.

An active matrix type liquid crystal display device is
It is composed of a liquid crystal to be driven for display and two substrates opposed to each other with the liquid crystal interposed therebetween, that is, an array substrate and a counter electrode substrate. Thin film transistors called TFTs are formed in a matrix on the array substrate, and a liquid crystal display is driven by pixel electrodes formed corresponding to the TFTs.

FIG. 3 is an equivalent circuit diagram for explaining a circuit configuration of a general active matrix type liquid crystal display device.

[0005] The array substrate includes a glass substrate and a plurality of transparent pixel electrodes 1 arranged in a matrix on a glass substrate based on a thin film process technology, and one of a source and a drain connected to each of the transparent pixel electrodes 1. TFT
2 is formed.

A plurality of address lines Y 1, Y 2, Y 3... Yn which are commonly connected for each row are connected to the gate of the TFT 2. Further, a plurality of data lines X1, X2, X3,... Xm which are commonly connected to each other are connected to one of the source and the drain of the TFT2. Each transparent pixel electrode 1 is connected to a commonly connected terminal 4 via a signal storage capacitor 3.

On the other hand, the opposing common electrode substrate disposed on the opposite side across the liquid crystal is formed of a glass substrate like the array substrate, and the opposing common electrode facing the transparent pixel electrode 1 on the array substrate is disposed. Be composed.

The periphery of the array substrate and the opposing common electrode substrate are hermetically sealed so as to enclose the liquid crystal, and the liquid crystal sandwiched in a gap of several microns between the two substrates is driven for display.

When driving this active matrix type liquid crystal display device, address lines Y1, Y2, Y3.
n, the write scan signal is applied to the data lines X1, X2, X3.
Xm is supplied with a gradation display signal based on display data, and the common electrode is supplied with a predetermined common electrode drive voltage. The terminal 4 to which the signal storage capacitor 3 is connected
Is supplied with a signal having the same voltage as that of the common electrode.

FIG. 4 is a waveform diagram for explaining a conventional liquid crystal display device driving method applied to the active matrix type liquid crystal display device having the structure shown in FIG.
(A), (B), and (C) show the address lines Y1,
The write scanning signal Vy1, supplied to Y2... Yn,
Vyn are drive voltage waveforms of Vyn2, and (D) is a drive voltage waveform of the gradation display signal Vxi applied to an arbitrary data line Xi. (E) shows the pixel electrode voltage Vp stored in the transparent pixel electrode 1 and the signal storage capacitor 3, respectively. As is clear from the figure, the gradation display signal Vxi is a signal whose polarity is inverted with respect to the center voltage Vcs in each frame scanning period Tf (vertical scanning period).

As is clear from (A), (B), and (C), the scanning signal Vyj (j = 1, 2,... N) is a scanning voltage that becomes a high potential every frame scanning period Tf. is there. On the other hand, the gradation display signal Vxi (i = 1, 2,.
..M) is an analog gray scale voltage corresponding to the pixel to which the high potential scanning voltage is applied.

That is, during the high potential period of the scanning signal Vyj,
A pixel at the intersection of the address line Yj and the data line Xi has T
An analog gradation display signal Vxi corresponding to the pixel is provided via the FT 2, and this voltage is written to the transparent pixel electrode 1 and the signal storage capacitor 3. Note that in this pixel, the written potential is held while the scanning signal Vyj is at a low potential. For example, in the period T, the scanning signal Vy1 is at the high potential voltage, and the gray scale display signal Vxi is written to the corresponding pixel.
As shown in (E), even after the period T has passed and the scanning signal Vy1 has a low potential, the potential of the pixel is changed to the pixel electrode voltage based on the capacitance components of the transparent pixel electrode 1 and the signal storage capacitor 3. It is held as Vp.

As described above, the pixel electrode voltage Vp is formed for each pixel by the scanning signal Vyj and the gradation display signal Vxi given to each pixel for each frame scanning period Tf.
According to the DC drive voltage Vc applied to the opposed common electrode,
The liquid crystal is driven, and the display of the pixel is performed.

Incidentally, the potential of the DC drive voltage Vc supplied to the opposed common electrode is adjusted so that no DC voltage is applied to the liquid crystal of the pixel.

[0015]

Since the conventional liquid crystal display device driving method is configured as described above, an analog gray scale voltage is used as the gray scale display signal Vxi supplied to the data line Xi. I was Therefore, even in a system in which a digital signal is output as display data, the data line drive circuit needs to include an AD converter for converting digital display data into an analog gray scale voltage. However, the analog grayscale signal tends to contain noise, and there is a problem that an attempt to construct a high-precision circuit inevitably complicates the drive circuit and increases the cost.

The present invention solves the above-mentioned problems of the prior art, and makes it possible to perform liquid crystal gradation display by applying a digital gradation signal instead of an analog gradation signal to a data line. Accordingly, it is an object of the present invention to provide a liquid crystal display device driving method which can be realized by a low-cost driving circuit having a simple configuration.

[0017]

In order to achieve the above object, a plurality of pixel electrodes formed on a first substrate and a plurality of pixel electrodes each having one of a source and a drain connected to the pixel electrodes are provided. A first thin film transistor; a plurality of address lines in which gates of these thin film transistors are commonly connected for each row; a plurality of data lines in which one of the source and drain of the thin film transistors is commonly connected for each column; A second substrate having a counter electrode formed on the inner surface thereof and having a counter electrode formed on the inner surface thereof, wherein a square wave signal having a constant amplitude and a frequency corresponding to a display gradation is provided by the data method. A method for driving a liquid crystal display device, comprising: using a square wave signal supplied to a line, and alternatingly changing the voltage of the counter common electrode up and down as the square wave signal. It is intended to provide.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a waveform diagram for explaining a liquid crystal display device driving method according to a first embodiment of the present invention, and is applied to the active matrix type liquid crystal display device shown in FIG. In the figure, (A), (B), (C), and (D) are digital gradation data V1, V2, V3, and V4 supplied to data lines X1, X2, X3, and X4, respectively, and (E). )
Is a write scan signal Vyj supplied to an arbitrary address line Yj.

Now, the digital gradation data V1, V2,
V3 and V4 exemplify data corresponding to four gradations, and are digitally applied signals at different frequencies corresponding to desired gradations. That is, the digital gradation data V1, V2, V3, and V4 are square wave voltages having a constant amplitude, and have different frequencies. The frequency ratio is V
1: V2: V3: V4 is 8: 4: 2: 1.

A plurality of digital gradation data V1, V2,
One of V3 and V4 is selected based on display data by a selection switch circuit (not shown), and the write period T
w, that is, each time the scanning signal Vyj is at the high potential voltage VgH, is cut out and supplied to the data line Xi.

At this time, the on-resistance of the switch circuit for selecting data is set to a high value, or a series resistor is provided on the output circuit side of the switch circuit. , On the data line,
As shown in (A), (B), (C), and (D), the voltage V
Peaks of 1P, V2P, V3P, V4P and voltages V1N, V2
A triangular waveform voltage V1A having valleys of N, V3N and V4N,
V2A, V3A and V4A appear.

That is, the digital gradation data V1, V
2, V3 and V4 are converted into analog gray scale voltages using the relationship between the frequency and the AC impedance of the circuit including the data line i.

This triangular waveform voltage is written to the signal storage capacitor 3 of the pixel and the capacitance of the liquid crystal during the high potential period Tw of the scanning signal Vyj supplied to the address line Yj, and the scanning signal Vyj becomes the low potential VgL. During the period, the peak voltage V1P, V2P, V3P, V4P or the valley voltage V1N, V2N, V3N, V4N of the triangular state voltage is held and becomes the voltage of the transparent pixel electrode 1. Whether the peak or the valley is held depends on the phase of the gradation display signal Vxi when the scanning signal Vyj shifts from the high potential VgH to the low potential VgL.

The liquid crystal between the transparent common electrode 1 and the common electrode is driven by the voltage of the transparent pixel electrode 1, and gradation display is performed.

In this embodiment, the liquid crystal display device driving method corresponding to the four gradation data of digital gradation data V1, V2, V3, V4 is exemplified. However, by further increasing the number of data, It goes without saying that fine gradation expression is possible. On the other hand, by arbitrarily setting the data step, that is, the frequency step, it is needless to say that finer gradation expression such as gamma correction and gradation expression suited to the characteristics of the liquid crystal can be performed. Embodiment 2 FIG. 2 is a waveform diagram for explaining a liquid crystal display device driving method according to a second embodiment of the present invention. In particular, FIG. 2 illustrates a case of frame inversion driving in which the polarity of a voltage applied to liquid crystal is inverted for each frame. Things. In the figure,
(A), (B), and (C) show scanning signals Vy1, Vy1, respectively.
Vy2 and Vyn, and (D) shows the gradation display signal Vxi.
Are respectively shown.

As shown in the drawing, in a certain frame scanning period Tf1, the writing periods Tw14 and Tw1 defined by the high potential voltage VgH of the scanning signals Vy1, Vy2 and Vyn.
3, Tw12, digital gradation data V4, V3,..., V2 of a certain phase are applied, and the scanning signals Vy1, Vy1,.
When Vy2 and Vyn become the low potential voltage VgL, one of the triangular state voltage peak voltages V4P, V3P, V2P or the valley voltages V4N, V3N, V2N is held. Whether the peak or the valley is held depends on the phase of the gradation display signal Vxi when the scanning signal Vyj shifts from the high potential VgH to the low potential VgL.

Therefore, the next frame scanning period Tf2
Then, the high potential voltage V of the scanning signals Vy1, Vy2, Vyn
Write periods Tw24, Tw23, Tw2 defined by gH
2, the digital gradation data / V4, / V3... / V of the opposite phase to the case of the frame scanning period Tf1
2 is applied, and when the scanning signals Vy1, Vy2, and Vyn become the low potential voltage VgL, the voltage of the triangular state voltage is held. In the scanning period Tf2, it is possible to hold the voltage of the valley, which is the opposite potential. Conversely, when the voltage of the valley is held in the frame scanning period Tf1, the potential of the mountain, which is the opposite potential, is changed in the frame scanning period Tf2. It is possible to hold.

That is, by inverting the phase of the gradation display signal Vxi every frame scanning period, the voltage held as the pixel electrode voltage can be inverted every frame scanning period Tf. Driving becomes possible.

[0029]

As described above, the method of driving a liquid crystal display device according to the present invention is configured such that the gradation data applied in driving the liquid crystal is provided as digital gradation data having different frequencies. When the grayscale data is given, a circuit for converting the grayscale data into an analog grayscale signal becomes unnecessary, and a liquid crystal display device driving device with high noise resistance and low cost can be realized.

[Brief description of the drawings]

FIG. 1 is a waveform diagram for explaining a liquid crystal display device driving method according to a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining a liquid crystal display device driving method according to a second embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram for explaining a circuit configuration of a general active matrix type liquid crystal display device.

FIG. 4 is a waveform chart for explaining a conventional liquid crystal display device driving method.

[Explanation of symbols]

 1 transparent pixel electrode 2 TFT 3 signal storage capacitor 4 terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA16 NA33 NA52 NC13 NC34 NC66 ND06 ND49 ND54 5C006 AA11 AC21 AF21 BB16 BC12 FA52

Claims (2)

[Claims] A plurality of pixel electrodes formed on a first substrate, a plurality of thin film transistors having one of a source and a drain connected to the pixel electrodes, and a gate of the thin film transistors common to each row. A plurality of connected address lines, a plurality of data lines in which one of the source and the drain of the thin film transistor is commonly connected for each column, and a counter electrode formed on an inner surface of the thin film transistor facing the first substrate. A method for driving a liquid crystal display device having a second substrate provided with a counter common electrode, wherein a square wave signal having a constant amplitude and a frequency corresponding to a display gradation is supplied to the data line. Drive method. 2. The liquid crystal display device driving method according to claim 1, wherein as the square wave signal, a square wave signal that alternately changes in the vertical direction across the voltage of the counter common electrode is used.