JPH0422923A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent a liquid crystal device from being degraded in display quality due to the uneveness in the positive and negative sizes of voltages impressed on the liquid crystal by detecting voltage impressed on a pair of electrodes and correcting the voltage. CONSTITUTION:Voltage impressed between a display electrode 9 and a counter electrode 12 is detected through a filter 22 such as a low pass filter and inputted to a voltage generating circuit 23. A DC bias DELTAV' is outputted from the means 23 to a data line driving circuit 5 or the electrode 12 in accordance with the voltage drop DELTAV of a source signal. Since the value DELTAV' corresponding to each voltage impressed on a liquid crystal panel can be set up, a DC component is not impressed on the liquid crystal, flicker or the deterioration of the liquid crystal is not generated and stable display corresponding to an operation environment and driving conditions can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a liquid crystal display device using active elements such as TPT, and particularly to control of driving voltage of a liquid crystal panel.

(b) Conventional technology Conventionally, in active matrix liquid crystal display devices that use thin film transistors (TPT) made of materials such as amorphous silicon (A-5I) as driving elements, voltage drop due to the parasitic capacitance of the TPT is due to the structure. It has been pointed out that problems such as flicker occur due to the application of direct current (DC) components to liquid crystals (TV Society Technical Report 10.
N.

45, pp25-29. ED “87-5).

The following is a brief explanation of the occurrence of the above problem.

FIG. 11 is a schematic diagram of each pixel of an active matrix substrate of an active matrix liquid crystal display device.

In the figure, the gate signal from the gate line drive circuit (1) is gate! (2) and is applied to the gate (4) of TPT (3), making this TPT conductive.

On the other hand, the data signal from the data line drive circuit (5) is transmitted through the data line (6), and the drain (
7) to the source (8) and then applied to the display electrode (9).

FIG. 12 shows an equivalent circuit diagram of each pixel of such an active matrix liquid crystal display device.

In Figure 12, the gate line (2) and data line (6) are the gate (4) and drain (7) of TPT (3), respectively.
It is connected to the.

The TPT (3) has a parasitic capacitance [Cgsco (]O) between the gate (4) and the source (8), and the liquid crystal (11) has a liquid crystal capacitance [Cgsco (]O) between the display electrode (9) and the counter electrode (12). C1c
] I have (13).

If the liquid crystal capacitance (13) is small, the auxiliary capacitance [Csc]
(14) is often provided.

Both of these capacitances [CIc] and [esc] are capacitances for displaying each pixel.

The above-mentioned parasitic capacitance [Cgs] exists because the gate (4) and source (8) of the TPT are generally configured to partially overlap with each other with an insulating layer interposed therebetween.

This parasitic capacitance [Cgs] causes a voltage drop ΔV expressed by the following equation due to capacitive coupling.

ΔV=VgXCgs/(C1c+Csc+Cgs) (2) Here, Vg is the voltage amplitude value of the gate signal.

FIG. 13 is a signal waveform diagram showing the voltage drop according to the above explanation, FIG. 13(a) is a waveform diagram of a data signal that is inverted for each field, and FIG. The signal waveform diagram (c) is a DC bias diagram for the data signal.

FIG. 3(d) is a waveform diagram of a data signal that is inverted for each field, and its signal level is higher than that in FIG. 4(a).

The figure (e) is a waveform diagram of the source signal for the data signal in the figure (d), and the figure (f) is a DC waveform diagram for the data signal.
A bias diagram is shown.

In these figures, the data signal (16) is normally inverted for each field for one gate signal (15) that makes the TPT conductive, and a pair of odd and even fields are inverted. The time of the data signal is called one frame.

When the data signal (16) passes through the TPT, the source signal (
17), the median value of the data signal (16) [Vc
enter] (18) is the counter electrode signal [Vc]
When (19) is set, an undesirable DC component is added to the liquid crystal due to the display electrode connected to the source.

As shown in FIGS. 3(b) and 3(e), the voltage applied to the liquid crystal becomes asymmetric between the odd and even fields, and the optical response waveform of the liquid crystal includes an oscillating component of the driving frequency.

A method for correcting such asymmetry in the voltage applied to the liquid crystal between odd and even fields is to uniformly shift the voltage Vc of the common electrode by a voltage drop ΔV across all display electrodes with respect to the center voltage Vcenter of the data signal (DC (bias voltage) is common.

However, since the liquid crystal capacitance [C]c] in equation (2) changes depending on the magnitude of the data signal as shown in FIG.
As shown in the figure, by adding an auxiliary capacitor [Csc], the liquid crystal capacitance [
It is necessary to cover changes in the auxiliary capacitance [esc], but the addition of this auxiliary capacitance [esc] requires an electrode that overlaps with the display electrode (9), which is related to problems such as a reduction in the aperture ratio, and the required area increases. difficult to do.

Therefore, a method is required for changing the DC bias Δ■' in accordance with the voltage applied to the liquid crystal.

On the other hand, the voltage drop Δ■ due to coupling may change over time.

In this case as well, the DC bias ΔV' must be changed.

In addition to this, active matrix liquid crystal display devices also experience a drop in the effective voltage due to discharge of the source signal.
Applicability to personal information equipment, "Electronic Technology? F15 Special Issue, Volume 32, No. 7, P36 (1990) for details.

Therefore, conventionally, counter electrodes are segmented and formed separately for each row, and each counter electrode is supplied with an alternating current radiation modulation pulse that can cancel the brightness change due to fluctuations in the display electrode potential corresponding to that line within its holding period. A method for driving an active matrix liquid crystal display device has been proposed (Japanese Unexamined Patent Publication No. 2-7780), which includes a counter electrode driving means for supplying a counter electrode signal superimposed on a counter electrode signal.

FIG. 14 is an explanatory diagram of a conventional driving method for compensating for a voltage drop accompanying discharge. FIG. 14(a) is a waveform diagram of a source signal and a gate signal, and FIG. Waveform diagram: (C) of the same figure shows a waveform diagram of the voltage applied to the liquid crystal.

The source signal (17) in FIG. 14(a) has an asymmetrical waveform with respect to the median value (18) of the data signal due to the voltage drop ΔV due to parasitic capacitance and the voltage drop due to discharge.

On the other hand, as shown in the same figure (b), the counter electrode potential (
19) is superimposed with a gradually increasing pulse that is inverted for each field with the center value of the data signal as the center.

As a result, the voltage applied to the liquid crystal (20) becomes parallel to the median value (18) of the data signal at the discharge portion, as shown in FIG.

However, with this driving method, it is necessary to add a means for inverting the pulse applied to the counter electrode for each field, and setting the timing thereof is extremely difficult. Furthermore, in the case of this driving method, the DC bias of one segmented counter electrode facing a large number of display electrodes to which source signals of different magnitudes are applied is constant, and the There was a habit of applying a DC component.

As described above, the DC bias voltage ΔV' cannot be uniformly determined, and it is necessary to respond flexibly to variations in the capacitor within the liquid crystal panel.

(c) Problems to be solved by the invention However, at present, it is possible to detect light transmitted from an arbitrary point (often at the center, which is often seen by humans) of a liquid crystal display device that is driven under a certain applied voltage condition. The optimum C bias voltage ΔV° was determined from the amount of light, and the DC bias voltage ΔV° fixed to the liquid crystal display device was incorporated into the device as the final driving condition. Since a direct current component is applied to the liquid crystal, there are problems such as occurrence of flicker and deterioration of the liquid crystal.

An object of the present invention is to detect the voltage between a pair of electrodes and perform voltage correction to solve the problem of deterioration in display quality of a liquid crystal display device due to non-uniformity in the magnitude of the voltage applied to the liquid crystal in the positive and negative directions. shall be.

(d) Means for solving the problem In order to solve the above problem, instead of detecting the voltage drop ΔV under certain conditions and setting the DC bias ΔV', it is necessary to constantly detect ΔV and detect it. The result may be fed back to Δ■" and ΔV° may be set variably.

Therefore, the active matrix type liquid crystal display device of the present invention includes a detection means for detecting the voltage applied to the liquid crystal, a voltage generation means for generating an output voltage that changes according to the voltage applied to the liquid crystal detected by the detection means, and a voltage generation means for generating an output voltage that changes according to the voltage applied to the liquid crystal detected by the detection means. The liquid crystal display device is provided with voltage correction means for correcting the DC bias voltage of the counter electrode of the liquid crystal panel or the data signal according to the output voltage, and the data signal and the counter electrode are set to either a seed signal or a storage capacitance signal. This superimposes a DC bias.

(e) Effect In the liquid crystal display device having the above means, instead of driving with the conventional DC bias ΔV′ under certain conditions, it is possible to set ΔV′ according to each applied voltage in the liquid crystal panel. Therefore, since no direct current component is applied to the liquid crystal, problems such as flicker and deterioration of the liquid crystal do not occur, and stable display can be provided in accordance with the operating environment and driving conditions.

(f) Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is an equivalent circuit diagram of a liquid crystal display device according to a first embodiment of the present invention.

In FIG. 1, the voltage between the display electrode (9) and the counter electrode (12) is passed through a filter (22) such as a low-pass filter (LPF) and then detected.
), and the voltage generating means (23) outputs a DC bias Δ■'' to the data line driving circuit (5) or the counter electrode (12) according to the voltage drop ΔV of the source signal.

FIG. 2 is an equivalent circuit diagram of a liquid crystal display device according to a second embodiment of the present invention.

In FIG. 2, different DC biases ΔV' are applied to the counter electrode (12) and the auxiliary capacitance electrode (21).

More specifically, the voltage of the electrode at a certain time is shown in FIG.

In Figure 3, the display electrodes (
9) voltage is +5V, the voltage of the counter electrode (12) facing the display electrode with the liquid crystal in between is 14V, and the voltage of the counter electrode (12), which is separated every dot, is parallel to the gate line with an insulating film in between. In addition, when the voltage of the auxiliary capacitor electrode in a band-like pattern that does not overlap with the gate line (for example, see Japanese Patent Publication No. 1-55460 for details) is -3V, the display electrode (9) and the counter electrode (12)
The capacitance CI between the electrodes is determined by the dielectric constant ε1, the effective area S1, and the distance between the electrodes [
CI=clS1/di C) as dl, and the display electrode (9) and the counter electrode (12)ffJ
The quantity of electricity Q1 of J is Q1=CIV1
■It will be hailed.

In the same way, the capacitance C2 and the quantity of electricity Q2 between the display electrode (9) and the auxiliary capacitor electrode (21) are obtained, but as shown in Figure 3, the absolute value of the voltage of the auxiliary capacitor electrode is the absolute value of the voltage of the counter electrode. Even if V2<Vl, it is possible to make Q2>Ql by adjusting the capacitance C, making it possible to compensate for the discharge of the source voltage.

In addition, in an active matrix liquid crystal display device using a mixed liquid crystal exhibiting positive dielectric anisotropy, the voltage drop ΔV of the equation 0 observed between the data signal and the source signal is the data signal (
16), it was found that there is an inversely proportional relationship as shown in FIG.

In FIG. 4, when the absolute value of the data signal ranges from 1 to 3V, the voltage drop Δ■ changes from 1.3V to 0.5V.

It is also possible to write the relationship between the voltage drop ΔV and the data signal in the RAM and refer to the data signal in the line memory or field memory to intermittently correct the DC bias ΔV.

The above method is suitable for short-term use of liquid crystal display devices, and determines the DC bias ΔV° applied to each electrode during startup, and fixes the correlation between the data signal and DC bias during startup until power-off. , it is possible to configure a liquid crystal display device with lower power consumption.

Next, how to superimpose the DC bias on each electrode will be explained.

FIG. 5 shows a three-dimensional diagram of each electrode of a liquid crystal display device in which the counter electrode (12) is composed of one common electrode.

In FIG. 5, the auxiliary capacitance electrode (21) is parallel to the gate line and overlaps the display electrode, which is separated for each door, with an insulating film in between.

The DC bias ΔV' applied to each electrode in the configuration shown in FIG. 5, in which the opposing electrode is a common electrode, is shown in FIG.
) is a distribution diagram of data signal bias △V゛1 in N data lines running vertically in the liquid crystal display device, and (b) of the same figure shows the auxiliary capacitor electrode bias in M auxiliary capacitor electrodes running left and right in the liquid crystal display device. It is a distribution diagram of ΔV'2.

In Figure 6, the data lines form columns and the auxiliary capacitor electrodes form rows, so a different DC bias ΔV° is applied to each display electrode by combining the data signal bias ΔV' 1 and the auxiliary capacitor electrode bias ΔV' 2. be able to.

FIG. 7 shows a three-dimensional view of each electrode of a liquid crystal display device in which a counter electrode is divided parallel to an auxiliary capacitance electrode.

In the configuration of FIG. 7, it is not necessary to apply different signals to the auxiliary capacitance electrode (21), and different DC biases ΔV° are applied to the data lines connected to the counter electrode (12) and the display electrode (9).

FIG. 8 shows a three-dimensional view of each electrode of a liquid crystal display device in which a counter electrode (12) is divided perpendicularly to an auxiliary capacitance electrode (21).

FIG. 9 shows the DC bias ΔV° applied to each electrode in the configuration shown in FIG. 8, in which the opposing electrode is a common electrode.
, ) is a distribution diagram of the counter electrode bias ΔV'3 in the N counter electrodes running vertically in the liquid crystal display device, and the same figure (b
) is a distribution diagram of auxiliary capacitor electrode bias ΔV′ 2 in M auxiliary capacitor electrodes running left and right in the liquid crystal display device.

In Fig. 9, the counter electrodes form columns and the auxiliary capacitor electrodes form rows, so a different DC bias Δ■' can be applied to each display electrode by combining the counter electrode bias ΔV' 3 and the auxiliary capacitor electrode bias ΔV' 2. can be added.

FIG. 10 shows a circuit diagram of a red signal in which the configuration of the present invention is applied to a liquid crystal display device using a digital IC controller.

In Fig. 1O, the red signal separated by the matrix circuit (24) passes through the LPF (25), is converted by the A/D converter (26), and is sent to the line memory (27), field memory (28), and signal adjustment. (29), it becomes an analog signal divided by a D/A converter (30).

Furthermore, the red signal passes through the LPF (31), the brightness regulator (32), the switching (33), and the level shifter (33).
4) and is applied to the TPT from data line drive circuits (5) arranged above and below the liquid crystal panel (35) every other column.

On the other hand, A/D conversion! The synchronization signal from (26) is applied to the gate line drive circuit (1) and data line drive circuit (5) by the digital IC controller (36).

The voltage drop ΔV extracted from the ITPT or several TFTs of the liquid crystal panel (35) to the filter (22) is applied to the red signal as a DC bias ΔV° by the voltage generating means (23).

(g) Effects of the Invention According to the present invention, the liquid crystal can be driven with AC under conditions where no DC component is always applied, regardless of external factors such as the environment, so that problems that conventionally occur due to the DC component being applied to and leaving the liquid crystal can be avoided. A uniform, high-quality display with no flicker or the like can be obtained.

Further, since some variations in TPT and gap of the panel can be compensated for by adjusting the DC bias, it also contributes to improving the yield of liquid crystal panels.

As described above, according to the present invention, the entire area of the liquid crystal panel can always be driven under optimal conditions without being affected by external factors such as the environment, so there are no problems caused by applying a DC component to the liquid crystal, and the image quality is stable and high. A liquid crystal display device can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a DC bias automatic adjustment system according to a first embodiment of the present invention, FIG. 2 is a block diagram of a DC bias automatic adjustment system according to a second embodiment of the present invention, and FIG. 3 is a block diagram of a DC bias automatic adjustment system according to a second embodiment of the present invention. An explanatory diagram of the amount of electricity supplied to each electrode, Figure 4 is a correlation diagram between voltage drop and data signal, Figure 5 is a three-dimensional diagram of the main electrode of a liquid crystal display device with a common electrode, and Figure 6 is a diagram showing the relationship between the voltage drop and the data signal. 7 is a three-dimensional diagram of the main electrode of a liquid crystal display device having counter electrodes divided parallel to the gate line, and FIG. 8 is a waveform diagram of the main electrode of the liquid crystal display device having counter electrodes divided parallel to the data line. 9 is a waveform diagram of the liquid crystal display device of the present invention in which the counter electrode and the auxiliary capacitance electrode are orthogonal to each other, and FIG. 10 is a diagram of the liquid crystal display device of the present invention having a digital IC controller. A circuit diagram of the display device, FIG. 11 is a schematic diagram of each pixel of an active matrix substrate of an active matrix type liquid crystal display device, FIG. 12 is an equivalent circuit diagram of each pixel of an active matrix type liquid crystal display device, and FIG. 13 14 is a waveform diagram of each signal and DC bias, and FIG. 14 is a compensation waveform diagram of a conventional signal. (1)...Gate line drive circuit, (2)...Gate line, (3)...TPT, (4)...Gate, (5)...
...Data line drive circuit, (6)...Data line, (7)
...Drain, (8)...Source, (9)...
Display electrode, (10) Parasitic capacitance, (11) Liquid crystal, (12) Counter electrode, (13) Liquid crystal capacitance, (14) Auxiliary capacitance, (15 )...Gate signal, (16)...Data signal, (17)...Source signal, (18)...Median value of data signal, (19)...
...Counter electrode signal, (20) ...Liquid crystal applied voltage, (2
1)...Auxiliary capacitance electrode, (22)...Filter, (
23) Voltage generating means, (24) Matrix circuit, (25) LPF, (26) A/D
Converter, (27)...Line memory, (28)...
Field memory, (29)...Signal adjustment, (30)
...D/A converter, (31) ...LPF, (32)
...Brightness adjuster, (33)...Switching, (3
4)... Level shift, (35)... Liquid crystal panel,
(36)...Digital ICl1l controller. Cgs・
...parasitic capacitance, Clc...liquid crystal capacitance, Csc...
Auxiliary capacitance, Vg...Voltage amplitude value of gate signal, Vce
nter...median value of data signal, △V...voltage drop, Vc...counter electrode signal, ΔV°...DC bias voltage, ΔV' 1...data signal bias, ΔV
'2...Auxiliary capacitor electrode bias, ΔV'3...
- Opposing electrode bias, ε... dielectric constant, S... effective area, d... distance between electrodes, ■... voltage, Q... quantity of electricity. Applicant Sanyo Electric Co., Ltd. Agent Patent attorney Takuji Nishino (2 others) Figure 1 Figure 2 Figure 3 Ql = CIVl 2V2 Figure 4 Data signal Figure 5 Figure 6 (a) (b) 1 column 2 Column N Column 1 Row 2 Row M Row 7 Figure 8 Figure 9 (a) (b) 1 Column 2 Column N Column 1 Row 2 Row M Row 1 Figure 1 2 Figure 1 3

Claims (3)

[Claims] (1) A liquid crystal is sandwiched between an active matrix substrate in which active elements are formed at the intersection of a data line to which a data signal is supplied and a gate line to which a gate signal is supplied and a counter substrate in which a counter electrode is formed. In an active matrix type liquid crystal display device, there is a detection means for detecting a liquid crystal applied voltage, a voltage generation means for generating an output voltage that changes according to the liquid crystal applied voltage detected by the detection means, and a liquid crystal display using the output voltage of the voltage generation means. A liquid crystal display device comprising voltage correction means for correcting a DC bias voltage applied to a counter electrode of the device. (2) A liquid crystal is sandwiched between an active matrix substrate in which active elements are formed at the intersection of a data line to which a data signal is supplied and a gate line to which a gate signal is supplied and a counter substrate in which a counter electrode is formed. In an active matrix type liquid crystal display device, there is a detection means for detecting a liquid crystal applied voltage, a voltage generation means for generating an output voltage that changes according to the liquid crystal applied voltage detected by the detection means, and a liquid crystal display using the output voltage of the voltage generation means. A liquid crystal display device comprising voltage correction means for correcting a DC bias voltage of a data signal of the device. (3) An active matrix substrate in which active elements are formed at the intersection of a data line to which a data signal is supplied and a gate line to which a gate signal is supplied, and a counter substrate in which a counter electrode is formed to which a counter electrode signal is supplied. In an active matrix liquid crystal display device in which a liquid crystal is sandwiched between the electrodes, a voltage applied to the liquid crystal is detected and a DC bias voltage is superimposed on at least two of the data signal, the counter electrode signal, and the auxiliary capacitance signal. Characteristic liquid crystal display device.