JPS63249896A - Liquid crystal display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal display in which each picture element arranged in an X-Y matrix is driven by a switching element to display a general television signal, such as an NTSC signal, as an image. It is related to the device.

2. Description of the Related Art As an example of a conventional liquid crystal display device, a block diagram of a liquid crystal display device shown in FIG. 4 is shown and explained in conjunction with FIG. 1. In Fig. 4, 1 is a switching transistor (generally a thin film transistor made of amorphous silicon or the like, hereinafter abbreviated as TPT) that switches each picture element, 2 is a liquid crystal cell, 3 is an auxiliary capacitor, and 4 is a drain electrode of TFTl. 5 is a GND electrode that serves as a signal reference voltage, 6 is a counter electrode common to all picture elements, 7 is τFT1
A scanning electrode 8 is connected to the gate electrode of TFτ1 to operate the TFT1, a signal electrode 8 is connected to the source electrode of TFτ1 and is used to apply a signal to the picture element electrode 4, and 9 is a signal electrode for applying a constant voltage to AC drive the liquid crystal. One vertical scanning period (
A video signal input terminal that inputs a video signal whose polarity is inverted every 1v).

1o samples and holds the video signal (hereinafter referred to as S and H).

Video signal sample and hold circuit (hereinafter abbreviated as video signal 8.1. circuit) for linear drive (abbreviated as video signal 8.1. circuit), 11
is a vertical scanning circuit that drives the TFT1i of each picture element. It is assumed that the screen is composed of rows 1 to 1 and columns 1 to j.

5(a) to (0) show operating waveform diagrams of this conventional liquid crystal display device. In FIG. 6, Vs shown in (!L) is the video signal 8.1. The voltage waveform T shown in (b) is a signal applied to the signal electrode 8 with a signal having an amplitude sufficient to apply a sufficiently large effective voltage to the liquid crystal and whose polarity is inverted every vertical scanning period (1V).

is a voltage waveform of a constant voltage applied to the counter electrode e.

Vox shown in (c) is a voltage waveform applied to the picture element electrode 4 of the first row, and "foxy" shown in (d) is a voltage waveform applied to the picture element electrode 4 of the first row, which is the last row of the screen. , VDXn shown in (e) is the voltage waveform applied to the n-th picture element electrode 4, and VDXH+1 shown in (0) is the voltage waveform applied to the n+1-th picture element electrode 4, respectively.

FIGS. 6(b) to 6(15) show light transmission waveform diagrams corresponding to the operating waveform diagram of FIG. 6, and the operation of the conventional example will be described below with reference to FIGS. 6 and 6.

In the above liquid crystal display device, the counter electrode 6 shown in FIG.
A counter signal Vct of a constant voltage shown in FIG. 6(b) is always applied to the counter signal Vct shown in FIG. 6(b), and a source signal vSt shown in FIG. 60 is applied to the signal electrode 8 shown in FIG. Then, the voltage applied to the liquid crystal is reduced by a voltage corresponding to the following ΔV because the gate pulse signal leaks into the picture element electrode 4 through the overlapping capacitance between the gate and drain.

However, CGD: overlap capacitance between gate and drain.

GX, c: liquid crystal cell equivalent capacitance, Codd: auxiliary capacitance, Vg: gate voltage.

Therefore, the effective voltage corresponding to the shaded portions shown in FIGS. 5(C) to (f) is small when the source signal vs is on the ←) side, and becomes large when the source signal Vs is on the (c) side.

Unbalance occurs every vertical scanning period (1v).

By the way, in the first row of the screen, the source signal vs and the pixel electrode voltage vD! 1 has the same polarity for a long time, and the influence of τFT off-leakage, which occurs when the charge stored in the liquid crystal cell is τF and is discharged to the signal electrode through the off-resistance of τFτ when it is off, is small, and the N shown in Figure 5 (0) An effective voltage such as 'D11 is applied to the liquid crystal cell. The magnitude of the effective voltage at this time affects the light transmittance of the liquid crystal.

On the side where the effective voltage is small (←), the light transmittance is small and the effective voltage is large (on the → side, it is large, and Vfx in Figure 6 (&)
As shown in FIG. 1, so-called flicker occurs in an unbalanced light transmission waveform every vertical scanning period (1v), with one cycle being two vertical scanning periods (2v) and a frequency of 30 Hz.

Also, in the last row of one screen, the source signal VS and the pixel electrode voltage
The period in which DXi, has the same polarity is short, and most of the period has different polarity, and contrary to the case of the first line of the screen, the influence of TPT off-leak is large, and VDXi and VMj shown in FIG. 6(d). As shown in the figure, only a smaller effective voltage is applied to the liquid crystal cell than in the case of the first row of the screen. Then, as shown in Vf'xl shown in FIG. 6), an unbalanced light transmission waveform occurs every one vertical scanning period (1v), and a flicker of 30.times.2 occurs. Similarly, in the n-th line of the screen, V shown in FIG. 6 (6)
DX. The effective voltage of
An effective voltage of "n+1" shown in FIG.
5, which are unbalanced every vertical scanning period (1V) and out of phase with each other by one horizontal scanning period (1H) like +1.
otlz flicker occurs. In this way, the phase of the 7-bit waveform shifts by one horizontal scanning period (1H) row by row.

Problems to be Solved by the Invention However, with the above configuration, when looking at the entire screen, the flicker of the 3011z component generated in each row will be felt as is, and the flicker will look like Vf shown in FIG. 8(e). This causes discomfort to human eyes, and a difference occurs between the effective voltage applied to the liquid crystal at the top of the screen and the effective voltage applied to the liquid crystal at the bottom of the screen, resulting in a difference in brightness between the top and bottom of the screen, so-called uneven brightness. This has the problem that this occurs. In addition, in order to apply a sufficiently large effective voltage to the liquid crystal, as shown in Figure 6 (
5)) It is necessary to increase the amplitude of the source signal VS shown in FIG. 4, and the power supply voltage of the video signals S and H shown in FIG. Ta.

In view of the above, it is an object of the present invention to provide a liquid crystal display device that is less perceptible to flicker, reduces brightness unevenness at the top and bottom of the screen, ensures a large number of gray levels for displaying halftones of images, and has low power consumption. shall be.

Means for Solving the Problems The present invention reverses the polarity of the signal applied to the signal electrode every horizontal scanning period or every plural horizontal scanning periods, and similarly reverses the polarity of the signal applied to the counter electrode for one horizontal scanning period. This is a liquid crystal display device that applies a rectangular wave having an opposite phase to a signal applied to a signal electrode every period or every plural horizontal scanning periods.

According to the above-described structure, when the polarity of the signal applied to the signal electrode and the counter electrode is reversed every horizontal scanning period or every plural horizontal scanning periods, the flickers generated in adjacent rows are out of phase with each other by about 180 degrees. They cancel each other out, making it difficult to perceive the flicker of the 30 tlz component on the entire screen. Also, the effect of TPT off-leak is the same for any line on one screen.

Brightness unevenness at the top and bottom of the screen can be reduced. In addition to that.

By applying a rectangular wave with the opposite phase to the signal applied to the signal electrode to the opposite electrode, the amplitude of the signal applied to the signal electrode can be made smaller than before, and the power supply voltage of the signal circuit can be lowered, reducing power consumption. can be significantly reduced.

Embodiment FIG. 1 shows a block diagram of a liquid crystal display device in an embodiment of the present invention. In FIG.

1 is a TPT that switches each picture element, 2 is a liquid crystal cell,
3 is an auxiliary capacitor, 4 is a picture element electrode connected to the drain electrode of TFTl, 6 is a counter electrode common to all picture elements, and 7 is a scanning electrode connected to the gate electrode of TFTl for operating TFTI. 8 is a signal electrode connected to the source electrode of TPTl and applies a signal to the picture element electrode 4;
9 is a video signal input terminal for inputting a video signal whose polarity is inverted every vertical scanning period (1V) in order to drive the liquid crystal with AC drive, and 10 is a video signal input terminal for video signals is, H, j,
Video signal for line sequential driving8. H, circuit.

Reference numeral 11 denotes a vertical scanning circuit for driving the TFTl of each picture element, and those having the same function as the conventional one are given the same numbers. 12 is an HD signal input terminal 112 into which a signal whose polarity is inverted every horizontal scanning period (1H) is input, and 13 is a video signal S.
, H, the signal output from the circuit 1o for one horizontal scanning period (
1H signal inversion circuit that inverts the polarity every 1H), 14 is 1
A phase inversion circuit 16 inverts the phase of the signal input from the 4HD signal input terminal 12, and a 1H counter inversion circuit 16 applies a rectangular wave having an opposite phase to the signal output from the 1H signal inversion circuit 13 to the counter electrode 6. It is. Figure 2 e) to (f
) shows an operating waveform diagram of the liquid crystal display device in the embodiment of the present invention. In FIG. 2, vs shown in (a)
is the video signal S, )1. The output from circuit 1o has an amplitude sufficient to apply a sufficiently large effective voltage to the liquid crystal, and its polarity is inverted every vertical scanning period (1V), and -horizontal scanning period (1H).
) is a voltage waveform applied to the signal electrode 8 with a signal whose polarity is inverted, and VC shown in (b) is a rectangular wave having an opposite phase to vs shown in (a).

If the amplitude of this signal Vc is increased, the same effective voltage as before will be applied to the liquid crystal even if the amplitude of the source signal Vs is small. When the amplitude of VC and the maximum amplitude of VS are made the same, the power supply of the signal circuit It requires the lowest voltage. Therefore, in this embodiment, the source signal Vs and the counter signal To are set so as to have the maximum amplitude of the conventional source signal Vs.

V D The voltage waveform applied to the picture element electrode 4 of the first row is V! shown in (e). 1! H indicates the voltage waveform applied to the picture element electrode 4 in the third row, and vD!n+1 shown in (0) indicates the voltage waveform applied to the picture element electrode 4 in the (n+1)th row.

The operation of the liquid crystal display device of this embodiment configured as described above will be described below. To the opposite electrode 6 shown in FIG. 1, the polarity of which is reversed every 1H as shown in FIG. 2(b), is applied to the signal electrode 8 shown in FIG.
A source signal V5f having a polarity opposite to that of c is applied. Then, the source signal vg and the pixel electrode voltage vD repeat the same polarity and different polarity every 1H in any row of the screen.

For this reason, the charge accumulated in the liquid crystal cell becomes T when the TPT is off.
The influence of TPT off-leak discharge to the signal electrode through the PT off-resistance is the same in all rows. And in the first line of one screen, like V D X 1 shown in Figure 2 (C) ←
) side and (c) side, an unbalanced effective voltage is applied to the liquid crystal cell, and 1 as shown in vf'x1 shown in Figure 3 (IL)
Unbalanced flicker of 30 Bz component occurs every vertical scanning period (1v). The same effective voltage as in the first row of the screen is applied to the liquid crystal cell even in the last row of the screen. Also, in the nth screen, VD! shown in Figure 2 (eJ)! . As shown in FIG. The phase is about 180
°It becomes a misaligned shape.

Along with this, the flicker of the 30) 1z component that occurs in each row is also affected by the vfxn and (
The phase is shifted by about 180° as shown in vrxn+1 shown in d). For this reason, each row is shown in Figure 3 (
As shown in &) to (d), flicker of 30 Hz component occurs, but when considering a set of two lines, the flicker of 30 Hz component cancels each other out.

As described above, according to this embodiment, the amplitude of the source signal Vs applied to the signal electrode is set to the conventional range, and -horizontal scanning period (
Similarly, the polarity of the signal V applied to the counter electrode is reversed every 1H), and the maximum amplitude of the source signal Va is reversed in phase to the source signal VS applied to the signal electrode every horizontal scanning period (1H). By applying the rectangular wave, the effective voltage applied to the liquid crystal cells in any row of the screen becomes equal, and it is possible to reduce brightness unevenness between the top and bottom of the screen. And regarding flicker, when looking at the entire screen, it is 60
It is characterized by flickering of the 11z component, which is difficult for the human eye to perceive. Furthermore, the power supply voltage of the signal circuit can be suppressed, resulting in a significant reduction in power consumption.

In this embodiment, a liquid crystal display device with an auxiliary capacitor has been described, but the same effect can be obtained even with a liquid crystal display device without an auxiliary capacitor. In addition, a 1H signal inversion circuit 13 is provided on the output side of the video signal S, H circuit 1o shown in FIG.
ft connection, but the same effect can be obtained even if it is connected to the input side.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, the amplitude applied to the signal electrode can be applied to a conventional rod, the power supply voltage of the signal circuit can be significantly suppressed, and the power consumption can be significantly reduced. Also,
Luminance unevenness at the top and bottom of the screen can be reduced, and even if off-leakage of the TF field is not sufficiently small, an image with uniform brightness can be obtained on the screen, making it possible to display many intermediate tones. Moreover, it has many effects such as making it difficult to reduce flicker on the entire screen.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention, Fig. 2 is an operation waveform diagram of the same embodiment, Fig. 3 is a flicker waveform diagram of the same embodiment, and Fig. 4 is a conventional liquid crystal display device. FIG. 6 is an operation waveform diagram of the conventional example, and FIG. 6 is a flicker waveform diagram of the conventional example. 1...TFT, 2...--Liquid crystal cell, 3...
...Auxiliary capacitance, 4...Pixel electrode, 6...
...Counter electrode, 7...Scanning electrode, 8...
...Signal electrode, 9...Video signal input terminal, 1
0...Video signal sample hold circuit. 11... Vertical scanning circuit, 12...14
HD signal input terminal, 13...1H signal inversion circuit, 14...phase inversion circuit, 16...1
H counter inverting circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure -2 o-----------+ + + -1-
0−−−−−−−+ +
+ + -Figure 3Figure 4Figure 5Figure 50--1------
Figure 6

Claims (1)

[Claims] A liquid crystal is sandwiched between two transparent substrates, and a plurality of bus wirings are arranged in an X-Y matrix on the first transparent substrate, and the areas divided by the bus wirings in the X and Y directions correspond to picture elements. death,
Each picture element consists of a three-terminal switching element and a liquid crystal cell, the bus wiring in the X direction is a scanning electrode for operating the switching element, and the bus wiring in the Y direction is a scanning electrode for applying a signal to the liquid crystal cell. A display device in which a second transparent substrate is provided with a counter electrode that is a signal electrode of a switching element and faces the picture element, and the polarity of a signal applied to the signal electrode is changed every horizontal scanning period or several times. Applying a rectangular wave that is reversed every horizontal scanning period, and the signal applied to the counter electrode is also in opposite phase to the signal applied to the signal electrode every one horizontal scanning period or every plural horizontal scanning periods. A liquid crystal display device featuring: