JPH07168158A - Active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To enable the impression of signals independently corrected even with different level shifts generated not only in black display signal waveforms and white display signal waveforms but in medium contrast display signal waveforms as well to liquid crystals. CONSTITUTION:This liquid crystal display device has a polarity inversion signal generating circuit 1 which generates plural AC gradation display signals individually varying in amplitude and independently sets the different amplification centers meeting the amplitudes of the respective gradation display signals by gradually shifting these centers and a digital driver IC 2 which properly select the individual gradation display signals set with the respective amplification centers and supplies these signals to source lines 3. Pulse signals to turn transistors successively on and off are supplied to gate lines 5 to charge and hold the signal voltages meeting the gradation display signals offset in the centers of the amplitude supplied to the source lines 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device used for office automation such as personal computers and workstations.

[0002]

2. Description of the Related Art As is already known, an active matrix type liquid crystal display device of this type has transistors turned on and off.
When the gate signal for F is inverted from ON to OFF, a level shift ΔV occurs between the signal writing of positive polarity and signal holding and the signal writing of negative polarity and signal holding. Therefore, the pixel electrode potential (drain signal) becomes a voltage shifted by the level shift ΔV, and positive and negative signal writing and signal holding are performed with this as a reference. However, since the level shift ΔV fluctuates in accordance with the change in the amplitude (display gradation) of the source signal, at this time, the DC reference voltage of the display signal is set and fixed according to a predetermined amplitude center of the source signal. The initial setting value of (common voltage) deviates from the center of the amplitude of the changed source signal, resulting in deterioration of display quality such as decrease in contrast.

Therefore, conventionally, in order to correct the level shift ΔV by adjusting the common voltage to the center of the source voltage, an active matrix type liquid crystal display device as disclosed in Japanese Patent Publication No. 4-76458 is proposed. ing.
According to this, in the polarity inversion signal generation circuit that supplies the display signal whose polarity is inverted every frame scanning period to the signal line drive circuit, by connecting the variable load resistor to the collector of a predetermined transistor, the polarity inversion reference potential is obtained. On the other hand, the amplitude of the display signal voltage on the positive potential side is adjusted with respect to the amplitude on the negative potential side.

[0004]

In the conventional active matrix type liquid crystal display device described above, a variable load resistor is connected in the polarity reversal signal generation circuit to correct the level shift variation, and in particular, a black display signal waveform is generated. The display signal voltage and the polarity inversion reference potential are initially set in consideration of the level shift in the white display signal waveform.
However, according to this configuration, the correction of different level shifts that occur in signal waveforms with different amplitudes everywhere, such as the halftone display signal waveform, depends on the correction for the black display signal waveform and the white display signal waveform. It wasn't quite satisfactory.

Therefore, since the correction is insufficient, the contrast is lowered, and the display quality is inevitably lowered. Therefore, the present invention has been made in order to achieve the above-described object, and provides a signal independently corrected not only for a black display signal waveform and a white display signal waveform but also for different level shifts occurring in a halftone display signal waveform. It is intended to be applied to the liquid crystal.

[0006]

In order to achieve the above object, the present invention provides a means for generating a plurality of alternating gray scale display signals each having a different amplitude, and a means for adjusting the amplitude of each gray scale display signal. Means for gradually shifting different amplitude centers and independently setting them, means for appropriately selecting each of the gradation display signals for which each amplitude center is set, and supplying it to a source line, turning on and off a transistor, The technical means consisting of means for supplying to the gate line a pulse signal for charging and holding a signal voltage corresponding to the gradation display signal supplied to the line is adopted.

[0007]

According to the present invention, at the same time as generating individual gradation display signals, different amplitude centers corresponding to the amplitudes are gradually shifted and set independently. Then, the gradation display signal whose amplitude center is independently set is appropriately selected and supplied to the source line. In the meantime, a pulse signal for turning the transistor on and off is supplied to the gate line, and when the transistor is turned on, the signal voltage corresponding to the gradation display signal supplied to the source line is charged, and then the transistor is turned off.
Then, this signal voltage is held.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a main part of the overall configuration of an active matrix type liquid crystal display device of the present invention. In the active matrix type liquid crystal display device having the configuration of FIG. 1, a pulse signal for sequentially turning on and off the transistor 6 is supplied from the gate driver 4 to the gate line 5, and at the same time, a polarity inversion signal input to the digital driver IC 2 Generation circuit 1
The gradation display signal (usually 8 to 16 gradations) is selected appropriately and supplied to the source line 3. When the pulse signal is turned on, the transistor 6 is turned on and the pixel 7
The storage capacitor 8 is charged with a signal voltage corresponding to the gradation display signal supplied to the source line 3. Subsequently, when the pulse signal is turned off, the transistor 6 is turned off, and the signal voltage charged in the pixel 7 and the auxiliary capacitor 8 is held until the next pulse signal is output.

FIG. 2 shows a polarity inversion signal generation circuit 1 which is connected to the active matrix type liquid crystal display device having such a configuration and inputs an alternating signal to the digital driver IC 2. In FIG. 2, a semi-fixed resistor 9a for amplitude adjustment is provided in the polarity inversion signal generation circuit 1 to adjust the amplitude of the halftone display signal waveform. Further, a semi-fixed resistor 9b for offsetting the center of amplitude is provided, and a liquid crystal (not shown) is provided.
The amplitude center of the waveform of the gray scale display signal applied to is offset by the amplitude. Specifically, as shown in FIG. 3, this offset waveform is based on the amplitude center d ₁ of the signal waveform of the white display signal waveform D ₁ and the amplitude center d ₂ of the signal waveform of the halftone display signal waveform D ₂ is the amplitude. It should be above the center d ₁ . In this way, all the gradation signal waveforms from the white display signal waveform D ₁ having the amplitude center d ₁ to the black display signal waveform D _n having the amplitude center d _n are created by gradually shifting the amplitude center of the signal waveform. ing. Subsequently, each gradation display signal D is turned on by the AC switch 10 shown in FIG.
₁ , D ₂ , ---, D _n are output to the gradation signal output terminal 11.

Next, the output gradation display signal D ₁ ,
FIG. 4 shows an example in which the multi-level driver IC 12 is used as the digital driver IC as the liquid crystal driving means by D ₂ ,-, D _n . In FIG. 4, the gradation display signal D ₁ output from the polarity reversal signal generation circuit _{1 described above} ,
One horizontal period of D ₂ , ..., D _n is fetched from a predetermined portion of the gradation signal input terminal 13 and stored in a data memory (not shown). Then, in the next horizontal period, the operation of the output circuit (not shown) is performed, and the selection switch 14
Gradation display signals D ₁ , D ₂ , ...
─, D _n are selected, and the input terminals Q ₁ and Q of the liquid crystal display device are selected.
_2, ───, it is output to Q _n. Then, the display unit 15 displays an image according to the output gradation display signal.

By the way, such a multi-level driver IC 12 has good compatibility with a digital system (not shown) using a computer and is normally applied to an active matrix type liquid crystal display device used in a personal computer or the like. is there. Here, in the polarity reversal signal generation circuit 1, the semi-fixed resistor 9 for offset is used.
b without using the multilevel driver I
When C12 is used, the gradation signal waveform shown in FIG. 5 is obtained. That is, as the waveform of the gradation display signal applied to the liquid crystal (not shown), the white display signal waveform D ₁ ^′ , the halftone display signal waveform D ₂ ^′ , ───, and the black display signal waveform D _n ^′ are respectively displayed. Amplitude centers of the signal waveform of d ₁ ^' , d ₂ ^' , ──
─, d _n ^′ are all fixed. In this case, when the pixel capacitance changes due to a change in the amplitude (display gradation) of the video signal and the level shift fluctuates, the level shift becomes uneven and the contrast of the liquid crystal display device deteriorates. Therefore, as in this embodiment,
It is very important to use the offset semi-fixed resistor 9b at the same time as using the multi-level driver IC 12.

According to the active matrix type liquid crystal display device having the above-mentioned structure, the gradation display signals D ₁ , D ₂ , which are offset from the amplitude centers d ₁ , d ₂ , ───, d _n of the respective signal waveforms, ───, D _n is input to the gradation signal input terminal 13 of the multi-level driver IC 12, and the gradation display signals D ₁ , D ₂ , which should be appropriately displayed by the selection switch 14,
───, D _n was output to the display unit 15. As a result, the display unit 15 is applied with the signals obtained by independently correcting the different level shifts, and the flicker of the display unit 15 is eliminated. Therefore, not only the black display signal waveform D _n and the white display signal waveform D _1, but also the halftone display signal waveform D ₂ ,
It becomes possible to independently and optimally correct the level shift occurring in D _n−1 , and it is possible to obtain an active matrix type liquid crystal display device having good contrast and excellent display quality. Further, since the level shift is corrected without increasing the auxiliary capacity, the display screen becomes brighter.

Next, as the driving means in this embodiment,
Even if a digital driver IC other than the multi-level driver IC 12 is used, the same effect can be obtained without any problem.
For example, a lamp sample type digital driver IC
This is also effective in the case of using, the ramp waveform (gradation display signal) at this time is shown in FIG. 6, and an example of the driving means using this is shown in FIG.

Here, in order to deepen the understanding of this embodiment,
First, a gradation display signal in which the center of the waveform is not offset will be described. Such a ramp waveform is a display signal waveform 16 whose center e ′ is constant as shown by the broken line in FIG.
^{_{(E 1 ', E 2'}} , ───, E n ') becomes. When this ramp waveform is input to the gradation signal input terminal 19 shown in FIG. 7, the sampling switch 20 samples the gradation display signal to be displayed, and the sample-hold circuit 21 at the subsequent stage.
Hold at. Then, the held gradation display signal is sent to the display unit 22, and an image corresponding to this is displayed. However, since the center e ′ of the ramp waveform input to the gradation signal input terminal 19 is constant, the level shift becomes uneven and the contrast of the liquid crystal display device deteriorates for the same reason as in the previous embodiment. Resulting in. Therefore, the center of the halftone display signal waveform was gradually offset using a semi-fixed resistor for offsetting. Such a ramp waveform is
The centers shown by the solid lines in FIG. 6 are e ₁ , e ₂ ,
──, the display signal waveform 17 obtained by e _n and the offset (E _1,
E ₂ , ───, E _n ). Therefore, by inputting the display signal waveform 17 to the gradation signal input terminal 19, there is no problem even when the lamp sample type digital driver IC 18 is used, and the multi-level driver I
The same effect as in the case of C12 can be obtained.

[0015]

As described above, according to the present invention,
Each gradation display signal set independently by gradually shifting different amplitude centers according to the amplitude is appropriately selected and supplied to the source line, while a pulse signal for turning on and off the transistor is supplied to the gate line. Since the signal voltage is charged and held in this manner, it is possible to independently correct not only the black display signal waveform and the white display signal waveform but also different level shifts that occur in the halftone display signal waveform. .

[Brief description of drawings]

FIG. 1 shows an overall configuration of an active matrix type liquid crystal display device of the present invention.

FIG. 2 shows a polarity inversion signal generation circuit for a video signal according to the present invention.

FIG. 3 shows a gradation signal waveform of the present invention.

FIG. 4 shows a driving means of the present invention.

FIG. 5 shows a gradation signal waveform when a semi-fixed resistor is not used.

FIG. 6 shows a display signal waveform when another driving means of the present invention is used.

FIG. 7 shows another driving means of the present invention.

[Explanation of symbols]

 1 polarity inversion signal generation circuit 2 digital driver IC 8 auxiliary capacitors 9a, 9b semi-fixed resistance 10 AC switch 11 gradation signal output terminal 12 multi-level driver IC 13, 19 gradation signal input terminal 14 selection switch 15, 22 display section 18 Digital sample IC of ramp sample type 20 Sampling switch 21 Sample and hold circuit

Claims (1)

[Claims] 1. Means for generating a plurality of alternating gradation display signals each having a different amplitude, and means for independently setting gradually different amplitude centers corresponding to the amplitudes of the respective gradation display signals. Means for appropriately selecting and supplying each of the gradation display signals with the respective amplitude centers set to the source line, and a signal voltage according to the gradation display signal supplied to the source line by turning on and off a transistor Charge the,
An active matrix type liquid crystal display device comprising: a means for supplying a pulse signal to be held to a gate line.