JPH0651272A - Method for driving liquid crystal display - Google Patents

Abstract

PURPOSE:To restrain brightness from being lowered and the flicker phenomenon from arising by superimposing a positive or negative pulse of width shorther than one scanning period on the driving voltage of the signal, or scanning, electrode of an XY matrix liquid crystal display. CONSTITUTION:At least one positive or negative pulse whose duration is shorter than one scanning period T/m (T is frame length and (m) is the number of scanning electrodes) is superimposed on a signal voltage VXi ((i)=1 to (n)) or a scanning voltage VYj ((j)=1 to (m)) for every scanning period. To superimpose the pulse on the scanning voltage VYj, however, the superimposing is carried out only during a non-selective period in a frame period, and the selective period can be omitted. This is the case where a positive or negative pulse whose width is T/4m and whose amplitude is slightly smaller than V(V= V0-V1=V1--V2=V3-V4=V4-V5) is superimposed on the voltage especially during the non-selective period of the scanning voltage VYj.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method for an XY simple matrix liquid crystal display device, and more particularly to a method for reducing the decrease in brightness and flicker phenomenon.

[0002]

2. Description of the Related Art Well known as a method for driving a liquid crystal display device.
The voltage averaging method used is briefly explained with reference to FIGS. 7 to 9.
Reveal The liquid crystal panel 1 includes a liquid crystal layer and a pair of holding the liquid crystal layer.
It consists of two substrates 2 and 3, and runs laterally on the inner surface of the substrate 2.
Inspection electrode (common electrode) Y₁~ Y ₆Is formed on the substrate 3
Signal electrode (segment electrode) X on the inner surface₁~ X₆Formed
Be done. Scan electrode Y₁~ Y₆And signal electrode X₁~ X₆Exchange with
The difference portion becomes a display dot (pixel).

A selection voltage and a non-selection voltage are sequentially applied to the scan electrodes Y _{1 to} Y ₆ . The time required to scan all the scanning electrodes is called one frame. Further, during the period in which each scan electrode Y _j is scanned (selected), the high-level or low-level signal voltage (lighting voltage or non-lighting voltage) to be displayed in the pixels in the j-th row is applied to all the signal electrodes X ₁ to X ₁ . Simultaneously applied to X ₆ .

Of the pixels in the second column in FIG. 7,
D _2,1 , D _2,3 , D _2,5 are not lit, D _2,2 , D _2,4 , D
_When lighting _2,6 , the applied voltage V of the lighting pixel D _2,4
2,4 the signal voltage V _X2, scanning voltage V _Y4 with 8, also applied voltage V _2,3 of the signal voltage V _X2 unlit pixel D _2,3,
It is shown in FIG. 9 together with the scanning voltage V _Y3 . In the frame period F ₁ , the selection voltage of the scanning electrode Y _j is V ₀ , the non-selection voltage is V ₄ , and the lighting voltage applied to the signal electrode X _i is
V ₅ and non-lighting voltage = V ₃ . Also, the frame period F ₂
Then, the selection voltage of the scan electrode Y _j = V ₅ , the non-selection voltage = V
₁ and the lighting voltage applied to the signal electrode X _i =
V ₀ , non-lighting voltage = V ₂ . _{Incidentally, V 0 -V 1 = V 1} -V 2 = V; is _{V 3 -V 4 = V 4 -V} 5 = V = aV LCD (1) V 0 -V 5 = V LCD (2). In the frame periods F ₁ and F ₂ , the polarity of the voltage V _{i, j} = V _Xi −V _Yj (3) applied to the pixel D _{i, j} is inverted and so-called AC driving is performed. As can be seen from the examples of FIGS. 8 and 9, whether a pixel is in a lighting state or a non-lighting state depends on the lighting voltage applied to the signal electrode when the selection voltage is applied to the scan electrode in which the pixel exists. Is applied or a non-lighting voltage is applied.

The voltage V ₀ to be the basis for forming the waveforms of the voltages V _Xi and V _Yj applied to the signal electrode and the scan electrode, respectively.
V ₅ is generated by the liquid crystal drive voltage generating circuit 4 in the liquid crystal display device shown in FIG. Of these voltages, V ₀ ,
The voltages V ₂ , V ₃ , and V ₅ are supplied to the segment driver 5, and the voltage V _Xi for driving the signal electrodes X _i (i = 1 to n) is generated therein. Further, the voltages V ₀ , V ₁ , V ₄ , and V ₅ are supplied from the voltage generation circuit 4 to the common driver 6, and the voltage V _Yj to be applied to the scan electrodes Y _j (j = 1 to m) is generated therein.

FIG. 11 shows a signal voltage V _Xi , a scanning voltage V _Yj and a pixel D when all the pixels in the i-th column are turned on.
_The voltage V _{i, j} = V _Yj −V _Xi applied to _{i, j} is shown. Further, in FIG. 12, the pixels D from the 1st row to the mth row of the i-th column
Signal voltage V _Xi , scanning voltage V _Yj and applied voltage V of pixel D _{i, j} when _{i, 1 to} D _{i, m} are alternately turned on and off
_{i, j} = V _Yj −V _Xi . Note that FIG. 11 and FIG.
In FIG. 2, the polarity of V _{i, j} is reversed from that of FIGS. 8, 9 and (3).

[0007]

A frame frequency f = 1 / T (T is a frame period) when driving a liquid crystal panel.
Is usually about 16 to 100 Hz, but when the number m of scanning electrodes is large, the time for scanning (selecting) one scanning electrode becomes short. In addition, since the response speed of the conventional general type liquid crystal panel is as slow as 400 to 500 mS, the light transmittance T rises only slightly by one scan as shown in FIG. 13B, and the scan is repeated many times to rise. . After the light transmittance rises to the maximum value Tmax by the selection pulse, the transmittance T decreases to some extent, but rises again to the maximum value Tmax by the next scanning. In this way, the brightness at the time of lighting is maintained.

On the other hand, in a high-speed response type liquid crystal panel having a response speed of 200 mS or less, as shown in FIG. 13C, the transmittance T reaches the maximum value Tmax with a smaller number of scans than the general type, but until the next scan. The brightness is significantly reduced, and thus the brightness is significantly reduced, and a flicker phenomenon occurs.
According to the present invention, a liquid crystal panel driven in a time-division manner has a shorter period for scanning one scan electrode due to an increase in the number of scan electrodes, and has a high-speed response. Therefore, a decrease in brightness and a flicker phenomenon occur. The purpose is to alleviate.

[0009]

[Means for Solving the Problems]

(1) According to the present invention, at least one positive or negative pulse having a width shorter than one scanning period is superimposed on the drive voltage of the signal electrode or the scanning electrode of the XY matrix liquid crystal display device. (2) In the above item (1), it is preferable to superimpose a pulse on the drive voltage of each scan electrode during the non-selection period of that scan electrode.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the signal voltage V _Xi (i = 1 to n) or the scanning voltage V _Yj (j = 1 to m) is applied to one scanning period T / m (T is a frame length, m is a scanning period). At least one positive or negative pulse shorter than the number of electrodes is superimposed per frame period. However, when superposed on the scanning voltage V _Yj , it may be superposed only on the non-selected period within the frame period and may be omitted during the selected period.

In the embodiment of FIG. 2, the pulse width is T / 4 m and the amplitude is V (V = V ₀₎ especially during the non-selection period of the scanning voltage V _Yj.
-V ₁ = V ₁ -V ₂ = V ₃ -V ₄ = V ₄ -V ₅ ). The waveform is enlarged and shown in FIG. In FIG. 3, in the frame F ₀ in which the scanning voltage V _Yj in the non-selection period is high level, when one scanning period T / m is divided into 4 from t ₀ to t ₃ , t ₁ , t
_Second period on the amplitude v _1, v ₂ positive or negative pulse is superimposed, respectively. In addition, the scan voltage V in the non-selected period of FIG.
_In the frame F ₁ in which _Yj is at a low level, negative and positive pulses with amplitudes v ₁ and v ₂ are superimposed during the periods t ₁ and t ₂ , respectively.

An example of such a liquid crystal drive voltage generating circuit 4
Is shown in FIG. Power supply voltage V⁺ _IN, V^- _INThe voltage between
Anti-R₁~ R₁₁Divides the voltage into 12 voltage levels. this
When R₁+ R₂= R₃+ R_Four= R₈+ R₉= R_Ten+ R₁₁ (4) Therefore, V₀-V_1b= V_1b-V₂= V₃-V_4b= V_4b-V_Five (5) Resistor R₁One end p₁, Resistor R_FourAnd R_FiveWith
Connection point p_Four, R₇And R₈Connection point p with₇, Resistor R₁₁of
One end p₁₁Is an operational amplifier (op amp)₁, Op_Five,o
p₆, Op_TenConnected to the input terminals of
Therefore, the voltage V₀, V₂, V₃, V_FiveIs output. Connection
Point p₂, P₃, P_Ten, P₁₁Is the op amp₂, O
p₃, Op₈, Op₉Connected to each input. Contact
Continuation point p_Four, P₆, P₇Is the switch SW₁Movable contact a,
b and c, respectively, and their fixed contacts d are operational
Pop_FourConnected to the input of. Also connection point p₉, P₇，
p₆Is the switch SW₂Connected to the movable contacts a, b, c of
The fixed contact d is an operational amplifier op.₇Connected to the input of
Be done.

Voltages V _1a = V ₁ + v ₁ , V _1b = V ₁ , V _1c = V ₁ −v ₂ (6) are obtained from the operational amplifiers op ₂ , op ₃ , and op ₄ , respectively, and the analog switch IC ₁ is supplied with the voltages. Supplied,
It is switched and selected, and one of them, voltage V ₁ ′, is output. From the operational amplifiers op ₇ , op ₈ , and op ₉ , the voltages V _4a = V ₄ + v ₂ , V _4b = V ₄ , V _4c = V ₄ −v ₁ (7) are obtained, respectively, and supplied to the analog switch IC ₂ .
It is switched and selected, and one of them, voltage V ₄ ′, is output. The analog switches IC ₁ and IC ₂ are controlled by a switch control circuit CTL to perform a switching operation,
As shown in FIG. 3, a waveform is obtained in which positive and negative pulses having amplitudes v ₁ and v ₂ are superimposed on the conventional voltages V ₁ and V ₄ .

As can be seen from FIG. 4, V _1a <V ₀ , V _1c >
It is V ₃ . That is set to _{V 3 <V 1 '<V} 0. Therefore, v ₁ = V _1a −V ₁ <V ₀ −V ₁ = V (8) Similarly, from FIG. 4, v ₂ = V ₁ −V _1c <V ₁ −V ₃ = V + V ₂ −V ₃ = V _LCD It is -3V (9). Further, V _4c > V ₅ and V _4a <V ₂ are set. That is, V ₅ <V ₄ ′ <V ₂ is set. Therefore, v ₁ = V ₄ −V _4c <V ₄ −V ₅ = V (10) v ₂ = V _4a −V ₄ <V ₂ −V ₄ = V ₂ −V ₃ + V = V _LCD −3V (11) FIG. 1 shows that in the frame F ₁ (F ₂ ), four negative, positive, negative, and positive (positive, negative, positive, negative) scans are made in one scanning period T / m.
This is a case where the individual pulses are superimposed on the scanning voltage V _{i, j} .
In this example, positive and negative pulse amplitudes v ₁ and v ₂ are differentiated.

FIG. 5 shows that in frame F ₁ (F ₂ ), one positive (negative) pulse having a pulse width of approximately ½ of one scanning period is scanned in one scanning period T / m. This is the case where it is superimposed on the voltage V _Yj . As already described with reference to FIG. 13, even if the transmittance T reaches the maximum value Tmax due to the selection pulse, it immediately starts to drop, but the transmittance T responds to the superposed pulse, so the degree of the drop is reduced. can do. FIGS. 6B and 6C show response waveforms of the transmittance T when the pulses are superimposed as shown in FIG. 6A (the same pulse waveform as that of FIG. 1B, with the amplitude being selected as V) when compared with the conventional driving method. The comparison is shown. It can be seen that in both the general type LCD and the fast response LCD, the drop of the transmittance is smaller when the pulse of the present invention is driven for superposition than that of the conventional driving method. In FIG. 6, the frame frequency f = 1 / T = 64 Hz and the number of scanning electrodes m = 200.

The pulse width is smaller than one scanning period T / m,
In many cases, it is selected to be a fraction of T / m to a fraction of ten. In addition, when the positive or negative pulse is superposed on either the signal voltage or the scanning voltage, the voltage waveform of V _Xi or V _Yj after superposition is the maximum voltage V ₀ and the minimum voltage V _{5 of} FIGS. It should not exceed the range. Therefore, the liquid crystal drive voltage generation circuit is not limited to the case of FIG.

[0017]

According to the present invention, at least one positive and negative pulse having a width narrower than one scanning period T / m is superimposed on the pixel applied voltage in one frame period, so that the light transmittance of the pixel is increased. T varies in accordance with those pulses, and as a result, the degree of the drop in the light transmittance that occurs between the selection pulses is reduced.

Therefore, there has been a problem in the past,
It is possible to mitigate a decrease in screen brightness and a flicker phenomenon due to a drop in transmittance caused by a short scan time of liquid crystal and high-speed response.

[Brief description of drawings]

FIG. 1 is a liquid crystal panel showing an embodiment of the present invention in which positive and negative pulses are superimposed during a non-selection period of a scanning voltage V _Yj when all pixels in the i-th column in the first row to the m-th row are turned on. Waveform diagram of the main part of.

FIG. 2 is a waveform diagram of a main part of a liquid crystal panel showing another embodiment of the present invention.

FIG. 3 is an enlarged waveform chart showing a part of the waveform of the scanning voltage V _{Yj in} FIG. 2B.

FIG. 4 is a circuit diagram showing an example of a liquid crystal drive voltage generation circuit used in the present invention.

FIG. 5 is a waveform diagram of a main part of a liquid crystal panel showing still another embodiment of the present invention.

FIG. 6 is a waveform diagram showing a response of light transmittance of a pixel to a voltage applied to the pixel.

FIG. 7 is a perspective view showing a configuration of an XY simple matrix liquid crystal display panel.

8 is a signal voltage V _X2 for turning on, off, turning on, and so on the pixels in the second column of the first row to the sixth row of FIG. 7, respectively.
The scan voltage V _Y4 and the applied voltage V _{2, to the} illuminated pixel D _2,4
Waveform diagram showing ₄ .

9 shows a signal voltage V _X2 , a scan voltage V _Y3, and a non-lighted pixel when the pixels in the second column of the first row to the sixth row of FIG. 7 are turned off, turned on, turned off, turned on, ... waveform diagram showing applied voltage V _2,3 of D _2,3.

FIG. 10 is a block diagram showing the configuration of an XY simple matrix liquid crystal display device.

11 is a diagram illustrating a liquid crystal panel 1 of FIG. 10, in which all the pixels in the i-th column in the first row to the m-th row are lit, the signal voltage V _Xi , the scanning voltage V _Yj, and the lit pixel D _{i, j.} 5 is a waveform diagram showing the applied voltage V _{i, j} of FIG.

12] In the liquid crystal panel 1 of FIG. 10, the pixels in the i-th column in the first row to the m-th row are lit, non-lit, lit, ...
FIG. 6 is a waveform diagram showing a signal voltage V _Xi , a scanning voltage V _Yj, and an applied voltage V _{i, j} of a pixel D _{i, j} to be turned on in the case of making it.

FIG. 13: Driving the liquid crystal panel of FIG. 10 by a conventional driving method.
Pixel D when_{i, 1}(X_i, Y ₁Pixel of intersection)
Waveform showing the response of pixel light transmittance to pixel applied voltage
Fig.

Claims (2)

[Claims] 1. A liquid crystal comprising at least one positive or negative pulse having a width shorter than one scanning period superposed on a drive voltage of a signal electrode or a scanning electrode of an XY matrix liquid crystal display device. Driving method of display device. 2. The method of driving a liquid crystal display device according to claim 1, wherein a pulse is superimposed on a drive voltage of each scan electrode of the XY matrix liquid crystal display device during a non-selection period of the scan electrode.