JP3229450B2 - Matrix driving method for flat display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix driving method which is applied to a flat display device having bistability and controls brightness by applying a voltage corresponding to a gradation to be displayed to a signal electrode. Things.

[0002]

2. Description of the Related Art Flat display devices such as ferroelectric liquid crystals having high-speed switching characteristics and bistability (memory characteristics) are known. Of this kind,
After forcibly resetting all pixels on the scanning electrode to dark (or light) by a reset signal applied to the scanning electrode, a signal electrode (display electrode) for a predetermined pixel is applied while a selection signal is applied to the scanning electrode. There is a method in which a pixel corresponding to the selection signal and the signal electrode is written to the brightness of a desired gradation by applying a voltage corresponding to the gradation to be displayed.

Here, as the liquid crystal, a liquid crystal having a characteristic that can be rewritten to a brightness of a predetermined gradation depending on the magnitude of a product of a voltage applied to a pixel and a time (hereinafter, this product is referred to as an effective value) can be used. In this case, the effective value of a signal (called an effective pulse) for writing a certain pixel to the predetermined gradation is
It may change under the influence of the signal immediately after this signal.

FIG. 10 is a diagram showing a driving waveform according to a conventional two-pulse method, FIG. 11 is a diagram showing a configuration example of a scanning signal for one frame applied to a certain scanning line, and FIG. FIG. 14 is a sequence diagram showing a combination of subsequent non-selection signals.

In the two-pulse method, a pre-reset signal PR (same as the reset signal of the present invention) is input immediately before a selection signal is input to the scan electrode, and the display signal is turned on and off.
Regardless of OFF, it is forcibly reset to dark. Here, the scanning signal (-COM) has a pulse width of 2τ and is applied to the scanning electrode, and the display signal (SEG) has a pulse width of 2τ and is applied to the display electrode (signal electrode).

The display signal (SEG) has gradations 3, 2, 1, 0
And the signal voltage is set so as to gradually decrease in order from brighter to darker ones. As a result, the voltage applied to the pixel changes variously as shown in FIG. 10 depending on the combination of the scanning signal (-COM) and the display signal (SEG).

For example, when the pre-reset signal PR is input to the scan electrode, the display signal (SEG) has a gradation of 3,
No matter which of 2, 1, 0 is input, the voltage of negative polarity (-1
2) is applied, and this pixel is forcibly reset to dark. Also, while the selection signal S is being input to the scanning electrode, 3, 2, 1, 0 of the display signal SEG is applied to the signal electrode.
Is input, the signals applied to the pixels are 12, 10,
8 and 6, and brightness is obtained for each gradation.

As shown in FIG. 11, a scanning signal including the selection signal S is applied to a predetermined scanning electrode at a predetermined timing corresponding to the scanning electrode. Here, one or more anti-pre-reset signals APR having a polarity opposite to those of the pre-reset signals PR are inserted before one or more pre-reset signals PR, and the DC component of the pre-reset signal PR is inserted. To the anti-pre-reset signal APR
Is cancelled.

As described above, positive and negative DC pulse voltages are applied to the pixel. If a DC component remains in the drive pulse, the liquid crystal of the element has a property of deteriorating. Therefore, positive and negative pulses are combined to cancel the DC component. In the present application, such driving is referred to as AC driving.

[0010]

2. Description of the Related Art When an existing pixel is written to a desired gradation by a selection signal S and a display signal SEG, a non-selection signal NS is input to the scanning electrode SEG immediately after this (immediately after selection).

The voltage of the pixel at this time is determined by the combination of the gradation (3, 2, 1, 0) of the display signal SEG at the time of selection.
There can be different types. FIG. 12 shows a pixel applied voltage waveform according to a combination of these.

As is apparent from FIG. 12, the waveform of the signal applied to the pixel depends on the type of the display signal immediately after selection.
In particular, the product of voltage x time that affects writing (effective value)
Varies greatly. For example, when the gray scale 1 is input to the display signal immediately after selecting the gray scale 2, the effective value becomes 11 as shown by a in FIG. The effective value is 14 as shown by b.

As is apparent from FIG. 10, the effective value 14 exceeds the brightness of the gradation 3 and does not become the proper brightness of the gradation 2. As described above, the gradation of the pixel largely changes depending on the state of the display signal immediately after selection, and there is a problem that accurate gradation display cannot be performed.

In this case, in the case of the non-interlaced scanning method in which adjacent scanning lines are sequentially scanned, an adjacent scanning line becomes a selection signal immediately after a certain scanning line becomes a selection signal. Will appear as crosstalk. In this case, the image blurs in the main scanning direction, and the image quality is remarkably deteriorated.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and is not affected by a display signal immediately after selection when selecting a desired gradation brightness by a voltage of a display signal. , Can display gradation to the correct brightness,
It is an object of the present invention to provide a method of driving a matrix of a flat display device capable of improving image quality.

[0016]

According to the present invention, it is an object of the present invention to form a pixel having bistability at the intersection of a scanning electrode and a signal electrode, and reset all pixels on the scanning electrode by a reset signal applied to the scanning electrode. After resetting to either dark or light,
A pixel at the intersection of the scanning electrode to which the selection signal is applied and the signal electrode to which a writing signal of a voltage corresponding to the gradation to be displayed is applied is controlled to have the brightness of the gradation and written and stored. In the flat-panel display device according to the above, a reverse assist signal having a polarity opposite to that of a valid pulse for inverting the reset state of the pixel is added to the scanning signal outside the selection signal and immediately after the valid pulse. At the same time, while making the effective area synthesized by the reverse assist signal substantially constant,
This is achieved by a matrix driving method for a flat display device, characterized in that an anti-inverse assist signal obtained by inverting the polarity of the inverse assist signal is added before the selection signal .

Here, the reverse reed formed immediately after the effective pulse
The strike signal and the anti-inverse assist signal can be signals having the same time width as the selection signal. This pulse can also be formed by advancing at least one of the scanning signal and the display signal.

The effective pulse can be formed by the selection signal and the display signal, the selection signal and its inverse reed immediately
It is also possible to add a forward assist signal having the same polarity as the effective pulse between the strike signal and the effective pulse to enlarge the effective effective pulse area.

[0019]

FIG. 1 is a diagram showing the arrangement of electrodes, FIG. 2 is a diagram showing driving waveforms of an embodiment in which the present invention is applied to a two-pulse method, and FIG.
FIG. 4 is a diagram showing an example of a scanning signal for one frame applied to a certain scanning line, and FIG. 4 is a sequence diagram showing a combination of a selection signal in a certain pixel and a non-selection signal immediately after that.

In FIG. 1, X _{1 to} X ₅ are scanning electrodes, and Y _{1 to} Y ₅
Is a display electrode (signal electrode). Here, for simplicity of description, only five electrodes are shown. However, it is needless to say that a large number of electrodes are actually provided. These electrodes are driven by drivers D _X and D _Y , respectively. Image signal is input to the controller C, the driver D _X, D _Y sends a predetermined signal to the electrodes _{X 1 ~X 5, Y 1 ~Y} 5 in accordance with the output of the controller C.

The scanning signal is, as shown in FIG.
And two pre-reset signals PR and two anti-pre-reset signals APR inserted immediately before them, a reverse assist signal AA added immediately after the selection signal S, and an anti-reverse assist added before the anti-pre-reset signal APR. It is composed of a signal AAA and a number of non-selection signals NS. The waveforms of these signals are set as shown in FIG. The pre-reset signal PR and the anti-pre-reset signal APR are the same as those described in FIG.

The anti-reverse assist signal AAA is obtained by inverting the reverse assist signal AA to the opposite polarity and adding it to cancel a direct current component generated by adding the reverse assist signal AA. The anti-reverse assist signal AAA should be inserted before the selection signal S and the pre-reset signal PR, and is particularly suitable before, during, and after the anti-pre-reset signal APR.

The reverse assist signal AA constitutes a pulse having a polarity opposite to that of the effective pulse in the present invention. The reverse assist signal AA has the same time width 2τ as the selection signal S, as shown in FIG. 2, and the voltage at the beginning τ changes to -6 and the latter τ changes to -12.

At the timing when the reverse assist signal AA is output, the drive signal waveform when the display signal has the gradation 3 is represented by “α ₃ ”. Similarly, the display signal has the gradations 2, 1, and 0. The driving signal waveform at this time is represented by “α ₂ ”, “α ₁ ”, and “α ₀ ”. As is apparent from FIG.
The effective area of the voltage applied to the pixel by combining the display signals is
It is constant regardless of the ON / OFF change of the signal. In FIG. 2, the pulse area is shown at the upper right of each drive signal waveform.

Since the reverse assist signal AA is added immediately after the selection signal S as shown in FIG. 3, the combination at this time may be as shown in FIG. The first 2τ of these driving waveforms is the selection signal S and the display signal SE of a predetermined gradation.
And G. The second half 2τ is the reverse assist signal A
A and the display signal SEG.

The upper right of each waveform in FIG. 4 shows the area of a pulse that contributes to gradation display in this waveform, that is, the area of an effective pulse that is shaded. Note that this area is voltage × time, but the display of time τ is omitted.

As apparent from FIG. 4, the selection signal S
Immediately after the positive voltage drive waveform, the reverse assist signal AA
, A negative voltage driving waveform is formed. Therefore, the area (effective value) of the effective pulse is not affected at all by the display signal immediately thereafter. That is, the effective value of the effective pulse for each of the gradations 3, 2, 1, and 0 is a constant value of 12, 1 and 1, respectively.
0, 8, and 6, the brightness of each gradation becomes accurate. As a result, the image quality is improved.

[0028]

Embodiment 2 In Embodiment 1 described above, the reverse assist signal AA is added immediately after the effective pulse by the selection signal S. However, the present invention forms a pulse of opposite polarity immediately after the effective pulse by another method. May be.

FIGS. 5 to 7 show an embodiment in which the pulse of the opposite polarity is formed by advancing the scanning signal and the display signal. FIG. 5 is a diagram showing the output waveforms of the respective parts according to the two-pulse driving method, FIG. 6 is a diagram showing the combined driving waveforms, and FIG. 7 is a sequence diagram showing a combination of a selection signal in a certain pixel and a non-selection signal immediately after that. .

Here, the principle of advancing the scanning signal and the display signal will be described. FIG each driver D _X shown in the 1, D respectively in the _Y plurality of constant voltage V _C1 ~V _C4, V _S1
~V _S4 is input, the driver D _X, D _Y is a built-in analog switch group for selecting and outputting one of these voltages. These switches are controlled to be turned on and off by a data signal sent from the controller C and an alternating signal (hereinafter referred to as an M signal or M), and a signal having a waveform shown in the “output” column of FIG. Output to the electrode Y.

In FIG. 5, SEG indicates a signal relating to the signal electrode Y, and COM indicates a signal relating to the scanning electrode X.
The driver D _X, a data signal that is the duration of ON of 2τ selection period, and the M signal for AC this is inputted. In the conventional device, the M signal changes from OFF to ON at a period of τ in synchronization with the data signal, and based on these signals, the driver D _X changes from V _C1 to V _C1 as shown in the “output” column of FIG. A step-like signal that changes to _VC2 is output. During 2τ in the non-selection period, the data signal is turned off.
F, and the "output" is a step-like signal that changes from _VC4 to _VC3 .

[0032] In the same manner as the driver D _Y, at the time of writing (ON
A data signal that is turned on when the signal is turned on at the time of writing, and an M signal that turns the data signal off at the time of non-writing (when the signal is turned off) is input, and the “output” of the data signal changes from V _S2 to V _S1 when turned on. When turned off, the waveform changes from V _S4 to V _S3 , but since both are set to the same voltage, they have a constant voltage.

When the "output" of the COM and the "output" of the SEG are applied to the scanning electrode X and the signal electrode Y in this manner, (SE) is applied to the pixel in the intersection area of both electrodes X and Y.
G output-COM output). This voltage waveform is shown in FIG. 5 as a “composite waveform”.

Here, in the present invention, SEG and COM
Are advanced by the same angle θ (= 60 °). That is, the controller C in FIG. 1 sends an M signal advanced by θ with respect to the data signal to both drivers D _X and D _Y. In FIG. 5, for simplicity of description, only one type of data signal is used, and only the ON and OFF states can be taken. However, actually, the data signal changes in accordance with the gradation.

A drive signal (composite waveform) at the time of selection when ON at which predetermined gradation is written in a certain pixel.
Is indicated by the oblique lines in FIG. 5, and the area, that is, the effective value is the same as when the advance amount is 0. At this time O
When N and OFF are selected, negative pulses P ₁ and P ₂ are formed next to the positive effective pulse due to the advance of the M signal.

[0036] The pulse P _1, P _2, even when the non-selection signal that follows the selection signal begins with positive pulses, blocking the positive both pulse enters between the positive pulse of the selection signal Therefore, the area of the oblique line, that is, the area of the effective pulse (effective value) does not increase. FIG. 6 shows the scanning signal COM and the display signal S output at the timing shown in FIG.
4 shows a drive waveform synthesized by the EG.

FIG. 7 shows that the pulses P ₁ and P ₂ act so that the effective value of the effective pulse is not affected by the next non-selection display signal. That is, since the respective composite driving waveforms are advanced by θ as shown in FIGS. 5 and 6, at the end of the selection period T _S , the pulses P (P ₃ , P ₂ , P ₁ ) having the opposite polarity to the effective pulse (indicated by oblique lines) , P ₀ ) are formed. The pulse P is because they disconnect the waveform of the next non-selection period T _NS of the selection period T _S.

For example, when the selection signal S is applied to the scanning electrodes (selection period T _S ), if the display signal becomes a signal of gradation 3, the effective pulse at that time appears as shown by hatching in FIG. negative pulse P ₃ is generated. Similarly, if the gradation at the time of selection becomes ₂ , ₁ , 0, the pulses P ₂ , P
_1, P ₀ is generated.

[0039]

Other Embodiments In each of the above embodiments, an effective pulse is formed by the selection signal and the display signal, but the present invention is not limited to this.

[0040] For example, the inverse assist signal immediately after the selection signal and its
A pulse having the same polarity as the effective pulse (referred to as a forward assist signal) may be added to the signal, a pulse generated by the forward assist signal may be added to the effective pulse, and the added pulse may be used as the effective pulse.

FIG. 8 is a diagram showing an output waveform of each part in this case, and FIG. 9 is a diagram showing a drive waveform obtained by combining the selection signal, the forward assist signal and the reverse assist signal. When such a forward assist signal is added, the effective pulse effective value (area)
And the difference between the effective value of the effective pulse for each gradation can be widened. For this reason, the drive margin can be increased and the image quality can be improved.

In the second embodiment, both the scanning signal and the display signal are advanced with respect to the data signal by the same angle θ, but the present invention is effective in that only one of these signals is advanced. Immediately after the pulse, a pulse of the opposite polarity may be formed between the effective pulse and the waveform of the subsequent display signal so that the waveform is not continuous with the same polarity. Each signal such as a selection signal uses a two-pulse method in which two pulses are set in a time width of 2τ, but the present invention uses a three-pulse method having three pulses and a four-pulse method having four pulses.
A pulse method or the like may be used.

[0043]

According to the first aspect of the present invention, as described above, immediately after an effective pulse for writing a predetermined gradation after resetting a pixel, a reverse assist signal having a polarity opposite to that of the effective pulse is added. Therefore, the effective value of the effective pulse is not affected by the display signal in the non-selection period that follows. Therefore, the gradation display becomes accurate. Here this reverse reed
So that the effective area synthesized by the strike signal is almost constant
The reverse assist signal outside the writing period.
Can be. That is, the write state by the selection signal is clear
Being outside the writing period without being affected by the shadow
it can. Therefore, when the reverse assist signal is included in the selection period,
The selection period can be shortened compared to
The time required to write all pixels of the
Quality can be improved. In the case of the non-interlaced scanning method, there is no possibility that adjacent scanning lines affect each other. Further, since the anti-inverse assist signal obtained by inverting the polarity of the inverse assist signal is added before the selection signal, the generation of the DC component due to the addition of the inverse assist signal can be canceled. Therefore, the image quality is improved.

In the reset period, it is necessary to write the
Pre-reset signal and dark or dark and light
And an anti-prereset signal of the opposite polarity
Add an assist signal immediately before the anti-pre-reset signal.
(Claim 2). The selection signal has a time width τ
Two pulses of a signal with a time width of 2τ in which the voltage changes negatively and positively
A driving method can be adopted (claim 3). In this case, the reverse assist signal having the polarity opposite to that of the effective pulse and the anti-reverse assist signal can have the same time width as the selection signal. Further, the reverse assist signal having the reverse polarity may be formed by advancing at least one of the scanning signal and the display signal (claims 5 and 6).

Of course, the effective pulse can be formed only by the selection signal and the display signal (claim 7). However, a forward assist signal having the same polarity as the effective pulse is added between the selection signal and the reverse assist signal added immediately after the selection signal, and a pulse formed by the added forward assist signal is added as an effective pulse. Good (claim 8). In this case, the drive margin can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electrode arrangement.

FIG. 2 is a diagram showing a waveform of a drive signal according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a scanning signal.

FIG. 4 is a sequence diagram showing a combination of a selection signal and a waveform immediately after the selection signal.

FIG. 5 is a diagram showing waveforms of respective units according to the second embodiment.

FIG. 6 is a diagram showing a driving waveform thereof.

FIG. 7 is a sequence diagram showing a combination of a selection signal and a non-selection signal immediately after the selection signal.

FIG. 8 is an output waveform diagram of each part when forward assist is added.

FIG. 9 is a diagram showing a driving waveform in that case.

FIG. 10 is a diagram showing a driving waveform by a conventional two-pulse method.

FIG. 11 is a diagram showing a configuration of the scanning signal.

FIG. 12 is a sequence diagram showing a combination of the selection signal and a non-selection signal immediately after the selection signal.

[Explanation of symbols]

X ₁ ~ ₅ scan electrodes Y ₁ ~ ₅ display electrodes D _X, D _Y driver S selection signal NS non-selection signal M AC signal θ advancement amount P _1, P ₂ opposite polarity pulse (inverse assist signal) AA inverse assist Signal AAA Anti-reverse assist signal

Claims (8)

(57) [Claims] 1. A pixel having bistability is formed at an intersection of a scanning electrode and a signal electrode, and all pixels on the scanning electrode are reset to one of dark and light by a reset signal applied to the scanning electrode. The pixel at the intersection of the scanning electrode to which the selection signal is applied and the signal electrode to which the voltage signal corresponding to the gradation to be displayed is applied is controlled to the brightness of the gradation and written and stored. In the flat-panel display device as described above, the scanning signal includes an effective assist pulse for inverting the reset state of the pixel and a reverse assist signal having a polarity opposite to that of the effective pulse.
The effective area added outside of the selection signal and immediately after the effective pulse and synthesized by the reverse assist signal
, While adding an anti-inverse assist signal obtained by inverting the polarity of the inverse assist signal before the selection signal . 2. A reset period, which is immediately before a selection signal.
Pre-reset signal and dark or dark and light
And an anti-pre-reset signal of the opposite polarity
The reverse assist signal is placed immediately before the anti-pre-reset signal.
2. The matrix of the flat display device according to claim 1, which is added.
Drive method. 3. The selection signal has a time width τ and a voltage of negative or positive or
2. A signal having a time width of 2 [tau] that changes between positive and negative.
2. A matrix driving method for a flat panel display device according to item 2. 4. The matrix driving method for a flat display device according to claim 1, wherein the reverse assist signal and the anti-reverse assist signal added immediately after the effective pulse have the same time width as the selection signal. . 5. The flat display device according to claim 1, wherein the reverse assist signal added immediately after the effective pulse is formed by advancing at least one of the scan electrode signal and the signal electrode signal. Matrix driving method. 6. The matrix driving method for a flat display device according to claim 5 , wherein the reverse assist signal is formed by advancing both the signal of the scan electrode and the signal of the signal electrode by the same angle. Wherein said effective pulse matrix drive method of any of the flat display device of claim 1 to 6, which is formed by the signal of the selection signal and the signal electrodes of the scan electrodes. 8. A forward assist signal having the same polarity as the effective pulse is added between the selection signal and a reverse assist signal added immediately after the selection signal, and is formed by the forward assist signal and a signal of a signal electrode. pulse and the selection signal and the matrix drive method of any of the flat display device according to claim 1-6, wherein the effective pulse is formed by the sum of pulse and formed by the signal of the signal electrode.