JPH0749480A - Method for driving matrix of flat type display device - Google Patents

Abstract

PURPOSE:To provide a driving method which dispenses with a compensation signal for canceling a DC component such as an anti-preset signal to enhance contrast, and is suitable for the case having the less number of scanning lines by alternately reversing the polarity of each frame formed by one reset signal, one selection signal and a number of non-selection signals. CONSTITUTION:A scanning signal having positive polarity is formed of a selection signal S, two pre-reset signals PR inserted just before it, and a number of non-selection signals NS. The scanning signal having the reversed polarity is similarly formed of a reversed polarity selection signal AS, reversed polarity pre-reset signals APR, and reversed polarity non-selection signals ANS. Since the signal contained in each frame is controlled to alternately reverse the polarity in this way, in the scanning signal, even when either one of positive and negative DC components of the picture element is increased in a certain frame, it is canceled because the DC component having the reversed polarity is increased in the following frame. Therefore, the DC component is averaged to 0 within the time for two frames.

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 applied to a flat display device having bistability.

[0002]

2. Description of the Related Art A flat-panel display device such as a ferroelectric liquid crystal having high-speed switching characteristics and bistability (memory property) is known. In this type, a reset signal applied to the scan electrode forcibly resets all the pixels on the scan electrode to dark (or bright), and then, while applying a selection signal to the scan electrode, By applying a bright (or dark) write signal to the signal electrode (display electrode), a pixel at which the selection signal and the signal electrode intersect is written bright (or dark).

There is also a writing signal in which a voltage signal corresponding to a gradation to be displayed is used, and a pixel at which a selection signal and a writing signal intersect is written and stored at a brightness of a desired gradation. Here, the liquid crystal has a characteristic of being rewritten bright (or dark) according to the size of the product of the voltage applied to the pixel and the time (hereinafter, this product is referred to as an effective value), or a characteristic of being rewritten to a predetermined gradation of brightness. Can be used.

FIG. 9 is a diagram showing a driving waveform by a conventional two-pulse method, and FIG. 10 is a diagram showing an example of a configuration of a scanning signal for one frame applied to a certain scanning line.

In the two-pulse method, a pre-reset signal PR (which is the same as the reset signal of the present application) is input immediately before the selection signal is input to the scan electrodes to turn on the display signal.
Forcibly reset to dark regardless of OFF. Here, the scanning signal (-COM) has a pulse width of 2τ and is applied to the scanning electrodes, and the display signal (SEG) has a pulse width of 2τ and is applied to the display electrodes (signal electrodes).

The display signal (SEG) corresponds to light and dark and is 2
Seeds are prepared and set to have a high voltage for bright (ON) gradations and a low voltage for dark (OFF) gradations. As a result, the voltage applied to the pixel depends on the combination of the scanning signal (-COM) and the display signal (SEG).
There are various changes as shown in.

For example, when the pre-reset signal PR is input to the scan electrodes, the display signal (SEG) is turned on and off.
Whichever FF is input, a negative voltage (effective value) is applied, and this pixel is forcibly reset to dark. If ON and OFF of the display signal SEG are input to the signal electrodes while the selection signal S is input to the scan electrodes, the signals applied to the pixels are as shown in FIG. It becomes the brightness of the gradation.

In this way, as shown in FIG. 10, the scanning signal including the selection signal S is applied to the predetermined scanning electrode at a predetermined timing corresponding thereto. One or a plurality of pre-reset signals PR are preceded by one or a plurality of anti-pre-reset signals APR having polarities opposite to those of the pre-reset signals PR. This anti-pre-reset signal A
It is canceled by PR.

As described above, positive and negative DC pulse voltages are applied to the pixel. Since the liquid crystal of the element is deteriorated when a direct current component remains in the drive pulse, positive and negative pulses (hereinafter referred to as compensation signal and compensation pulse) are combined to cancel the direct current component. In the present application, such driving is referred to as AC driving.

[0010]

In the conventional driving method as described above, the time T (AP of the compensation signal for canceling the DC component is canceled.
R) (the time of the anti-pre-reset signal in this example) is required.

Now, let T _F be the time for one frame, and light (O
If the longest time of N) is T _B , the contrast C is
The C = T _B / T _F. Here, T _F includes the time of the anti-prereset signal APR. This time T
Since (APR) is indispensable in the conventional technique, T _F cannot be further shortened, and it is difficult to increase the contrast.

Further, the frame period T _F includes a number of non-selection signals corresponding to the number of scanning lines, but if the number of scanning lines is small, the time ratio of the compensation signal in the frame period T _F increases. Become. Therefore, there is a problem that the conventional driving method is not practical for an optical exposure (image reading) head having a particularly small number of scanning lines, for example, several line sensors arranged in the length direction. .

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to enhance contrast by eliminating the need for a compensation signal such as an anti-prereset signal for canceling a DC component. Another object of the present invention is to provide a matrix driving method for a flat panel display device which is suitable even when the number of scanning lines is small.

[0014]

According to the present invention, an object of the present invention is to form a pixel having bistability at the intersection of a scan electrode and a signal electrode, and to reset all pixels on this scan electrode by a reset signal applied to the scan electrode. After resetting to either dark or light,
In a flat-panel display device in which a pixel at an intersection of the scanning electrode to which a selection signal is applied and the signal electrode to which a writing signal is applied is controlled to have a predetermined brightness for writing and storing, one reset signal and one reset signal This is achieved by a matrix driving method for a flat panel display device, characterized in that the polarities of the frames formed by one selection signal and a large number of non-selection signals are alternately reversed.

Immediately after the effective pulse for inverting the reset state, a forward assist signal having the same polarity as the effective pulse or a reverse assist signal having the opposite polarity may be added to increase the drive margin.

[0016]

Embodiment 1 FIG. 1 is a diagram showing an electrode arrangement, FIG. 2 is a diagram showing drive 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 arrangement example of scanning signals for two frames applied to a certain scanning line, and FIG. 4 is a diagram showing waveforms of scanning signals for two frames.

In FIG. 1, X _{1 to} X ₅ are scan electrodes, and Y _{1 to} Y ₅
Is a display electrode (signal electrode), and only five electrodes are shown here for simplification of description, but of course, in reality, it has a very large number of electrodes. 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.

As shown in FIG. 3, the positive scanning signal is composed of a selection signal S, two pre-reset signals PR inserted immediately before it, and a large number of non-selection signals NS. The reverse polarity scanning signal is similarly composed of a reverse polarity selection signal AS, a reverse polarity pre-reset signal APR, and a reverse polarity non-selection signal ANS.

The waveforms of these signals are set as shown in FIG. The pre-reset signal PR and the selection / non-selection signals S and NS are the same as those described in FIG. The reverse polarity signal is a signal in which the respective signals have opposite polarities.

The signal contained in each frame is
Since the polarities are controlled so as to be alternately reversed, the scanning signal becomes as shown in FIG. 4, and even if the pixel has a large positive or negative DC component in one frame, the scanning signal is completely opposite in the next frame. The polar DC component increases and is offset. Therefore, the DC component is averaged and becomes zero within the time of two frames.

[0021]

Second Embodiment In the first embodiment described above, one frame is composed of the pre-reset signal PR, the selection signal S and the non-selection signal. However, the present invention can be applied to the one in which the forward assist signal A having the same polarity as the effective pulse contributing to the writing at the time of selection is added after the selection signal S.

5 and 6 show an embodiment in which the forward assist signal A is added. FIG. 5 is a diagram showing the drive signal waveform in this case, and FIG. 6 is a diagram showing the configuration of the scanning signal. In these figures, signals of opposite polarities are indicated by adding A at the beginning of the symbols S, NS, PR and A indicating positive polarity signals.

According to this embodiment, since the forward assist signal A and the reverse polarity forward assist signal AA are provided immediately after the selection signals S and AS, the pulse (effective pulse) that contributes to the writing of the selection signals S and AS is next. Must always have a pulse of the same polarity as this effective pulse. Therefore, a signal having the same polarity as the effective pulse continues immediately after the effective pulse, and the effective value of the effective pulse substantially increases. As a result, the driving margin is increased and the image quality is improved.

In FIG. 5, when the scanning signal is the forward assist signal A and the display signal is ON, a pulse having a polarity opposite to that of the effective pulse (shown by the diagonal lines in the figure) enters in the first half cycle, but the effective value is small. Moreover, since the effective value of the positive pulse immediately after that is large, the pulse in the shaded area can be substantially ignored.

[0025]

[Third Embodiment] FIG. 7 is a diagram showing drive signal waveforms of still another embodiment, and FIG. 8 is a diagram showing a configuration of a scanning signal thereof. In this embodiment, the reverse assist signals A and AA having a polarity opposite to that of the effective pulse are added immediately after the selection signals S and AS.

Therefore, next to the pulse (effective pulse) that contributes to the writing of the selection signals S and AS, the reverse assist signals A and AA cause a pulse having a polarity opposite to that of the effective pulse. This reverse polarity pulse is used for selecting signals S and AS.
To prevent the following signal from affecting the effective value of the effective pulse. As a result, the drive margin can be increased and the image quality can be improved.

[0027]

Other Embodiments In each of the above embodiments, the two-pulse method in which the signal such as the selection signal is set to have two pulses in the time width of 2τ is used, but the present invention uses three or four pulses. A three-pulse method or a four-pulse method in which each signal is composed of pulses may be used.

In the above embodiment, the pixels are written in either light or dark in the selection period after reset (time division gradation control system). However, the voltage of the display signal is changed in a plurality of stages. A device capable of writing with multi-level brightness (pulse intensity gradation control system) may be used. Furthermore, although it is desirable to reverse the polarity of the signal every one frame, the present invention includes one in which the polarity is inverted every two frames or every fixed number of frames.

[0029]

As described above, according to the first aspect of the present invention, a signal for one frame consisting of one reset signal, one selection signal, and a large number of non-selection signals is reversed in polarity every predetermined number of frames. Therefore, it is not necessary to add a compensation pulse for canceling the DC component of the voltage signal applied to the pixel, such as an anti-pre-reset signal. Therefore, the time T _{F of} one frame can be shortened, and the time of maximum brightness is set to T _B , and T _B / T
_The contrast indicated by _F can be increased.

In general, when the time width of the compensation pulse occupied in one scanning line increases, the time ratio of the compensation pulse increases when the number of scanning lines is small (that is, when the number of non-selection signals is small), and the contrast is increased. It drops and becomes impractical. However, according to the present invention, since the compensation pulse is not necessary, the contrast can be maintained high even when the number of scanning lines is small. Therefore, for example, a driving method suitable for an apparatus having a very small number of scanning lines such as a head for light exposure in which a plurality of line sensors are arranged in the length direction can be provided.

[Brief description of 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 for two frames.

FIG. 4 is a diagram showing waveforms of scanning signals for two frames.

FIG. 5 is a diagram showing drive waveforms according to the second embodiment.

FIG. 6 is a diagram showing an array of drive signals thereof.

FIG. 7 is a diagram showing drive waveforms according to the third embodiment.

FIG. 8 is a diagram showing an arrangement of the scanning signals.

FIG. 9 is a diagram showing a drive waveform according to a conventional 2-pulse method.

FIG. 10 is a diagram showing the configuration of the scanning signal X ₁ to ₅ scanning electrodes Y ₁ to ₅ display electrodes S selection signal AS reverse polarity selection signal NS non-selection signal ANS reverse polarity non-selection signal PR pre-reset signal APR reverse polarity pre Reset signal

Claims (3)

[Claims] 1. A bistable pixel is formed at the intersection of a scan electrode and a signal electrode, and all pixels on the scan electrode are reset to either dark or bright by a reset signal applied to the scan electrode. In a flat-panel display device in which a pixel at an intersection of the scanning electrode to which a selection signal is applied and the signal electrode to which a writing signal is applied is controlled to have a predetermined brightness and written and stored, one reset signal and A matrix driving method for a flat-panel display device, characterized in that the polarities of the respective frames formed by one selection signal and a large number of non-selection signals are reversed every fixed number of frames. 2. The matrix driving method for a flat panel display device according to claim 1, wherein a forward assist signal having the same polarity as the effective pulse is added immediately after the effective pulse for inverting the reset state. 3. The matrix driving method for a flat panel display device according to claim 1, wherein an inverse assist signal having a polarity opposite to that of the effective pulse is added immediately after the effective pulse for inverting the reset state.