JPH0643430A - Matrix drive method for plane type display device - Google Patents

Abstract

PURPOSE:To provide the matrix driving method by which a display can always be executed in a satisfactory state even if a display condition is varied such as a temperature variation, in the plane type display device having bistability. CONSTITUTION:Pulse width of an effective pulse for inverting a reset state of a picture element is variable by allowing at least one AC converting signal to lag, in two drivers for driving a scanning electrode (COM) and a signal electrode (SEG). In this case, it is allowable that the AC converting signals of both drivers of the scanning electrode and the signal electrode are both allowed to lag, or only one of them is allowed to lag. As for this lag angle amount, manual control is allowable, and also, it is allowable that the control is executed automatically by detecting a temperature, etc.

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 pixels on the scan electrode to dark (or bright), and a selection signal is applied to the scan electrode,
By applying a bright (or dark) write signal to the signal electrode (display electrode) for a predetermined pixel, there is a write period in which a pixel at which this selection signal and the signal electrode intersect is written bright (or dark).

Some of the liquid crystals have a characteristic of being rewritten brightly or darkly by a product of a voltage applied to a pixel and time (hereinafter, this product is referred to as an effective value). In such a case, it is necessary to apply a pulse signal having an effective value in a predetermined range as a signal (referred to as an effective pulse) for writing in bright (or dark).

However, in this type of display device, the optimum pulse width (effective value) of the effective pulse changes depending on the display conditions. For example, this optimum pulse width changes depending on conditions such as the temperature of the liquid crystal, deterioration of the liquid crystal over time, variations in product characteristics, and changes in the frame frequency depending on the display target, that is, the software used. Therefore, there is a problem in that the image quality changes due to changes in these display conditions.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a flat-panel display device capable of always displaying in a good state even when display conditions such as temperature change change. It is an object to provide a matrix driving method.

[0006]

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. A flat-type display having a reset period for making dark or bright, and a writing period for writing or storing a pixel at an intersection of the scanning electrode to which a selection signal is added and the signal electrode to which a writing signal is added to be bright or dark. In the device, the pulse width of the effective pulse for inverting the reset state of the pixel is variable by delaying at least one of the signal of the scan electrode and the signal of the signal electrode. This is achieved by the matrix driving method.

Here, both the scanning electrode signal and the signal electrode signal may be retarded together, but only one of them may be retarded. The retard amount may be manually controlled, but may be automatically controlled by detecting temperature or the like.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view showing the concept of the arrangement of scanning electrodes and the overall configuration, and FIG. 2 is a waveform diagram of each part in the conventional two-pulse driving method. In the present invention, there is no delay angle of an AC signal. Show. FIG. 3 is a diagram showing the waveforms of the drive signals resulting from the combination of the signals shown in FIG. In this two-pulse driving method, a pre-reset period is provided immediately before the selection period to forcibly reset the display state of the pixel. Therefore, it should be said that the pre-reset 2-pulse drive method is correct, but it is omitted as appropriate and simply referred to as the 2-pulse method or the like.

In FIG. 1, X _{1 to} X ₅ are scan electrodes (COM),
Y _{1 to} Y ₅ are display electrodes (signal electrodes) (SEG),
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 is elect a predetermined signal to the electrodes _{X 1 ~X 5, Y 1 ~Y} 5 in accordance with the output of the controller C.
Here, only five electrodes are shown for simplification of description, but it is needless to say that in reality, a large number of electrodes are provided.

[0010] Each driver D _X, 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 selects one of these voltages Built-in analog switch group for output. This switch group is on / off controlled by a data signal sent from the controller C and an alternating signal (hereinafter referred to as M signal or M), and outputs a signal having a waveform shown in FIG. 2 to the scan electrode X and the signal electrode Y. .

In FIG. 2, SEG represents a signal related to the signal electrode Y, and COM represents a signal related to the scan electrode X. To the driver D _X , a data signal that is turned on during 2τ of the selection period and an M signal for converting the data signal into an alternating current are input. The M signal changes from OFF to ON in the period of τ, and based on these, the driver D _X causes the “output” of COM in FIG.
The step-like signal changing from V _C1 to V _C2 is output as shown in the column. Further, during 2τ of the non-selection period, the data signal is turned off, and the “output” is a step signal changing from V _C4 to V _C3 .

Similarly, when writing to the driver D _Y (ON
Data signal which is turned on at the time of writing) and turned off at the time of non-writing (when the writing is off) and the M signal for making this alternating current are inputted, and its "output" is changed from V _S2 to V _S1 when turned on. It has a waveform, and changes from V _S4 to V _S3 when it is OFF, but since both are set to the same voltage, the voltage becomes a constant voltage.

When the "output" of COM and the "output" of SEG are applied to the scan electrode X and the signal electrode Y in this manner, the pixel in the intersection region of both electrodes X and Y is (SE
The voltage of (G output-COM output) is applied. This voltage waveform is shown by the "composite waveform" in FIG. The following S
The output of EG is called SEG signal and the output of COM is called COM signal.

In this way, 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 are combined to cancel the direct current component. In the present application, such driving is referred to as AC driving.

FIG. 3 shows a drive signal applied to a pixel when the same pixel is not written (unselected) after being written (selected) ON or OFF to a pixel. As shown. When the SEG signal is turned ON and when the SEG signal is turned OFF during non-selection after ON or OFF is selected, that is, the pixel (next pixel) on the adjacent scanning line is O
Since there are cases where it becomes N · OFF, four cases (A) to (D) may occur depending on their combination. In each of these cases, the effective pulse that contributes to writing is shaded.

The present invention is based on the conventional method as described above.
By delaying the signal, the display image quality is improved. Therefore, in this embodiment, as shown in FIG.
A manual operator 10 for delaying a signal, a deterioration detecting means 12, a voltage detecting means 14, a frame cycle detecting means 16, and a temperature sensor 18 are provided.

The manual operator 10 is for the operator to perform a manual operation while looking at the liquid crystal display screen, and to detect the amount of retardation of the M signal that gives the best image quality by this operation. The deterioration detecting unit 12 detects deterioration of the liquid crystal over time, and is configured to integrate the display time of the liquid crystal display plate and automatically change the retard angle amount according to the integrated time.

The voltage detecting means 14 detects a variation in the driving voltage of the liquid crystal and automatically changes the retard amount. The frame cycle detecting means 16 automatically controls the retard amount in accordance with the frame cycle when the frame cycle of the display screen differs depending on the software used. The temperature sensor 18 detects the temperature of the liquid crystal display panel and the operating environment temperature, and automatically controls the retard angle amount in accordance with this temperature.

The M signal to be retarded may be of either SEG or COM, or may be either one of them. FIG. 4 is a diagram showing waveforms of respective signals when retarding both M signals, and FIG. 5 is a diagram showing combinations thereof. Further, FIGS. 6, 7 and 8 show a case where the M signal is not retarded (pre-reset 2 pulse) and a case where it is retarded (pre-reset 2 pulse 60 ° retard), and FIG. FIG. 7 shows a waveform of a selection signal, FIG. 7 shows a signal waveform obtained by combining the signals, and FIG. 8 shows a state of a bias waveform.

When both the M signals of SEG and COM are both retarded in this way, the effective pulse that contributes to writing is as shown by the diagonal lines in FIG. By comparing this with the case of the retardation amount 0 shown in FIG. 2, the effective value of the effective pulse can be reduced. That is, the effective value can be controlled by the retard amount of the M signal. Therefore, the effective value can be controlled by adapting to the change of the display condition by the M signal.

In the case of this embodiment, the effect that the drive margin is increased to improve and stabilize the image quality is also obtained. Here, the drive margin is obtained by actually measuring the change in the light / dark intensity ratio with respect to the drive pulse width in the actual liquid crystal, but here, the ratio of the effective value, which is a standard of the drive margin, is used as the drive margin. It is used by defining it as an index. That is, this drive margin index is
It is the ratio of the minimum valid value needed to invert and write the reset pixel to the maximum valid value that must not be exceeded to keep the reset state.

Now, it is assumed that the drive signal, that is, the voltage of the composite waveform is V _S1 = V _c1 = 4, V _S2 = V _C2 = 0, V _S3 = V _S4 = 2, V _C3 = 3, and V _C4 = 1. In this case, the region which is considered to be a substantially effective pulse is the region shown by hatching in FIGS. 3 and 5 or the region shown by hatching in FIG. 7, and the effective value of each hatched region or hatching region is added.

In the left column of FIG. 3 or FIG. 7 in which the retard amount is 0, the driving conditions become the most severe in the cases of (A) and (D). The margin index is 4/3 = 1.3.

On the other hand, in FIG. 5, the retardation amount θ is 1 pulse
When 80 °, for example, θ = 60 ° (right column in FIG. 7), the severest driving conditions are in the cases of (A) and (D), and the driving margin index in this case is 3 / 2 =
It becomes 1.5. As a result, it can be seen that the drive margin index increases from 1.3 to 1.5.

Further, during the period when there is no selection signal, a voltage having a bias waveform that changes between positive and negative as shown in FIG. 8 is applied. As is clear from this figure, the maximum effective value in the non-selection period is 2 in the conventional method (when there is no delay angle), whereas it is in the method of the present invention (when the delay angle is 60 °). The maximum effective value will be reduced to 4/3.

That is, in the non-selection period, a voltage that changes between positive and negative with the amplitude of the maximum effective value is applied to the pixel. Generally, the amplitude voltage at this time (that is, the maximum effective value)
In particular, the minute fluctuations of the liquid crystal intensify in the darkly selected pixels, which causes an increase in the amount of light leaking through the pixels.
Therefore, the contrast is lowered and the image quality is lowered. However, according to the present invention, since the maximum effective value becomes small as described above, it is possible to obtain the effect of increasing the contrast and improving the image quality.

The voltages V _{s1 to} V _s4 and V _c1 used here are
~ V _c4 is optimally determined according to operating environment conditions (temperature, humidity, pressure, etc.), liquid crystal element configuration (liquid crystal component, alignment film, insulating film, assembly method, injection method, gap thickness, etc.), drive voltage waveform, etc. It is what is done. In this way the maximum drive voltage,
These voltages are determined so as to optimize the bias ratio.

[0028]

[Second Embodiment] This embodiment is applied to a 3-pulse driving method. FIG. 9 is a waveform explanatory view of a conventional example to the 3-pulse driving method, and FIG. 10 is a waveform explanation when the present invention is applied. It is a figure. According to the 3-pulse method, the driving margin index of 1.5 in the conventional method is 1.75 according to the present invention.
Can be increased to

[0029]

[Third Embodiment] This embodiment relates to the 4-pulse driving method, and FIG. 11 is a waveform explanatory view of the conventional example, and FIG.
FIG. 4 is a waveform explanatory diagram when the present invention is applied. According to the 4-pulse method, the driving margin index is 1.33 as compared with the conventional method.
Can be increased from 1.5 to 1.5.

Each of the above embodiments is the M of SEG and COM.
Although the signals are both retarded by the same amount (60 °), the present invention may delay the M signal of either SEG or COM. Alternatively, the SEG signal and the COM signal may be directly retarded without using the M signal.

Needless to say, the retard amount is set so that the image quality of the display screen is optimized. When detecting the deterioration, voltage, frame period, temperature, etc. and automatically controlling the amount of delay angle, the optimum amount of delay angle for these changes in display conditions is stored in advance and the optimum amount of delay angle is adjusted according to changes in display conditions. Then, the contents of this memory can be read out appropriately to control the retard amount.

Further, although the liquid crystal display device is used in the above embodiments, the present invention is not limited to this, and any other display device having a bistability, for example, a dispersion type liquid crystal, SBIND or the like can be used. Applicable and includes this.

[0033]

[Experimental example] An experiment was conducted under the following conditions. Substrate: Glass substrate Electrode: ITO pattern created by etching Insulation film: SiO ₂ , electron beam evaporation, 100 nm Alignment film: SiO diagonal evaporation about 40 nm Assembly: Cell gap 2 μm (SiO ₂ as a gap agent [Catalyst Kasei Co., Ltd. product Name: True sphere] Injection: 100 ° C. for 30 minutes Liquid crystal: Liquid crystal composition shown in Table 1 Measurement method: Liquid crystal display device at 35 ° C., pre-reset 2
Apply each drive waveform by pulse drive method (± 32
V, duty 120, bias ratio 1/4), microscope (Nikon OPTIPHOTO2-POL, objective lens MPlan10)
And a photodiode was used to measure the brightness of the bright frame (B) and the brightness of the dark frame (D).
The B / D ratio was measured while gradually increasing the pulse width.

[0034]

[Table 1]

From the above experiment, the measurement results shown in Table 2 were obtained.

[0036]

[Table 2]

[0037]

As described above, according to the first aspect of the present invention, the pulse width of the effective pulse for inverting the reset state is retarded by the alternating signal of at least one of the driver of the scan electrode and the signal electrode. The effective value of the effective pulse suitable for the display condition can be easily set without controlling the voltage or frequency of the drive signal. For this reason, the drive margin index is increased, the contrast is increased, and a good image quality is always obtained in response to changes in display device characteristics due to temperature changes and deterioration, product variations, and changes in frame frequency due to software used. Will be possible.

When the drivers for both the scan electrodes and the signal electrodes are retarded by a predetermined angle at the same time, the drive margin can be improved (claim 2). However, the present invention can achieve the intended purpose by delaying the AC signal of either one of the drivers.

The retard amount of the AC signal can be manually adjusted by the operator while looking at the display screen to optimize the image quality (claim 3). The retard amount may be automatically adjusted (claim 4). In this case, a means for detecting a change in the display condition is provided, and the optimum delay angle amount according to this change can be read from the memory to control the delay angle amount.

[Brief description of drawings]

FIG. 1 is a plan view showing the concept of electrode arrangement and overall configuration.

FIG. 2 is a diagram showing a waveform of each part in the case where there is no retardation of the AC signal in the pre-reset 2-pulse driving method.

FIG. 3 is a diagram showing a waveform of a drive signal according to a combination of the signals.

FIG. 4 is a diagram showing a waveform of each part when an AC signal is retarded by a pre-reset two-pulse driving method.

FIG. 5 is a diagram showing a waveform of a drive signal according to a combination of the signals.

FIG. 6 is a diagram showing a waveform of a selection signal or the like by comparing the conventional method with the present invention.

FIG. 7 is a diagram showing a signal waveform in which each signal is also combined.

FIG. 8 is a diagram showing a state of a bias waveform.

FIG. 9 is a diagram showing a waveform of a conventional example of the 3-pulse method.

FIG. 10 is a diagram showing a waveform according to the present invention.

FIG. 11 is a diagram showing a waveform of a conventional example of the 4-pulse method.

FIG. 12 is a diagram showing a waveform according to the present invention.

[Explanation of symbols]

X ₁ to X ₅ scan electrodes Y ₁ to Y ₅ display electrodes D _X, D _Y driver M AC signal θ retard amount

Claims (4)

[Claims] 1. A reset period in which a pixel having bistability is formed at an intersection of a scan electrode and a signal electrode, and a reset signal applied to the scan electrode makes all pixels on the scan electrode dark or bright. And a writing period in which a pixel at the intersection of the scanning electrode to which a selection signal is applied and the signal electrode to which a writing signal is applied is written or stored in a bright or dark manner, and a reset state of the pixel is set. A matrix driving method for a flat-panel display device, wherein a pulse width of an effective pulse to be inverted is made variable by delaying at least one of a signal of the scanning electrode and a signal of the signal electrode. 2. The matrix driving method for a flat panel display device according to claim 1, wherein the signals of the scanning electrodes and the signals of the signal electrodes are retarded by the same angle. 3. The method for driving a matrix of a flat-panel display device according to claim 1, wherein the retard amount of the alternating signal is controllable by a manual operator. 4. The retardation amount of the AC signal is automatically controlled according to the display condition of the flat display device.
Alternatively, the matrix driving method of the flat-panel display device of item 2.