JPS6349239B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for driving a line unit display liquid crystal display panel capable of displaying a flash display in which a display pattern blinks. Liquid crystal display panels have features such as low power consumption, low driving voltage, and non-emissive display, and are widely used for various displays. For example, alphanumeric characters are displayed using a segment display method, characters are displayed using a matrix display method, and graphic displays are used. Furthermore, the liquid crystal display panel displays line units,
In other words, using a group of lines in two directions that are perpendicular to each other,
It is also used to display crosshairs, double crosses, squares, etc. When performing such line-by-line display, a display panel having the same structure as the matrix display method is used. Therefore, as in the case of matrix displays, the electro-optical effects of liquid crystals applied to displays include DSM (dynamic scattering mode), TN (twisted nematics), and even GH (guest host).
etc., and each has its advantages and disadvantages.
In other words, DSM has a wide viewing angle but has a high driving voltage and consumes a lot of power; TN has a low driving voltage but requires a polarizing plate, which limits the display's lifespan; and GH has a bright display but , it is difficult to perform so-called positive type display in which a colored pattern appears on a white background. However, by applying CNT (cholesteric-nematic phase transition), which is another electro-optical effect of liquid crystals used in matrix displays, it is possible to produce bright displays with low power consumption and a wide field of view. The following describes the phenomenon of CNTs applied to phase change liquid crystal display panels.
CNTs are observed in a cell constructed by vertically aligning the inner surface of the electrode substrate and sandwiching a cholesteric liquid crystal with positive dielectric anisotropy. The cholesteric liquid crystal in a cell having such a structure is in a transparent cholesteric phase (hereinafter referred to as the S state) in an initial state where no voltage is applied. When voltage is applied in this state, the applied voltage is extremely low.
When the applied voltage exceeds a certain value V _a and is below the threshold voltage value V _H , a light-scattering cholesteric phase (hereinafter referred to as F state) is formed, and when the applied voltage is above V _H , a transparent nematic phase is formed. (hereinafter referred to as the H state) is formed. The F state formed under the application of a voltage V ₂ where V ₂ < V _H is another state of the cholesteric phase that also scatters light when the voltage V ₂ is zero (hereinafter referred to as the F ₀ state). , and this state accumulates for a long time. On the other hand, V ₁ > V _H
When the voltage V ₁ is set to zero, the _H state formed under the application of a voltage _{V 1} of Returns to the transparent S state. However, the voltage
After V ₁ (>V _H ) is set to zero, when a low voltage (V _a ≦) V ₂ (<V _H ) is applied again after time τ _NC , a cholesteric phase exhibiting light scattering (hereinafter referred to as F' state) is applied. When the voltage V ₂ is set to zero in this state, it transitions to the F ₀ state of light scattering and is accumulated for a long time.
Another form of voltage change is to directly change the voltage from the state where V ₁ > V _H to a low voltage without passing through the voltage zero state.
Considering the case where V _H /2 < V ₂ < V _H , in this case the transparent H state formed under the application of V ₁ > V _H is also transformed into a transparent transient state (hereinafter referred to as
H' state) and is held for a time T that depends on the value of _V2 . After time T, it transitions to a light scattering state. In addition, the H′ state maintained under the application of V ₂ <V _H is V ₁ (>V _H ) when the voltage V ₂ is zero.
→Similar to the case of O voltage change, S passes through G′ state
Return to state. The above is the main behavior of the CNT phenomenon. To help understand the driving and operation of a liquid crystal display panel that utilizes the CNT phenomenon, the main points of the above behavior are summarized in a table below.

[Table] However, V ₁ > V _H , V _H /2 < V ₂ < V _H , and among the states, ◯ indicates a transparent state, and □ indicates a light scattering state. Next, we will explain how this CNT phenomenon is applied to line-by-line liquid crystal display panels. First, static drive, which is the simplest drive method, will be explained. This is done by applying a voltage V ₂ (<V _H ) to the display pixels in the selected line to bring them into the F state, and applying a voltage V ₁ (>V _H ) to the display pixels at the intersection of non-selected lines. This is a method to bring it into the H state. However, with this driving method, the display pattern changes, and in the display pixel that should change from a transparent non-selected display pixel to a light scattering selected display pixel, V ₁
A voltage change occurs from (>V _H ) to V ₂ (<V _H ), and as mentioned above, even after the voltage changes to V ₂ , it does not immediately become a light scattering state and remains transparent for a period of time T. The H′ state persists. In other words, the characteristic of the display panel is that the response time is extremely long. In order to shorten this response time, matrix display type dynamic driving is performed. Next, the dynamic driving method will be explained. In this driving method, first, when writing a display pattern, a voltage V ₁ (>V _H ) is applied to all display pixels as pre-excitation to bring them into an H state. Next, change the voltage V ₁ to V ₂ (<
At this _time , the voltage applied to the selected display pixel becomes zero for a time t ₀ (>τ _NC ), and then changes to V ₂ , and the voltage applied to the non-selected display pixel changes directly from V ₁ → V ₂ without passing through zero.
As a result, as described above, the selected display pixel whose voltage changes from V ₁ → O → V ₂ causes a state transition from H → F' and becomes a light scattering state, while the non-selected display pixel whose voltage changes from V ₁ → V ₂ The selected pixel undergoes a state transition from H to H' and remains transparent for a period of time T. Therefore, the matrix display is either a refresh type in which such voltage changes are repeated at a cycle shorter than time T, or a storage type in which the voltage applied to all display pixels is zeroed within time T to fix and accumulate the display pattern. becomes possible. In other words, in the refresh type, mode 1 and mode 3 in the above table are created and displayed in the light scattering F' state and the transparent H' state, whereas in the storage type, mode 2, mode 4, and of light scattering.
This means that the display is performed in the F ₀ state and the transparent S state. In either driving method, a voltage V 1 higher than the cholesteric nematic phase transition threshold voltage V _H is first applied to the selected (light scattering) pixel, and then a voltage V ₁ that does not form a 0 or light scattering state is applied to the selected (light scattering) pixel. After setting the voltage to an extremely low value of _H /2 or less,
The cholesteric-nematic phase transition threshold voltage V _H or below causes the formation of a light scattering state.
A voltage value V ₂ of V _H /2 or more may be applied. This is a matrix display type dynamic drive method, and compared to static drive, where the response time is limited by a relatively long relaxation time T (several seconds),
The response time is the pre-excitation time τ _h (several tens to hundreds of milliseconds) and
It is only limited by t ₀ (several milliseconds), and extremely high-speed image writing is possible. However, when such a dynamic driving method is used, although the response speed is improved, the entire display screen becomes transparent during the pre-excitation time τ _h , resulting in so-called flicker. When performing a flash display in which the display pattern blinks, the above-described dynamic driving method can be used as is, taking advantage of the phenomenon that the entire display screen becomes transparent during the time τ _h . However, this dynamic driving method has the disadvantage that the driving is complicated because it consists of three steps of changing the voltage value, such as applying 2V, applying V or O, and applying V. An object of the present invention is to provide a driving method for displaying an image using a phase change type liquid crystal display panel, which enables flash display with a simple configuration. The present invention provides a method for displaying lines in line units using a cholesteric nematic phase change matrix display liquid crystal panel in which the inner surface of an electrode substrate is vertically aligned. The voltage value applied to the display pixel is low enough to form a light scattering state below the cholesteric-nematic phase transition threshold voltage value, and the voltage value applied to the display pixel at the intersection of non-selected lines is low enough to form a light scattering state. The first step is a cholesteric-nematic phase transition threshold voltage that is high enough to form a transparent state, and the voltage applied to all display pixels is zero or does not form a light scattering state. A method for driving a phase change type liquid crystal display panel, in which a second step in which the degree of change is extremely low is periodically repeated;
Or at least the voltage value applied to the display pixels in the selection lines other than the intersections of the selection lines is
The voltage value is zero or extremely low enough not to cause a light scattering state, and the voltage value applied to the display pixel at the intersection of non-selected lines is cholesteric.
The first step is such that the voltage is at least 1/2 of the nematic phase transition threshold voltage, and a transparent state is formed when the voltage applied to all display pixels is at least the cholesteric nematic phase transition threshold voltage. A method for driving a phase change type liquid crystal display panel is obtained in which the second step in which the second step has a high value such that the second step is periodically repeated. Next, the present invention will be explained in detail with reference to the drawings.
FIG. 1 is a diagram showing an example of the voltage arrangement of the driving method according to the present invention. Figure 1 shows the nth matrix display.
This is an example of selectively displaying a row line and an m-th column line, and the voltages applied to the (n-2) to (n+2)-th row electrodes and the (m-2) to (m+2)-th column electrodes. and the voltage value applied to each display pixel according to the voltage arrangement. Due to the voltage arrangement as shown in FIG.
2) Voltage values applied to display pixels at the intersections of (n-1), (n+1), (n+2) rows and (m-2), (m-1), (m+1), (m+2) columns becomes 2V.
Therefore, by periodically repeating the first step of applying a voltage as shown in Figure 1 and the second step of setting the voltage applied to all line electrodes to zero (or less than V _a ), Therefore, the voltage applied to the selected display pixels other than the intersection of the selected lines changes from V→O→V→O→, and the voltage applied to the non-selected display pixels changes from 2V→O→2V.
It will change as →O→. Therefore, V _H /2
If <V<V _H is set, the selected display pixel changes its state as F′→F ₀ →F′→F ₀ → by the driving method of this embodiment, and is always maintained in a light scattering state. Ru.
On the other hand, the non-selected display pixels change state as H→G'→H→G'→, and alternately repeat a transparent state and a light scattering state. That is, in the first step of driving, a display pattern is displayed in a light-scattering region on a transparent background, and in the second step, the entire screen becomes a light-scattering state, and this is alternately repeated to realize a flash display. That will happen. As explained earlier, the G' state that has transitioned from the H state transitions to the transparent S state after the time τ _rp . Therefore, it is preferable that the connection time of the second process to maintain the G' state is shorter than τ _rp , but even if it is longer than τ _rp , the overall transparent state time is shorter than the connection time of the second process. It only becomes longer, but does not affect display. As can be seen from the examples, the driving method of the present invention can be realized by simply applying a voltage of ±V to the non-selected line electrodes in the first step, so it is extremely simple compared to the conventional dynamic driving method. It also has the advantage that the drive circuit can be easily configured.
Figure 2 shows a second version with an improved flash display format.
FIG. 3 is a diagram showing an example of voltage arrangement of the driving method according to the invention. Similar to FIG. 1, FIG. 2 is an example of selecting the n-th line and the m-th line of the matrix display. According to the voltage arrangement as shown in FIG. 2a, a voltage of 2V is applied to all display pixels.
Next, according to the voltage arrangement shown in FIG. 2b, the voltage value applied to the display pixels in the selected line other than the intersection of the nth row and mth column of the selected line becomes zero, and the voltage value applied to the display pixels in the selected line other than the intersection of the selected line ), (n-1), (n+1), (n
+2) row and (m-2), (m-1), (m+
1), the voltage value applied to the display pixel at the intersection of the (m+2) columns is V. Therefore, by periodically repeating the first step of applying a voltage as shown in FIG. 2a and the second step of applying a voltage as shown in FIG. 2b, the selected display pixel can be adjusted. Applied voltage is 2V→O→
The voltage applied to the non-selected display pixel changes as 2V→O→, and the voltage applied to the non-selected display pixel changes as 2V→V→2V→V→.
(However, the value 0 in the figure is sufficient as long as it is less than the threshold voltage V _a that causes the transition from the transparent state to the light scattering state.) Therefore, if V _H/2 < V < V _H is set. ,
By the driving method of this embodiment, the selected display pixel is
The state changes as →G′→H→G′→, and the transparent state and light scattering state are alternately repeated. On the other hand, the non-selected display pixels change state as H→H'→H→H'→,
Always kept transparent. That is, in the first step of driving, the entire screen becomes transparent,
In the second step, a display pattern is displayed in light scattering areas on a transparent background, and this is alternately repeated to realize a flash display. As explained earlier, the transparent H' state that has transitioned from the H state gradually begins to exhibit light scattering after time T. Therefore, from the viewpoint of display characteristics, it is preferable that the connection time of the second step of driving is within T.
Since the value of T is usually several seconds, it does not restrict normal flash display. According to the driving method of the present invention, a visually familiar flash display is realized in which a display pattern in a light scattering state flashes on a transparent ground, and a flash display in which the ground state repeats a transparent state and a light scattering state is realized. The display form is improved compared to flash display. In addition, although the case where DC voltage was applied was described in each Example, AC drive is preferable from the viewpoint of the lifespan of the liquid crystal display panel. For example, in the figure, instead of the DC voltages +V and -V, by using AC voltages V(O) and V(π) whose phases differ from each other by π,
The driving method of the present invention using an AC signal can be easily implemented. In addition, in the driving method of this embodiment, the voltage value applied to the display pixel at the intersection of the selection lines is
It may change from 2V to 0, in this case,
As explained on page 5, the state becomes transparent (S) after the time τ _rp . Therefore, when displaying a moving crosshair, the center point of the crosshair may become transparent if the moving speed is slow, but this does not pose any problem in terms of display image quality. do not have. As described above, according to the present invention, in a driving method for displaying images using a phase change type liquid crystal display panel, it is possible to obtain a driving method that enables flash display with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the driving method of the present invention, and shows an example of the voltage to be applied to each electrode and the voltage value to be applied to each display pixel. Second
The figure is a diagram for explaining the driving method of the second invention with a different display format.

Claims (1)

[Claims] 1. In a driving method for performing line-by-line display using a cholesteric-nematic phase change matrix display liquid crystal panel in which the inner surface of an electrode substrate is subjected to vertical alignment treatment, at least The voltage value applied to the display pixels in the selected line is less than the cholesteric-nematic phase transition threshold voltage value and is greater than or equal to the threshold voltage value V _a that causes the transparent state to transition to the light scattering state, and the voltage value applied to the display pixel in the non-selected line A first step in which the voltage applied to the display pixels at the intersection points is such a high value as to form a transparent state above the cholesteric-nematic phase transition threshold voltage, and the voltage is applied to all display pixels. a second step in which the voltage value is zero or an extremely low value less than V _a is periodically repeated. 2. In a driving method for performing line-by-line display using a cholesteric nematic phase change matrix display liquid crystal panel whose inner surface of an electrode substrate is subjected to vertical alignment treatment, at least display pixels in selected lines other than intersections of selected lines The voltage value applied to is zero or an extremely low value less than V _a (V _a is the threshold voltage value for transitioning from a transparent state to a light scattering state), and is applied to display pixels at the intersection of non-selected lines. The first step is such that the voltage value applied to all display pixels is equal to or more than 1/2 of the cholesteric-nematic phase transition threshold voltage value, and the voltage value applied to all display pixels is equal to the cholesteric-nematic phase transition threshold voltage value. A method for driving a phase change type liquid crystal display panel, characterized in that the second step in which the value is high enough to form a transparent state is periodically repeated.