JPS636875B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for driving a line-by-line display liquid crystal display panel that allows high-speed and high-quality image writing. 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, the electro-optical effects of liquid crystals applied to displays include DSM (dynamic scattering mode), TN (twisted nematics), and GH (guest host), just as in the case of matrix displays. Each has 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 dark life, and GH has a bright display, but For example, it is difficult to perform so-called positive display in which a colored pattern appears on a white background. However, CNT, which has an electro-optical effect of another liquid crystal used for matrix display,
By applying cholesteric, nematic, and phase transition, 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 vertically aligned on the inner surface of the electrode substrate.
It is also observed in a cell configured to sandwich cholesteric liquid crystals with positive dielectric constant 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 a voltage is applied in this state, if the applied voltage is extremely low or exceeds a certain value and is below the threshold voltage value V _H , the cholesteric phase (hereinafter referred to as F
A transparent nematic phase (hereinafter referred to as the H state) is formed when the applied voltage is greater than or equal to V _H . The F state formed under the application of a voltage V ₂ where V ₂ < V _H changes to another state of the cholesteric phase that also scatters light (hereinafter referred to as the F _p state) when the voltage V ₂ is reduced to zero. transition, 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 Return to the initial transparent S state with _rp . However, the voltage V ₁ (>
V _H ) becomes zero, and after time τ _NC the voltage becomes low again.
When V ₂ (<V _H ) is applied, it transitions to a cholesteric phase (hereinafter referred to as the F′ state) that exhibits light scattering,
If the voltage V ₂ is made zero in this state, the light will transition to the F _p state of light scattering and will be accumulated for a long time. As another form of voltage change, consider the case where the voltage changes directly from the state of V ₁ > V _H to the lower voltage V _H /2 < V ₂ < V _H without passing through the voltage zero state. In this case, is V ₁ > V _H
The transparent H state formed under the application transitions into a transparent transient state (hereinafter referred to as the H' state) and is maintained for a time T that depends on the value of _V2 . After time T, it transitions to a light scattering state. Also,
When the voltage V ₂ is set to zero, the H' state maintained under the application of V ₂ <V _H changes to the S state via the G' state, as in the case of a voltage change from V ₁ (>V _H ) to 0. Return to 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】

[Table] Among the states, ○ indicates a transparent state, and □ indicates a light scattering state.
to show that
However, V ₁ >V _H , V _H /2<V ₂ <V _H , and 〇 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, in this driving method, the display pattern changes, and the voltage from V ₁ (>V _H ) to V ₂ (<V _H ) is applied to the display pixel that should change from a transparent non-selected display pixel to a light scattering selected display pixel. As mentioned above, even after the voltage changes to _V2 , 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, the voltage V ₁ is changed to V ₂ (<V _H ), but at this time,
The voltage applied to the selected display pixel is the time t _p (>τ _NC )
The voltage applied to the non-selected display pixels changes directly from V ₁ to _{V 2 without} going through zero. As a result, as mentioned above, V ₁ →0
The selected display pixel that undergoes a voltage change of →V ₂ undergoes a state transition of H→F′ and enters a light scattering state.
An unselected pixel whose voltage changes from V ₁ to V ₂ 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.
In the storage type, mode 2 and mode 4 are created separately, and display is performed using the light scattering F _p state and the transparent S state. In either drive method,
For the selected (light scattering) pixel, first, the cholesteric
Voltage above nematic phase transition threshold voltage V _H
After applying V ₁ , the voltage is once set to 0 or an extremely low voltage value below V _H /2 that does not form a light scattering state, and then a light scattering state is formed below the cholesteric nematic phase transition threshold voltage value V _H What is necessary is to apply a voltage value V ₂ of V _H 2 or more that causes the voltage to increase. This is a matrix display type dynamic drive method, and compared to static drive where the response time is limited by the relatively long relaxation time T (several seconds), the response time is limited by the pre-excitation time τ _h (several tens to hundreds of seconds). (milliseconds) and t _p (several milliseconds), making extremely high-speed image writing possible. However, when such a dynamic driving method is used, although the response speed is improved, on the other hand, the entire display screen becomes transparent during the pre-excitation time τ _h , resulting in so-called flicker. Furthermore, since the driving process consists of three steps, the circuit configuration is complicated. An object of the present invention is to provide a driving method for displaying images using a phase change type liquid crystal display panel, which allows image writing to be performed at high speed, and which enables high-quality image display without noticeable flickering. The purpose is to provide a simple driving method. The method for driving a phase change type liquid crystal display panel of the present invention is such that when performing line-by-line display using a cholesteric nematic phase change type matrix display liquid crystal panel whose inner surface of an electrode substrate is vertically aligned, at least τ During _{the NC} time, the voltage value applied to all display pixels is set to zero or a very low value that does not cause a light scattering state, and then the display of the same pattern is maintained for a period of time at least at the intersection of selected lines. The voltage value applied to the display pixels in the non-selected lines is maintained at a low value that causes the formation of a light scattering state below the cholesteric-nematic phase transition threshold voltage value, and the voltage applied to the display pixels at the intersection of the non-selected lines is It consists of maintaining the applied voltage at a high value above the cholesteric nematic phase transition threshold voltage to form a transparent state. Next, the present invention will be explained in detail with reference to the drawings. The figure is a diagram showing an example of voltage arrangement of the driving method according to the present invention. The figure shows an example of selectively displaying the n-th line and the m-th column line in a matrix display, and the (n-2)th N(n+2)th row electrode and the (m-2)N(m+2)th line The voltage values applied to the column electrodes and the voltage values applied to each display pixel depending on the voltage arrangement are shown. According to the voltage arrangement as shown in the figure, a voltage of V is applied to the display pixels in the selected line other than the intersection of the nth row and mth column of the selected line, and the voltage of V is applied to the display pixels of the non-selected lines (n-2) and (n- 1), (n+
1), (n+2) row and (m-2), (m-1),
The display pixel at the intersection of (m+1) (m+2) columns has 2V
voltage is applied. Therefore, if the voltages applied to all electrodes are set to zero for a certain period of time _tp , and then voltages arranged as shown in the figure are applied, a voltage change from 0 to V occurs in the selected display pixel, A voltage change from 0 to 2 V occurs in the non-selected display pixels. Considering that before the display pattern shown in the figure is displayed, a voltage of V or 2V is applied to each display pixel in order to display the previous display pattern. The voltage applied to selected display pixels other than 2V
(or V) → 0 → V, and the voltage applied to the non-selected display pixel changes as 2V (or V) → 0 → 2V. Therefore, V _H /2<V<V _H
If this is set, the selected display pixel will be in the F' state of light scattering and the non-selected display pixel will be in the transparent H state by the driving method of this embodiment. Further, since the voltage applied to the selected display pixel remains zero for a certain period of time t _p (>τ _NC ), this image writing can be performed at extremely high speed. Furthermore, the non-selected display pixels are displayed at time t _p
During this period, light scatters for a moment, but this time t _p is
It can be as short as τ _NC , so it is extremely short, only a few milliseconds.
This is hardly noticeable as a flicker in the case of so-called static drive, in which signals with the same voltage arrangement are continued to be applied while the same pattern is displayed, as in this embodiment. This improves the drawback that in conventional dynamic driving methods, the entire screen becomes transparent during the pre-excitation period of several tens to hundreds of milliseconds, resulting in noticeable flicker. As a driving method that does not cause flicker, in the driving method of the present invention, the voltage applied to all display pixels is set to an extremely low value including zero for a certain period of time, and only unselected display pixels are A method in which a high voltage higher than _H is applied is also considered, but such a driving method requires changing the voltage value of the signal to be applied into three types, including zero, making the driving circuit complicated. become. However,
As shown in the embodiments, the driving method of the present invention is a simple driving method in which the applied voltage is composed of only a signal of one voltage value V, and this is simply applied to the unselected line electrode for a certain period of time. It has the advantage that the drive circuit can be easily configured. Note that when writing the first display pattern, that is, when starting up the display panel, the voltage applied to the selected display pixel changes from 0 to V.
The response speed may be slow due to this, but if this becomes a problem, apply a voltage of 2V to all display pixels only at startup, i.e. write a display pattern without selection line at startup. This can be easily solved by using methods. Furthermore, in the driving method of this embodiment, the voltage value applied to the display pixel at the intersection of the selection lines may change from 2V or V to 0. In this case, as explained on page 4, After the time τ _rp , the state becomes transparent (S).
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. It's not a thing. In addition, although the case where DC voltage is used in this example is shown,
AC drive is preferable in terms of the lifespan of the liquid crystal display panel. For example, in the figure, instead of the DC voltages +V and -V, the AC voltages V each have a phase difference of π.
(0) and V(π), the driving method of the present invention using an AC signal can be easily realized. As described above, according to the present invention, in a driving method for displaying an image using a phase change type liquid crystal display panel, image writing can be performed at high speed.
In addition, a simple driving method that enables high-quality image display without noticeable flickering can be obtained.

[Brief explanation of the drawing]

The figure 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.

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 whose inner surface of an electrode substrate is subjected to vertical alignment treatment, an electric current is applied to all display pixels at least during the nematic-cholesteric transition time. Set the voltage value to zero or an extremely low value that does not cause a light scattering state, and then apply the voltage to at least the display pixels in the selection lines other than the intersections of the selection lines for a period in which the same pattern is to be displayed. The voltage value applied to the display pixels at the intersection of the non-selected lines is maintained at a low value that causes the formation of a light scattering state below the cholesteric-nematic phase transition threshold voltage value, and the voltage value applied to the display pixels at the intersection of the non-selected lines is controlled to induce the cholesteric-nematic phase transition. A method for driving a phase change type liquid crystal display panel, characterized in that the voltage is maintained at a high value such that a transparent state is formed above a threshold voltage value.