WO2010095686A1

WO2010095686A1 - Method for driving dot-matrix display using bistable nematic liquid crystal

Info

Publication number: WO2010095686A1
Application number: PCT/JP2010/052457
Authority: WO
Inventors: 真一野川; 雅文星野; ジャン－デニス、ラフィット
Original assignee: セイコーインスツル株式会社; ネモプティック
Priority date: 2009-02-19
Filing date: 2010-02-18
Publication date: 2010-08-26

Abstract

Provided is a method for driving a dot-matrix display using a bistable nematic liquid crystal. At a low temperature, a negative side drive mode (Mode-G) is selected to perform a drive control with a higher voltage efficiency, and at room temperature or a high temperature, a positive side drive mode (Mode-E) is selected to perform a drive with a lower current consumption. When driving at a small amplitude at a high temperature, modes (Mode-F, Mode-H) in which the output voltages of common terminals and segment terminals change at a small amplitude are selected to minimize an increase of the resistance in saturation of the output transistor. The selective use of the drive modes makes it possible to carry out rational drive in accordance with the characteristics of a bistable manetic liquid crystal panel.

Description

[Name of invention determined by ISA based on Rule 37.2] Method for driving dot matrix display using bistable nematic liquid crystal

The present invention relates to an electrical drive signal and a drive device for controlling the display of a liquid crystal display.

Most of the liquid crystal displays currently manufactured are monostable, and after an electrical signal is given to the electrode that holds the liquid crystal to display something, the liquid crystal returns to a specific state when the electrical signal is turned off. Disappears. On the other hand, a bistable liquid crystal display has two kinds of stable states in a state where an electric signal is cut off, and the two kinds of stable states can be switched by applying an appropriate electric signal.

Since the two kinds of stable states have different light transmission states, an image can be displayed in combination with a polarizing element, and the image can be changed by adding a specific electric signal. Since the display image is in a stable state even when the electric signal is turned off, it becomes a stored image and is useful for many applications. Since no power is required to maintain the display, it is effective in reducing the power consumption of the portable device.

Such a bistable liquid crystal panel having two kinds of stable states has been proposed as a screen called BiNem (registered trademark). In Patent Document 1, a method for adding an electric signal when changing a stored display is also disclosed. It is disclosed.

Japanese Patent Laid-Open No. 2004-4552

In order to change the display image of such a bistable liquid crystal panel, it is necessary to switch between two types of stable states, and control with a large drive voltage is generally required. Further, since the viscosity of the liquid crystal changes greatly depending on the temperature, for example, the driving voltage amplitude to be switched is large (for example, about 40 volts) at a low temperature, and conversely, the driving voltage amplitude is small (for example, 10 volts or less) at a high temperature.

When the drive voltage amplitude is small, such as when the temperature is high, either the drive of the common segment drive device is driven down, or the waveform of small voltage amplitude is output with the power supply voltage kept high. . When driving with the power supply voltage of the drive device lowered, there is a restriction that the lower the voltage, the greater the ON resistance of the output transistor, and the lower the operation voltage range of the drive device.

Also, when a waveform with a small voltage amplitude is output while the power supply voltage is kept high, there is a characteristic that the ON resistance increases due to the substrate effect of the output transistor.

In general, a bistable liquid crystal panel has a larger equivalent load capacity than a normal monostable STN liquid crystal panel, so the charge / discharge charge amount is large, and the drive device requires a high current supply capability. The segment signal output transistor is required to have a low ON resistance even when the drive voltage amplitude is small, such as at high temperatures. For this reason, the driving device needs to have a high driving capability and quickly charge and discharge charges between the common and the segment.

In addition, when the voltage between the common and segment terminals serving as the drive signal is VCOM-VSEG (the voltage obtained by subtracting the VSEG potential from the VCOM potential), the bistable liquid crystal panel displays the switching voltage change on the negative side of the terminal voltage. The characteristics differ between the case of control and the case of control on the positive electrode side, and a difference in drive voltage necessary for switching, a certainty of switching, that is, a difference in display image quality, and the like occur.

In general, control on the negative electrode side enables efficient drive control with a small voltage amplitude, and the display quality is good, but in the drive device, the majority of the charge transfer during switching occurs at a high potential, so panel consumption The current increases. On the other hand, in the control on the positive electrode side, in the driving device, the majority of charge transfer during switching occurs at a low potential, so that the current consumption of the panel can be reduced.

The present invention provides an optimum driving means for the characteristics of such a bistable liquid crystal panel.

As a first invention, a pair of substrates arranged to face each other substantially in parallel, a plurality of common electrodes and a plurality of segment electrodes formed in a matrix on the surface on the opposite surface side of the substrate, the common electrode, An alignment film formed on the segment electrode, a nematic liquid crystal molecule having two stable alignment states sandwiched by the alignment film and having bistability even when the electric field is cut off, and a nematic liquid crystal Consists of at least one polarizing plate arranged outside the liquid crystal molecules, and applies either a selection signal or non-selection signal for rewriting the liquid crystal to the nematic liquid crystal from a common driving unit connected to the common electrode. Then, a signal for selecting two stable alignment states is selectively applied to the nematic liquid crystal from the segment drive unit connected to the segment electrode, and the common electrode and the segment In a dot matrix display using a bistable nematic liquid crystal that displays an image by a common-segment voltage, which is the electric field between the electrodes, the output of all common electrodes and all segment electrodes when scanning each common electrode is the same potential In addition, a dot matrix display using a bistable nematic liquid crystal having a mode in which all common electrodes and all segment electrodes output the same potential to GND in a drive mode whose potential is not GND Driving method and driving means.

As a second invention, in the first invention described above, when the voltage between the terminals of the common electrode and the segment electrode holding the dot pixel is VCOM-VSEG, the dot display is in the first orientation state or the second orientation. There is a positive side drive mode that controls the voltage change that determines the state on the positive side of the voltage across the terminals, and a negative side drive mode that controls the voltage on the negative side, both of which can be selected A driving method and driving means.

As a third invention, in the first invention described above, the output potential of each terminal of the common and the segment holding the dot pixel is avoided with a small amplitude while avoiding the central potential of the maximum amplitude that can be output for both the common and the segment. A driving method and a driving means including a driving mode for shifting and driving VCOM-VSEG which is a voltage between both terminals with a smaller amplitude.

In other words, when the voltage between the common and segment terminals holding the dot pixel is VCOM-VSEG, the positive side drive mode for controlling the voltage change that determines whether the dot display is white or black on the positive side of the terminal voltage. And a negative side drive mode that is controlled on the negative side, and by selecting either of them, the negative side drive mode can be selected at low temperatures where a large drive voltage amplitude is required. Efficient drive control is performed with a small voltage amplitude, and a positive-side drive mode that is controlled on the positive side is selected except when the temperature is low to achieve driving with lower current consumption.

When a large drive voltage amplitude is required, such as at low temperatures, the common segment is driven and shifted with the maximum amplitude that can be output, and the voltage between both terminals: VCOM-VSEG is driven with a larger amplitude, while high temperature When a small drive voltage amplitude is required, the ON resistance of the drive transistor generally increases, so the common potential of each terminal of the common and segment is set to the center potential of the maximum amplitude that can be output for both the common and segment. By avoiding and shifting with a small amplitude and driving the voltage between both terminals: VCOM-VSEG with a smaller amplitude, it is possible to realize a smaller voltage amplitude drive while minimizing an increase in the ON resistance of the output transistor.

Voltage between both terminals of common and segment: When VCOM-VSEG is driven with smaller amplitude, all common and segment outputs are the same potential when scanning each COM line, and the potential is not GND For the drive mode, the location where all commons and all segments output the same potential is changed to the GND potential so that a specific output amplifier capability is not used.

According to the present invention, it is possible to rationally drive according to the characteristics of the bistable liquid crystal panel by selecting the drive mode.

In other words, the negative side drive mode is selected at low temperatures where a large drive voltage amplitude is required, and drive control with higher voltage efficiency is performed, and the positive side drive mode is selected at times other than low temperatures, resulting in lower current consumption. Realization of driving.

When a general-purpose STN driver is used as a segment drive device, the output amplitude of the segment decreases and the ON resistance of the output transistor generally increases. However, by using the drive mode of the present invention, a high temperature can be obtained. It is possible to minimize an increase in the ON resistance of the driving transistor when driving with a smaller amplitude.

In addition, when the voltage between both terminals of the common and the segment: VCOM-VSEG is driven with a smaller amplitude, the output of all commons and all segments during scanning of each COM line is the same potential, and the potential is GND No drive mode, all common and all segments output the same potential to GND potential, no need to use a specific output amplifier capability, only switching directly to GND, maximum drive Potential transition is possible with force.

It is a general functional block diagram for display control of a bistable liquid crystal panel. It is a figure explaining switching of a bistable liquid crystal. It is a schematic diagram of a bistable liquid crystal panel. It is a figure which shows the example of the waveform of the common and segment applied to a bistable liquid crystal panel. It is a figure which shows the example of the waveform of the common and segment applied to a bistable liquid crystal panel. It is a figure which shows the example of the waveform of the specific mode (Mode-G) which drives a bistable liquid crystal panel. It is a figure which shows the example of the waveform of the specific mode (Mode-E) which drives a bistable liquid crystal panel. It is a figure which shows the example of the waveform of the specific mode (Mode-F) which drives a bistable liquid crystal panel. FIG. 6 is a diagram illustrating an example of a waveform of a specific mode (Mode-D) for driving a bistable liquid crystal panel. It is a figure which shows the example of the waveform of the specific mode (Mode-H) which drives a bistable liquid crystal panel.

The driving method and driving device of the bistable liquid crystal display panel of the present invention can be implemented without changing the hardware of the driving device of the bistable liquid crystal display panel and by partially changing the conventional driving method. is there.

Before describing the embodiment of the present invention, the structure of the bistable liquid crystal display panel will be described.

FIG. 1 is a general functional block diagram for controlling the display of the bistable liquid crystal display panel 10. The bistable liquid crystal display panel 10 generates a common drive unit 11 that drives a horizontal common line, a segment drive unit 12 that drives a vertical segment line, and drive potentials (V0, V12, V34, V5, and VCX). It is driven by a drive device comprising a power supply circuit 13, a common drive unit 11, a segment drive unit 12, and a control unit 14 that controls the power supply circuit 13.

The signal and role for the control unit 14 to control the common drive unit 11 and the segment drive unit 12 are the same as those of a normal STN drive driver circuit. For the common drive unit 11, there is an initialization signal RESETX, C-Data for determining scan timing and CL for writing, and an AC signal FRCOM and DispOffx for display erasure and CCX. For the segment driver 12, there is an initialization signal RESETX, there are S-Data for giving display image data and a writing clock XCK, and there are an alternating signal FRSEG and a display erasing DispOffx. It is naturally possible to incorporate the power supply circuit 13 into the common drive unit 11 and further incorporate the segment drive unit 12 into one IC.

FIG. 2 is a diagram for explaining switching which is switching of the state of the bistable nematic liquid crystal. A pair of substrates 1 arranged substantially opposite to each other, and an electrode 2 and an alignment film 3 are arranged in layers on a substrate on the opposite surface side of the substrate 1, and nematic liquid crystal molecules 4 are sandwiched by the substrate 1. ing. The molecules 4 of the nematic liquid crystal are aligned in a predetermined direction by fine grooves carved in the alignment film 3. A polarizing plate 5 is provided outside the substrate 1 on the upper surface side of the drawing. A state is shown in which a specific signal is applied to the common electrode and the segment electrode of the bistable liquid crystal display panel 10 to switch the twist direction of the nematic liquid crystal molecules between two states, a twist state and a uniform state. One of the write signals to be applied to the pair of electrodes 2 arranged opposite to each other in parallel is the selection COM signal shown in FIGS. 2 (a) and 2 (d), and the other is shown in FIG. 2 (b). There are two types of SEG signals for twist or uniform SEG signals shown in FIG. The voltage between the common terminal and the segment terminal applied to the liquid crystal is of two types: a twist COM-SEG signal shown in FIG. 2C and a uniform COM-SEG signal shown in FIG. When receiving the twist COM-SEG signal, the bistable liquid crystal display panel 10 can display white by the orientation of the polarizing plate 5, and can receive black by receiving the uniform COM-SEG signal. Moreover, white display and black display can be reversed by changing the state of the polarizing plate 5.

First, the case where white is displayed by the intersection pixel of the common electrode and the segment electrode of the bistable liquid crystal display panel 10 will be described. The common electrode and the segment electrode are substantially synonymous with the common terminal and the segment terminal, respectively. In FIG. 2A, the voltage waveform of the selection COM signal applied to the common terminal is such that the first time interval a of the selection period T is level 0, the time intervals b and c are negative levels −V, and the following time The intervals d and e are waveforms having a positive level + V, the following time interval f is a positive level + V−v, and the remaining time interval g is a level 0 waveform.

As shown in FIG. 2B, the voltage waveform of the twisted SEG signal applied to the segment terminals is level 0 for the first time interval a to e of the selection period T, and negative level −v for the subsequent time interval f. , And the remaining time interval g is a waveform at level 0.

When the selection COM signal and the twist SEG signal that change with time are applied as described above, the waveform of the twist COM-SEG signal, which is the voltage difference between the common terminal and the segment terminal, changes with time. It becomes. That is, as shown in FIG. 2 (c), the waveform of the twisting COM-SEG signal is such that the first time interval a of the selection period T is level 0, the subsequent time intervals b and c are negative level -V, and the subsequent time. The interval d to f is a waveform having a positive level + V, and the remaining time interval g is level 0. Thus, the waveform of the twisting COM-SEG signal causes a voltage transition between the negative level −V volts and the positive level + V.

The twisted COM-SEG signal having such a waveform is applied to the nematic liquid crystal by first destroying the stable state of the alignment of the nematic liquid crystal molecules with a negative level −V voltage and a positive level + V voltage. The nematic liquid crystal molecules 4 are lifted in the vertical direction (see the schematic diagram in FIG. 2 (g)), and then opened to a level 0 voltage to lay the nematic liquid crystal molecules 4 in the alignment direction (see FIG. 2). (Refer to the schematic diagram of (h)). In this way, the intersection pixel of the bistable liquid crystal display panel 10 to which the twisting COM-SEG signal having the waveform shown in FIG. 2C is applied displays white in this example.

Next, the case where black is displayed by the intersection pixel of the common electrode and the segment electrode of the bistable liquid crystal display panel 10 will be described. FIG. 2D showing the voltage waveform of the selection COM signal applied to the common terminal is the same as the waveform of FIG.

As shown in FIG. 2 (e), the voltage waveform of the uniform SEG signal is such that the first time interval a to c of the selection period T is level 0, the subsequent time interval d is a negative level −v, and the remaining time interval. e to g are waveforms having a level 0.

As described above, when the selection COM signal and the uniform SEG signal that change with time are applied, the uniform COM-SEG signal, which is the voltage difference between the common terminal and the segment terminal, has a waveform that changes with time. . That is, as shown in FIG. 2 (f), the waveform of the uniform COM-SEG signal is such that the first time interval a of the selection period T is level 0, the subsequent time intervals b and c are negative level -V, and the subsequent time. The interval d is a positive level + (V + v), the following time interval e is a positive level + V, the following time interval f is a positive level + V−v, and the remaining time interval g is a level 0 waveform. As described above, the uniform COM-SEG signal makes a voltage transition between −V and + (V + v).

Applying the COM-SEG signal for uniforms having such a waveform to the nematic liquid crystal first causes the stable state of the molecular alignment of the nematic liquid crystal at a negative level −V voltage and a positive level + (V + v) voltage. The nematic liquid crystal molecules 4 are lifted in the vertical direction (see the schematic diagram of (i) in FIG. 2), and then the positive level + (V + v) is set to the positive level + V and the positive level + V is set to positive. The nematic liquid crystal molecules 4 are oriented almost in parallel by gradually decreasing the positive level + Vv to the level 0 in the order of the level + V−v and finally the positive level + V−v (see the schematic diagram of FIG. 2 (j)). ), To make the uniform state. In this way, the intersection pixel of the bistable liquid crystal display panel 10 to which the uniform COM-SEG signal shown in (f) of FIG. 2 is applied displays black in this example.

FIG. 3 shows a general electrode configuration of the bistable liquid crystal display panel 10. Each intersection of the common terminal arranged in the horizontal direction and the segment terminal arranged in the vertical direction is a pixel that determines display black and white, and the display is determined by applying a specific common waveform and a specific segment waveform.

In FIG. 3, a waveform that sets the intersection pixel of the m-th column and the n-th row to a uniform state, the intersection pixel of the m-th column and the (n + 1) -th row to a twisted state, and the intersection pixel of the m-th column and the (n + 2) -th row to a uniform state. An example of this is shown in FIG.

FIG. 4 shows an example of voltage waveforms applied to the common terminal and the segment terminal of the bistable liquid crystal display panel 10. 4A shows a voltage waveform applied to the n-th row common terminal COM [n] arranged in the horizontal direction in the bistable liquid crystal display panel 10 shown in FIG. FIG. 4B shows the voltage waveform applied to the common terminal COM [n + 1] in the (n + 1) th row, and FIG. 4C shows the voltage waveform applied to the common terminal COM [n + 2] in the (n + 2) th row. This is a voltage waveform. FIG. 4D shows a voltage waveform of the segment terminal SEG [m] in the m-th column arranged in the vertical direction in the bistable liquid crystal display panel 10 shown in FIG.

The voltage waveform of the selection COM signal 31 applied to the common terminal is as shown in the portion surrounded by the broken-line circle in FIGS. 4A to 4C, and the first time interval a of the selection period T is level 0. The following time interval b is a positive level + V2, the following time intervals c and d are level 0, the following time interval e is + VCX, and the remaining time interval f is level 0. However, V2> VCX.

As shown in FIGS. 4A to 4C, the voltage waveform of the non-selection COM signal 32 applied to the common terminal is as follows. The first time intervals a and b of the selection period T are level 0 and the subsequent time interval c. e is a waveform with a positive level + V2, and the remaining time interval f is level 0.

The voltage waveform of the signal applied to the common terminal is greatly different between FIG. 2 and FIG. The voltage waveform of the selection COM signal shown in (a) and (d) of FIG. 2 is a voltage waveform that changes greatly between positive and negative, whereas the voltage waveform of the selection COM signal 31 shown in FIG. The waveform changes greatly only in FIG. Note that the non-selection COM signal 32 shown in FIG. 4 also has a waveform that changes greatly only on the positive side.

As shown in FIG. 4A, the selection COM signal 31 is applied to the n-th common terminal COM [n] in the scan time interval t1, and the non-selection COM signal 32 is applied in the scan time intervals t2 and t3. Are respectively applied. As shown in FIG. 4B, the non-selection COM signal 32 is applied to the subsequent common terminal COM [n + 1] in the (n + 1) th row, and the selection COM signal 31 is supplied in the scan time interval t2. Further, the non-selection COM signal 32 is applied in the scan time interval t3. Further, the non-selection COM signal 32 is applied to the subsequent common terminal COM [n + 2] in the (n + 2) th row in the scan time intervals t1 and t2, as shown in FIG. 4C, and in the scan time interval t3. Each signal 31 is applied.

The segment voltage applied to the segment terminals, that is, the voltage waveforms SEG [m] of the uniform SEG signal 34 and the twist SEG signal 35 are as shown in FIG. Here, the uniform SEG signal 34 is applied in the scan time interval t1, the twist SEG signal 35 is applied in the scan time interval t2, and the uniform SEG signal 34 is applied in the scan time interval t3. Here, V1> V2.

The voltage waveform of the uniform SEG signal 34 shows that the first time intervals a and b of the selection period T are level 0, the subsequent time intervals c and d are positive level + V2, the subsequent time interval e is positive level + V1, and the rest The time interval f is a waveform at level 0.

Further, the voltage waveform of the twist SEG signal 35 is such that the first time intervals a and b of the selection period T are level 0, the subsequent time interval c is positive level + V1, the subsequent time intervals d and e are positive level + V2, and The remaining time interval f is a waveform having level 0.

As described above, when the selection COM signal 31 or the non-selection COM signal 32 is applied to the common terminal, and the uniform SEG signal 34 and the twist SEG signal 35 are applied to the segment terminal, the common signal between the common terminal and the segment terminal The voltage between segments, that is, the uniform COM-SEG signal 36 and the twist COM-SEG signal 37 are as shown in FIGS.

At the intersection pixel of the common terminal COM [n] in the n-th row and the segment terminal SEG [m] in the m-th column, as shown in FIG. A waveform in which 0, the following time interval b is positive level + V2, the following time intervals c and d are negative level −V2, the following time interval e is negative level −V3, and the remaining time interval f is level 0 The uniform COM-SEG signal 36 is applied.

In the time interval t2, the first time intervals a and b are level 0, the subsequent time interval c is negative level −V5, and the remaining time intervals d to f are level 0. Applied. Further, in the time interval t3, the parasitic signal 39 by the uniform SEG signal in which the first time interval a to d is level 0, the subsequent time interval e is negative level −V5, and the remaining time interval f is level 0 is Applied. The uniform COM-SEG signal 36 and the

parasitic signals

38 and 39 are applied to the intersection pixel of the common terminal in the n-th row and the segment terminal in the m-th column at the times t1, t2, and t3. Since the voltage amplitude is small, it does not affect the switching of the intersection pixel. Therefore, the intersection pixel is switched to the uniform state by the uniform COM-SEG signal 36.

Next, an intersection SEG signal between the common terminal COM [n + 1] in the (n + 1) -th row and the segment terminal SEG [m] in the m-th column has a uniform SEG signal in the time interval t1, as shown in FIG. The parasitic signal 39 is applied to the twist COM-SEG signal 37 in the time interval t2, and the parasitic signal 39 is applied to the uniform SEG signal in the time interval t3. The twisted COM-SEG signal 37 has an initial time interval a of level 0, a subsequent time interval b of a positive level + V2, a subsequent time interval c of a negative level −V1, and a subsequent time interval d of a negative level −V2. The subsequent time interval e is a negative level −V4, and the remaining time interval f is a voltage having a waveform of level 0. Similarly, at the intersection pixel of the common terminal in the (n + 1) th row and the segment terminal in the m-th column, the parasitic signal 39 does not affect the switching of the intersection pixel because the voltage amplitude is small. Therefore, the intersection pixel is switched to the twist state by the twist COM-SEG signal 37.

Further, the intersection pixel of the (n + 2) -th row common terminal COM [n + 2] and the m-th column segment terminal SEG [m] is subjected to the uniform SEG signal in the time interval t1, as shown in FIG. The parasitic signal 39 is applied with the parasitic signal 38 by the twist SEG signal in the scan time interval t2, and the uniform COM-SEG signal 36 is applied in the scan time interval t3. The uniform COM-SEG signal 36 indicates that the first time interval a of the selection period T is level 0, the subsequent time interval b is positive level + V2, the subsequent time intervals c to d are negative level −V2, and the subsequent time interval e is The negative level −V3, and the remaining time interval f is a voltage having a waveform of level 0. Similarly, in the intersection pixel of the common terminal in the (n + 2) th row and the segment terminal in the m-th column, the

parasitic signals

38 and 39 do not affect the switching of the intersection pixel because the voltage amplitude is small. Therefore, the intersection pixel is switched to the uniform state by the uniform COM-SEG signal 36.

FIG. 6 shows an example of two types of voltage waveforms applied to the common terminal, two types of voltage waveforms applied to the segment terminals, and four types of COM-SEG waveforms generated by a combination thereof. The time interval indicated by T is a unit of one output waveform. There are a selection COM signal 61, a non-selection COM signal 62, a uniform SEG signal 63 applied from a segment terminal, and a twist SEG signal 64. In addition, four kinds of voltages applied to the intersection pixel of the common terminal and the segment terminal, uniform COM-SEG signal 65, twist COM-SEG signal 66, parasitic signal 67 by uniform SEG signal, and parasitic by twist SEG signal Signal 68 is shown. The voltage waveform shown in FIG. 6 differs from that shown in FIG. 4 in the waveform applied to the segment terminals.

Further, the Mode-G shown in FIG. 6 shows a voltage change (a broken line surrounded by a circle) that determines whether the dot display is white or black when the voltage between the terminals of the common and the segment, for example, the COM-SEG signal 65 for uniform is viewed. Are controlled on the negative electrode side. This is defined as a negative side drive mode. In the Mode-G waveform, the parasitic signal when the common is not selected is generated at a high potential (V0, V12) of the segment waveform. That is, since charge and discharge of charges are performed on the pixel electrodes between the common and segment from a high potential (V0, V12), it is necessary to inject charges from a high voltage power source, and current consumption as a driving device increases.

The numbers “1” and “0” shown in FIG. 6D are control signals for the waveform of the common voltage applied to the common terminal and the waveform of the segment voltage applied to the segment terminal. The waveform of the common voltage is controlled by four signals of CCX, C-Data, FR, and DispOffx. It is controlled by three signals of the segment voltage waveform S-Data, FR, and DispOffx. Table 1 below shows the segment drive driver (SEG-Drv.) For a segment drive device that uses a driver (not the SA drive method) for driving a typical STN liquid crystal that is already commercially available. It is a truth table of an input / output table. Since the output voltage is controlled by three control signals, the correspondence between the segment control signal and the segment voltage waveform as shown in FIG.

Since the waveform of the common voltage for driving the bistable liquid crystal display panel 10 has a potential of VCX that does not exist in normal driving of a general STN liquid crystal, the control signal for outputting the potential is CCX. Table 2 shown below is a truth table of the input / output table of the common drive driver (COM-Drv.). In Table 2, if the common output is controlled as shown in the column of driving mode G (Mode-G), four common control signals (CCX, C-Data, FR, DispOffx) shown in FIG. And the correspondence of the common voltage waveform as shown in FIG.

In the bistable liquid crystal display panel, when a COM signal for selection is applied to one common terminal arranged in the horizontal direction, whether the signal of each segment terminal intersecting in the vertical direction is a signal for twisting or not. The display of one pixel in the horizontal direction is determined depending on whether it is a signal. Applying (scanning) selection COM signals to all common terminals while sequentially shifting the selection COM signals one by one, and applying the signals of all segment terminals each time determines the display of the entire screen. .
When the selection COM signal is applied to one common terminal, a non-selection COM signal is applied to the majority of other common terminals, and a parasitic signal is applied to the intersecting segment terminals. When considering the charge / discharge charge amount of the panel, it is necessary to pay attention to the potential difference between the non-selection COM signal applied to the majority of the common terminals and the segment waveform. That is, the parasitic signal greatly contributes to the charge / discharge charge amount for driving the liquid crystal panel, and affects the current consumption.

7 to 10 show examples of four types of drive modes (Mode-E, F, D, and H), respectively.

FIG. 7A shows a common drive waveform of Mode-E, the left two waveforms are the selection COM signals and the right two waveforms are the non-selection COM signals. FIG. 7B shows a uniform SEG signal 73 and a twist SEG signal 74. Looking at the voltage between the terminals of the Mode-E common and the segment, for example, the uniform COM-SEG signal 75, first the negative side drive is followed by the positive side drive, and whether the positive side drive is twisted or uniform? A voltage change (a broken line part surrounded by a circle) is given. Driving to both sides of the negative electrode and the positive electrode is a general consideration for preventing and balancing DC bias to the liquid crystal. The same applies to the twisted COM-SEG signal 76. In this case, the positive side drive mode means that the voltage change (the broken line part circled) that determines whether the pixel display is twist or uniform is controlled on the positive side. In the waveform of Mode-E which is the positive side drive mode, a parasitic signal generated when the common is not selected, for example, a parasitic signal 77 by the uniform SEG signal is generated at a low potential (V34, V5) of the segment waveform. That is, since charge and discharge are performed on the pixel electrode between the common and the segment from a low potential (V34, V5), it is not necessary to use a high voltage power supply, and current consumption as a driving device can be suppressed small. The same applies to the parasitic signal 78 by the twisted SEG signal.

The Mode-F shown in FIG. 8 is also the positive electrode side drive mode like the Mode-E. A uniform SEG signal 83 and a twist SEG signal 84 are shown. A uniform COM-SEG signal 85, a twist COM-SEG signal 86, a parasitic signal 87 due to the uniform SEG signal, and a parasitic signal due to the twist SEG signal. Signal 88 is shown. The parasitic signal generated when the common is not selected is generated at a low potential (V34, V5) of the segment waveform.

The waveform of Mode-D shown in FIG. 9 is the negative side drive mode, similar to Mode-G of FIG.

The waveform of the selection COM signal 111 will be described. The first time interval a is positive level + V34, the subsequent time interval b is positive level + V12, the subsequent time intervals c and d are positive level + V34, and the subsequent time interval e is positive. Level + VCX, and the last time interval f is positive level + V34.

Explaining the waveform of the non-selection COM signal 112, the first time intervals a and b are positive level + V34, the subsequent time intervals c to e are positive level + V12, and the last time interval f is positive level + V34. .

Similarly, the waveform of the uniform SEG signal 113 will be described. The first time intervals a and b are positive level + V34, the following time intervals c and d are positive level + V12, the following time interval e is positive level + V0, and The last time interval f is a positive level + V34.

Explaining the waveform of the twisted SEG signal 114, the first time intervals a and b are positive level + V34, the following time interval c is positive level + V0, the following time intervals d and e are positive level + V12, and the last time. The interval f is a positive level + V34.

Further, the waveform of the uniform COM-SEG signal 115 will be described. The first time interval a is positive level +0, the following time interval b is positive level +3, the following time intervals c and d are negative level -3, and so on. The time interval e is negative level -2, and the last time interval f is positive level +0.

Explaining the waveform of the twisted COM-SEG signal 116, the first time interval a is positive level +0, the following time interval b is positive level +3, the following time interval c is negative level -4, and the following time interval d is Negative level -3, the following time interval e is negative level -1, and the last time interval f is positive level +0.

The waveform of the parasitic signal 117 based on the uniform SEG signal is described as follows. The first time interval a to d is positive level +0, the subsequent time interval e is negative level −1, and the last time interval f is positive level +0. Become.

In the parasitic signal 118 by the twist SEG signal, the first time intervals a and b are positive level +0, the subsequent time interval c is negative level −1, and the last time intervals d to f are positive level +0.

The COM signal 111 for selection, the COM signal 112 for non-selection, the SEG signal 113 for uniform, and the SEG signal 114 for twist are shown. The COM-SEG signal 115 for uniform, the COM-SEG signal 116 for twist, and the uniform A parasitic signal 117 by the SEG signal and a parasitic signal 118 by the twist SEG signal are shown. However, the common amplitude is from V12 to V34, which is two steps smaller than the maximum amplitude from V0 to V5. The segment also has a basic amplitude from V12 to V34, which is two steps less than the maximum amplitude from V0 to V5. Thus, if the common and segment are both two steps smaller than the maximum amplitude, the amplitude of the combined waveform COM-SEG will be four steps smaller.

Similarly to Mode-G, Mode-H shown in FIG. 10 is also a negative electrode side drive mode. The COM signal for selection 121, the COM signal for non-selection 122, the SEG signal for uniform 123, and the SEG signal for twist 124 are shown. The uniform COM-SEG signal 125, the COM-SEG signal for twist 126, and the uniform A parasitic signal 127 based on the SEG signal and a parasitic signal 128 based on the twisted SEG signal are shown.

The waveform of the selection COM signal 121 will be described. The first time interval a is positive level + V5, the subsequent time interval b is positive level + V12, the subsequent time intervals c and d are positive level + V34, and the subsequent time interval e is positive. Level + VCX and the last time interval f is a positive level V5.

Explaining the waveform of the non-selection COM signal 122, the first time interval a is positive level + V5, the following time interval b is positive level + V34, the following time intervals c to e are positive level + V12, and the last time interval f becomes a positive level V5.

Similarly, the waveform of the uniform SEG signal 123 will be described. The first time interval a is positive level + V5, the following time interval b is positive level + V34, the following time intervals c and d are positive level + V12, and the following time interval. e is a positive level + V0 and the last time interval f is a positive level + V5.

The waveform of the twisted SEG signal 124 will be described. The first time interval a is positive level + V5, the following time interval b is positive level + V34, the following time interval c is +0 V, and the following time intervals d and e are positive level + V12. , And the last time interval f becomes a positive level + V5.

Further, the waveform of the uniform COM-SEG signal 125 will be described. First time interval a is positive level +0, subsequent time interval b is positive level +3, subsequent time intervals c and d are negative level -3, and so on. The time interval e is negative level -2, and the last time interval f is positive level +0.

To explain the waveform of the twisted COM-SEG signal 126, the first time interval a is positive level +0, the following time interval b is positive level +3, the following time interval c is negative level -4, and the following time interval d is Negative level -3, the following time interval e is negative level -1, and the last time interval f is positive level +0.

The waveform of the parasitic signal 127 based on the uniform SEG signal is described as follows. The first time interval a to d is positive level +0, the subsequent time interval e is negative level −1, and the last time interval f is positive level +0. Become.

In the parasitic signal 128 by the twist SEG signal, the first time intervals a and b are positive level +0, the subsequent time interval c is negative level −1, and the last time intervals d to f are positive level +0.

The parasitic signal generated when the common is not selected is generated at a high potential (V0, V12) of the segment waveform.

The ON resistance of the output transistor is most increased due to the substrate effect when the central potential (1/2 potential) of the maximum amplitude that can be output by the transistor is output. When a lower ON resistance is required, Output should be avoided.

In addition to the case where a common STN normal drive driver that is commercially available is used as a common or segment drive device, both the common and segment are output at the maximum amplitude (V0-V5), one stage from the upper limit, When output with a potential (V12-V34) with one stage lower than the lower limit and a total of two stages of amplitude reduced, the COM-SEG voltage is driven with an amplitude that is four stages smaller than when the maximum amplitude (V0-V5) is output. Is done. For example, when the voltage between V0 and V5 is about 10V, if both the common and segment are output with the maximum amplitude (V0-V5), the COM-SEG voltage will have an amplitude of ± 10V, but the potentials of V12 and V34 will be If the common and segment are output with amplitudes of V12 and V34 by setting 2V inside from the upper and lower limits, the COM-SEG voltage has an amplitude of ± 6V.

Even if the minimum drive voltage (voltage between V0 and V5) of the drive device for common or segment is 10V, the output transistor is not used near the central potential (= 10V / 2 = 5V) where the ON resistance increases due to the substrate effect. A small amplitude drive of ± 6 V can be realized without significantly increasing the ON resistance of. By avoiding the central potential of the maximum amplitude that can be output for both the common segment and shifting with a small amplitude, the COM-SEG voltage can be driven with a smaller amplitude without increasing the ON resistance of the output transistor. it can.

In Mode-D shown in FIG. 9, the beginning and end of the time interval T at which the waveform is output in both the selection COM signal 111 and the non-selection COM signal 112 are the potential of V34, and the potential of V34 is also in the segment signal. It is. In other words, the voltage waveform between COM and SEG does not change even if the potential is changed to V5 (= GND) as shown by a circle in FIG. If the beginning and end of the time interval T for outputting the COM and SEG waveforms is changed to V5 (= GND) instead of V34, the output amplifier capability of V34 is not used, and only switching to V5 (= GND) is performed directly. The potential transition to V5 (= GND) is possible with the maximum driving force. This is shown as Mode-H in FIG.

8 Mode-F is a small amplitude waveform of the positive side drive mode as opposed to Mode-H in FIG. In Mode-F, as in Mode-H, the end of COM and SEG is changed to V5 (GND) instead of V34, and it is possible to drive without using the output amplifier capability of V34 at the end of voltage transition. is doing.

Mode-E in FIG. 7 and Mode-G in FIG. 6 are both driven at the maximum amplitude, although there are differences between the positive side and negative side drive modes. The output of the common and the segment changes with the maximum amplitude of V0-V5, and the voltage waveform between COM and SEG also has the maximum amplitude. When driving with a larger voltage amplitude, Mode-E or Mode-G is selected, and when driving with a smaller voltage amplitude, Mode-F or Mode-H is selected.

If the characteristics of the bistable liquid crystal panel are improved in the future and a good display image quality can be secured in the positive drive mode, select Mode-E or Mode-F to achieve low current consumption drive.

Each potential (V0, V12, VCX, V34, V5) of the drive waveform shown in FIG. 7 is optimum according to the size of the liquid crystal panel, the number of pixels, the ambient temperature, and the like, similar to the drive potential of a general-purpose STN driver. Set to voltage. Since a high driving voltage is required for the liquid crystal at a low temperature, the voltage between V0 and V5 is increased and the liquid crystal is driven in the negative side driving mode (Mode-G) with good voltage efficiency. In addition, at normal temperature or high temperature, drive with positive side drive mode (Mode-E) to reduce current consumption. At high temperature, reduce voltage between V0 and V5 and drive with Mode-F or Mode-H. Although the drive amplitude between COM and SEG is small, the voltage between V0 and V5 is kept as large as possible to minimize the increase in the ON resistance of the output transistor.

As described above, by using a driving method and a driving device that freely select a driving mode according to the environment, rational driving according to the characteristics of the bistable liquid crystal panel becomes possible.

Industrial applicability

By using the present invention, it can be used for all liquid crystal displays. Among them, the industrial applicability is particularly high particularly in the use of electronic shelf labels and electronic paper.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Electrode 3 Alignment film 4 Nematic liquid crystal molecule 5 Polarizing plate 10 Bistable liquid crystal display panel 11 Common drive unit 12 Segment drive unit 13 Power supply circuit 14

Control unit

31, 61, 111, 121

COM signal

32, 62 for selection, 112, 122

Non-selection COM signal

34, 63, 73, 83, 113, 123

Uniform SEG signal

35, 64, 74, 84, 114, 124

Twist SEG signal

36, 65, 75, 85, 115, 125 Uniform COM-

SEG signal

37, 66, 76, 86, 116, 126 COM-SEG signal for

twist

38, 39, 67, 68, 77, 78, 87, 88, 117, 118, 127, 128 Parasitic signal

Claims

A pair of substrates disposed substantially parallel to each other;
A plurality of common electrodes and a plurality of segment electrodes formed in a matrix on the opposite surface of the substrate;
An alignment film formed on the common electrode and the segment electrode;
Bistability nematic liquid crystal molecules having two stable alignment states held by the alignment film and maintaining the alignment states even when the electric field is cut off;
Composed of at least one polarizing plate disposed outside the molecule of the nematic liquid crystal,
Applying one of a selection signal and a non-selection signal for rewriting liquid crystal to the nematic liquid crystal from a common driving unit connected to the common electrode;
A signal for selecting two stable alignment states is selectively applied to the nematic liquid crystal from a segment driver connected to the segment electrode,
In a method of driving a dot matrix display using a bistable nematic liquid crystal that displays an image by a common-segment voltage that is an electric field between the common electrode and the segment electrode,
When scanning each common electrode, all common electrodes and all segment electrodes output the same potential, and all common electrodes and all segment electrodes output the same potential to a drive mode in which the potential is not GND. A method for driving a dot matrix display using a bistable nematic liquid crystal having a mode in which the location is changed to GND.
In the driving method,
When the voltage between the terminals of the common electrode and the segment electrode holding the dot pixel is VCOM-VSEG, the voltage change that determines whether the dot display is in the first alignment state or the second alignment state is the voltage of the terminal voltage. A positive side drive mode controlled on the positive side;
2. The method for driving a dot matrix display using a bistable nematic liquid crystal according to claim 1, comprising: a negative electrode side drive mode controlled on the negative electrode side, and any of which can be selected.
In the driving method,
The output potential of each terminal of the common and segment that holds the dot pixel is shifted with a small amplitude while avoiding the central potential of the maximum amplitude that can be output for both the common and segment, and the VCOM-VSEG that is the voltage between both terminals is further increased. 2. The method for driving a dot matrix display using a bistable nematic liquid crystal according to claim 1, further comprising a drive mode driven with a small amplitude.
A pair of substrates disposed substantially parallel to each other;
A plurality of common electrodes and a plurality of segment electrodes formed in a matrix on the opposite surface of the substrate;
An alignment film formed on the common electrode and the segment electrode;
Bistability nematic liquid crystal molecules having two stable alignment states held by the alignment film and maintaining the alignment states even when the electric field is cut off;
Composed of at least one polarizing plate disposed outside the molecule of the nematic liquid crystal,
Applying one of a selection signal and a non-selection signal for rewriting liquid crystal to the nematic liquid crystal from a common driving unit connected to the common electrode;
A signal for selecting two stable alignment states is selectively applied to the nematic liquid crystal from a segment driver connected to the segment electrode,
In a drive device for a dot matrix display using a bistable nematic liquid crystal that displays an image by a common-segment voltage that is an electric field between the common electrode and the segment electrode,
When the voltage between the terminals of the common electrode and the segment electrode holding the dot pixel is VCOM-VSEG, the voltage change that determines whether the dot display is in the first alignment state or the second alignment state is the voltage of the terminal voltage. A positive side drive mode controlled on the positive side;
On the other hand, a drive device for a dot matrix display using a bistable nematic liquid crystal that includes a negative electrode side drive mode that is controlled on the negative electrode side, and can select either of them.
A pair of substrates disposed substantially parallel to each other;
A plurality of common electrodes and a plurality of segment electrodes formed in a matrix on the opposite surface of the substrate;
An alignment film formed on the common electrode and the segment electrode;
Bistability nematic liquid crystal molecules having two stable alignment states held by the alignment film and maintaining the alignment states even when the electric field is cut off;
Composed of at least one polarizing plate disposed outside the molecule of the nematic liquid crystal,
Applying one of a selection signal and a non-selection signal for rewriting liquid crystal to the nematic liquid crystal from a common driving unit connected to the common electrode;
A signal for selecting two stable alignment states is selectively applied to the nematic liquid crystal from a segment driver connected to the segment electrode,
In a drive device for a dot matrix display using a bistable nematic liquid crystal that displays an image by a common-segment voltage that is an electric field between the common electrode and the segment electrode,
The output potential of each terminal of the common and segment that holds the dot pixel is shifted with a small amplitude while avoiding the central potential of the maximum amplitude that can be output for both the common and segment, and the VCOM-VSEG that is the voltage between both terminals is further increased. A drive device for a dot matrix display using a bistable nematic liquid crystal having a drive mode driven with a small amplitude.