CN1058850A - The multiplex addressing of ferroelectric liquid Crystal - Google Patents

Abstract

A ferroelectric liquid crystal element, using X, Y matrix to display the rows and The column electrodes are addressed. The row electrodes are sequentially applied with the strobe waveform, and the column electrodes Plus the data waveform. Each display unit receives the addressing waveform and converts it to one of two transition states. Generated with two addressing waveforms Two different conversion characteristics. at least one switching characteristic in an electrical The response time is the shortest under the voltage value, and the display works under the voltage higher than this do. The data waveform is an alternating positive and negative pulse. The strobe waveform enables the adjacent Addressing overlap for adjacent row electrodes. with a strobe or de- Hidden pulses switch display cells to one state and some display cells to Change to another state.

Description

The present invention relates to multiplex addressing of ferroelectric liquid crystal displays. These displays use C, I or F type liquid crystal materials with tilted chiral smectic structures.

Liquid crystal devices are usually provided with a thin layer of liquid crystal material between two glass slides. Light-transmitting electrodes are formed on the inner surfaces of the two slides. When a voltage is applied to these electrodes, the generated electric field changes the molecular alignment of the liquid crystal molecules. Changes in molecular alignment are easily observed, and this becomes the working principle of many liquid crystal display devices.

In a ferroelectric liquid crystal device, each liquid crystal molecule switches its alignment between two different alignment directions according to the polarity of the applied voltage. These devices are somewhat bistable and have a tendency to remain in one of the two switching states until transitioning to the other. This capability allows us to multiplex address fairly large displays.

A conventional multiplexed display typically has a number of display elements, or pixels, arranged in an X,Y matrix format for displaying eg alphanumeric characters. The matrix format is formed by having the electrodes on one slide form a series of column electrodes and the electrodes on the other slide form a series of row electrodes. The intersections between columns and rows form addressable cells or pixels. There are other forms of matrices that everyone knows, such as polar coordinates (r-theta) and seven-line digital displays.

There are many different schemes for multiplex addressing. These schemes have a common feature, that is, to sequentially apply a voltage to each column and each row electrode, which is called a strobe voltage (strobe voltage). While applying the gate voltage to each column electrode, an appropriate voltage is applied to all the column electrodes, which is called the data voltage (data voltage). The different schemes differ in the shapes of the gate voltage and data voltage waveforms.

European Patent Application 0,306,203 describes a multiplex addressing scheme for ferroelectric liquid crystal displays. In this patent application, the gate voltage is a unipolar pulse with alternating polarity, and the waveforms of the two data voltages are rectangular waves with opposite signs. The width of the strobe pulse is half the period of the data waveform. The combination of the gate voltage and an appropriate data voltage can switch the molecular arrangement of the liquid crystal material.

Other addressing schemes are introduced in the following documents: GB2,146,473-A; GB-2,173,336A; GB-2,173,337-A; GB-2,173,629-A; WO89/ 05025; articles written by Harada et al. in S.I.D Digest Paper 8.4, 1985, pp. 131-134; and articles published by Lagerwall et al., in IEEE, IDRC, pp. 213-221, 1985; P, Maltese et al., in Proc1988IEEE, Article entitled "Fast Addressing of Ferroelectric Liquid Crystal Display Panels" written on pages 98-101 of the IDRC.

The liquid crystal material is switched between its two states with two strobe pulses of opposite sign together with a data waveform. Alternatively, blanking pulses may be used to switch the liquid crystal material to one state, and a single strobe pulse in conjunction with an appropriate data pulse may be used to selectively switch pixels back to the other state. To keep the overall DC value at zero, the sign of the blanking pulse and the strobe pulse are alternated periodically.

Usually, these blanking pulses are larger in amplitude and longer in duration than the strobe pulses, so that the liquid crystal material can switch its state regardless of which of the two data waveforms is applied to any intersection point . The blanking pulse can be applied line by line before the strobe, or to blank the entire display at once, or to blank a group of lines simultaneously.

One known blanking scheme uses blanking pulses whose voltage (V) times time (t) product VT is equal to the VT product of the strobe pulse but opposite in polarity. The blanking pulse has half the amplitude of the strobe pulse and is applied for twice the time of the strobe pulse. These values ensure that the blanking and strobe do not periodically change their polarity to zero the total DC component. Experiments show that this scheme has poor performance.

Another known solution for blanking pulses is described in European patent EP 0,378,293. This scheme uses the commonly used balanced strobe pulse (with the same period and opposite polarity), together with a similar DC balanced blanking pulse (with the same period and opposite polarity), where the width of the blanking pulse can be the width of the strobe pulse. Several times. This scheme zeros the total DC component without periodically changing the blanking and gating waveforms.

This feature of dc balance is particularly important in projection displays because periodic polarity changes are not tolerated if the gap between the individual picture elements is to be switched to one optical state.

One problem with current displays is the time required to address a complex display. In order to drive a composite display at the image frame rate, the display needs to be addressed quickly. Fast addressing also improves the contrast ratio so that the column waveforms are at corresponding high frequencies. But just increasing the encoding speed doesn't always make the conversion process work correctly. The purpose of the present invention is to shorten the time required for addressing the matrix display and improve the display contrast.

A kind of method that the present invention carries out multiplex addressing to the ferroelectric liquid crystal matrix display formed by each intersection of the first group of electrodes and the second group of electrodes comprises the following steps:

Individually addressing each electrode of the first set of electrodes by applying a pulse strobe waveform of positive and negative value or by applying a blanking pulse followed by a strobe pulse of periodically changing polarity , to keep the total DC component value equal to zero;

Apply one of the two data waveforms to each electrode in the second group of electrodes synchronously with the strobe pulse, the two data waveforms alternately take positive and negative values, and the phase of one data waveform is opposite to that of the other data waveform, The period (2ts) of the data waveform is twice the period (ts) of a single strobe pulse;

It is characterized in that: the end time of each strobe pulse is extended in time, so that each intersection point is addressed with a pulse of appropriate symbol and size, so that the intersection point enters the required display state once every complete display addressing cycle, and the total The DC component of is zero.

The strobe pulse may be zero for the first period ts, and then be a non-zero voltage (main) pulse for a time greater than ts such as (1.5, 2.0, 2.5, 3.0 or more) xts. The voltage of the strobe waveform can also be non-zero during the first ts period, with the same or different polarity than the rest of the strobe pulses; the amplitude of this first voltage pulse is adjustable to provide temperature compensation. The voltage of the strobe waveform may then be unequal to zero for a period of time of opposite polarity to the main voltage pulse, which may be, for example, greater than, equal to or less than ts.

By aligning the strobe pulse with the appropriate data waveform, the liquid crystal material can be toggled between its two states. Alternatively, a blanking pulse can be used to switch the liquid crystal material to one of the states, and selected pixels can be switched back to the other state by matching the strobe pulse with an appropriate data waveform.

The blanking pulse can be divided into two parts, the polarity of the first part is opposite to that of the second part. The two parts of the blanking pulse are arranged so that the combination of the voltage time product VT and the VT product of the single gate can make the DC component value equal to zero.

Prolonging the duration of the strobe pulse means that the electrodes of the first set of electrodes are sequentially and repeatedly addressed. This repetition effectively widens the width of the switching pulse without affecting other waveforms, thereby reducing the total time to address the entire display and maintaining a good contrast ratio for each pixel in the two different switching states .

Each strobe may be immediately followed by a smaller prepulse of the same or opposite sign as the associated strobe. The pre-feed pulse can be used to change the switching characteristics of the liquid crystal material and can be used as part of temperature compensation. In this case, it is necessary to detect the temperature of the liquid crystal material and adjust the amplitude of the pre-feeding pulse appropriately.

Each strobe pulse may be followed by a pulse of opposite sign.

Multiplex addressing liquid crystal display of the present invention comprises:

A liquid crystal element, made of a layer of liquid crystal material installed between two element walls, the liquid crystal material is a material with a tilted chiral disk structure, with negative dielectric anisotropy, formed on one wall of the element wall with electrodes There is a first series of electrodes and a second series of electrodes formed on another element wall, the electrodes being arranged so that they collectively form a matrix of addressable intersections, at least one of the element walls being surface treated to enable The surface is aligned with the liquid crystal molecules in one direction;

The first group of electrode excitation circuits are used to sequentially apply the gating waveform to each electrode in the first group of electrodes;

The second group of electrode excitation circuit is used to add the data waveform to the second group of electrodes;

a waveform generator for generating a strobe waveform and two data waveforms applied to the excitation circuit;

The control device is used to control the sequence of data waveforms to obtain the required display graphics;

It is characterized in that there is a data waveform generator and a gate pulse generator, the former is used to generate two sets of waveforms with equal amplitude and frequency but opposite signs, and each data waveform includes DC pulses with alternating signs; the latter Used to generate strobe pulses that last longer than half a period of the data waveform, and each strobe pulse lasts until the addressing period of the next electrode.

The display may also include a temperature sensor for detecting the temperature of the display; and a voltage regulator for adjusting the magnitude of the addressing voltage.

A simple analysis of liquid crystal switching characteristics ("Liquid Crystals", 1989, Vol. 6, No. 3, pp. 341-347) leads to the following expression for the electric field under which the response time of the liquid crystal material is - The shortest response time of the voltage conversion characteristic:

Where Emin is the electric field at the shortest response time of the response time of the liquid crystal material-voltage conversion characteristic, ∈ ₀ is the permittivity of free space, △∈ is the (negative) dielectric anisotropy of the liquid crystal material, and θ is the Taper angle, Ps is the spontaneous polarization.

This simple analysis is only applicable to some liquid crystal materials, and their Ps and △∈ values can be adjusted to achieve the required operating voltage. Recent work (see EP Raynes, "Refining Chemicals for the Electronics Industry II, Chemical Applications in the Nineties," pp. 130-146, entitled "Display Physics in the Nineties"; Jones, Paper entitled "Importance of Dielectric Biaxiality in Ferroelectric Liquid Crystal Devices" presented by Raynes and Towler at the Third International Symposium on Ferroelectric Liquid Crystals held at Bonlder Colorado University, USA, June 24-28, 1991) It was shown that the dielectric biaxiality is an important factor for making a minimum value appear in the response time-voltage characteristic. The data for Figures 16-20 described below were obtained from experiments.

The present invention will now be described, by way of example only, with reference to the accompanying drawings. In the attached picture:

Fig. 1 is the schematic diagram of X, Y matrix of time multiplexing addressing;

Figure 2 is an enlarged cross-sectional view of a portion of the display of Figure 1;

Figure 3 is a log-log graph of time versus voltage showing the switching characteristics of a disc-shaped structured material for two differently shaped addressing waveforms;

Figures 4-8 show the various strobe and data waveform diagrams that can be used;

Fig. 9 shows that the gating waveform is a waveform diagram modified on the basis of Fig. 4;

Figure 10 shows the waveform diagram of blanking, strobe and data;

Figure 11 shows strobe, data and addressing waveforms used in prior art displays;

Fig. 12a, b have shown the waveform diagram to 4X4 pixel display shown in Fig. 13;

Figure 13 is a 4×4 pixel array, it can be seen that some intersections are turned into "on" state, and the rest of the intersections are in "off" state;

Figures 14 and 15 show the relationship between the contrast ratio of two different materials and the pulse width of the applied voltage;

Figures 16-20 are log-log plots of time versus applied voltage showing the switching characteristics of a material with different waveforms applied;

Figures 21 and 22 show various blanking, strobe and data waveforms;

Figures 23 and 24 show row waveforms and column waveforms of prior art displays;

Figures 25 and 26 show the row and column waveforms used to modify Figure 6 .

The display 1 shown in Figures 1, 2 comprises two glass walls 2, 3 spaced from each other by a spacer ring 4 and/or distributed spacers at a distance of about 1-6 micrometers.

Electrode members 5, 6 made of transparent tin oxide are formed on the inner surfaces of the two walls. It can be seen that these electrodes are arranged in rows and columns to form an X, Y matrix, but other forms are also possible. For example, radial and curved shapes are used for r, theta displays, while digital seven-line displays are segmented.

A layer of liquid crystal material 7 is provided between the walls 2,3 and the spacer ring 4 .

Polarizers 8 and 9 are arranged at the front and back of the element 1 . Row and column drivers 10 and 11 apply voltage signals to the elements. The generated two groups of waveforms are applied to row and column drivers 10,11. Strobe waveform generator 12 provides row waveforms and data waveform generator 13 applies "on" and "off" waveforms to column driver 11. The overall control of the timing and display format is performed by the control logic unit 14 . The temperature of the liquid crystal layer 7 is measured by a thermocouple 15 whose output is fed to a gate pulse generator 12 . The output of the thermocouple 15 can be fed directly or via a proportional element 16 (such as a programmed ROM chip) to a generator to vary the strobe pulse or a portion of the data waveform.

Before assembly, the surface of the element wall is treated in a known manner, e.g. by applying a thin layer of polyimide or polyamide, drying, curing if necessary and applying a cloth (e.g. rayon fabric) in a single direction R1, R2 rub on. Otherwise, a thin layer such as silicon monoxide can also be evaporated at an oblique angle. These treatments make the liquid crystal molecules surface aligned. The alignment/rubbing directions R1, R2 may be parallel or non-parallel to each other. When an appropriate unidirectional voltage is applied, the molecules are arranged in one direction of D1 and D2 according to the polarity of the voltage. The angle between D1 and D2 is preferably about 45 degrees. When no electric field is applied, the molecules are arranged in the middle direction between the R1, R2 and D1, D2 directions.

The device can operate in either transmissive or reflective mode. In the former mode, light passing through the device, for example from a tungsten bulb, is selectively transmitted or blocked to form the desired display pattern. In reflective mode of operation, a mirror is placed behind the second polarizer 9 to reflect ambient light back through the element 1 and both polarizers. Displays can be made to work both in transmissive and reflective modes by making the mirror partially reflective.

Multicolor dyes can be added to the liquid crystal material 7 . In this case, only one polarizer is needed, and the thickness of the coating can be taken as 4-10 microns.

Applicable liquid crystal materials are:

The product numbered SCE8 in Merck’s product catalog (available from Merck Ltd Poole in the UK), the Ps of this product is about 5 nanolibrary/square centimeter (nc/cm ² ) at 30°C, and the dielectric anisotropy The opposite sex is about -2.0, and the phase sequence is: Sc59℃Sa79℃N98℃.

Mixture A, host contains 5% racemic dopant and 3% chiral dopant;

Mixture B, 9.5% racemic dopant and 3.5% chiral dopant in the matrix.

＊ means chirality, and those without ＊ mean the material is racemic.

The Ps of mixtures A and B at 30°C are both about 7 nanocubes/cm2, and the dielectric anisotropy is about -2.3.

The phase sequence of mixture A is Sc100°C Sa111°C N136°C.

The phase sequence of mixture B is Sc87°C Sa118°C N132°C.

The liquid crystal material at the intersection of the row and column electrodes is switched by applying an addressing voltage. The addressing voltage is obtained by combining the strobe waveform Vs applied to the row electrodes and the data waveform Vd applied to the column electrodes.

That is, Vr=Vs-Vd

Among them, Vr=instantaneous value of addressing waveform;

Vs = instantaneous value of strobe waveform;

Vd = instantaneous value of the data waveform.

Chiral tilted disk materials switch according to the product of voltage and time. Figure 3 illustrates this characteristic. The voltage-time product above the curve causes the liquid crystal material to switch, and below the curve is the non-switching region. It should be noted that the switching characteristics are independent of the sign of the voltage, ie the liquid crystal material is switchable at positive or negative voltages of a given magnitude. The direction in which the liquid crystal material switches depends on the polarity of the voltage.

Two curves are shown in FIG. 3 because the switching characteristics depend on the form of addressing voltage pulse combination. The upper curve is obtained when the addressing voltage is immediately followed by a small prefeed pulse of opposite sign, eg a small negative pulse followed by a larger positive pulse. The liquid crystal material behaves the same when a small positive pulse is applied followed by a large negative pulse. The upper curve usually represents the shortest transition or response time at a certain voltage. This is different from that provided by (1), because the transfer characteristic has been changed by the prefeed pulse. The small prefeed pulse may be called the leading pulse (LP), and the larger addressing pulse may be called the trailing pulse (Tp). The upper curve is the curve when the Lp/Tp ratio is negative.

The following curve is obtained when a small pre-feed pulse of the same sign comes before the addressing voltage, that is, there is a larger positive pulse immediately after the small positive pulse. The same curve results when a small negative pulse is followed by a large negative pulse. The lower curve has a positive Lp/Tp ratio. The lower curve has a different shape than the upper curve. The voltage-time curves of some liquid crystal materials may not have a minimum.

The shapes of the two curves are different so that the display can operate unambiguously over a fairly wide range of time values. This is achieved by operating the display in the region between the two curves, such as the hatched region in the figure. Each intersection point to be switched is addressed with an addressing voltage whose shape corresponds to the curve below and whose voltage and pulse width lie above the curve. Those intersections that do not require transitions receive addressing voltages whose shape fits the upper curve with voltages and pulse widths below that curve, or data waveform voltages only. This is described in more detail below.

Figure 4 shows strobe, data and address waveforms for one embodiment of the present invention. The strobe waveform starts at zero for a period of ts and then +3 for twice ts. This is true for each row sequentially (ie, one time frame period). The next part of the strobe waveform is zero for one ts, followed by +3 for twice ts. The same applies to successive rows within a time frame period. It takes two time frame periods for the display to be fully addressed. The values of +3 and -3 are just the voltage units given for illustration, and the actual values will be given later when specific materials are involved.

The data waveforms can be arbitrarily named "on" data and "off" data, or D1 and D2. The value of the "on" data is +1 in the first ts time, and then -1 in the next ts time, and so on; that is, the amplitude of the "on" data is 1, and the same period is 2ts the alternating signal. The "off" data is similar, except that its value is -1 at the beginning and then +1; that is, it is the opposite of the "on" data. The first part of the data waveform (ie, +1 for ts for "on" data) coincides with the first part of the strobe waveform (ie, zero for ts).

The addressing waveform is the sum of the strobe and data waveforms. The combinations of positive strobe and "on" data are: -1, 4, 2, 1, -1, 1, etc. A -1 before the value 4 ensures that the switching characteristics of the liquid crystal material are controlled by the upper curve in Figure 3. The combinations of negative strobe pulses and "on" data are: -1, -2, -4, 1, -1, 1, etc. The combination of smaller pulses of the same sign as the large (-4) pulse ensures that the switching characteristics of the liquid crystal material are governed by the lower curve in Figure 3. Likewise, a positive strobe combined with "cut off" data gives 1, 2, 4, -1, 1, etc.; a negative strobe combined with "cut off" data gives 1, -4, -2, -1, 1 , -1 etc.

When not receiving a strobe pulse, each row is grounded, ie receives zero voltage. Each column receives either "on" data or "off" data throughout. The effect is that all crosspoints receive the alternating signal caused by the data waveform when not addressed. This AC biases the cross points and helps the liquid crystal material maintain its switching state. Increasing the AC bias value results in improved contrast due to the well-known AC stabilization described in Proc 4 th IDRC, 1984, pp. 217-220.

Alternatively, an AC bias can be supplied from, for example, a 50 kHz source, applied directly to those rows not receiving strobe pulses. Figures 14 and 15 show the effect of AC bias magnitude and pulse width on contrast ratio for material SCE8 and mixture A. From these figures it can be seen that the intrinsic contrast ratio (CR) is measured as a function of AC frequency as the element transitions between its two bistable states; Measured at different levels.

Figures 5 to 8 show additional gating waveforms. In Figure 5, the strobe waveform is first zero for a time of 1*ts, then 3 for a time of 3*ts, and then its inverse. In Figure 6, the strobe waveform is first zero for a time of 1 x ts, then 3 for a time of 4 x ts, and then its inverse. In Fig. 7, the strobe waveform is first zero for 1×ts time, then 3 for 2×ts time, then -1 for 1×ts time, and then vice versa.

Figure 8 is a modification of Figure 4, with a non-zero prefeed pulse used in the strobe waveform. As shown, the first part of the strobe waveform is between -1 and 1, rather than the zero value of Figure 4. The rest of the strobe waveform is the same as in Figure 4, that is, the amplitude is 3, and the duration is twice ts. The addressing waveform thus obtained is: the first pulse is between -2 and -1 under both the first and second electric fields. The effect of this pre-feed pulse is to change the position of the transfer curves in Fig. 3 et al. Changing the value of the prefeed pulse changes the shape and vertical position of the individual curves, as will be described below with reference to Figures 16 and 17. Table 8 below shows the transition time as a function of temperature. Changing the amplitude of the prefeed pulse can reduce this variation.

FIG. 9 is a modification of FIG. 4 . In this modification, the strobe waveform is zero for the first ts and 3 for the next 1.5ts. The 1.5ts time is just an example, any time greater than ts up to about 5ts can be used .

Figure 10 shows a single blanking pulse of amplitude 4 for 4ts. This blanking pulse switches all crosspoints to a switching state. A strobe pulse is then used to switch some selected crosspoints to another switching state. Periodically invert the sign of the blanking and strobe pulses so that the total DC voltage component is zero. Each of the schemes of Figures 4-8 can use blanking pulses and a single strobe pulse. The blanking and gating system has the advantage that the entire display can be addressed within a single field time.

For comparison, Figure 11 shows the strobe, data and addressing waveforms for a prior art display scheme, which is a single pulse addressing scheme.

Figures 21 and 22 illustrate the addressing scheme of the present invention using blanking pulses and a single strobe pulse to bring the total DC component value to zero.

In Fig. 21, the blanking pulse is divided into two parts, and the sign of the pre-feeding pulse is opposite to that of the main pulse and the blanking pulse. The role of the pre-feed pulse is to offset the DC component and make it zero. The value of the prefeed pulse is 3, which lasts 4ts, followed by -3 value, which lasts 6ts. The strobe pulse is first zero, which lasts 1 ts, followed by 3, which lasts 1 hour and 2 ts; this strobe is the same as the strobe shown in Figure 4. Data waveforms D1, D2 are also the same as those in FIG. 4 . The combination of blanking and D1 or D2 increases the negative Vt product which switches all pixels in the addressed row to the "off" state. The strobe pulse in combination with D2 switches the desired pixels to the "on" state, as discussed above with reference to Figure 4.

Figure 22 is similar to Figure 21, but with a different shape of the blanking pulse. The prefeed pulse amplitude of the blanking pulse is 3, which lasts 4ts, followed by -4.5, which lasts 4ts. The strobe pulse has an amplitude of 3 and a duration of 2ts, the same as in Figure 4. It can be seen that the blanking pulse combined with D1 and D2 causes a large negative Vt product which switches all addressed rows to the "off" state. The selected pixel here is also switched to the "on" state by the strobe pulse and D2.

The blanking pulses of Figures 21 and 22 can be used with other forms of strobe pulses as shown in Figures 5-9, with the amplitude and/or Vt product arranged so that the total DC component value is zero. For example in the case of Fig. 8 where the first time slot of the gate varies with eg temperature, the amplitude of the prefeed and/or main blanking pulses is also adjusted such that the overall DC component value remains zero.

How much the blanking pulses lead the strobe pulses can vary, but there is a sweet spot that corresponds to the display's response time, contrast, and degree of visible flicker. It is typical for the blanking pulse to start six lines earlier than the strobe pulse, but this depends on various parameters of the material and the details of the multiplexing scheme.

Figures 12a,b show the waveforms used to address a 4x4 matrix array showing the information shown in Figure 13 . Here, arbitrarily selected solid dots represent “on” electrode intersections, that is, display pixels, and unmarked dots indicate that they are in the “off” state. The addressing scheme is the addressing scheme adopted in FIG. 4 .

The positive or leading strobe pulses are sequentially applied to rows 1 through 4, which forms the first field. After the leading strobe addresses the last row, negative or trailing strobes are applied to rows 1 through 4 in sequence, which forms the second field. It should be noted that there is overlap between rows. For example, the third ts time in line 1 occurs at the same time as the first ts time in line 2. This overlap is even more noticeable when the display uses the strobe waveforms shown in Figures 5 and 6.

The "on" data that the data waveform adds to column 1 remains unchanged because each intersection in the column is always "on". Likewise, the data waveform applied to column 2 is "off" data and remains unchanged since all intersections in column 2 are "off". The data waveform added to the third column is "off" data when the first and second rows are in the addressing state, and becomes "on" data when the third row is in the addressing state, and then is in the fourth row. The address status time changes back to "cut-off" data. That is to say, column 3 receives “off” data for 4×ts time, receives “on” data for 2×ts time, receives “off” data for 2×ts, and the period is one field time , that is, the time required for the positive strobe pulse to address each row. Also for column 4, the data waveforms are "off" data for 2ts; "on" data for 2ts; "off" data for 2ts; and "on" data for 2ts. While applying the negative strobe pulse, the above process is repeated for another field period. Two field periods are required to form one frame period and complete addressing of the display. Repeat the above process until a new display graphic is required.

Figure 12b shows the resulting addressing waveform. The liquid crystal material at the intersection of row 1 and column 1 (R1, C1) does not switch during the first field period, because the switching of the material is carried out according to the upper curve of Figure 3, and the time and the applied voltage level is below the conversion curve. In contrast, the liquid crystal material switches during the second field period, when the liquid crystal material switches due to the lower voltage/time value required by the lower curve of FIG. 3 . This reasoning also applies to the junction R1, C2 where the liquid crystal material switches during the first field period.

As for the intersection point R3, C3, the liquid crystal material switches during the second field period because the time/voltage applied during the first field period does not reach the higher value required by the upper curve of FIG. 3 . Intersection R4, C4 switches at the end of the second field period when the negative strobe is applied.

The shape of the waveform added to column 4 presents a difficult problem. Since the display takes the form of on-off-on-off, the period of the data waveform is, for example, twice that of the first column. This means that the contrast is reduced as shown in Figures 14 and 15, when the pulse width is increased (low frequency), so that the contrast ratio is significantly reduced. Furthermore, the address pulses in the first field do not switch but have a large amplitude in sharp contrast to the switching pulses of smaller amplitude in the second field. For this reason, a large gap between the two conversion curves, such as that shown in FIG. 3, is required for reliable conversion.

The contrast ratio (CR) curves in Figure 14 (Mixture A) and Figure 15 (Mixture SEC 8) represent the intrinsic contrast ratio of a display when switched between its two bistable positions with an applied AC bias. Obviously, for good and uniform contrast, it is best to operate the display on the flat portion of the curve with short pulse widths. The contrast of the display may vary due to the multiplexing of the AC bias from the column waveforms with variable frequency components related to the form of the pixels. This is most noticeable when all pixels are in one state (highest frequency component) and the pixels are alternately in the opposite state (lowest frequency component), where there is a factor of the difference in the column waveform frequency . Figures 12 and 13 show columns 1 and 4 in both cases.

FIG. 16 shows the time/voltage logarithmic curve of the switching characteristic at 250° C. of the liquid crystal material SCE 8 with a layer thickness of 1.8 μm in a parallel rubbed element. The coordinate axes of the curve are the logarithmic ts value and the logarithmic pulse amplitude voltage value respectively.

The curves were obtained in calibration elements simulating the addressing waveforms shown in FIG. 4 . Two different addressing waveforms are used. The first waveform, waveform I, is a small negative pulse (amplitude -1) with an on-pulse duration of ts, followed by a larger positive pulse (amplitude 5) with an on-pulse duration of 2ts, ie the Lp/Tp ratio is -0.166. After a period of zero volts, the opposite follows, a small positive pulse (amplitude 1) followed by a larger negative pulse (amplitude -5). In addition, a 50 kHz square wave signal is added during addressing, thereby providing an AC bias voltage and simulating a data waveform. The small pulse is 0.166 the value of the large pulse at all voltage levels used to plot the curves. This first addressed waveform gives the upper curve. Time/Voltage values above this curve will switch the device, values below the curve will not.

The second addressing waveform, waveform II, starts with a small positive pulse with an amplitude of 1 and a duration of ts, followed by a larger positive pulse with an amplitude of 4 and a duration of 2ts. After a period of zero voltage, the waveform turns into the opposite situation. The small pulse is 0.25 of the large pulse value, that is, Lp/Tp=0.25. A 50 kHz signal is also added here to provide AC bias. This second addressing waveform gives the following curve. Time/Voltage values above this curve will cause the device to switch, values below the curve will not cause the device to switch. In the case of gate voltage Vs=50 volts and data voltage Vd=10 volts, the operating range is Vs-Vd=40 volts, switching at 52 microseconds, Vs+Vd=60 volts, switching at about 480 microseconds .

Figure 17 shows the time-voltage characteristics of the same addressing scheme used in Figure 16 (i.e., the addressing scheme of Figure 4), but with a small pre-feed pulse in the strobe waveform as in Figure 8. improved. It can be seen from Figure 17 that the function of the pre-feed pulse is to move the vertical position of the curve. This can be used for temperature compensation; changing the pre-feed pulse value to counteract the shift of the curve due to temperature changes.

The analog addressing waveform of the above curve is a zero voltage lasting ts first, followed by a relatively large positive pulse with an amplitude of 6 lasting 2ts, that is, Lp/Tp=0. After a time interval ts at zero voltage, an opposite pulse is applied to keep the total DC voltage at zero. To provide an AC bias, a 50 kHz waveform is superimposed on it.

The addressing waveform of the lower curve is first a small positive pulse with a duration of ts and an amplitude equal to 1, followed by a larger positive pulse with a duration of 2ts and an amplitude of 2, that is, Lp/Tp=0.5. After this, reverse its polarity. To provide an AC bias, a 50 kHz waveform is superimposed on it.

When Vs=50 and Vd=10, the working range of each curve is as follows: the lower curve is Vs-Vd=40, which is converted at 42 microseconds, and the upper curve is Vs+Vd=60, which is converted at about 500 microseconds.

Figure 18 is similar to Figure 16, with the same liquid crystal elements, but using analog waveforms of the addressing waveforms of Figure 5. Therefore, the addressing waveforms of the upper curve are -1, 6, 4, 6 (Lp/Tp=-0.166); the addressing waveforms of the lower curve are 1, 4, 6, 4 (Lp/Tp=0.25). When Vs=50 and Vd=10, the lower curve is switched at 38 microseconds, and the upper curve is switched at about 210 microseconds.

FIG. 19 is similar to FIG. 16, with the same liquid crystal elements, but using analog waveforms of the FIG. 7 addressing waveforms. The addressing waveform is as shown in the figure, that is, the curve formed by the points marked with "+", whose values are -1, 6, 6, -6 (Lp/Tp=-0.166), and the points marked with "0" The resulting curve has values 1, 4, 4, -4. The switching process is complicated because the upper curve has a new region (re-entrantarea) in which the liquid crystal material switches not at the main pulse but at the trailing pulse. When Vs=50 and Vd=10, the following curve Vs-Vd=40 is converted at 58 to 240 microseconds, and the conversion process is carried out when the trailing pulse occurs when it is greater than 300 microseconds. The upper curve Vs+Vd=60 does not switch at 60 volts. Multiplexing of the main pulse occurs between 58 and 240 microseconds, and multiplexing of the trailing pulse occurs above 300 microseconds.

For comparison, the time/voltage logarithmic characteristic of a general single-pulse addressing scheme using the strobe and data waveforms of Figure 11 in the same liquid crystal cell as in Figure 11 is shown in Figure 20 Analog waveform. The analog addressing waveform for the upper curve is a negative pulse with an amplitude of 1 unit for ts followed by a positive pulse with an amplitude of 6 units for ts. The addressing waveform of the lower curve is a positive pulse with a ts amplitude of 1 unit, followed by a positive pulse with a ts amplitude of 4 units. Here pulse amplitudes are given in units to indicate relative values; the curves are plotted at the exemplified voltages. When Vs=50 and Vd=10, the lower curve Vs-Vd=40 is converted at 80 microseconds, and the upper curve Vs+Vd=60 is converted at about 950 microseconds.

After introducing the characteristics of various liquid crystal material displays and different addressing waveforms, let's talk about some details. We fabricated a single-pixel test element and addressed it with a 50-line display of the analog waveform. In order to give each addressing voltage value, different strobe, Vs and data, Vd voltage amplitudes are selected, so that the switching voltage is above the lower curve in Figure 3, and the non-switching voltage is on the upper curve of Figure 3 Below the curve, the microsecond value of ts is additionally adjusted to give a clear display of transitions. Doing so ensures that the liquid crystal cell operates within the region shown hatched in FIG. 3 . The contrast ratio, CR, is the ratio of the light transmitted in one switching state to the light transmitted in another switching state; it is a measure of display clarity. CR is measured at the pulse width limit value ts or a specific ts value. CR can be optimized by adjusting the position of a switch in the orientation factor in the liquid crystal so that it corresponds to the minimum amount of transmission.

In the following tables, the range of time ts does not quite correspond to the information provided by the voltage/time curves of Figs. 16-20. There are three reasons. First, the simulation approach used in Figures 16-20 is not entirely appropriate for all situations in which graphics are displayed. Second, with longer pulse widths and correspondingly longer frame times, since the transition is instantaneous, the operator can see flicker, which can be explained by the lack of multiplex addressing. Third, when the pulse width is longer, the contrast ratio becomes lower, see Figures 14 and 15. For example, at 200 microseconds CR is 2, so it is difficult to determine whether the liquid crystal material is in the switching state.

SCE8 liquid crystal material with a layer thickness of 1.8 microns at 25°C

Table 1, addressing scheme of Figure 4

Vs Vd ts CR

50 5 36-53 8-7

50 7.5 46-115 45-15

40 10 46-88 77-21.5

50 10 57-140 71-9.5

Table 2, addressing scheme of Figure 5

50 7.5 40-73 26-11

40 10 34-57 64-23

50 10 47-100 67-17

Table 3, addressing scheme of Figure 7

50 5 44-280 17.5-5.4

50 7.5 62-225 62-5

40 10 56-186 87-5.8

50 10 69-213 70-4.8

Table 4, Addressing scheme of Figure 11 (single pulse)

50 5 65-450 23-3

50 7.5 75-480 65-2.2

40 10 95-345 49-2.7

50 10 83-370 63-2.3

Mixture B with a layer thickness of 1.7 μm at 30°C

Table 5, Addressing scheme of Figure 4

Vs Vd ts CR (at minimum ts)

50 10 22-78 51

50 7.5 17-82 33

40 10 16-47 56

Figure 6, the addressing scheme of Figure 5

50 10 20-68 51

50 7.5 14-62 24

40 10 13-36 53

40 7.5 10-37 7.2

45 7.5 10-42 10

Figure 7, the addressing scheme of Figure 7

50 10 24-80 52

50 7.5 19-98 35

40 10 18-66 68

Table 8, Figure 4 Addressing scheme at different temperatures

50 10 39-123 48 25℃

50 10 21-73 59 30℃

50 10 12-43 58 35℃

50 10 7-25 26 40℃

50 10 5-10 5 45°C

Table 9, Figure 5 Addressing scheme at different temperatures

50 10 18-64 52 30℃

50 10 8-20 13 40℃

50 10 8-37 44 35℃

50 10 35-120 48 25℃

Table 10, Figure 11 Addressing scheme at 30°C (single pulse)

50 10 28-93 47

50 7-5 24-148 33

40 10 32-120 44

Mixture A with a layer thickness of 1.7 μm at 30°C

Table 11, Addressing scheme of Figure 4

40 10 39-100 46

50 10 59-120 26

Table 12, Addressing scheme for Figure 5

40 10 33-85 48

50 10 52-110 30

Table 13, Addressing scheme of Figure 7

40 10 40-150 46

50 10 64-220 23

Table 14, Addressing scheme of Figure 11 (single pulse)

40 10 56-150 32

50 10 66-300 22

Merck company material product sample No. 917

Temperature 30°C; Vs=60 volts; Vd=15 volts

Table 15

Addressing Scheme Figure 11 Figure 4 Figure 5 Figure 7

Fastest slot time, microseconds 27 15 12 17

Longest slot time, microseconds 116 37 28 70

Working range (time) 4.3X 2.5X 2.3X 4.1X

Contrast ratio (CR) 41 84 80 76

Width (%) 63 63 60 63

The working range is: longest gap time/fastest gap time

Brightness (%) is compared without a liquid crystal element between parallel polarizers.

Material RSRE A206: temperature 30°C, Vs=30 volts, Vd=10 volts.

Table 16

Addressing Scheme Figure 11 Figure 4 Figure 5

Fastest slot time, microseconds 60 27 20

Working range (time) ＞2X 2.6X 2.2X 1X

Contrast ratio (CR) 14 48 55

Brightness (%) 77 67 60

Material RSRE A206 is: AS500: A151 1:1+5% dopant

AS500: A151 1:1+5% dopant

2% Chiral

3% racemic

＊ means chirality, and those without ＊ mean the material is racemic.

So in an actual display, it should be considered to have reached the upper limit of time when it can no longer effectively convert. This may be much shorter than the actual conversion time.

In ferroelectric liquid crystal devices, it is well known that the row and column peak voltages can be reduced by applying additional waveforms to the row and column electrodes. Accordingly, the display of the present invention may also include an additional waveform generator for generating additional waveforms and applying them to the two sets of electrodes.

For example, FIGS. 23-24 show two different schemes for reducing the peak voltage of the prior art single-pulse drive system shown in FIG. 9 .

In Figure 23, the strobe (row) waveform is alternately zero for 1 ts and positive pulse Vs for another 1 ts in the first field, followed by zero for 1 ts and another 1 ts in the second field For the negative pulse -Vs. The additional waveform is positive Vs/2 during the first field, followed by -Vs/2 during the second field. It can be seen that the resulting strobe waveform varies between Vs/2 and -Vs/2. The data (column) waveform is an alternating pulse of Vd and -Vd, each with a duration of 1ts. The additional waveform applied to each column is Vs/2 for the first field, followed by -Vs/2 for the second field. It can be seen that the obtained data waveform varies between Vd+Vs/2 and -(Vs/2+Vd). The effect of the additional waveform is to reduce the peak voltage, for example 50 volts to 35 volts.

FIG. 24 shows another alternative to FIG. 23 . As above, a normal strobe is zero for 1ts in the first field time, then positive Vs for 1ts, and zero for 1ts in the second field time, then -Vs for 1ts. The additional waveform applied during the first field time is a rectangular waveform with a period of 2ts, followed by the opposite waveform during the second field time, each waveform varying between Vs/2 and -Vs/2. The resulting strobe (row) waveform is shown in the figure. Likewise, the data (column) waveform is a rectangular waveform varying between +Vd and -Vd. The additional waveforms are the same as those applied to the row electrodes. The resulting data (column) waveform is shown in the figure, and the waveform varies between Vs/2+Vs and -(Vs/2+Vd). This also reduces the peak voltage required for the driver of the display from, for example, 50 volts to 35 volts.

The principles of Figures 23 and 24 are equally applicable to the addressing schemes of Figures 4-8 described above. This is shown in FIG. 25 , which is a modification of FIG. 5 . In the first field time, the strobe pulse is first zero for 1ts, followed by Vs for 3ts. During the second field time, the strobe pulse is zero for 1 ts, followed by -Vs for 3 ts. The figure shows the strobe waveforms of the 1st, 2nd, 3rd and 4th lines of the 4-line display; the figure shows two different strobe waveforms of the 4th line, the reason will be explained below. The additional waveform applied to the row (and also to the column) electrodes, as shown, is Vs/2 for the first field time and then -Vs/2 for the second field time. It can be seen that the obtained line waveform of the first line is -Vs/2 in the first field and the second field, which lasts 1ts; Vs/2, which lasts 3ts; -Vs/2, which lasts 4ts; Vs/2 , for 1ts; -Vs/2 for 3ts and Vs/2 for 4ts. As can be seen from the resulting strobe and additional waveforms and the row denoted row 4a, the waveform has large peaks of + and -3Vs/2. The reason for this phenomenon is that the strobe pulse length is extended, overlapping into adjacent fields. To solve this problem, row 4 can be left blank, or addressed with a zero strobe voltage as shown in 4b. In a more practical example such as a 128-line display, the generated waveforms are programmed for a 128-line display, but in the arrangement of Figure 25, only 127 lines are used. Even if a longer strobe is used as shown in Figure 6, some lines or even more lines will be left unused. Figure 26 shows the waveforms applied to the column electrodes. Data 1 and its inverse data 2 are the same as in FIG. 5 . The additional waveform is Vs/2 during the first field and -Vs/2 during the second field. It can be seen that the obtained column waveforms vary between ±(Vd+Vs/2). Thus for the scheme of Fig. 5, at Vs = 50 volts and Vd = 10 volts, the schemes of Figs. 25, 26 reduce the peak voltage to 35 volts.

Claims (12)

1, a kind of method that the ferroelectric liquid crystal matrix display that each intersection point of the first group of electrodes and the second group of electrodes is formed carries out multiplex addressing, comprises the following steps: Individually addressing each electrode of the first set of electrodes by applying a pulse strobe waveform of positive and negative value or by applying a blanking pulse followed by a strobe pulse of periodically changing polarity , to keep the total DC component value equal to zero; Apply one of the two data waveforms to each electrode in the second group of electrodes synchronously with the strobe pulse, the two data waveforms alternately take positive and negative values, and the phase of one data waveform is opposite to that of the other data waveform, The period (2ts) of the data waveform is twice the period (ts) of a single strobe pulse; It is characterized in that: the end time of each strobe pulse is extended in time, so that each intersection point is addressed with a pulse of appropriate symbol and size, so that the intersection point enters the required display state once every complete display addressing cycle, and the total The DC component of is zero. 2. The method as claimed in claim 1, characterized in that the gate waveform is zero voltage at the time of the first ts, and is a non-zero voltage for a period of time greater than ts, and then at several ts representing a frame period Time is zero voltage, followed by similar waveforms with opposite polarities. 3. The method according to claim 1, wherein the gate waveform is a non-zero voltage within the first ts time, this voltage is smaller than the next voltage, and the amplitude is variable to compensate for the liquid crystal material conversion characteristics change with temperature. 4. A method as claimed in claim 1, characterized in that two strobe pulses of opposite polarity are used to address each intersection. 5. A method as claimed in claim 4, characterized in that a further waveform is applied to the two sets of electrodes to reduce the peak voltage applied to the respective electrodes. 6. A method as claimed in claim 1, characterized in that the blanking pulse has two parts of opposite polarity, the voltage time product (Vt) of which is combined with the voltage time product of the strobe pulse such that the DC component value is equal to zero . 7. A multiplex addressing liquid crystal display, comprising: A liquid crystal element, made of a layer of liquid crystal material installed between two element walls, the liquid crystal material is a material with a tilted chiral disk structure, with negative dielectric anisotropy, formed on one wall of the element wall with electrodes There is a first series of electrodes and a second series of electrodes formed on another element wall, the electrodes being arranged so that they collectively form a matrix of addressable intersections, at least one of the element walls being surface treated to enable The surface is aligned with the liquid crystal molecules in one direction; The first group of electrode excitation circuits are used to sequentially apply the gating waveform to each electrode in the first group of electrodes; The second group of electrode excitation circuit is used to add the data waveform to the second group of electrodes; a waveform generator for generating a strobe waveform and two data waveforms applied to the excitation circuit; The control device is used to control the sequence of data waveforms to obtain the required display graphics; It is characterized in that there is a data waveform generator and a gate pulse generator, the former is used to generate two sets of waveforms with equal amplitude and frequency but opposite signs, and each data waveform includes DC pulses with alternating signs; the latter It is used to generate two strobe pulses with opposite polarities or blanking pulses and strobe pulses with opposite polarities. The duration of the strobe pulse is longer than half the data waveform period and lasts until the addressing time of the next electrode ; And make such an arrangement: each cross point is addressed with a pulse of appropriate symbol and size, so that the cross point enters the required display state once every complete display addressing cycle, and the total DC component value is zero. 8. A display as claimed in claim 7, characterized in that the gate waveform generator is designed such that it generates a zero voltage for a first time period ts, and then generates a non-zero value voltage for a period of time greater than ts, This is followed by zero voltage for a number of ts representing a frame period, followed by a similar waveform with opposite polarity. 9. A display as claimed in claim 8, further comprising an additional waveform generator for generating an additional waveform and applying the additional waveform to the two sets of electrodes. 10. The display as claimed in claim 7, further comprising a temperature sensor for detecting the temperature of the display; and a voltage regulator for adjusting the magnitude of the addressing voltage. 11. A display device as claimed in claim 10, characterized in that the gate waveform generator is designed such that it generates a non-zero value voltage during the first time period ts, which voltage is smaller than the next adjacent voltage, and its magnitude The value and sign can be changed in order to compensate the switching characteristics of the liquid crystal material so that it is not affected by temperature changes. 12. A display device as claimed in claim 7, characterized in that the strobe waveform generator is designed to generate a blanking pulse having two oppositely polarized portions whose voltage time product (vt) is equal to the voltage of the strobe pulse. The voltage time products add up to make the total DC component value of the waveform equal to zero.

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