JPS58220180A - Liquid crystal element driving system for liquid crystal display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method (device) for driving a liquid crystal element in a segmented numerical display type liquid crystal digital display device.

Since a liquid crystal display device is a passive device that uses ambient light as a light source, its display can be viewed even in bright places, and its power consumption is extremely low.

It has the following characteristics: it can operate at low voltage, and the liquid crystal panel can be constructed extremely thin.

Coupled with the development of C-MOB type L8'I which has excellent low crawling force characteristics, its practical application has been rapidly promoted in recent years. That is, it is no exaggeration to say that liquid crystal digital display devices are already the mainstream display in digital watches and calculators.

Furthermore, the use of liquid crystal displays is increasing day by day in fields such as small instruments and various consumer appliances used for various purposes. By the way, as for the driving method of the liquid crystal digital display device.

For example, this is the same as in the case of electron tube type display devices such as Nixie tubes and light emitting diode display devices.

Static drive system and dynamic (or.

It is broadly divided into two types: maltezolexing) drive system.

To put it simply, the static drive method is a method characterized by lighting up segments to be displayed at the same time.On the other hand, the dynamic drive method is a method in which the segment electrodes are divided into several groups and each group is illuminated for 7 hours. This method divides the image and displays it repeatedly. It goes without saying that both have their own advantages, but in general, liquid crystal display devices have a slower rise response speed than the above-mentioned electron tube type or diode display devices, so dynamic drive is required to prevent flickering. In this case, it is necessary to use the charge accumulated between the opposing electrodes for operation, and for this purpose, the value of the drive voltage must be set somewhat higher than the threshold voltage of the liquid crystal display element. This dynamic drive method can minimize the number of lead wires and drive circuits for segment electrodes, etc.

We inevitably have to rely on calculators with a large number of digits, or as display means for microcomputer terminals, but they have a small number of zero digits.

For clocks or instruments with simple displays, static drive systems are considered more advantageous.

By the way, in one of the most basic of conventional static drive systems, each segment)! For each pole, an alternating current rectangular wave voltage (repetition frequency of about 10117.~10K1) is applied between the segment electrode and the common electrode opposite to the segment electrode, which is higher than the threshold voltage of the liquid crystal element.
1z) and by short-circuiting one electrode and the other when turned off, the rise and fall response times of the liquid crystal display element can be shortened χ. Here, the use of the alternating current rectangular wave 7 not only speeds up the response time (as described above), but also prevents *gas decomposition from occurring in the liquid crystal vDa itself, thus extending the life of the liquid crystal display element. However, in a drive system like this one, which is driven by an applied voltage of a -radio waveform only when it is on, the viscosity coefficient of the liquid crystal material increases as the temperature decreases, which can lead to At present, we are faced with the problem of slow response times for the rise and fall of liquid crystal display elements.Currently, research and development into liquid crystal materials and their manufacturing methods is progressing, and attempts to improve various characteristics are bearing fruit. Although it came, especially -200
The response speed in the low temperature range below Celsius is a problem.

A second conventional technique developed with the aim of shortening the response time is particularly the lower the temperature.

As mentioned above, the viscosity coefficient of the liquid crystal becomes thicker and the response becomes slower (
In recognition of this, there is a method in which a bias voltage slightly lower than the threshold voltage of the liquid crystal display element is applied in advance. This can be said to be effective in solving the problem of the low temperature on the slope and in particular improving the rise of the response time, but the fact that the bias voltage is applied even when off is particularly important. However, this is not a very good idea since it requires a large amount of power consumption.

In addition, as a proposal for a further improved drive system,
As in the first prior art, the drive voltage (when on) and 0
■In addition to applying only two levels of voltage (when off), a bias voltage below the threshold is applied during off to shorten the rise response time, and only for a certain period of time when the on state transitions to off state. By setting the bias voltage to Ov.

There is also a method that prevents the fall response time from being delayed.

Typical embodiments based on this idea include, for example, the following. That is, a unipolar rectangular wave voltage with a peak value v0 is applied to the common electrode,
For each segment electrode, when on, a voltage having a waveform equal in magnitude to the peak value v1 of the rectangular wave and having an inverted polarity (that is, a different polarity) is applied to the corresponding segment electrode; Further, during one period during the off period, the peak value was v2, and the voltage level was shifted by l/2v□. - Applying a polar square wave pulsating voltage to each segment electrode, thereby biasing them below the threshold voltage of the liquid crystal element.

Similarly, during other periods, a unipolar rectangular wave voltage and a total (equivalent equivalent) voltage to each segment electrode are applied to the common electrode.
By bringing the Y Ov voltage between these two electrodes into a state of application, the above-mentioned aim has been achieved to some extent. However, in such a drive method, the voltage applied to the common electrode is a constant rectangular wave, and it can be said that it is quite simple in terms of means because it can be applied all the time, but it is structurally more difficult than the common electrode. For segment electrodes that are somewhat complex and have a much larger number, it is necessary to prepare voltage waveforms that are continuous when on, when biasing, and when Ov is applied, as shown above, and apply these as appropriate. As a result, the first military source circuit itself becomes complicated, and due to the design of one circuit, it is forced to have a 4N IMY layout for each building. Not only that, but the #A drive circuit of each individual segment electrode would need to be significantly changed, and as a result, the circuit configuration would inevitably become more complex. The C-MO8 type IC used is dedicated to driving the 7-segment field-effect liquid crystal (for example.

Toshiba TC4055BP) can be applied as is.

There were drawbacks such as the inability to

The main purpose of the present invention is to solve all of the problems of slanting that existed in the prior art, and to further enhance the usefulness of liquid crystal display devices. A new liquid crystal element driving method Z based on the basic idea of
This is what we provide.

In other words, in the device of the present invention, the segments occupy the majority of the electrode elements to be coupled to the drive circuit, so that they can be optionally used with existing liquid crystal drive ICs (for example, the above-mentioned T04055 BP). II, apply a knee-shaped rectangular wave voltage to the other electrode group, and simply alternating only the phases of the segment electrodes for on-display and those for off-display (for example, by making them different by 90 degrees). ) and on the other hand, counterclockwise to these segment electrodes.

The voltage waveform for the common electrode, which has a relatively simple structure and is small in number, is different from the voltage waveform used in conventional drive systems of this type. Apply a special waveform.

This is the result of a dispute over the adoption of a circuit configuration that embodies this idea. In order to further clarify the technical contents of the present invention, the structure and operation of an embodiment embodying the present invention will be described below with reference to the drawings.

First, Figure 1 is a cross-sectional view showing the general structure of a liquid crystal display element, which is well known in itself. In Figure 1, 1 is a glass plate, and 2 is a gap formed to keep the thickness of the sealed liquid crystal layer constant. do. A spacer such as a Teflon film, 3 a common electrode, 4 a seven-element segment electrode arranged opposite to the common electrode 3 and forming a day shape, 5 a sealing agent such as an epoxy resin, and 6 a liquid crystal. Figure 2 shows 1, for example, h N-(p'
-ethoxybenzylidene)-p-aminobe7zonitride in twisted nematic liquid crystal materials. The change characteristic of light transmittance (relative value) with respect to the applied voltage of IKtlzO is shown. In fig.

vth is the boundary voltage at which the electro-optical effect of the liquid crystal transitions from an off state to an on state or in the opposite direction, that is, a threshold voltage. Also, va and Vb
are specific critical voltages corresponding to the immediately lower and uppermost points of the threshold voltage vth, that is, the off-voltage limit value and the on-voltage limit value, and these are, for example, the light transmittance, respectively. This corresponds to a voltage at which the ratio is 90% and 10%. The present invention focuses on the characteristic shown in the second N so that the differential voltage applied between the common electrode and the segment electrode of the liquid crystal display element becomes V2 in the case of off-display and Vb in the case of on-display. By controlling
This is to improve the response time of the liquid crystal. This dotega 6th
To explain in detail using the waveform diagram in the figure, in FIG. 6(a), the voltage is applied to the common electrode. It shows the rectangular wave voltage pulse of the above-mentioned special waveform, and has a peak value Vl''+1 corresponding to the above-mentioned limit value Vb.

and a unipolar voltage level equal to or higher than the reference voltage level (for example, O' voltage) and a peak value Va corresponding to the above limit value va.
Y, and for a predetermined time interval (for example, τ
1 and every τ2. however.

Usually τl = τ2) alternating binary square wave pulses.

In addition, FIGS. 6(b) and ()→ are the segment electrodes that should be displayed as off, and 1. A voltage level v3 of a binary unipolar rectangular wave voltage pulse applied to the segment electrode and the segment electrode that is to display an on-state, both of which have a peak value corresponding to the difference (■ゎ-va) between the above two limit values. Begging and alternating periods with each other.

It alternates between this voltage level vr4 and the reference voltage level mentioned above. Therefore, the waveform of the driving voltage applied between the common electrode and the segment electrode to be turned off is as shown in FIG. It will look like Kano 9. In this Fig. 3,
> To 0, and.

v, -v, =v2=va, V, -==vb are the above two driving voltage waveforms) and (the slopes are respectively,
Since the - polarity voltage level and the other polarity voltage level are equal, no direct current component is included in either of them. In the end, the DC bias becomes zero, and the original driving conditions of the liquid crystal are effectively satisfied.
For this, Vl ”” Vb 41v2=va
, v, = v, -v2 = vbva. Figure 4 shows an example of a drive circuit used in an embodiment of the liquid crystal element drive method of the present invention, where TC1 is i11 The above-mentioned normal liquid crystal driving XC (for example.

TCA O55). D Engineering, D2. D3 is a Zener diionide for potential setting, Trl, T 2 t'z
This is a t-pressure level shift transistor. In the drive circuit shown in FIG. 4, the cutting edge to each segment electrode is determined by the voltage level vr as shown in the waveform diagrams in FIGS.
It oscillates between and V2O. In addition, the output to the common electrode is level-shifted by transistors T,1 and T,2, so that the voltage levels 1 and 2 are level-shifted as shown in FIG. 6(a).
It oscillates between 8. Zener diode D1 is v1+v
By using Zener diodes D2 and D3 with the same characteristics, and setting ■3==-■ to -VgY between both terminals of resistor R2, .

The above-mentioned drive line Ir+ for the liquid crystal element is satisfied. Here, if the voltage level V is regarded as the ground level in Fig. 6, the output to the segment electrodes and the output to the common electrode are respectively Fig. 6 (a) and (b), (/→
Output waveform and null like.

In the drive circuit of the embodiment shown in FIG. 4, the power supply circuit section is set to voltage level v and Y ground level.

Create a negative voltage using a DC-DC converter, etc.

-V, lacking is also a solution. In addition, there is no restriction that it is necessary to use the dedicated ICY mentioned above as a liquid crystal drive circuit, and instead, an exclusive OR (EX -
OR) D) ICY may be adopted and used at voltage levels V, -V, and Vq -V.

As is clear from the above, depending on the driving method of the liquid crystal element in the liquid crystal display device of the present invention, it is possible to easily improve the response characteristics of the liquid crystal by using extremely simple means and configuration. A goal can be achieved effectively. Namely.

In the present invention, for a large number of segment electrodes,
Together with the segment electrode that should display OFF Y and the segment electrode that should display OFF.

-Polar square wave voltage pulses having substantially the same waveform and only opposite phases are applied.

In addition, since the rectangular wave voltage pulse with a special waveform for bias is applied to a small number of common electrodes, there is no need for major modifications to the circuit configuration compared to conventionally well-known drive systems without bias. Further, the response time of the liquid crystal element can be shortened with a relatively simple circuit configuration including the power supply circuit applied to each electrode.

In addition to this, in the driving method of the present invention, all drive pressure (including bias pressure) applied between the common electrode and each segment electrode during operation of the liquid crystal display device.

) does not contain any direct current, so the main objective of improving responsiveness can be achieved with low power consumption and without sacrificing the inherent lifespan of the liquid crystal material. These technical effects are unique to the present invention,
and.

Since this is truly desirable for this type of liquid crystal display device, it is worthy of mentioning that the present invention further enhances its usefulness.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the structure χ of a liquid crystal display element, Figure 2 is a characteristic curve diagram of the applied voltage vs. light transmittance of the liquid crystal material, and
FIGS.
1 is a circuit diagram of an embodiment of a liquid crystal element driving method according to the present invention; FIG. In the figure, Dl, D2. D3... Zener diode, 'r1+'r2... Voltage level shift transistor r r resistor, IC1... Liquid crystal drive IC1 R1+ R2yR3+R4+R5+R6yRma, Re.
·····resistance. Agent Asamura Kakugai 4 people 2nd and 3rd figure

Claims (1)

[Scope of Claims] A driving method for a liquid crystal element in which a predetermined bias voltage is applied between opposing electrodes of each liquid crystal element in order to shorten the response time of the liquid crystal element in a liquid crystal display device, comprising: an electro-optical method for a liquid crystal element; Threshold voltage (vth) for the effect
) corresponds to the most recent upper limit value (vb) of the peak value (Vl
) '1M: has and has a unipolar voltage level equal to or higher than the reference voltage level and a peak value (v2) corresponding to the immediately lower limit value (va) of the threshold voltage (vth),
and applying a rectangular wave pulsating voltage that alternates between a reference voltage level and a voltage level of the other polarity for a predetermined time interval to a common electrode that is one of the opposing electrodes in each liquid crystal element; Among the segment electrodes that are the other of the opposing electrodes in each liquid crystal element, for the segment electrode that is to perform off display, during the period when the rectangular wave pulsating voltage is at the voltage level of the - polarity, A unipolar voltage level (v3) with a peak value equal to the difference (V, -Va) between the most recent upper and lower limit values of the threshold voltage; A rectangular wave voltage pulse of negative polarity is applied such that the reference voltage is level during the period when the voltage level is at the level; takes the second reference voltage level during the period when the voltage level is at the voltage level of the negative polarity, and during the period when the rectangular wave pulsating voltage is at the voltage level of the other polarity. Applying a rectangular wave voltage pulse of negative polarity such that a unipolar voltage with a peak value equal to the difference (vb-va) between the respective limit values described above is pel (v3)'Y; Alternatively, each of the drive voltages applied between the segment electrodes to perform the on-display and the common electrode substantially does not include a direct current component. A driving method for liquid crystal elements in liquid crystal display devices.