KR790001797B1 - Driving method of liquid display body - Google Patents

Abstract

An improvement on a display system which displays multi-digit numeral information on a timeshared basis in response to application of bipolarity alternating voltage to liquid crystal display units. Each of the liquid crystal display units has a common electrode actuated by one of sequentially phase shifted timing signals and a preetermined number of segment electrodes actuated by segment signals of which combinations are representative of the multi-digit numeral information to be displayed.

Description

Liquid crystal display driving method

1 is a simplified block diagram illustrating a time division driving scheme.

2 is an explanatory diagram of liquid crystal characteristics.

3 is a block diagram of a driving method according to the present invention.

4 is a time chart illustrating the operation of FIG.

5 is an explanatory diagram illustrating the operation of FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using nematic liquid crystals (hereinafter referred to as liquid crystals). In particular, the time-division display is performed while applying alternating voltages to liquid crystals to improve response speed, lifespan, and scattering effect. It is to provide a driving method for.

BACKGROUND ART A liquid crystal display, which has recently attracted attention as a display, injects a liquid crystal between two electrodes having at least one transparent surface and applies a DC voltage, a pulse voltage, or an alternating voltage between the anodes to scatter external light to scatter the scattering portion and The difference of the brightness of a non-scattering part is made into the display object.

As a method of displaying information such as a numerical value, a symbol, or a character by using the liquid crystal display, there are generally a method of applying a static signal and a method of supplying a time-divisional signal. Is about the latter.

As shown in FIG. 1, the display driving method using the time division signal has a plurality of display elements D ₁ . … The signal supplied to each of the electrodes of D _n is a signal S ₁ ... … Time division signal T ₁ ... Synchronized with S ₄ and its repetition; … Divided by T _n , the display contents are selected based on the logic of these signals, which can reduce the number of driving circuits and input players for signal transmission, and most displays in various devices. The circuit uses this method.

When such a time division display system is introduced into a liquid crystal display body, it has the following characteristics compared with conventional display bodies, such as a character display discharge tube and a fluorescent character display tube.

1. The response speed is remarkably lower than other indicators.

2. The method of alternating the applied voltage polarity is superior in terms of service life than single polarity (direct current or DC pulse).

3. The scattering control can be performed by the absolute value of the applied voltage without directivity to the electrode.

4. As shown in Fig. 2, the relationship between the applied voltage and the degree of scattering shows that in some types of liquid crystals, there is a clear limit or no limit, but when the specific voltage is reached nonlinearly, the degree of scattering changes rapidly. This limit value is also changed by the pulse ratio (ratio of scattering time to non-scattering time).

SUMMARY OF THE INVENTION The present invention has been made in view of the various aspects described above in order to achieve a liquid crystal display efficiently.

Therefore, the technical idea of the present invention

1. In the light scattering effect of the liquid crystal, there is a limit to the applied voltage, and when a voltage is applied above the threshold voltage, a specific bias below the threshold is lower than the state in which the transient change time of transmittance is not applied at all when no selection is made. By using the phenomenon that the time when the voltage is applied is shortened, the service life is improved again by applying the same voltage as that having the bias effect at the time of non-selection and supplying the voltage alternately instead of supplying it directly.

2. By adopting the logical method of phase control by alternating voltage, the signal given between electrodes is not only selected but also the alternating voltage is actually applied at the time of selection. Therefore, the life is improved regardless of the pulse ratio. The alternating voltage control circuit can be configured relatively simply.

3. Furthermore, an alternating pulse of 4-40 ms width is applied to the common electrode by the time-divided time by an alternating voltage having an effective value of about twice the threshold voltage as described above. Let it be the center level of voltage.

On the other hand, for the segment electrode, an alternating pulse having substantially the same width as that of the alternating pulse applied to the common electrode at the alternating voltage having an effective value of about the limit value is supplied in such a manner as to be phase-controlled between the information common electrode. .

That is, as a signal having at least one cycle within a unit time of change of information, the phase difference corresponds to the information value so that a signal of high amplitude that generates scattering when the phase with the signal supplied to the common electrode is 180 ° is obtained. It is. 3 shows an embodiment of the present invention in a four-line display device.

Liquid crystal display LC ₁ . … LC ₄ represents a common electrode A ₁ . … A ₄ and segment type counter electrode (hereinafter referred to as segment electrode) K ₁ . … K _n , K ₁ . … It is assumed that a value of 0-9 is formed by a combination of K _n .

On the other hand, X is a four-row shift register circuit that codes and stores information to be displayed, and is circulated in the display state.

This information is taken out from the lowest row X ₁ , introduced into the one row time storage buffer X ₁ , and converted into a signal corresponding to each segment of the display through the Nico Order DC.

On the other hand, the time-division signal (timing signal) generating circuit TC has the information in the first row of register X in T ₁ , the information in the second row in T ₂ , the information in the third row in T ₃ , and the information in the fourth row in T _4. At the time of, each is extracted at X ₁ .

Indicator LC ₁ ... … A common electrode of the LC ₁ ... ₄ … A ₄ is a signal related to the timing signal, segment electrode K ₁ . … K _n is supplied with signals related to the above numerical information. Therefore, numerical information when the timing signal is supplied is displayed in correspondence with each segment.

Up to now, the conventional dynamic display driving method is conventional. When using a liquid crystal as a display, consideration should be given to the points already mentioned.

As a means thereof, the present invention provides the above timing signal T ₁ . … T ₄ and segment decoder output DC ₁ . … The _n DC is not directly supplied to the display element signal exchange circuit AT ₁ ... … AT ₄ and KD ₁ ... … KD _n is converted into a special signal for a liquid crystal display and then the outputs AT ₁₀ . … AT ₄₀ and KD ₁₀ ... … KD _no is supplied to each electrode of a liquid crystal display body.

In such signal conversion, the exchange signal S ₁ , S ₂ is generated by the conversion signal generation circuit SG and used.

In FIG. 4, the timing signal T ₁ , T ₄ , the decoder output signal DC ₁ to DC _{n of the} segment, the signal for conversion S ₁ , S ₂ , the signal conversion circuit output AT ₁₀ to AT ₄₀ , KD ₁₀ to KD _n0 and actually The voltage state applied between the electrodes of the liquid crystal is displayed.

The operation will be described below with reference to the time chart art.

The timing signals T ₁ to T ₄ now supplied to the supply electrodes are the row selection signals, and in this example, one row time width, that is, a pulse ratio of 1: 3, is used for four row times.

The signal conversion circuits AT ₁ to AT ₄ convert the phase of the selection time into a signal for controlling phase between the segment signals described later.

Hereinafter, a specific example of the signal exchange circuit of AT ₁ will be described.

The final amplitude conversion circuit output AT ₁₀ becomes either + 12V or -12V depending on the level of the conversion signal S ₁ within the selection time of the timing signal, and becomes 0V, which is its intermediate level within the non-selection time.

The input to the amplitude converting circuit is given a level of two values of + 6V and -6V, and this level is almost equal to the threshold voltage of the liquid crystal, and the control circuit, for example, the timing circuit TC, the peripheral circuit of the register X It is assumed that it operates with this power supply voltage.

And, + 12V and -12V are selected almost twice the threshold voltage here.

Tr Tr ₁ ~ ₄ are respectively + 6V, the -6V a MOS transistor serving as a power supply voltage Tr _1, Tr ₂ by a P-type, Tr _3, Tr ₄ in the N-type source electrode of Tr ₁ is -6V, The drain electrode is connected to the source electrode of Tr ₂ , and the terminal O ₁ is output.

The gate electrode of Tr ₁ is connected to the inversion signal T ₁ by the inverter I ₁ of the timing signal T _1. The gate electrode of Tr ₂ is coupled to the gate electrode of Tr ₃ , and is connected to the output of the gate circuit G ₁ , and the source electrode is connected to the drain electrode of Tr ₄ .

The source electrode of Tr ₄ is connected to -6V and the gate electrode is connected to the timing signal T ₁ .

Since the input of the AND gate G ₁ is the timing signal T ₁ and the conversion signal S ₁ , the same signal as S ₁ is obtained at the time of selecting the timing signal as the output. Input gates of T ₁ and in the non-selection time of the first timing signal salpimyeon the state of the output O ₁ under the terms of the S _{1 4} Tr is -6V, the Tr gate is inverted so as to be I ₁ + 6V, both Transistor is turned off. Since the transistors Tr ₂ and Tr ₃ are connected in series with Tr ₁ and Tr ₄ , respectively, they are not turned on regardless of their gate inputs. Therefore, the output O ₁ becomes the OV potential through the load resistor R ₁ .

On the other hand, if the timing signal to the selection state, that is the gate of the Tr ₄ + 6V is applied to the gate of the -6V + 6V, transistor Tr ₁ in both Tr ₁ and Tr ₄ are turned on. Here, when the input of the gate G ₁ is seen, the timing signal T ₁ is + 6V, the conversion signal S ₁ is -6V, and the output of the gate G ₁ is -6V at the time t ₁ shown in FIG. .

When the gate output becomes -6V, Tr ₃ becomes the substrate and coincidence, so it is off, but Tr ₂ becomes + 12V with respect to the substrate, so the limit is on.

As mentioned above, Tr _{1 is} also on, so the output O ₁ is + 6V.

Next, at the time t ₂ , the input of gate G ₁ is + 6V, so the gate output is + 6V. In this case, Tr ₂ is the substrate and the gate is coincident, and Tr ₃ is -12V to the substrate. As voltage is applied, it is turned on and the output O ₁ is -6V. As mentioned above, although the two-value ring signal is converted to a three-level signal, as mentioned above, signals of +12 V and -12 V are required to be applied to the common electrode, and the amplitude conversion is a bipolar type transistor (Tr ₅ ~). This is done using Tr ₈ .

PNP transistor Tr base (base) of the NPN transistor ₇ and by connecting the collectors of Tr ₈ and the complementary binding to a -12V voltage of + 12V to the emitter, the emitter of the Tr Tr ₈ to _7, the NPN transistor Tr ₇ The base of Tr ₈ is connected to the collector of Tr _{5 and} the collector of the PNP transistor Tr ₆ , respectively.

The bases of Tr ₅ and Tr ₆ are connected in common to OV, which is the intermediate level of the input level.

On the other hand, the emitters of Tr ₅ and Tr ₆ are commonly connected to the output point O ₁ .

In particular, the conversion circuit is IC-based peripheral circuitry, and when the amplitude of the output is changed in accordance with the type of liquid crystal or the pulse ratio of the voltage given to the liquid crystal, the change from the outside of the IC is simply followed by the change. The drive current can be limited. That is, the auxiliary transistors Tr ₅ and Tr ₆ which control the base current of the control transistors Tr ₇ and Tr _{8 form} an emitter follow type with the common resistor R ₂ as the emitter load. It is made constant as OV.

Therefore, when the power is + 6V, the input side of the circuit constant -6V, the emitter current of the transistors Tr _5, Tr ₆ are constant.

This makes the base currents of the main transistors Tr ₇ and Tr ₈ constant, and the current value has a characteristic that can be arbitrarily selected by R ₂ .

Therefore, the use of this circuit makes it preferable to use an amplitude conversion circuit as an IC or module circuit in view of the improvement of the degree of integration and the decrease in temperature rise.

However, when the input / output relationship of the amplitude conversion circuit is described again, when the potential is 0 and the potential is + 6V, a forward bias is applied between the base emitters of the transistor Tr ₆ so that the collector current flows, and thus the transistor Tr ₈ ion state becomes the potential of the collector. Is approximately equal to -12V of the emitter potential.

On the other hand, transistor Tr ₇ is in an OFF state because the transistor coupled to the base side is reverse biased.

Next, when the potential of 0 and is -6V, forward bias is applied to the transistor Tr ₅ , and the transistor Tr ₇ is turned ON and the collector potential is almost equal to the emitter + 12V.

When the next to O ₁ is OV Tr _5, Tr ₆ that are as bias is added to the support SHALL to be in the off (OFF) state thereby Tr _7, Tr ₈ also because the off-state Tr _7, the collector junction of Tr ₈ AT ₁₀ has a potential of OV is added through the load resistance R _3.

By using the amplitude conversion circuit as described above, the signal supplied to the common electrode becomes as AT ₁₀ -AT ₄₀ shown in 4 degrees. In this example, the amplitude of the alternating output on the input circuit side is almost the limit voltage (6V). At the selection time, an output having an effective value approximately twice the threshold voltage is applied.

On the other hand, for the signal conversion to the segment electrode, the segment decoder outputs DC ₁ to DC _n are input to the conversion circuits KD ₁ to KD _n for converting the signal to phase control. This segment side signal conversion circuit is composed of an OR gate G ₄ as two AND gates G ₂ and G ₃ operating at + 6V and -6V.

The gate circuit G ₂ performs processing when selecting a segment, and introduces a segment signal at one input and a signal S ₂ at 180 ° out of phase with the converted signal S ₁ used in the signal conversion circuit of the common electrode at the other input. .

On the other hand, the gate circuit G ₃ performs processing when no segment is selected, and introduces S ₁ into the signal inverting the segment signal to one input and the other input.

The AND gate G _2, the output of G ₃ G ₄ of the OR (OR) is selected as the output that by putting the gate circuit signals of -6V to the signal S ₂ that is + 6V, t ₂ time t ₁ sigan In non-selection, a signal of S ₁ , that is, a signal of -6 V at t ₁ and time and +6 V at t ₂ time is obtained.

These amplitudes become alternating voltages having an effective value nearly close to the threshold voltage of the liquid crystal.

The outputs KD ₁₀ to KD _no of KD ₁ to KD _n for the signal examples of DC ₁ to DC _n are shown in 4 degrees.

In this way, when a signal is supplied to the common electrode and the segment electrode, the voltage substantially applied to the liquid crystal will be described taking the Kn segment of the liquid crystal display LC ₁ and the K ₂ segment of LC ₂ as an example.

First, as for the Kn segment of LC ₁ , the common electrode is selected at the time of ①②, and becomes -12V at ① and + 12V at ②.

On the other hand, since it is selected about the segment Kn at this time, it is + 6V in (1) and -6V in (2). Thus, looking at the liquid crystal on the common electrode A cross-Kn, ① the common electrodes A ₁ with respect to the segment electrodes, and Kn are turned by applying a potential difference of -18V, ② the addition of the common electrode A ₁ + 18V with respect to the segment electrode Kn The potential difference is added.

When the common electrode and the segment electrode are selected together, the phases of AT ₁₀ and KD _no are 180 ° different, and the maximum potential difference becomes about three times the threshold voltage between the electrodes, and the polarity thereof changes every 90 °.

That is, in the selection time, a potential difference of 18 V occurs between the electrodes, but the polarities are reversed in (1) and (2).

In the end it means that they are applied alternately. Therefore, the liquid crystal causes scattering with an alternating voltage approximately three times the limit value.

Next, at time ③, A ₁ is non-selection time, so OV and Kn are also non-selection time, so it is -6V in ③ and + 6V in ④.

Accordingly, the liquid crystal is applied with a potential difference of + 6V with respect to the segment electrode at (3) and -6V with respect to the segment electrode at (4).

Therefore, in this state, it means that an alternating voltage of 6 V is applied between A ₁ and Kn, and since the alternating voltage of 6 V is applied to the liquid crystal, it is not scattered. In addition, the threshold voltage of the liquid crystal is a voltage in a state where the light scattering phenomenon rapidly changes as described above, and when a digital expression is expressed as a difference in scattering degree, it is generally scattered to a voltage of more than twice the threshold voltage. In this case, it was confirmed that sufficient comparison with the state below the threshold voltage was possible.

However, to the last, this is judged from the practical point of view in the case of treating the liquid crystal display as a commodity, and since such a thing is originally based on the human perspective, there are individual differences and it is clear that it has an analog element.

Thus, if the two states can be distinguished simply, they may be possible below the above voltage.

Next, at the time of ⑤⑥, the common electrode A ₁ continues to be unselected, and OV and the segment electrode Kn are selected, so the phase of 180 ° is different from that at the time of ③④, that is, at -6V and 6 at ⑤. At + 6V, a liquid crystal voltage of 6V is applied to the liquid crystal. Therefore, the liquid crystal is not scattered as in? In the time of ⑦⑧, it is the same as ③④.

It can be seen from the above description that practical scattering occurs only at the times ① and ② when the common electrode and the segment electrode are selected together between A ₁ and Kn. Since the state is repeated because of the dynamic display method, the scattering voltage is applied whenever the times ① and ②, that is, the T ₁ time, cause the Kn segment to generate light scattering.

Next, the K ₂ segment of the liquid crystal display LC ₂ is checked.

At the time of ①②, since the common electrode A ₂ is unselected and the segment electrode K ₂ is selected, A ₂ becomes ①6 and OV, K ₂ becomes + 6V from ① and -6V from ②, and segment electrode K _{2 from} ①. With respect to the common electrode A ₂ at-6V, and ( ₂₎ , the common electrode A ₂ is applied at + 6V to the segment electrode K ₂ and thus does not become a scattering state.

At the time of ③④, since the common electrode A ₂ is selected and segment electrode K ₂ is not selected, A ₂ is -12V at ③, + 12V at ④, K ₂ is -6V at ③, and + 6V at ④. . Therefore, in the liquid crystal, a voltage of 6 V is applied to the segment electrode at-6V for the segment electrode, and 6 V at the? Electrode for the segment electrode, so that the liquid crystal does not become scattered.

In the case of ⑤ to ⑧, since the common electrode is always in an unselected state, only a 6V cross voltage is applied and the liquid crystal is not scattered. Although the state of the two segments has been described as an example, the state and the scattering state of the signals given to the common electrode and the segment electrode are displayed as a table as shown in FIG. 5.

However, VTH is a voltage close to the limit value of the liquid crystal and 6V is selected in the above-mentioned example.

As can be seen from this, in the case of using the method of the present application, an intersecting voltage is applied between the common electrode and the segment electrode at the time of selection and non-selection. This can be said to be extremely advanced in terms of lifetime.

For example, the amplitude of the signal given to the common electrode to be equal to that of the segment, i.e., ± 6 V, would certainly be advantageous in terms of power supply, but in this way the scattering and non-scattering control would be the same, but in the state where the common electrode and the segment electrode were selected at the same time, No position occurs at the electrode.

If the pulse ratio is large, the ratio of the common electrode to the non-selection state is large, and in this state, there is an effect of alternating bias, but as the pulse ratio decreases, the weight of the selected state of the common electrode becomes high. Becomes less obvious.

In this case, since the alternating voltage is applied to the liquid crystal in all states irrespective of the pulse ratio, it is very effective. Since the bias voltage is always applied in the state where the liquid crystal is not scattered again, the time required from scattering to scattering is shortened when a voltage for scattering is applied.

This means that when the electricity applied to the liquid crystal is loaded, the first large molecular group is divided into differentials, and the stacks and moments in the direction shifted from the long axis of the molecules of the liquid crystal molecules are first arranged in the direction of the field of the liquid crystal, and then the dissociation of the liquid crystal heavy component Since the traveling from the negative electrode to the positive electrode of the negative ion group causes the molecular axis to be directed in the array direction, the orientation direction of the molecular group is not determined, which causes disturbance and scatters light that reaches the interface of the molecular group. When the voltage and the light scattering phenomenon are prepared, the applied voltage when the molecular group grows and the molecular group starts to cause the disturbance phenomenon seems to correspond to the so-called threshold voltage. Therefore, when a voltage below the threshold voltage is applied, the above-mentioned physical phenomenon progresses, and when a scattering signal exceeding the threshold voltage is applied next, the time until light scattering can be shortened.

In addition, the following effects may be further exhibited. That is, the present invention has an idea that an alternating bias signal is applied even when the light scattering is not desired, and the signal is also applied to scattering control.

Therefore, when a pulse voltage is applied because the response from the non-scattering state to the scattering state is significantly slower than that of a conventional display discharge tube or a fluorescent display panel, a liquid crystal displays a signal corresponding to the effective value of the pulse voltage within the pulse width. The disturbance state of the liquid crystal generated when it is always applied does not reach immediately, and eventually the disturbance state is advanced in the form integrated by continuous pulse supply. Therefore, as the pulse ratio increases, the threshold voltage increases substantially. However, even if this threshold voltage is determined as the pulse ratio of the time division signal given to the common electrode, since the virus signal is applied even within the time-divided unit time even when the common electrode is not selected, for example, 1: 3 Even if it is time-division, it is reasonable to select the threshold voltage when the pulse ratio is 1: 1.

In this way, when the selection signal for scattering is applied at the ratio of 1: 3, the value is higher than the limit set by 1: 1.

That is, it is VTHV + ΔV.

This is set to 2VTH of the amplitude of the selection signal given to the common electrode in the above example, but in practice, even when the voltage is raised to 2VTH + ΔV, the common electrode is in the selected state and the segment electrode is not selected (2VTH + ΔV)-(VTH) = Since the potential difference occurs only VTH + ΔV, the liquid crystal maintains a desired non-scattered state.

Thus, when the common electrode segment electrodes are selected together, a potential difference of 3VTH + ΔV occurs, so that the liquid crystal molecules are more disturbed and the light scattering effect is increased. For example, as a result of experimenting with a liquid crystal with a so-called threshold voltage of about 6 V when the light-scattering state in 1: 1 is transient, a common electrode is selected when the period is 40m sec and the pulse ratio is 1: 3. It was confirmed that the threshold voltage of 1 hour) was about 8V, and there was a difference of about 2V as ΔV. Therefore, in the case of the example of FIG. 4, when the amplitude of the segment electrode is ± 6V, it is possible to increase the amplitude at the time of selecting the common electrode from ± 12V to ± 14V. In this way, when the common electrode is selected and the segment electrode is not selected, there is a potential difference of +/- 8V and it does not become a scattering state.

And when both electrodes are selected, the potential difference of +/- 20V generate | occur | produces and a liquid crystal can be disturbed with the amplitude larger than +/- 18V of FIG. Therefore, the amplitude at the time of selection of the common electrode of the example of FIG. 4 may be set to ± 14V.

This is unique to the liquid crystal, and time-divisionally drives the liquid crystal, and the bias voltage is changed even when the common electrode is selected and the segment electrode is not selected, and the threshold voltage is changed so that a new effect is found. In addition, the present invention has a bias effect on the alternating voltage by adopting the logic of phase control of the common electrode signal and the segment electrode signal, and does not need to set the alternating signal other than the above signal, and the peripheral circuit is simplified. There is also.

Claims (1)

A method of driving a plurality of rows of a liquid crystal display made of a common electrode, a plurality of segment electrodes facing the electrode, and a liquid crystal interposed between the common electrode and the segment electrode, is applied between the common electrode and the segment electrode and applied to the liquid crystal. When the threshold voltage at which light caused scattering occurs is set to VTH, the liquid crystal display of the above multiple rows is time-divisionally driven so that a voltage higher than the above threshold voltage VTH at all times of lighting is used as the threshold voltage of the above multiple row determination display. Liquid crystal display drive method characterized in that.

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