JPS5945493A - Driving of liquid crystal electrooptic apparatus - 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] Liquid crystal electro-optical bag frffi has recently been developed as an optical switch,
It has become extremely popular as a display device for digital watches and electronic clocks. Furthermore, there is a growing demand for use as display bags for small personal computers and the like. However, with current liquid crystal materials, the duty number that can be driven multiplex is at most about /30, and they lack the ability to display a large amount of information. The display methods devised from this background are ■Address method using non-linear elements as switching elements % type % ) O discharge tube address ■ Address method using active elements as switching elements 0 Thin film transistor address OM OS ) Lange Meta-address 0 Try-ack address ■ Light/thermal/writing method 0 Laser thermal writing 0 Photoconductor writing ■ Displays such as two-layer liquid addressing method (Report 9) 11 Large liquid crystal display devices Vl are being actively developed.

The present invention relates to a method of driving a liquid crystal 'T41 optical device using a non-linear characteristic element (2) and a switching element, and a liquid crystal 7 (L optical device) using an active element (2) as a switching element.

More specifically, the present invention relates to a multiplex driving method for suppressing fluctuations in effective voltage applied to pixels of the liquid crystal electro-optical device.

FIG. 1 shows the current-voltage characteristics of a typical M]:M element, which is a nonlinear element. Barista.

A reverse series connected diode that utilizes the breakdown voltage of a Pn junction also has a nonlinear current-voltage characteristic similar to that shown in FIG. Further, any element having nonlinear characteristics such as the one shown in FIG. 1, which exhibits high resistance in the low voltage region and low resistance in the high voltage region, can be used as the switching element.

It is known that when a liquid crystal electro-optical device is constructed using these nonlinear elements, multiplex driving with a higher order of magnitude than general multiplex driving becomes possible. This can be understood as follows.

Figure 2 is an equivalent circuit diagram for one pixel electrode, including the liquid crystal capacitance QLO■, the resistance RLO■, and the equivalent capacitance ONL of the nonlinear element.
(2) and equivalent resistance RNL (2). 1 (NL■
Depending on the voltage applied to the nonlinear element, it has a low resistance at high voltage and a high resistance at low voltage.

Now, consider applying a liquid crystal drive signal to the terminal of the equivalent circuit.

Figures 3 (A) to (0) are 150 duty.

This is an example of the 115 bias method. FIG. 3(A) shows scanning electrodes 5-1 to 5-10. A matrix display pixel consisting of signal electrodes 6-1 to 6-50 is shown.

Each scan electrode 5-1 to 5-50 receives a scan signal SOA.
, N1-5OAN50 are applied. In addition, each signal electrode 6
-1 to 6-50 respectively indicate display signals S-G1 to S-G.
50 is applied. Here, consider a case where the display pixel CMIN corresponding to the scanning electrode 5-M9 signal electrode 6-N is lit, and the other display pixels (plurality) on the column of the signal electrode 6-N are not lit. . The waveform of the scanning signal in this case is shown in FIG. 6(CB), and the waveform of the display signal is shown in FIG. 6(0). In these figures, tF4 is the scanning period 17i in which the signal is applied to the entire display pixel, and tsel in the same figure (B) is the selection period of the scanning signal SOANM in which the scanning electrode 5-M is selected. be. According to FIG. 3(0), the signal electrode 6-N takes the lighting level VON during this station selection/station period tsel, and has the non-lighting level VOFF during the period m1 of the other scanning signals except SOANM.

Therefore, the voltage applied to display pixel CM9N) is C
As shown in D), ■(M.

N)=SOANM-8GGN. Figure 4 (α
) is the waveform of the applied voltage ('y' e N) when the display pixels (M, N) are at the lighting level, and the solid line in (h) is the waveform of the applied voltage when the display pixels (M, N) are at the lighting level. Element voltage waveform VN
In addition, the solid line in the same figure (C) shows the voltage waveform Vr,o applied to the liquid crystal layer. That is, the following relationship exists.

V(M, N)='VNL-4-Vb.

Further, the broken lines shown in (0,), (b), and (C) in the figure indicate the case where the display pixels (M, N) are at the non-lighting level.

Next, the concept of operation of the nonlinear element and the liquid crystal layer will be schematically explained based on FIG. 5(α)9Ch)9CC). FIG. 5(a) shows the relationship between the applied voltage VNL and the current value of the nonlinear element. In the region 7, the nonlinear element has a low resistance, and in the region 8, the nonlinear element has a high resistance.

The figure (b) shows that the resistance RNL4 of the non-ημ type element has a low resistance (
The figure shows the current flow t in the case of zero (
) shows the current flow when the resistor 4 has a high resistance (assumed to be infinite/infinite).

First, as shown in Figure Cb), when the nonlinear element enters a low resistance region, most of the driving voltage is applied to the liquid crystal layer, and the liquid crystal layer is charged.

The time constant at this time can be calculated from the equivalent circuit shown in FIG. is almost 0
If so, 'Iu current t flows transiently and charges 0Le1. At this time, all of the electric currents are connected to the liquid crystal layer.

Next, when the display pixel V (M, N) enters the non-selection period, it shifts from the low resistance region 7 to the high resistance region (2). Therefore, R.L.
O<< RN r, and most of the transiently flowing current i flows through R1,a as shown in FIG. 5(b). Approximately, the time constant is τ= (OLO+0N
L) RLO... It is given by (2). in general,
It is entirely possible that it is used in field-effect liquid crystal display panels.

When the display pixel indicated by the broken line in Fig. 4 (α) * (5) I (?) is at the non-lighting level, a P F mll
:.

Since VNL does not enter the lighting region even at its peak, the liquid crystal layer is not charged and Vl,0 remains at a low level.

Therefore, the effective value ratio of the lighting level to the non-lighting level of the liquid crystal layer is larger than that of the conventional driving method using the voltage averaging method that does not include a nonlinear element. Therefore, the liquid crystal driving method using non-linear elements enables multiplex driving with a higher number of orders of magnitude, and can realize a larger capacity of the liquid crystal display device f6.

However, in the multiplex drive as explained above, the display in the non-selection period 1ijJ (as described above, the effective 1fli applied to the liquid crystal layer depending on the state of g)
The disadvantage is that the pressure fluctuates. Figure 6(a)9
(h) 9 (C) + Based on this, this drawback will be fully explained.

In this way, the non-linear element liquid crystal display device is capable of increasing the display capacity, but in multiplex driving, the effective effect applied to the liquid crystal layer by the display signal during the non-selection period is limited. There is a drawback that the IL pressure fluctuates. (α) is the voltage waveform VLO5(h) when only the display signal electrode row 5-M of the signal electrode row 6-H is lit;
The voltage waveform VLθ when every other row is lit is the voltage waveform VLO when all columns 6 to N are lit.

The broken line is the voltage V (M, N) applied to the display pixels M and N, and the solid line is the voltage n:, vbθ applied to the liquid crystal layer.

(Z), Cb). Looking at (C), the same signal electrode (S engineering G)
The VLO changes significantly depending on whether other pixels above are turned on or off. The same thing is true for display pixel CMO.
This applies even if N) is not lit.

Therefore, conventionally, the minimum value of the effective voltage of the lighting waveform E ot
i min was set larger than the saturation voltage Vsat of the liquid crystal, and the maximum value E OFF maX of the effective value of the non-lighting waveform was set smaller than the threshold value vth of the liquid crystal, thereby providing a binary display. For this reason, non-linear element liquid crystal display devices have been applied only to binary display, and gradation display has been considered impossible. Also, the above-mentioned K ON min.

When E OFF maX is used as a margin, the characteristics of the nonlinear element required are strict, and it becomes a point of evaluation in manufacturing. Furthermore, in cases where the saturation voltage is not clear, such as in the Guest-Bost effect, there is a problem in display quality in that variations in effective values are displayed as variations in contrast.

The present invention was made in view of these drawbacks, and was devised for the purpose of application to gradation display, prevention of contrast variation, and increase of margin by completely suppressing fluctuations in effective 'rF+ pressure due to display signals. It has been
By bringing E ON min and HOFF max close to intermediate levels, variations in the effective voltage can be suppressed. Another object of the present invention is to keep the disCharge of the liquid crystal constant when the switching element is in the OFF state by dividing one scanning period into a plurality of selection levels and non-selection levels. Therefore, as a switching element, the driving method of the present invention can be applied not only to nonlinear elements but also to active switching elements (TFT, MOS, transistor).

Next, the present invention will be explained based on examples. Do J. to 7th
The figure shows a display panel (A
, ) is compared with the conventional driving method (B) and the driving method (0) of the present invention. In the same figure (A), the display pixel column 6-0 is the case where only the pixel row 5-M is lit, and the display pixel column 6-N is the case where each pixel row is lit every other row. The display pixel column 6-P is a case in which all pixel rows are lit.

In FIG. 7, the 150 duty and 15 bias method is considered as in the explanation of the conventional example. In the normal voltage averaging method shown in FIG.
This one unit period is called one scanning period 9). Each scanning signal 5CAN takes the selection level for one scanning period T8e1 once in each half-scanning cycle, and takes the non-selection level for the other scanning periods.

On the other hand, in the driving method of the present invention shown in FIG.
One scanning period Tsel, which takes a selection level in each half-scanning period, is further divided into multiple periods (this is called a fine scanning period [phase]), and only some of the fine scanning periods are at a selection level, and the others are not selected. It creates a scanning signal that is used as a level. The manner in which one scanning period is divided into fine scanning periods can be selected from various ratios such as 9 unequal intervals or 2 equal intervals, but the case where it is divided equally into /2 for 1ett will be explained.

FIG. 7(C) shows that in the case of this /2 equal division, in the driving method of the present invention shown in FIG. is the same as Also, display pixel row 6
The display signals added to -0, 6-N, and 6-P by GP are shown as S-Go, S-GN, and S-GP, respectively. Each display signal, like the scanning signal SOANM, divides one scanning period ■ into multiple parts (in this case, halves), and only a part of the fine scanning period (φ (in this case, the first half scanning period) is set to the same level as the normal voltage averaging method, and the remaining fine scanning period is set to the opposite level 1, that is, the selection level is set to the non-selection level 1, and the non-selection level is set to the selection level. As a result, display pixel row 6-0,
The display signal waveforms applied to each of 6-N and 6-P are S-Go, S-GN, and S-GP. In the driving method (0) of the present invention, the waveform is centered around the reference level.

. The waveform changes apparently the same as in the case of duty, but if you consider the average value of the non-selected period within the half-scanning period, you can see that the average value is almost the same in both cases.
Figures (α), (b), and CC) are respectively display images i(M, o)CM in the driving method of the present invention. N) (M,
The voltage VLO applied to the liquid crystal layer (shown as a solid line) with respect to the voltage applied to each of the liquid crystal layers (shown as a broken line) is shown. Now, when compared with the case of the conventional drive method shown in FIG. 6, the VLO waveform according to the present invention shown in FIG. I understand. This means that the present invention suppresses fluctuations in the effective voltage of the liquid crystal layer due to display signals.

In this way, the effective voltage applied to the pixel is determined without being influenced by 0N-OFF on the same signal electrode, so by changing the peak level of the selection period, the time to take the selection level, and the peak level Wt1, it is possible to Gradation display, which was considered impossible with linear element liquid crystal display devices, is now possible, and in addition, the maximum effective pressure in the OFF waveform and the voltage margin in the ON waveform, which was the voltage margin of conventional non-linear element liquid crystal display devices, have been improved. According to this book, the minimum effective voltage of OFF waveform,
ON waveform σ] can be changed between specific levels, and has the advantage of expanding the margin. However, in the present invention, even when N digits of multiplexes are driven, G is actually one 2N digits of multibranchs. Increasing the number of digits was not possible in conventional matrix panels because it would reduce the margin, but in the case of non-linear element liquid crystal display devices, sufficient As long as there is time for the equivalent capacitance OI,0 of the liquid crystal layer to be charged to the same level, there is no problem even if the number of driving digits increases.

In fact, this charging period can be considerably shortened, and depending on the characteristics of the nonlinear element, a duty of several tenths is possible.

In the following embodiments, one scanning period is divided into 1/2 equal parts, but the present invention is not limited to 1/2 equal parts. The point is that (jLO only needs time to charge to a sufficient level within the fine scanning period in which it takes its peak voltage value, and there are multiple fine scanning periods in which it takes its peak voltage value in one scanning period. It is also possible to use a fine scanning period in which the scanning period is divided into unequal intervals of 1?, ?.However, considering the ease of the drive circuit and the small fluctuation of the effective 1u pressure,
Equal division is considered the best.

In addition, one scanning period is not necessarily a period obtained by dividing one scanning period 78 into 2N equal parts, since the time for setting the scanning signal to the selected level only needs to be the time for QLQ to be charged to a sufficient level within the selection period of the ON waveform. It doesn't have to be. That is, 1
The period xts (σ×X≦1) which is less than the scanning period js is set to 2
The period divided into N equal parts can also be set as one scanning period.

FIG. 9 shows the 115 bias method w N"" 8 e x-
Scanning signal 5OAN1 and SOA-N8 when set to o8
, which shows the display signal S engineering G1. In FIG. 9, the display period tD is a set of eight scanning periods, and the rest period t
p is a period that does not belong to any scanning period, and all signal electrodes are at the non-selection level during this ty+ period. In this case, t
During the period p, the display signal always has a non-selected waveform as used in the present invention, but it may also have a selected waveform.

Further, the selection level and non-selection level described in the present invention are not limited to the selection level and non-selection level of the conventional drive system.

Next, a circuit for generating a drive signal according to the present invention will be described.

FIG. 10 is a panel and panel drive circuit diagram of the liquid crystal display level of the present invention, and shows a non-linear element dot matrix liquid crystal panel σ, 9 display electrode drivers, part 0, scanning' (1L
Polar driver part 0. It consists of a drive signal generating section 0. The liquid crystal panel 0 is composed of a scanning electrode 0 and a display electrode (φ).If the number of display electrodes is J, the display electrode driver part [phase] is composed of a 5-stage shift register 0 and each of the shift registers. J latch circuits connected to the output (level shifter [phase] that converts the logic level of the Φ1 circuit to the liquid crystal display level, M that changes the lighting level and non-lighting level of the display signal by the signal from the level shifter ◎ The scanning electrode driver part [phase] consists of a 2N stage shift register 0, level shifter 0,
It consists of a demultiplexer 23 which switches between selection and non-selection of scanning signals according to the signal from the level shifter. The drive signal generation section 14 is composed of demultiplexers [phase] to [phase] and drive voltage generation resistors [phase] to [phase].

11 and 12C, a) 9 (h) Fig. 10 will be explained in detail using the timing chart.

The φ day in FIG. 11 is the transfer lock of the shift register O, and the display data DATA is transferred from left to right on the φ day. When one line of J data is transferred,
Clock pulse CLt of latch circuit [phase] increases, i
gh level, and data is latched from the shift register O to the latch circuit [phase].

The data is level-shifted in [phase], and is input to the control terminal of the multiplexer (Φ) at the drive signal generator multiplexer [phase]. ,
DOFF is switched. The shift l-1/sister Qv of the scanning electrode driver 13 is as shown in FIG. 5
This 11'l (・2 uko 41:+ of the pulse to do::; i
)l sum of ice-C clocks CLsQ are used as clock pulses, and data Drca,n with i:J h 1.8 h is inputted once in one cycle IJl. In the shift register, only the odd-numbered stages of the output from the 2Nl father are level sister a2. 11□It's been revealed. Therefore, the output SCI + S(1
! 2 1 S Ci s accommodation is as shown in Section 12-σ diagram. The signal is supplied to the demultiplexer 0 as a level sister I"k:iti'I. In the demultiplexer (c), the scanning signal selection signal '5OOON,・Selection signal S
Ci OF F is changed to ', I).

Resistor (short to
- Make it. The demultiplexer (c), qO, switches the level of the scanning signal to match the frequency signal φf of the AC drive of the cutting crystal, and selects the scanning electrode 4'Qs a ON.
, creates a non-select 5OOFF signal. Demultiplexer 4
-f;) + Φ force ζ; 1, display ′ according to φf, conventional drive system of
No. D S E TJ + non-selected belief - D N S F
Make L. C! +b, (c) is required in the present invention and tl
It is a demultiplexer that uses OLBc'&: /
D S I G L by 70 signals JSC divided by 2
, DN S E L is terminated. In this way, the signal 1) ON of the display electrode is formed.

FIG. 16 is an example of the control amount j'i'i for generating the 1id (reliable 4r clock noculus of the subcircuit) of the present invention.

In the false example, J=160. = 120, and a 6-bit binary counter Q (yet, N0F (gate Q).

RS flip 70. Shin Nobu. Inverter G core, D Harifuri 7 Puff C17 (++'+, (+5, (a'
), (2W, NOR gate (iφ, 6ψ, 6-bit binary counter (si), AAND gate
41;・1° is formed from Yu. Display electrode driver 12 shift registers (r'7J to fl (clam 41
．． The clock pulse φ is counted by a 6-bit binary counter 6 [phase], and when it counts ①=80, the gate ② detects this and sets R5-FF [phase]. R3-F F (, +:') is immediately C, RESET in synchronization with the rising edge of φS. [Phase] output 0Lsc
is input to the R1 and S Tjfiia of the counter, and also becomes the input to the D type rFe7. D clip 70 tube 94) OLBc 72 minutes 1. ', ] t,, A, B'-2-(! Create LBC and supply it to D person of D type TIF (c). Signal T CL S Q is D type 1i'
F (c) NOR game) (lj@ 4. 1 from 2; □
・(It becomes a signal CLt with a cycle of one scanning period, and is a clock/gleus input of the latch circuit Q-Φ)':!
provided to the if child. OL on the counter
Count the clock pulses 0TJ8Q from the s O to L/ RS Fritzbuf ■ Kotpu 62, and when 239 pulses are counted, the output of the gate [phase] becomes high.
4r, this high signal is delayed (+
, l; is differentiated by (io). DFF3
The signal delayed by 9 becomes a delayed signal D5CAN and is supplied to the shift register 21 of the scan electrode driver. Also, the pulse differentiated by the gate @ is D-type yrQ
clock pulse every half period (high,
As the AC drive signal φf that changes low, it is applied to the demultiplex brakes 24 to 26 of the frame set 1 signal generator;
be provided.

As described above, the 1-< operation of the present invention can be realized with a relatively f7ii jii circuit. On the other hand, by using Honzu C: Akira, ! ; Display pixel lights up. Astigmatism] Depending on r2, the variation in the effective value (f) becomes smaller, so 1) IJ
Along with the effects mentioned above, the minimum value of EONl17) increases, and the maximum value of li;OFF (p'+ decreases,
It can also be expected that the driving margin will be improved. Therefore,
It is believed that when the present invention is used in a non-adhesive liquid crystal display system, it is possible to achieve an effect of even gradation display over the entire panel image.

1 x 1 side frii) It's Etsumei Figure 1 shows the V-King general of a typical non-stone J-type military child.

21st. :<l is non-iξ・I↓ type element liquid crystal display device ji
This is the equivalent circuit of knee j.

FIG. 6 is an example of a liquid crystal panel drive waveform using the conventional weighted averaging method.

FIG. 4 shows the operation of the non-linear element liquid crystal display device bffi. (a) shows an example of an operating waveform, and (b) shows an ON region and an OFF region of a nonlinear element.

FIG. 5 schematically shows the operational concept of a non-linear element liquid crystal display device. (σ) indicates when the nonlinear element is turned on, and Cb) indicates when OFI]'l.

FIG. 6 shows a pixel applied voltage waveform (broken line) and a liquid crystal layer applied waveform (solid line) of a non-linear element liquid crystal display device. (α) indicates that the pixel in question is ON, and the other side 1O is above the signal level.
When FF, Ch) is alternately ON and OFF, and (C) is when all ii2'7i elements are ON. Figure 7 is a comparison between an example of the drive waveform according to the present invention and a conventional drive waveform. It is something. (α) is a conventional example, and Cb) is an example of the present invention. The figure in parentheses is the voltage waveform applied to the pixel at the intersection of the scanning electrode and the signal electrode. S GA is a signal waveform when the relevant pixel is ON and the pixel ClFF is on the same signal electrode, S OB is a signal waveform when it is alternately ON and OFF, and S and TGO are the signal waveforms when the pixel ClFF is on the same signal electrode. This is a signal waveform in the case of ON.

FIG. 8 shows the voltage waveform applied to the liquid crystal layer when the present invention is applied. (When σ is the pixel in question ON, and the pixel on the same signal electrode is OFF, (b) is alternately CIN,
In the case of OFF, (C) is when all pixels are ON.

FIG. 9 is an example of a drive waveform when a pause period tp according to the present invention is provided.

FIG. 10 is a driving circuit diagram of the liquid crystal display device of the present invention.

FIGS. 11 and 12 (σ)G (b) are timing charts.

FIG. 16 is an example of a control circuit of the drive circuit of the present invention.

Applicant Seiwa Seikosha Co., Ltd. Agent Tsutomu Mogami (4) (b) (c) v (H
Kasuri-: : : ;

Claims (5)

[Claims] (1) Liquid crystal display bag f4 in which an element with non-linear characteristics is installed on at least one substrate constituting the liquid crystal display panel
When driven by the two-frame AC method, the absolute value of the average value of the L pressure applied to pixels during the non-selected period within one frame period is almost equal for all pixels or some pixels. A method for driving a liquid crystal display device. (2) In the driving method of the non-linear element-equipped liquid crystal display device, line scanning is performed in which one scanning period, which is formed by dividing all or part of each half-scanning period equally by the number of scanning lines, is further divided into a plurality of periods. The liquid crystal display device according to claim 1, wherein the scanning signal takes a selection level during a part of the line scanning period within the selection period and takes a non-selection level during the remaining line scanning period. Driving method. (3) During a period synchronized with the line scanning period in which the scanning signal takes the selected level, the display signal changes to the dot bar level, non-lighting level, and one scanning period in response to the ON and OF\F of the pixels, respectively. 3. The method of driving a liquid crystal display device according to claim 1, wherein the non-lighting level and the lighting level are respectively set to opposite levels during the remaining line scanning period. (4) When one line scanning period is divided into a plurality of parts, some of the line scanning periods are at the selection level and the rest are at the non-selection level. Claims 1-1 characterized in that the times are equal.
7. A method for driving a liquid crystal display device 6 according to any one of Item 6. (5) The above-mentioned one scanning period is divided into two equal parts to form a line scanning period.
A method for driving a liquid crystal display device G according to any one of Item 4.