JP2529696C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electro-optical display medium held between two support plates and a matrix of pixels arranged in a matrix constituted by image electrodes provided on opposing surfaces of the support plates. And a series of row and column electrodes, further comprising means for sequentially supplying a row signal to a pixel row and means for supplying a data signal to a column electrode, wherein each pixel is provided with a row electrode or a column electrode through a non-linear element. And a display device connected to the display device. In the present application, the terms row electrode and column electrode are interchangeable as needed, and references to row electrodes can be replaced by column electrodes and references to column electrodes can be replaced by row electrodes. Note that this can be done. This type of display is suitable for displaying character-number and video information using passive electro-optical display media such as liquid crystals, electrophoretic suspensions and electrochromic materials. The above-mentioned display device using a back-to-back connection (anti-parallel connection) diode as a switching element is known from US Pat. No. 4,223,308. The switching element is used to obtain a memory effect so that the information supplied to the driven row remains between the pixels to a sufficient extent during the period in which the other row electrodes are driven. However, the value of this information can change due to capacitive crosstalk caused by the capacitance of the nonlinear switching element. The reason is that the same column is used to supply the data signal during the selection of different pixel rows. In this case, the voltage between both ends of the pixel changes, and the transmission level shifts to a higher transmittance or a lower transmittance (gray level). If the gray levels need to be fixed by a transmittance curve, the number of gray levels is severely limited due to the aforementioned crosstalk associated with the maximum signal level. Crosstalk due to signal changes depends primarily on the capacitance of the nonlinear switching element. Another possible way to achieve gray levels is to divide the pixel into a plurality of sub-sections and determine the gray level according to the number of selected sub-sections. This requires extra column electrodes and extra drivers. Such pixel division can also be used to provide redundancy without providing an extra drive. This is because the connection line may be disconnected. This pixel division results in small sub-pixels, which consist of small image electrodes. However, this will reduce the pixel capacitance (relatively) to the capacitance of the non-linear switching element. As a result, the crosstalk increases. It is an object of the present invention to provide a driving method of the above type which substantially eliminates the above-mentioned disadvantages. To this end, the display device of the present invention is the display device according to the first paragraph, wherein the row signal supply means supplies a selection voltage during a part of each row signal period and supplies a non-selection voltage during the rest of each row signal period, The data signal supply means supplies a data voltage of a first polarity during a part of the row signal period to display image information, and a data voltage of a second polarity opposite to the first polarity during the rest of the row signal period. And supplying the first polarity data voltage to compensate for crosstalk. It is preferable to select a value of 0 volt as the reference voltage. The present invention, so to speak, compensates for crosstalk by generating oppositely-signed crosstalk having approximately equal amounts of energy. This can only be achieved in practice for non-linear switching elements having IV characteristics symmetrical with respect to the origin, such switching elements being practically, for example, anti-parallel connected diodes, metal-insulator-metal (MIM) switches. , Or NIN, PIP type semiconductor switch, or "IEEE Vol. 59, No. 11," November 1971, 1566
Pp. 1579 (especially page 1572). Lechner et al., “Liquid Crystal Matrix Disp
lays ". The data signal shall consist of two sub-signals having approximately equal voltage values (absolute values) and approximately half the duration of the selection period. In this case, signals of opposite signs can be obtained by a simple inverter circuit.Especially, when a high-speed nonlinear switching element such as a diode ring is used, for example, a line cycle of 64 .mu. Switching can be performed at such a rate that a selectable time can be used, which makes the method of the invention a color television with twice the number of lines (high resolution T
V) Make it attractive for use. Since the crosstalk can be substantially ignored, the pixel can be divided into a plurality of small pixels. In a first apparatus using the method of the present invention, an electro-optical display medium held between two support plates, and a pixel array in a matrix arrangement composed of image electrodes provided on opposing surfaces of the support plates, In a display device having a row and column electrode system for driving an image electrode via a non-linear switching element, the image electrode is divided into a plurality of sub-electrodes, and each sub-electrode is driven via one non-linear switching element. To do. In another display device according to the present invention, a column electrode is connected in parallel with two branches having complementary operation switches, and one of the branches is displayed via a parallel branch including an inverter circuit in series with the switch. Connect to the input of the signal to be done. Complementary operation switch means that when one switch is open, the other switch is closed and vice versa. Preferably, the display also includes a control circuit for the complementary switch. The invention will be described with reference to the drawings. FIG. 1 shows a sectional view of a part of a display device 1 comprising a liquid crystal 4 between two support plates 2 and 3. An electrically and chemically insulating layer 5 is provided on the inner surfaces of the support plates 2 and 3. Further, a large number of image electrodes 6 and 7 arranged in rows and columns are arranged on the inner surfaces of the support plates 2 and 3, respectively. The opposing image electrodes 6 and 7 constitute a pixel of the display device. A strip-shaped column electrode 11 is provided between the rows of the image electrodes 7. The column electrodes 11 and the image electrodes 7 can be integrally formed as strip electrodes. The strip-shaped row electrodes 8 are provided between rows of the image electrodes 6. Each image electrode 6 is connected to, for example, a row electrode 8 via a non-linear switching element (not shown). This non-linear switching element gives the liquid crystal 4 a sufficient threshold value for the voltage supplied to the column electrode 11 by the voltage at the row electrode 8 and also gives the liquid crystal 4 a memory effect. Further, a liquid crystal alignment layer 10 is provided on the inner surfaces of the support plates 2 and 3. As is known, by applying a voltage between the liquid crystal layers 4, different alignment states of the liquid crystal molecules and thus different optical states can be obtained. The display device is a transmission type device,
It can be realized as a reflection type device, and a polarizer can be provided. FIG. 2 shows a transmittance / voltage characteristic curve of a display cell as occurs in the display device of FIG. Below a predetermined threshold voltage (V ₂ or V _th ), the cell transmits little light, but above a predetermined saturation voltage (V ₁ or V _sat ), the cell becomes almost completely light transmissive. FIG. 3 diagrammatically shows a part of such a display device. The pixel 12 has one end connected to the row electrode and the column electrode 11 arranged in a matrix in this example via the image electrode 7. The other end of the pixel 12 is connected to the row electrode 8 via the non-linear switching element 9. FIG. 4 shows a pixel 12 represented by an associated capacitance C _LC and an associated non-linear switching element (C
(High ohmic state) C _NL . A non-linear element connected to a fixed voltage is considered to be connected to ground for the following description (using the superposition principle). This non-linear element may be a reverse parallel connection diodes, diode rings, MIM switches, PIP switch, also can be made of NIN switch or other two terminal device, also the element C _NL, for example Japanese Patent Application No. Showa 61-
As described in JP-A-228496 (JP-A-62-83722), the image electrode 6 may be connected to an adjacent row electrode via a plurality of diodes, for example. For example, when a signal change ΔV occurs in a column electrode in an image display (TV) device, a point 13 is generated.
To Signal change occurs. Since the maximum signal change on the column electrode or data line 11 occurs when it changes from -V _dmax to + V _dmax or vice versa (V _d = data voltage), point 1
The maximum change ΔV _{m of} 3 is become. For example, in the case of a TV, the data voltages of the even and odd fields are considered to be equal in magnitude and opposite in polarity. _sat )), the control of the N gray levels (ie, the N division of the horizontal axis between V _th and V _{sat in} FIG. 2) Must hold. Typical liquid crystal pixels (size 300 × 300 μm ^2, the thickness of 6μ _m, ε _r ≒ 6) and S _i -
In the case of a NIN switch (size of about 10 × 10 μm ² , I layer thickness of about 400 nm), N ≧ 21 because C _LC ≒ 600 fF and C _NL ≒ 30 fF. Japanese Patent Application No. 61-2
In the example of No. 28496, since the diode is provided on both sides of the image electrode, the value of C _NL is 2
Double. In this case, N ≧ 11. If redundancy is desired, as described above, one pixel can be divided into r sub-elements, each with its own drive element. This is shown first in 5 and 6 Figure diagrammatically, wherein the three sub-electrodes comprises a respective dedicated drive element 9 ^a, 9 ^b, 9 ^c of the picture electrodes 6 provided with a driving switching element 9 ^6a , ^6b and ^6c . The electrode 7 facing the image electrode 6 is not divided. When the image electrode is divided into sub-electrodes, the capacitance C _LC also decreases. Dividing the pixel into r sections can roughly be assumed that the number of gray levels decreases from N to N '= N / r due to crosstalk. Because of this,
In the above two examples, when the image electrode is divided into three sub-electrodes (r = 3), the number of usable gray levels becomes about 7 and about 4, respectively. In particular, the latter number of levels is generally too low for a satisfactory display. With an image electrode, the situation becomes less desirable when divided into a large number of sub-electrodes. As shown above, the maximum crosstalk in this example is It is. In the present invention, the selection voltage V _S is supplied to the row electrode during a part (T _D ) of the selection period T _S to select a row, and the column electrode is driven by the data signal V _D during this period to write image information to the pixel. The voltage on the row electrode is then changed to a value at which the row is no longer selected (connected to the value V _NS ), so that the pixel is no longer written. After mowing斯, in the column electrode time (T _S -T _D), driven by the data signal V _'D = -V _D opposite polarity. T _S is at most equal to the effective line period (64 μsec in the PAL system). In order to compensate for crosstalk as completely as possible, Select For the effective voltage of the selected pixel having the desired voltage V _PO , Or Holds. This is approximately One. In this case, since the data signal and the compensation signal have the same absolute value, the compensation signal can be easily obtained from the data signal. Since T _D is smaller than the selection period, the switching element 9 does not conduct during the entire selection period (for example, 64 μsec for television). In this case, the pixels are not fully charged, but this problem can be neglected due to the steep slope characteristics of such switching elements. Furthermore,
Since the loss of this voltage is substantially the same for all switching elements, this loss can be compensated by the selection voltage if necessary. FIG. 7 shows the selection signal T _S , the data signal V _D and the crosstalk signal ΔV when the device of FIG. 3 operates in a conventional manner, and FIG. 8 uses the above-described crosstalk compensation method according to the invention. 3 shows the data signals V _D and V ′ _D and the crosstalk signals ΔV ₁ and ΔV ₂ in the case. Common input terminal 14 of the compensation signal V _'D is the signal V _D to follower circuit 15 inverter circuit 16
Supplied to, it can be obtained from the signal V _D simply by connecting the column electrode 11 the output terminals of these circuits via complementary switches 17 and 18 (Figure 9). Switch 17 Signals V _D and V ′ _D are obtained at column electrode 11. For the drive mode used in Japanese Patent Application No. 61-228498, It is. From now, using equation (1) become. Terms in this expression Is maximum for V _PO = V _th . Substituting V _PO = V _th into equation (5) gives become. This is because the N gray levels without compensation are Gray levels. Because of this, the number of gray levels Increase by a factor of two. In the case of a liquid crystal (ZLI 84460, Merck), typically V _th = 2.1 volts and V _sat = 3.6
Bolts, in other words, the number of clay levels increases by 2.8N times. In the case of the above-mentioned two examples shown in FIG. 6 which is divided into three sub-electrodes, the number of gray levels is four and seven.
From 2.8N times to 45 and 140. The present invention is not limited to the illustrated embodiment, but can be variously modified. For example, for a non-linear switching element, if the switching speed is sufficiently high, a diode ring, an anti-parallel connected diode, a MIM switch, a PIP or PI
NIP switch can be selected. Several modifications are also possible to realize the drive circuit of FIG. It is also possible to choose a different electro-optical medium, for example an electrophoretic suspension or an electrochromic material. The embodiment is based on a switching mode in which the data voltage switches a voltage sweep 2V _dmax limited to VV _sat -V _th around zero volts. Possible deviations of the TV curve from the exponential curve can be compensated for in practice simply by a suitable choice of the data voltages assigned to the gray level values.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of a display device using the present invention, FIG. 2 is a diagram showing a transmittance-voltage characteristic curve of a display cell of the display device, and FIG. FIG. 4 is a circuit diagram showing a part of a control circuit of the display device, FIG. 4 is an equivalent circuit diagram of a pixel of the display device, FIG. 5 is a plan view of a display cell, and FIG. FIG. 7 is a plan view of a modification, FIG. 7 is a waveform diagram showing signals generated when the apparatus of FIG. 3 is operated in a conventional manner, FIG. 8 is a similar waveform diagram generated when using the method of the present invention, FIG. The figure is a circuit diagram showing a circuit for realizing such a signal. 1 ... Display device 2 ... support plate 4 ... liquid crystal 5 ... insulating layer ^{6 (6 a, 6 b,} 6 c) 7 ... picture electrodes 8 ... row electrodes ^{9 (9 a, 9 b,} 9 c) ... nonlinear switching Element 10 Alignment layer 11 Column electrode T _S Selection period V _S Selection voltage V _ns Non-selection voltage V _D Data signal V ′ _D Compensation signal ΔV, ΔV ₁ , ΔV ₂ Cross-talk signal 14 Common Input terminal 15: Follower circuit 16: Inverter circuit 17, 18, Complementary switch

Claims (1)

Claims 1. An electro-optical display medium held between two support plates, a matrix of pixels arranged in rows and columns formed by image electrodes provided on opposing surfaces of these support plates, And a series of column electrodes, further comprising means for sequentially supplying a row signal to a pixel row and means for supplying a data signal to a column electrode, wherein each pixel is connected to a row electrode or a column electrode via a non-linear element. A display device for displaying a gray level, wherein the row signal supply means supplies a selection voltage during a part of each row signal period and supplies a non-selection voltage during the rest of each row signal period, Supplies a first polarity data voltage during a portion of the row signal period to display image information and a second polarity data voltage opposite to the first polarity with respect to a 0 volt reference voltage during the remainder of the row signal period. Supply And comparing the value of the data voltage of the second polarity with the duration of the remainder of the row signal period.
The product of the value of the data voltage of the first polarity and the duration of a portion of the row signal period
A display device configured to compensate for crosstalk caused by the supply of the first polarity data voltage by making the absolute value equal to the absolute value . 2. The data signal supply means is two parallel branches each including a complementary operation switch, and one branch includes a parallel branch including an inverter circuit in series with the switch for each column electrode, A control circuit for controlling the complementary operation switch,
The control circuit is configured to control the switches such that a data signal is provided to a column electrode during a portion of the row signal period and an inverted signal thereof is provided during the remainder of the row signal period. The display device according to claim 1, wherein: 3. The display device according to claim 1, wherein the image electrode is divided into a plurality of sub-electrodes, and each sub-electrode is driven through one non-linear switching element. "