JPH07122784B2 - Liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device such as a television using a matrix type liquid crystal display panel.

[0002]

2. Description of the Related Art Various display devices have been devised or put into practical use by utilizing the electro-optical effect of liquid crystals. These are due to a combination of alignment characteristics of liquid crystal molecules, dielectric anisotropy, optical anisotropy, etc., which are commonly known as DSM, TN, GH,
There are names such as.

Common features of these liquid crystals are that they have a light-receiving type display effect, that they have a relatively high resistance, and that the threshold value in display characteristics is slow or unstable with respect to each parameter. .

Here, the light-receiving type and the high resistance are the reason why the liquid crystal is superior to other display bodies and is put into practical use as a display body. It is inferior to the device, and the driving conditions of the liquid crystal are complicated and difficult.

Furthermore, the fact that the life for DC drive is short is
This is a factor that makes the driving conditions difficult.

FIG. 1 is a circuit diagram around a display panel showing a conventional embodiment. For example, reference SID77DIGEST P.
Examples can be found in 64-65 and the like.

In the figure, 2-1 is an image signal input such as a television video signal, 2-2 is a sync separation signal, and 2-3 is a circuit for generating a control signal such as a timing clock from the sync separation signal. Reference numerals 2-4 and 2-5 are circuits for controlling the vertical lines or the horizontal lines of the matrix display section to distribute and scan the display signal to each matrix pixel. Reference numeral 2-4 is a drain drive circuit that parallel-exchanges the serial image signal input from 2-1 and supplies the serial image signal to the drain side of the transistor connected in series to each pixel.
Reference numeral 21 denotes a gate of a transistor serially connected to each pixel in accordance with a 2-3 output clock, turning on and off sequentially for each line.
It is a gate drive circuit that controls F to read an image signal into a pixel. The drains 2-6 on the output side of the transistors arranged in each matrix are coupled to the respective pixel electrodes of the liquid crystal display.

Document SID79DIGEST P96-9
As described in No. 7, in the conventional matrix display by the circuit of FIG. 1, the liquid crystal drive is DC drive.

In FIG. 1, of the electrodes sandwiching the liquid crystal of the liquid crystal matrix display unit, the electrode facing each pixel electrode is a common electrode over the entire display image, and the potential is set to the GND level and the MOS is used. It corresponds to the common electrode potential of the transistor substrate and the capacitors arranged in parallel. For this reason, the liquid crystal material needs to be treated with a redox agent or the like for the purpose of maintaining a long DC life.

FIG. 2 shows the relationship between the signal waveform and the potential in the circuit of FIG. 3-1 is an image signal supplied to the terminal 2-1, and 3-2 is a synchronizing signal when the image signal is sampled for each data line of each matrix in the block 2-4. The horizontal axis t represents time, and the vertical axis V represents voltage. Reference numeral 3-3 represents a black level of the image signal and 3-4 represents a white level, which correspond to the threshold voltage and the saturation voltage of the liquid crystal, respectively. Voltage 0 corresponds to GND in FIG. 1 and is the substrate and common electrode potential.

Further, another conventional circuit example related to the present invention is shown in FIG. Specifically, SID78D engineering GEST P9
Examples can be found in 4-95. In FIG. 3, 4-1 is shown in FIG.
2-1 corresponds to the image signal input. 4-2 is a low-pass filter, 4-3 is an amplifier, 4-4 is an A / D converter, 4-5 is a data encoder, and 4-8 is a serial-parallel conversion shift register. The image signal input 4-1 is converted into an image signal in a band corresponding to the display performance of the corresponding display panel through a low pass filter and an amplifier, and then digital code converted by an A / D converter. Reference numeral 4-8 outputs the converted image digital image data in parallel to each data line of the matrix. The parallel output data is input to the D / A converter provided for each data line and restored to an analog image signal.

At this time, the gain of the D / A converter output signal is
Controlled by the gain control circuit 4-9, the (voltage-
The contrast is adjusted so that the correlation characteristic and the contrast of the image signal match. Further, the D / A output is input to the buffer amplifier 4-12. An offset bias level adjusting circuit 4-10 adjusts a reference level 4-12 so that the reference level of the image signal corresponds to the vicinity of the threshold value of the liquid crystal and outputs the image signal to the data line. Reference numeral 4-6 is a sync separation circuit, 4-7 is a timing signal generation circuit, and 4-13 is a circuit for controlling a clock line of the matrix display portion, which corresponds to 2-15. 4-
Reference numeral 16 is a display matrix portion, which is omitted because it has the same structure as 2-7 in FIG.

In the circuit example shown in FIG. 3, the liquid crystal is driven by direct current as in the case of FIG. Also, in FIG.
There is a gain control circuit 4-9 and an offset bias level control circuit 4-10 for the image signal supplied to the data line of the matrix display section, which makes it possible to adapt the signal level to the characteristics of the liquid crystal display. There is.

[0014]

In the conventional liquid crystal display device, the liquid crystal is driven by direct current, and the life of the liquid crystal is shortened. Therefore, a redox agent is added to the liquid crystal material for the purpose of keeping the direct current life longer. And so on.

Further, if the applied potential of the counter electrode facing the pixel electrode is always constant, the polarity of the data signal (image signal) must be inverted with reference to this applied potential, and the operating voltage range must be increased. did not become. Therefore, a power supply circuit that generates a large voltage has been required.

The present invention provides an image display device that improves the conventional drawbacks and makes full use of the liquid crystal display performance. According to the invention, the document Display
conf. Even if the number of matrix scanning lines is significantly increased as compared with the so-called dynamic driving method of 1976 P51, the display contrast performance of the liquid crystal is not impaired at all.
Further, the applied voltage required for driving the display does not increase.
Furthermore, flicker on the screen (so-called flicker) does not occur. Further, since the present invention drives the liquid crystal by an alternating current, the life of the liquid crystal can be maintained for a long time, and it is not necessary to mix an additive such as a redox agent.

[0017]

According to the present invention, a liquid crystal is sealed between a pair of substrates, a pixel electrode arranged in a matrix on one of the substrates, a switching element connected to the pixel electrode, A scanning line which supplies a scanning electrode to the switching element, and a data signal line which supplies a data signal to the pixel electrode through the switching element, and opposes the pixel electrode on the other substrate. In the liquid crystal display device having the counter electrode at the position, the phase of the data signal is inverted for each pixel or for each scanning line, and inverted for every one vertical scanning period, and applied to the data signal line. Therefore, the potential applied to the counter electrode is a two-level potential that is inverted in synchronization with the phase inversion cycle of the data signal.

[0018]

FIG. 4 is a block diagram showing an overall view of a television receiver using the liquid crystal image display device according to the present invention.

In the figure, reference numeral 5-1 is a tuner section for selecting the frequency of a predetermined channel from the received radio wave input from the antenna. Reference numeral 5-2 is a circuit from the intermediate frequency amplifier to video detection, 5-4 is a circuit for audio intermediate frequency, detection, output, etc., and 5-5 is a circuit for separating horizontal, vertical and other synchronizing signals from the video signal. is there. A video amplification circuit block 5-3 according to the present invention outputs a liquid crystal display image signal to the matrix display section data signal latch circuit 5-8 in the subsequent stage. 5-
Reference numeral 9 is a data line drive circuit.

Specific circuit configurations and mutual relationships of the video amplifier circuit block 5-3, the matrix display portion data signal latch circuit 5-8 and the data line drive circuit 5-9 will be shown in detail later in FIG. Also, the video amplification circuit block 5-
Another embodiment of No. 3 is shown in FIG.

Reference numerals 5-6 and 5-7 denote sync signal separation circuits 5-.
In response to the output of the data 5, the data latch signals are supplied to 5-8, and the timing signal for driving the matrix display clock line (horizontal line) is supplied to 5-10. 5-11 is a power supply,
A common electrode voltage described later is supplied to the common electrode 5-13 (-dot chain line). Reference numeral 5-12 represents a matrix type liquid crystal display panel, the details of which are as shown in FIG.

Reference numeral 6-1 is a gate drive circuit, 6-2 is a drain drive circuit, and a transistor for selectively supplying an image signal to a pixel electrode is supplied to each pixel 6-3 of the matrix display portion. The electrodes of the pixels to which the outputs of the respective transistors are coupled are all located on one of the pair of flat plates that sandwich the liquid crystal, and each electrode is electrically and independently separated on the flat plate on which the electrodes are arranged. is doing. Among the flat plates sandwiching the liquid crystal, a single common electrode is provided over the entire display portion on the flat plate facing the flat plate. Here, the substrate potential of each transistor and the electrode potential on one side of the capacitor provided for each pixel are in common with the GND potential, but the liquid crystal display section common electrode potential 6-4 is not the GND potential.

6 and 7 show partial views of an example in which a transistor and a capacitor are formed for each pixel as shown in FIG.

FIG. 6 is a cross-sectional view of a pair of flat plates sandwiching a liquid crystal, the flat plate on the side having electrodes separated for each pixel and arranged in a matrix. In the figure, 7-1 is a silicon substrate. 7-
Reference numeral 2 denotes a diffusion layer having a conductivity type opposite to that of 7-1, and 7-3 denotes a diffusion layer having the same conductivity type as 7-1, which functions as a stopper and an electrode of a capacitor. Further, 7-4 is a gate oxide film having a film thickness of about 400 to 2000A.

7-5 is polysilicon, and 7-5
(A) is a gate electrode of a MOS transistor, 7-5
(B) is a capacitor electrode. Reference numeral 7-6 is a field oxide film, 7-7 is an insulating film, and 7-8 is an aluminum electrode.

In FIG. 6, the transistor for switching each pixel is composed of a silicon gate MOS transistor, and the electrodes of the capacitor arranged in parallel with each pixel of the liquid crystal are the silicon substrate itself and the polysilicon substrate. It becomes silicon 7-5 (b). In this case, the silicon substrate is GN
The potential is held at the D potential, and as shown in FIG. 6, the electrode on one side of the capacitor and the substrate potential of the transistor coincide with each other and reach the GND level.

FIG. 7 is a plan view of the driving circuits arranged in a matrix form, and a sectional view taken along the line AA ′ in FIG.
Equivalent to. In the figure, 7-2 from 8-2 to 8-8
Corresponds to 2 to 7-8. Further, in FIG. 7, the drain electrode 7-8 (b) in FIG. 6 is omitted so that the drawing is not complicated.

In FIG. 7, a pixel is an area indicated by a chain double-dashed line. Therefore, a so-called pixel electrode for applying a voltage to the liquid crystal is a transistor or a signal line 8-5 running in vertical and horizontal directions.
Insulated from (a), 8-8 (a), etc., they are arranged on the upper side of the pattern of FIG.

As mentioned above, 7-1 is a monolithic silicon crystal substrate, but the method of forming the circuit of FIG.
There are various other types, including thin film technology.

In FIG. 5, each transistor is a MOSFE.
Although it is composed of T, other switching elements may be used.

Next, an example of the waveform of the signal according to the present invention is shown in FIG.
Shown in. In the figure, 9-1 and 9-2 are both image signals. A dotted line indicated by 9-6 indicates the potential on the liquid crystal matrix display body section common electrode side, and the voltage polarity of the image signal applied to each matrix image electrode of the liquid crystal repeats inversion at a certain cycle.

For example, in the case of an image signal for television broadcasting, the video signal of the screen is set as one frame, the one frame is further divided into two fields, and the interlaced scanning of the screen is performed for each one field.

Here, in FIG. 8, for example, 9-1 corresponds to one horizontal scanning line in the image signal of one frame including the first and second fields. And 9-2
Is an image signal corresponding to the same display portion in the image signal for the next one frame following the signal for the one frame. 9-3 is an image sampling synchronization signal, and 9-4
The period shown by corresponds to the period for displaying one display pixel in the horizontal direction on the matrix display panel. 9-5 corresponds to the horizontal blanking period of the television image signal.

On the vertical axis in FIG. 8, 0 potential, that is, 9-11
Is the potential of the display substrate 7-1, and 9-10 is 9
The circuit voltage of the display unit corresponding to −11. in this case,
The switching transistor arranged in each pixel of FIG. 5 is, for example, a P-channel type enhancement MOSF.
It can consist of ET. When 9-10 is set to the potential of the substrate 7-1, the switching transistor may be formed by an N-type MOS.

The amplitude of the image signal 9-1 is between the wavy line 9-7 and the wavy line 9-8. 9-7 is a black image signal, 9-8
Corresponds to white. Regarding the linearity of the signal, the linearity of the original image signal may be prevented from being distorted by the liquid crystal by interposing an amplifier corrected by the correlation characteristic of the applied voltage of the liquid crystal and the display contrast.

The purpose of alternately applying the image signals 9-11 and 9-2 to each liquid crystal display pixel electrode is to prolong the life of the display by driving the liquid crystal in an alternating current. When the liquid crystal is driven by exchanging the AC signal, the display image flickers due to the alternating voltage driving of the liquid crystal. This is because the direction in which the electric dipoles of the liquid crystal molecules face changes according to the reversal of the applied voltage polarity.

In order to reduce this flicker or to make it effectively negligible, the following is done in the present invention.

That is, the inversion period of the AC signal applied to the display screen within one frame period is switched and applied on a pixel-by-pixel basis or on a scanning-line basis to accelerate the effective AC inversion period. If the positive and negative polarities of the image signal applied to the display pixels are switched in pixel units or in scanning line units, and if the AC cycle of each pixel is in frame units, the linearity of the amplifier or in each pixel unit The linearity of the switching characteristics of the selected transistor is determined by the operating voltage range (9
Even if it is not sufficiently obtained in the range of −11 to 9-10), the nonlinearity in terms of display effect can be effectively ignored.

As described above, in the present invention, the data signals are applied to the data signal lines by inverting the phases of each pixel or each scanning line and inverting the phases every vertical scanning period. , The inversion period of the effective voltage applied to the liquid crystal is increased.

FIG. 9 shows a specific example of a circuit that switches the polarity in pixel units or in scanning line units when an AC drive signal is supplied to the liquid crystal. Reference numerals 10-2, 10-3, and 10-4 denote image signal amplifiers, and the image amplification circuit block 5 of FIG.
Equivalent to 13. Further, 10-5 corresponds to the matrix display data signal latch circuit 5-8 in FIG. Also, 1
0-7 and 10-8 are the data line drive circuits 5-9 of FIG.
Equivalent to. Further, 10-6 is a changeover switch circuit, and the output of 10-6 becomes the image signal input of 6-8 in FIG.

The operation will be described below. Reference numeral 10-1 is an original image signal input, 1012 is a stage amplifier, and 10-9 has an amplification factor adjusting terminal. Reference numerals 103, 10-4 denote differential amplifiers. The same signal, that is, the 10-2 output is coupled to the positive input terminal 10-3 and the negative input terminal 10-4. 1
The 0-3 negative polarity input terminal and the 10-4 positive polarity input terminal are combined to form a terminal at 10-10. 10-3 and 10-4 are preset so that almost the same characteristics as the amplifier can be obtained.

The terminal 10-10 is a terminal for adjusting the brightness of the image displayed by the liquid crystal, to which a variable DC voltage is applied. For example, the output signals 10-3 and 10-4 are as shown in FIG.
9-1 and 9-2, respectively. At this time, 10
-9 adjusts the difference between 9-8 and 9-7, that is, the amplitude, in other words, the contrast of the surface image. 10-10 is 9-
Adjust the difference between 7 and 9-6. 10-3 (10-4)
The gain may be set as appropriate.

10-6 is a switch circuit, and 10-1
The image signal of positive polarity obtained by amplifying the image signal input to 10 to the differential amplifier of 10-3 and the image signal input to 10-1 are amplified and inverted by the differential amplifier of 10-4. It is a circuit that switches the obtained negative-polarity image signal for each horizontal scanning period or each period in which an arbitrary pixel is selected.

By switching the image signal by this switch circuit every horizontal scanning period or every pixel selection period,
Image signals having different polarities are generated every horizontal scanning period or every pixel selection period.

As a switch element, a bipolar or M
Transistors such as OS and various other methods are conceivable. However, when a semiconductor is used for the display substrate and the block 6-2 is housed inside the semiconductor substrate as shown in FIG. A so-called transmission gate or the like may be used.

The same applies to the circuit 10-7 in the subsequent stage. 10-
Reference numeral 5 denotes a circuit that sequentially generates signals for controlling the switch elements 10-7, for example, from left to right, and is composed of a shift register. Reference numeral 10-8 is a circuit for storing and holding the image sampling signal sampled by the switch and distributing it to each pixel electrode. 10-8 and thereafter correspond to the liquid crystal matrix display unit including the drive unit, that is, FIG.

FIG. 10 shows still another embodiment.
Is a modification of the configuration of the amplifiers 10-2, 10-3, and 10-4 in FIG. In the embodiment of FIG. 9, an image signal having a negative polarity is passed through two differential amplifiers to obtain two signals having different polarities to be applied to the liquid crystal display device. In the tenth embodiment, image signals 11-1 and 11-2 whose amplitudes are substantially the same and whose polarities are opposite to each other are prepared in advance, and the signals to be added to the liquid crystal display device are amplified by amplifying these and switching them. It differs in the point that it has gained.

In the figure, the upper amplifier circuit (transistor 11
-3, 11-5) and the lower amplifier circuit (transistor 11
-13, 11-14) are designed so that the circuit configuration and the amplification characteristics match.

Reference numerals 11-4 and 11-8 are variable resistors for use in gain control of the amplification system, which adjust the contrast of the liquid crystal display image. 11-4 and 11-8 are interlocked by a dotted line 11-10, and can be manually adjusted from the outside. 11-7,
Reference numeral 11-9 is a variable resistor for controlling the output potential level, that is, changing the brightness of the liquid crystal image display, which is interlocked with the broken line 11-11 and can be manually adjusted from the outside. However, 11-
7 and I1-9 operate in opposite potential levels, and their outputs maintain symmetry about level 9-6 as in 9-1 and 9-2 in FIG.

Reference numeral 11-12 is an image signal polarity switching switch circuit corresponding to 10-6 in FIG. 9, which is obtained by amplifying an image signal composed of image signals 11-1 and 11-2 having opposite polarities. The positive image signal and the negative image signal,
A circuit that switches an image signal for each pixel period applied to a pixel or for each scanning period of an image signal.

By switching the image signal for each pixel period or each scanning period by this switch circuit, each pixel electrode of the liquid crystal display device has an image signal having a different polarity for each pixel period or each scanning period. Will be applied.

The present invention can also be realized by a configuration other than the circuits given as examples. Further, the adjustment of the contrast lightness can be manually controlled as described above, or the display degree of the liquid crystal can be automatically detected in accordance with the reference pattern display signal level to automatically control the gain or bias level. Things can of course be possible.

In the description of the embodiments of the present invention, as shown in FIG. 6, a silicon substrate is used as one plate sandwiching a liquid crystal, and a transistor is formed in the silicon substrate. Alternatively, for example, a polycrystalline material is used. It can be realized by forming each element on a glass substrate by the thin film technology according to 1., or by other methods.

In FIG. 5, the transistor provided for switching each pixel is one MOS type transistor, but in order to improve the linearity of the element, the response speed, the operating voltage, etc., It is also possible to perform switching by combining two types of N-type MOSFETs in a complementary type. Of course, it is also possible to configure with elements other than MOSFET.

In FIG. 5, a capacitor is arranged in parallel with each pixel of the liquid crystal, but in this case, both electrodes of the capacitor are not connected in parallel with the liquid crystal pixel electrode as described above, but are common. The electrode side potentials are set separately. This is because the substrate on the common side of the capacitor can be substituted by adopting the structure shown in FIG.

At this time, the polarity and the magnitude of the bias potential applied to the capacitor according to the image signal printed on the liquid crystal pixel are different from the bias potential of the liquid crystal pixel electrode, but the effective electric characteristics concerning the display are obtained. Has the same effect as that shown in FIG.

As the liquid crystal used in the display device according to the present invention, only the TN type liquid crystal has been explained, but the operation performance of the first mentioned DSM, GH and other liquid crystals is basically the same.

[0058]

According to the present invention, liquid crystal is sealed between a pair of substrates, pixel electrodes arranged in a matrix on one substrate, switching elements connected to the pixel electrodes, and scanning electrodes for the switching elements. And a data signal line for supplying a data signal to the pixel electrode through a switching element, and a counter electrode at a position facing the pixel electrode on the other substrate. In a liquid crystal display device, the phase of a data signal is inverted pixel by pixel or scanning line by pixel, and inverted every 1 vertical scanning period and applied to a data signal line. The following effects can be obtained by using the two-level potentials that are inverted in synchronization with the phase inversion period.

(A) In the conventional liquid crystal display device, an image signal is converted into an AC signal and driven by an alternating voltage in order to prolong the life of the liquid crystal, but the applied voltage is applied in units of one frame or one field. Since the polarity of is reversed, the polarity of one screen of the liquid crystal display device will change at once in a fixed cycle.
The flicker on the display screen was very noticeable. However, if the inversion period of the data signal applied to the liquid crystal is switched and applied on a pixel-by-pixel basis or on a scanning-line basis as in the present invention, the polarity may be changed on a pixel-by-pixel or scanning-line by , The polarity of the voltage applied to the liquid crystal partly changes, and the flicker on the screen is almost eliminated.

(B) Since the polarity of the data signal applied to the liquid crystal is inverted, the life of the liquid crystal is extended.

(C) Since the potentials of the opposing electrodes are also changed in synchronization with the data signal inversion period, the voltage required to drive the liquid crystal becomes about half or less of the conventional voltage, and a power supply circuit that generates a large voltage is used. No longer needed.

[Brief description of drawings]

FIG. 1 is a conventional display circuit diagram.

FIG. 2 is a conventional signal diagram.

FIG. 3 is another conventional display circuit diagram.

FIG. 4 is a block diagram showing an embodiment of the present invention.

FIG. 5 is a display circuit diagram according to the present invention.

FIG. 6 is a partial cross-sectional view of a display device.

FIG. 7 is a plan view of FIG.

FIG. 8 is a signal waveform diagram according to an embodiment of the present invention.

FIG. 9 is a circuit diagram of an embodiment of the present invention.

FIG. 10 is a circuit diagram of an embodiment of the present invention.

[Explanation of symbols]

 5-12 ... Matrix display section 7-1 ... Silicon substrate 8-8 (a) ... Matrix display driving data line 8-5 (a) ... Matrix display driving Black line 8-5 (b) ... Capacitor electrodes 3-1, 9-1, 9-2 ... Image signal 10-2 ... Image signal amplifier 10-3, 10-4 ... Difference Dynamic amplifier

Claims (1)

[Claims] 1. A liquid crystal is sealed between a pair of substrates, pixel electrodes are arranged in a matrix on one of the substrates, a switching element connected to the pixel electrode, and a scanning electrode is supplied to the switching element. And a data signal line for supplying a data signal to the pixel electrode through the switching element, and an opposite electrode at a position facing the pixel electrode on the other substrate. In the liquid crystal display device, the phase of the data signal is inverted pixel by pixel or scan line by pixel and inverted every one vertical scanning period to be applied to the data signal line, and then applied to the counter electrode. A liquid crystal display device, wherein the potential is a two-level potential that is inverted in synchronization with the phase inversion cycle of the data signal.