JPH0529916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device such as a television set using a matrix type liquid crystal display panel.

[Conventional technology]

Various display devices have been devised or put into practical use using the electro-optic effect of liquid crystals. These are due to the combination of alignment characteristics of liquid crystal molecules, dielectric anisotropy, optical anisotropy, etc., and are commonly known as DSM,
There are names such as TN, GH, etc.

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

The fact that it is a light-receiving type and has high resistance is why liquid crystals are superior to other display elements and are put into practical use as display elements; however, on the other hand, their threshold characteristics are inferior to other display elements. This makes the driving conditions for liquid crystals complicated and difficult.

Furthermore, the short lifespan compared to DC drive is another factor that makes the drive conditions difficult.

Figure 1 is a circuit diagram around the display panel showing a conventional example.
Examples can be found in .

In the figure, 2-1 is a circuit for inputting an image signal 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. 2-4 and 2-5 are circuits that control the vertical lines or horizontal lines of the matrix display section and distribute and scan display signals to each matrix pixel. 2-4 is 2
This is a drain drive circuit that exchanges the serial image signals inputted from -1 in parallel and supplies them to the transistors connected in series to each pixel and the drain side. 2-5
The gates of the transistors connected in series to each pixel are sequentially connected line by line using the 2-3 output clock.
This is a gate drive circuit that controls ON/OFF to read image signals into pixels. Output side drains 2-6 of transistors arranged in each matrix section
are coupled to each pixel electrode of the liquid crystal display.

As described in the document SID78DIGEST P96-97, in the conventional matrix display using the circuit shown in FIG. 1, the liquid crystal was driven by direct current.

In Figure 1, among the electrodes that sandwich the liquid crystal in the liquid crystal matrix display section, the electrodes facing each pixel electrode are common electrodes over the entire display surface, and the potential is set at the GND level. The common side electrode potential of the substrate of the transistor and the arranged capacitor coincides with each other. For this reason, liquid crystal materials required treatments such as doping with redox agents in order to maintain a long DC life.

Here, the relationship between the signal waveform and potential in the circuit of FIG. 1 is shown in FIG. 3-1 is an image signal supplied to terminal 2-1, and 3-2 is an image signal supplied to block 2.
-4 is a synchronization signal when sampling the image signal for each data line of each matrix. The horizontal axis t represents time, and the vertical axis V represents voltage. 3-3 represents the black level of the image signal, and 3-4 represents the white level, which correspond to the threshold voltage and saturation voltage of the liquid crystal, respectively. The voltage O corresponds to NGND in FIG. 1 and is the substrate and common electrode potential.

Furthermore, another example of a conventional circuit related to the present invention is shown in FIG. Specifically, examples can be found in SID78DIGEST P94-95. In FIG. 3, 4-1 corresponds to 2-1 in FIG. 1 and is an 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, 4-
8 is a serial/parallel conversion shift register. The image signal input 4-1 is converted into an image signal of a band corresponding to the display performance of the display panel through a low-pass filter and an amplifier, and then converted into a digital code by an A/D converter. 4-8 outputs the converted image digital image data to each data line of the matrix in parallel. The parallel output data is input to a 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, and adjusted so that the (voltage-contrast) correlation characteristic of the liquid crystal matches the contrast of the image signal. Further, the D/A output is input to a buffer amplifier 4-12. 4-1
2 is an offset bias level adjustment circuit 4-10
The reference level of the image signal is adjusted so as to correspond to the vicinity of the threshold value of the liquid crystal, and the image signal is output to the data line. 4-6 is a synchronization separation circuit, 4-7 is a timing signal generation circuit, and 4-13 is a circuit for controlling the clock line of the matrix display section, which corresponds to 2-5. Reference numeral 4-16 is a display matrix section, and its configuration is the same as 2-7 in FIG. 1, so its illustration is omitted.

In the circuit example shown in FIG. 3, the liquid crystal is driven by direct current, as in FIG. 1. Also, the third
In the figure, a gain control circuit 4-9 and an offset bias level control circuit 4-10 are connected to the image signal supplied to the data line of the matrix display section.
This makes it possible to adapt the signal level to the characteristics of the liquid crystal display.

[Problems with conventional technology]

In conventional liquid crystal display devices, the liquid crystal is driven by direct current, which shortens the lifespan of the liquid crystal, so treatments such as doping the liquid crystal material with an oxidation-reducing agent are necessary to maintain the long lifespan of the liquid crystal.

[Purpose of the invention]

The present invention aims to improve the conventional drawbacks and provide an image display device that fully utilizes the display performance of liquid crystal. According to the invention, the document Display
conf.1976 P51, even if the number of matrix scanning lines is greatly increased compared to the so-called dynamic drive method of P51, the display contrast performance of the liquid crystal will not be impaired in the slightest, and the applied voltage required for display drive will not increase. Furthermore, screen flickering (so-called flicker) does not occur.

Furthermore, since the present invention drives the liquid crystal with alternating current, it is possible to maintain the life of the liquid crystal for a long time, and there is no need to mix additives such as redox agents.

The circuit for carrying out the present invention is greatly simplified compared to the circuit shown in FIG. There are no factors that cause variation.

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

In the figure, 5-1 is a tuner section that selects the frequency of a predetermined channel from received radio waves input from an antenna. 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., 5-5 is a circuit from the video signal to the horizontal,
This is a circuit that separates each vertical synchronization signal. 5-
3 is a video amplification circuit block according to the present invention, which is a matrix display section data signal latch circuit 5-8 in the subsequent stage.
, outputs a liquid crystal display image signal. 5-9 is a data line driving circuit.

The specific circuit configuration and mutual relationship of the video amplification circuit block 5-3, the matrix display section data signal latch circuit 5-8, and the data line drive circuit 5-9 will be shown in detail later in FIG. 10. Also, regarding the video amplification circuit block 5-3, another embodiment is shown in the first example.
Shown in Figure 1.

5-6 and 5-7 receive the output of the synchronization signal separation circuit 5-5 and supply a data latch signal to 5-8 and a timing signal for driving the matrix display clock line (horizontal line) to 5-10, respectively. . 5-1
is a power supply, which supplies a common electrode voltage, which will be described later, to the common electrode 5-13 (-dotted chain line). 5-12 represents a matrix type liquid crystal display panel, the details of which are shown in FIG.

6-1 is a gate drive circuit, and 6-2 is a drain drive circuit, each of which is provided with a transistor for selectively supplying an image signal to a pixel electrode for each pixel 6-3 of the matrix display section. All of the pixel electrodes to which the outputs of each transistor are connected are located on one of a pair of flat plates sandwiched between liquid crystals, and each electrode is electrically separated and independent on the flat plate on which the electrode is placed. ing. Among the flat plates sandwiching the liquid crystal, a single common electrode is provided on the flat plate facing the above flat plate over the entire display section. Here, the substrate potential of each transistor and the one-side electrode potential of the capacitor provided for each pixel commonly match the GND potential, but the liquid crystal display section common electrode potential 6-4
is not at GND potential.

FIG. 6 and FIG. 7 show partial views of an example in which transistors and capacitors are configured for each pixel as shown in FIG. 5.

FIG. 6 is a sectional view of a pair of flat plates sandwiching a liquid crystal, the side having electrodes separated for each pixel and arranged in a matrix. In the figure, 7-1 is a silicon substrate. 7-2 is a diffusion layer of a conductivity type opposite to that of 7-1, and 7-3 is a diffusion layer of the same conductivity type as 7-1, which functions as a stopper and a capacitor electrode. Further, 7-4 is a gate oxide film, and its film thickness is about 400 to 200 Å.

7-5 is polysilicon, 7-5a is
The gate electrode of the MOS transistor, 7-5b, is the electrode of the capacitor. 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 that switches each pixel is composed of a silicon gate MOS transistor, and the electrode of the capacitor arranged in parallel with each pixel of the liquid crystal is connected to the silicon substrate itself and the polysilicon 7. -5b. in this case,
The silicon substrate is held at the GND potential, and as shown in FIG. 6, the one side electrode of the capacitor and the substrate potential of the transistor match and become the GND level.

FIG. 7 shows a plan view of the drive circuits arranged in a matrix, and the sectional view taken along line A-A' in the figure corresponds to FIG. In the figure, 8-2 to 8-8 correspond to 7-2 to 7-8, respectively. Also, the seventh
In the figure, the drain electrodes 7-8b in FIG. 6 are omitted so as not to complicate the figure.

In FIG. 7, the pixels are areas indicated by two-dot chain lines. Therefore, the so-called pixel electrode that applies voltage to the liquid crystal is a transistor or a signal line 8 running vertically and horizontally.
-5a, 8-8a, etc., and are arranged above the pattern in FIG. 7 as shown by the two-dot chain line.

As mentioned earlier, 7-1 is a monolithic silicon crystal substrate, but there are various other methods of constructing the circuit shown in FIG. 5, including thin film technology.

In FIG. 5, each transistor is composed of a MOSFET, but other switching elements may be used.

Next, FIG. 8 shows an example of a signal waveform according to the present invention. In the figure, both 9-1 and 9-2 are image signals. The dashed line 9-6 indicates the potential on the common electrode side of the liquid crystal matrix display body, and the voltage polarity of the image signal applied to each matrix image electrode of the liquid crystal is repeatedly inverted at a certain period.

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

Here, in FIG. 8, for example, 9-1 is the first
This corresponds to one horizontal scanning line of one frame of image signals including the second field and the second field. And 9-2 is an image signal corresponding to the same display portion of the image signal for the next one frame following the signal for one frame. Reference numeral 9-3 is an image sampling synchronization signal, and the period shown at 9-4 corresponds to the period during which one display image is displayed horizontally on the matrix display panel. 9-5 corresponds to the horizontal retrace period of the television image signal.

On the vertical axis of FIG. 8, the O potential, that is, 9-11
For example, let 9-1 be the potential of the display substrate 7-1,
Let 0 be the display body circuit voltage corresponding to 9-11.

In this case, the switching transistor arranged for each pixel in FIG. 5 can be configured, for example, by a P-channel enhancement MOSFET. 9-
10 is set to the potential of the substrate 7-1, the switch transistor may be constructed of an N-type MOS.

The amplitude of the image signal 9-1 is between the dotted line 9-7 and the dotted line 9-8. 9-7 is the black of the image signal, 9-
Corresponds to 8 white. Regarding the linearity of the signal, it is sufficient to prevent the linearity of the original image signal from being distorted by the liquid crystal by interposing an amplifier that is corrected according to the correlation characteristic between the applied voltage of the liquid crystal and the display contrast.

The purpose of alternately applying the image signals 9-1 and 9-2 to each liquid crystal display image electrode is to extend the life of the display by AC driving the liquid crystal. When driving the liquid crystal using an alternating current signal, flickering of the displayed image occurs 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 are oriented also changes in accordance with the reversal of the applied voltage polarity.

In order to reduce this flickering or to make it effectively negligible, the present invention takes the following steps.

That is, the inversion period of the AC signal applied to the display screen within one frame period is switched and applied pixel by pixel or by scanning line, thereby increasing the effective AC inversion period. If the positive polarity and negative polarity of the image signal applied to the display pixels are switched for each pixel or each scanning line, and the AC cycle of each pixel is set for one frame, the linearity of the amplifier or the The linearity of the switching characteristics of the transistor is determined by the operating voltage width (9-11
to 9-10), the nonlinearity from the viewpoint of display effect can be effectively ignored.

FIG. 9 specifically shows an example of driving waveforms for a liquid crystal display device according to the present invention, and is a diagram illustrating an example in which the phase of an image signal is inverted for each scanning line.

In FIG. 9, the image signal Vds indicated by the solid line
The image signal Vds2 indicated by 1 and a dotted line is an image signal whose phase is inverted every vertical scanning period, and the image signal Vds1 is an image signal applied to the data signal line in the first field constituting one frame. The image signal Vds2 indicates the image signal applied to the data signal line in the second field constituting one frame.

In this way, in the present invention, the phase of the image signal for one row is mutually inverted for each scanning line between the n-th line and the n+1-th line, and the phase is inverted for each vertical scanning period, so that the image signal is By applying a signal to the data signal line, the inversion period of the effective voltage applied to the liquid crystal is increased.

FIG. 10 shows a specific example of a circuit that switches polarity on a pixel-by-pixel or scanning-line basis when supplying an AC drive signal to a liquid crystal. 10-2, 10-3 and 10-4 are image signal amplifiers, which correspond to the image amplification circuit block 5-3 in FIG. Also,
10-5 corresponds to the matrix display section data signal latch circuit 5-8 in FIG. 10-7 and 10-8 are the data line drive circuits 5-9 in FIG.
corresponds to Further, 10-6 is a changeover switch circuit, and the output of 10-6 becomes the image signal input shown in FIG. 5, 6-8.

The operation will be explained below. 10-1 is an original image signal input, 10-2 is an initial stage amplifier, and 10-9 is an amplification factor adjustment terminal. 10-3 and 10-4 are differential amplifiers. 10-3 positive polarity input terminal and 10-
The same signal, that is, 10-
Combine the two outputs. 10-3 negative polarity input terminal and 1
0-4 positive polarity input terminal is connected, 10-1
There is a terminal at 0. 10-3 and 10-4 are
It is set in advance so that almost the same characteristics can be obtained as an amplifier.

The 10-10 terminal is a terminal for adjusting the brightness of an image displayed by the liquid crystal, and a variable DC voltage is applied thereto. For example, the output signals 10-3 and 10-4 correspond to FIG. 8, 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 adjusts the difference between 9-7 and 9-6. The gain of 10-3 (10-4) may be set appropriately.

10-6 is a switch circuit, and the image signal inputted to 10-1 is amplified by the differential amplifier 10-3, and the positive polarity image signal obtained, and the image signal inputted to 10-1 are combined. This circuit switches between a negative polarity image signal obtained by amplifying and inverting a 10-4 differential amplifier every horizontal scanning period or every period in which an arbitrary pixel is selected.

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

As a switch element, bibolar or MOS
Various methods such as transistors such as
It is desirable that 10-6 be made with a similar structure, and examples include a structure such as a so-called transmission gate.

The same applies to the subsequent circuit 10-7. 10-5 sequentially transmits signals for controlling each switch element 10-7.
For example, it is a circuit that occurs from left to right and is made up of shift registers. 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 corresponds to the liquid crystal matrix display unit including the drive unit, that is, FIG. 4.

FIG. 11 shows yet another embodiment, in which the configurations of the amplifiers 10-2, 10-3, and 10-4 in FIG. 10 are changed. In the embodiment of FIG. 10, the image signal having one polarity is
By passing two signals through two differential amplifiers, two signals with different polarities to be applied to the liquid crystal display device are obtained. In contrast, in the example shown in FIG. The difference is that the signals 11-1 and 11-2 are prepared in advance, amplified, and mutually switched to obtain the signal to be applied to the liquid crystal display device.

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

11-4 and 11-8 are resistors that can be used to control the gain of the amplification system, and adjust the contrast of the liquid crystal display image. 11-4, 11-8 are 11 shown by the wavy line
-10, and can be manually adjusted from the outside. 11-7 and 11-9 are resistors that control the output potential level, that is, change the brightness of the liquid crystal image display, and are linked by the dotted line 11-11, and can be manually adjusted from the outside. However, 11-7 and 11-9
The potential levels operate in the opposite direction, and the symmetry of each output is maintained around level 9-6 as shown in FIG. 8, 9-1 and 9-2.

11-12 is an image signal polarity changeover switch circuit corresponding to 10-6 in FIG. This circuit switches between an image signal and a negative image signal every pixel period when the image signal is applied to one image or every one scanning period of the image signal.

By switching the image signal with this switch circuit every pixel period or every scanning period, image signals with different polarities are applied to each pixel electrode of the liquid crystal display device every pixel period or every scanning period. The Rukoto.

The present invention can also be realized by a configuration other than the circuit described in the embodiment. Furthermore, the contrast and brightness can be adjusted manually as described above, or the gain or bias level can be automatically controlled by automatically detecting light by matching the display degree of the liquid crystal to the reference pattern display signal level. Of course it is also possible to do so.

In the description of the embodiments of the present invention, as shown in FIG. 6, a silicon substrate is used as one of the flat plates sandwiching the liquid crystal, and a transistor is formed within the silicon substrate. Configuring each element on a glass substrate using technology, etc.
Alternatively, it can be realized by other methods.

In Figure 5, the transistor provided for switching each pixel is a single MOS transistor, but in order to improve the linearity, response speed, operating voltage, etc. of the element, P-type and N-type transistors are used. Switching can also be performed by combining two types of MOSFETs in a complementary manner. Of course, it is also possible to configure it with elements other than MOSFET.

In Fig. 5, a capacitor is arranged in parallel with each liquid crystal pixel, but in this case, as mentioned earlier, both electrodes of the capacitor are not connected completely in parallel with the liquid crystal pixel electrode, but a common electrode is connected to the liquid crystal pixel electrode. The side potentials are set separately. This is the fifth
This is because by adopting the structure shown in the figure, the common side electrode of the capacitor can be replaced by the substrate.

At this time, the polarity and magnitude of the bias potential applied to the capacitor in accordance with the image signal applied to the liquid crystal pixel are different from the bias potential of the liquid crystal pixel electrode, but the effective electrical characteristics related to display are shown in Figure 1. This has the same effect as the case shown in .

Regarding the liquid crystal used in the display device according to the present invention, only the TN type liquid crystal has been described, but the operating performance is basically the same for the DSM, GH, and other liquid crystals mentioned at the beginning.

[Effects of the Invention] With the above configuration, the following effects can be obtained.

In other words, (a) Conventional liquid crystal display devices convert the image signal into an alternating current signal and drive it with an alternating voltage in order to extend the life of the liquid crystal. Since the polarity is reversed, the polarity of one screen of the liquid crystal display changes at once at a certain period, and the flickering of the display screen was very noticeable. If you shorten the effective AC inversion period by changing the inversion period on a pixel-by-pixel or scanning-line basis, the polarity of the signal applied to the liquid crystal will partially change, which will prevent flickering on the screen. It almost disappears.

(b) If the positive and negative polarities of the image signals applied to the display pixels are switched pixel by pixel or by scanning line, and the AC cycle of each pixel is set by one frame, the linearity of the amplifier or each pixel The linearity of the switching characteristics of the transistor provided in the unit is determined by the operating voltage width (from 9-11 to 9
-10 range), the nonlinearity can be effectively ignored from the viewpoint of display effects.

(c) Since the phase of the data signal applied to the liquid crystal is inverted and driven, the life of the liquid crystal is extended.

[Brief explanation of the drawing]

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 one embodiment of the present invention. FIG. 5 is an example of a display circuit diagram according to the present invention. FIG. 6 is an example of a partial cross-sectional view of a display device. Figure 7 shows the 6th
Top view of the figure. FIG. 8 is a signal waveform diagram in an embodiment of the present invention. FIG. 9 is a signal waveform diagram for explaining an embodiment of the present invention. Figures 10 and 11 are
FIG. 2 is a circuit diagram of an embodiment of the present invention. 5-12...Matrix display section, 7-1...Silicon substrate, 8-8a...Data line for driving matrix display, 8-5a...Clock line for driving matrix display, 8-5b...Capacitor electrode, 3 −
1,9-1,9-2...image signal, 10-2...
Image signal amplifier, 10-3, 10-4...differential amplifier.

Claims (1)

[Claims] 1. A liquid crystal sealed between a pair of substrates, a pixel electrode arranged in a matrix on the substrate, a switching element connected to the pixel electrode, and a scanning signal supplied to the switching element. The scanning line formed by
In a liquid crystal display device having a data signal line that supplies a data signal to the pixel electrode via the switching element, the phase of the data signal is inverted in units of pixels or in units of scanning lines, and A liquid crystal display device characterized in that the voltage is inverted and applied to the data signal line every scanning period.