JPH0241039B2 - - Google Patents

Description

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

[Prior Art] Various display devices have been devised or put into practical use by making use of the electro-optic effect of liquid crystals. These are due to the combination of alignment characteristics, dielectric anisotropy, optical anisotropy, etc. of liquid crystal molecules, and are commonly known as DSM.
There are names such as TN, GH, etc. A common feature of these liquid crystals is that they have a light-receiving display effect,
Examples include that the resistance is relatively high, and that the threshold value in display characteristics is 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 materials and are put into practical use as display materials. driving conditions are becoming more complex and difficult. Furthermore, the short lifespan compared to DC drive is another factor that makes the drive conditions difficult.

FIG. 1 shows an example of the display characteristics of a display using a TN-type nematic liquid crystal. Figure 1 is from 1976
DISPLA conf. This is a quotation from Fig. 5 on page 51. In the figure, the effective value Vs of the voltage applied to the picture element in the selected state (display state), the non-selected state (non-display state)
The effective value of the voltage applied to the picture element at is expressed as V _NS . When driving a matrix address method in which a plurality of liquid crystal picture elements are time-divided and dynamically scanned and driven, formulas (4) and (5) on page 51 of the above-mentioned document, where the number of scanning picture elements is N and the applied display voltage is Vo, are used. Than, It is expressed as Obviously, as N increases in the above equation, V _NS approaches. In FIG. 1, the difference between V _S and V _NS and the corresponding relative amount of transmitted light decreases, resulting in a large display contrast between the selected state and the non-selected state.

As a specific example, if N is 50, then V _S /V _NS 1.15 From Figure 1, if V _NS = V _Th 3.0Vrms, V _{S 1.15} 3
It's only about 1/10th of that. That is, in this type of driving method, as the value of N increases, it becomes difficult to obtain a large contrast of the displayed image. Further, if the ratio of the applied voltage at the time of selection and the applied voltage at the expected time is b, then from equation (3) on page 50 of the literature, b = √ + 1, and there are drawbacks such as the fact that as N increases, the operating voltage must be increased. Furthermore, although detailed description is omitted, the viewing angle also becomes narrower. (Reference 1976
Proceeding of the SID Vol.17／1First
Quarter P34) The object of the present invention is to overcome these drawbacks of liquid crystal displays and to effectively display images including halftones by liquid crystal. Furthermore, in order to achieve the above-mentioned object, a long lifespan is ensured without impairing the performance of the liquid crystal, and at the same time, the circuit is simplified.

Prior to describing embodiments of the present invention, conventional embodiments related to the present invention will be described.

FIG. 2 is a circuit diagram around a display panel showing a conventional embodiment related to the present invention.
Examples can be found in SID77DIGEST P64-65.
2-1 in the figure is an image signal input such as a TV video signal,
2-2 is a synchronous separation signal, and 2-3 is a circuit for generating a control signal such as a timing clock from the synchronous 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 picture element. 2-4 is 2-1
A drain drive circuit converts the serial image signal inputted from the input into parallel and supplies it to the drain side of the transistor connected in series to each picture element. 2-5 is a gate drive circuit that uses the 2-3 output clock to sequentially control the gates of transistors connected to each picture element on and off line by line to read image signals into the picture elements, and has a shift register structure. go. Output side drain 2 of transistor placed in each matrix section
-6 is coupled to each picture element electrode of the liquid crystal display. As shown in the figure, a capacitor is arranged in parallel with the liquid crystal picture element.

As described in the document SID78DIGEST P96-97, in the conventional matrix display using the circuit shown in FIG. 2, the liquid crystal was driven by direct current.

In Figure 2, among the electrodes that sandwich the liquid crystal in the liquid crystal matrix display section, the electrodes facing each picture element electrode are common electrodes over the entire display surface, and the potential is GND.
It is taken as a level and matches the common side electrode potential of the substrate of the MOS transistor and the capacitor arranged in parallel. For this reason, it has become necessary to take measures such as doping liquid crystal materials with redox agents in order to maintain a long DC life.

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. 3-1 in Figure 3 is 2-1
It corresponds to the image signal input. 3-2 is a low-pass filter, 3-3 is an amplifier, 3-4 is an A/D converter, 3-5 is a data encoder, and 3-8 is a serial-parallel conversion shift register 3-8. The image signal input 3-1 passes through a low-pass filter 3-2 and an amplifier 3-3, is converted into an image signal of a band corresponding to the display performance of the relevant display panel, and is then sent to an A/D converter 3.
The digital code is converted by -4. The serial/parallel conversion shift register 3-8 outputs the converted image digital image data in parallel to each data line of the matrix. The parallel output data is input to an A/D converter 3-4 provided for each data line and restored to an analog image signal. Finally, the gain of the D/A converter output signal is controlled by a gain control circuit 3-9 so that the (voltage-contrast) correlation characteristic of the liquid crystal matches the contrast of the image signal. Furthermore, the D/A output is a buffer amplifier 3-1.
2 is input. 3-12, an offset bias level adjustment circuit 3-10 adjusts the reference level of the image signal so that it corresponds to the vicinity of the threshold value of the liquid crystal, and outputs the image signal to the data line. 3-6 is a synchronization separation circuit, 3-7 is a timing signal generation circuit, 3-1
3 is a circuit for controlling the clock line of the matrix display section, and corresponds to 2-5. 3-16 is a display matrix section whose configuration is the same as 2-7 in FIG. 2, so its illustration is omitted. In the circuit example shown in FIG. 3, the liquid crystal is driven by direct current as in FIG. 2.
In addition, in FIG. 3, a gain control circuit 3-9 and an offset bias level control circuit 3-10 are provided for the image signal supplied to the data line of the matrix display section to adapt the signal level to the characteristics of the liquid crystal display. is made possible. The method of control in this case is to provide a D/A converter for adjusting the gain and a buffer amplifier for adjusting the offset for each data line, and to adjust each using the same control signal line. As is clear from the figure, the number of D/A converters and buffer amplifiers equal to the number of data lines is required, making the data line driving circuit extremely complicated. Furthermore, D/
A or the amplifiers constituting the buffer must have the same gain and other amplification characteristics. It is nearly impossible to match the characteristics of each amplifier without adjustment in terms of element manufacturing, and therefore adjustment must be made for each amplifier in advance. Needless to say, in FIG. 3, as in FIG. 2, the liquid crystal is driven by direct current, so deterioration of the display becomes a problem.

The present invention improves the conventional drawbacks and provides an image display device that takes full advantage of the display performance of liquid crystal. According to the present invention, the document Display Conf.
Compared to the so-called dynamic drive system of the 1976 P51, even if the number of matrix scanning lines is greatly increased, the display contrast performance of the liquid crystal will not be impaired in the slightest, nor will the applied voltage required for display drive increase. Furthermore, in contrast to the embodiments shown in FIGS. 2 and 3, 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. It also disappears. The circuit embodying the present invention is greatly simplified compared to the one shown in FIG. 3, and the contrast, brightness, etc. can be adjusted very easily, making it highly practical and contributing to the variations shown in FIG. does not have

Hereinafter, the present invention will be explained by specific examples using the drawings. Of course, the present invention can be implemented using other circuit systems, but these also naturally belong to the present invention.

FIG. 4 is a block diagram showing an overall view of a television receiver configured according to the present invention. In the figure, 4-1 is a tuner section that selects the frequency of a predetermined channel from received radio waves input from an antenna. 4-2 is a circuit from the intermediate frequency amplifier to video detection; 4-4 is a circuit for audio intermediate frequency, output, etc.; and 4-5 is a circuit for separating horizontal, vertical, etc. synchronization signals from the video signal. Reference numeral 4-3 denotes a video amplifying circuit block according to the present invention, which outputs a liquid crystal display image signal to a subsequent stage matrix display section data signal latch circuit 4-8. 4-9 is a data line drive circuit. 4-6 and 4-7 receive the output of the synchronizing signal separation circuit 4-5, and provide data latch signals to 4-8 and timing signals for driving clock lines (horizontal lines) of the matrix display section to 4-10, respectively. 4-1
Reference numeral 1 denotes a power supply, which supplies a common electrode voltage to be described later to the common electrode 4-13 (dotted chain line). 4-12
represents a matrix type liquid crystal display panel;
It will look like the figure. 5-1 is a gate drive circuit, 5-2
is a drain drive circuit, which is connected to a transistor for selectively supplying an image signal to a picture element electrode for each picture element 5-3 of the matrix display section. All the electrodes of the picture elements to which the outputs of each transistor are connected are located on one of a pair of flat plates that sandwich the liquid crystal, and each electrode is electrically separated and independent on the flat plate on which the electrode is placed. are doing. 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 potential of one side electrode of the capacitor provided for each picture element are common.
Although it matches the GND potential, the liquid crystal display section common electrode potential 5-4 is not the GND potential. An example of configuring a transistor and a capacitor for each picture element is shown in the sixth section.
As shown in Fig. 7. FIG. 6 is a cross-sectional view of the flat plate on the side where the electrodes are separated for each picture element and arranged in a matrix. In the figure, 6-1 is a silicon substrate. 6-2
is a diffusion layer of the opposite conductivity type to 6-1, and 6-3
is a diffusion layer of the same conductivity type as 6-1, and functions as a stopper and a capacitor electrode. Further, 6-4 is a gate oxide film, and its film thickness is approximately 400 to 2000 Å. 6-5 is polysilicon; 6-5
a is the gate electrode of the MOS transistor, 6-5b
is the electrode of the capacitor. 6-6 is a field oxide film, 6-7 is an insulating film, and 6-8 is an aluminum electrode. In Figure 6, the transistors that switch each picture element are silicon gate MOS transistors.
The electrode of the capacitor, which is composed of a transistor and arranged in parallel with each picture element of the liquid crystal, is made of the entire silicon substrate and polysilicon 6-5b. In this case, the silicon substrate is held at GND, and as shown in FIG. 5, 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, 7-2 to 7-8 correspond to 6-2 to 6-8, respectively. Further, in FIG. 7, the drain electrode 6-8b in FIG. 6 is omitted so as not to complicate the diagram. In FIG. 7, one picture element is an area indicated by a two-dot chain line. Therefore, the so-called picture element electrodes that apply voltage to the liquid crystal are insulated from the transistors or the signal lines 7-5a, 7-8a, etc. running vertically and horizontally, and are located approximately at the upper side of the pattern in FIG. It is supposed to be arranged as follows.

Here, the relationship between the signal waveform and potential in FIG. 2 is shown in FIG. Reference numeral 8-1 is an image signal supplied to the terminal 2-1, and reference numeral 8-2 is a synchronization 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. 8-3 represents the black level of the image signal, and 8-4 represents the white level, which correspond to the threshold voltage and saturation voltage of the liquid crystal, respectively. Voltage 0
corresponds to GND in FIG. 2 and is the substrate and common electrode potential. In contrast to such conventional DC voltage driving, in the present invention, the potential level of the signal is set as shown in FIG. In the figure, 9-1 and 9-2 are both image signals. The one-dot chain line shown at 9-6 indicates the common electrode potential of the liquid crystal matrix display body, and the image signal applied to each matrix picture element electrode of the liquid crystal repeats inversion at a certain period based on the potential level of 9-6. .

For example, in the case of an image signal for television broadcasting, one screen of video signal is one frame, one frame is further divided into two fields, and interlaced scanning of the screen is performed for each field. In FIG. 9, for example, 9-1 corresponds to one horizontal scanning line of one frame of image signals including the first and second fields. 9-2 is an image signal corresponding to the same display part of the image signal for one frame following the signal for one frame, and 9-1 and 9-2 are arranged around the dashed line 9-6. , are symmetrical for the same image input. Reference numeral 9-3 is an image sampling synchronization signal, and the period shown at 9-4 corresponds to the period during which one picture element 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 in Figure 9, 0 or 9
-11 is, for example, the potential of the display substrate 6-1, and 9-
10 is the display body circuit voltage corresponding to 9-11. In this case, the switch transistors arranged for each picture element in FIG. 5 can be constructed of, for example, a P-channel type enhancement MOSFET. 9-1
When the potential of the substrate 6-1 is set to 0, the switch transistor may be formed of an N-type MOS.

The amplitude of the image signal 9-1 is from the broken line 9-7 to the broken line 9.
It is between -8. 9-7 is the black of the image signal, 9-8
corresponds to white. When using a liquid crystal with the characteristics shown in Figure 1, 9-7 is in the range from V _NS to V _th ,
9-8 is taken near V _S. Figure 1 0Vrms is 9
Corresponds to -6. 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 picture element electrode is to extend the life of the display by AC driving the liquid crystal. When converting the signal into an alternating current signal to drive the liquid crystal, 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 characteristics. The following methods can be considered as methods for reducing flickering or making it effectively negligible. That is, it is sufficient to invert the phase at a cycle faster than the eye can respond.

(1) Invert the phase at the frame period and make the frame period approximately 30 Hz or more.

(2) Invert the phase in units of picture elements or in units of scanning lines within one frame period to increase the effective inversion period.

Furthermore, various methods can be considered depending on the above application. When displaying TV images in a matrix,
There are cases where it is attempted to realize a matrix with a smaller number of picture elements than the effective number of picture elements (or resolution) of a television video signal. At this time, for example, if a liquid crystal image is composed of a matrix for one field (1/2 frame) of a TV video signal, the phases of the first and second field signals are inverted, and the same pixel contains two fields. It becomes possible to display signals at a frequency of 60Hz. Although the resolution in terms of image quality is reduced, flickering due to the difference in original image signals is canceled out by the response performance of the liquid crystal itself, and the average pixels of the first and second fields are displayed.

Furthermore, in method (2), the polarity direction is switched on a pixel-by-pixel basis so that the pixel display signal within one frame is both a positive polarity signal and a negative polarity signal, and the alternating current cycle of each pixel is If it is taken as one frame unit, the linearity of the amplifier or the linearity of the switching characteristics of the transistor provided in each picture element is the operating voltage width (9-
11 to 9-10), the nonlinearity can be effectively ignored from the viewpoint of the display effect.

FIG. 10 shows one embodiment of a circuit that realizes the above description. 10-2, 10-3, 10-4 are image signal amplifiers, 10-5, 10-7, 10-8 are fifth
This corresponds to block 5-2 in the figure. 10-6 is a changeover switch circuit, and the output of 10-6 is shown in Fig. 5-5-
8 image signal inputs.

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. 10-2 may have an amplification factor characteristic (FIG. 1) that matches the slope of the voltage-contrast characteristic of the liquid crystal.
10-3 and 10-4 are differential amplifiers, and such differential amplifiers have 2 amplifiers as shown in Figure a on page 197 of the Electronic Device Dictionary (Radio Gijutsu Co., Ltd.) published on March 20, 1976. Connect two transistors symmetrically and put two input signals at their bases,
There is a differential amplifier that extracts an output signal proportional to the difference between the collectors. The same signal, ie, the output of 10-2, is coupled to the positive input terminal of 10-3 and the negative input terminal of 10-4. 10-3 negative polarity input terminal and 10-4 positive polarity input terminal are connected to 10
-10 has a terminal. 10-3 and 10-4
are set in advance so that almost the same characteristics as the amplifier can be obtained. The terminal 10-10 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, 10-3, 10-
Each output signal of 4 corresponds to FIG. 9, 9-1 and 9-2, respectively. At this time, 10-9 is 9-8 and 9-
7, that is, the amplitude, in other words, the contrast of the displayed image is adjusted. 10-10 is 9-7 and 9-
Adjust the difference with 6. The gain of 10-3 (10-4) may be set appropriately. Reference numeral 10-6 is a switch circuit, which switches and selectively outputs the respective output signals of 10-3 and 10-4 when supplying an AC drive signal to the liquid crystal as described above.

Bipolar or MOS as a switch element
Although various methods such as transistors such as
It is desirable that 0-6 be made with a similar structure, and an example of this is a structure such as a so-called transmission gate.
The same applies to the subsequent circuit 10-7. Reference numeral 10-5 is a circuit that sequentially generates signals for controlling the switch element 10-7, for example from left to right, and is constituted by a shift register. 10-8 is a circuit for storing and holding the image sampling signal sampled by the switch and distributing it to each picture element electrode. 10-8 and subsequent parts correspond to the liquid crystal matrix display section including the driving section, that is, FIG. 5. FIG. 11 shows yet another embodiment. Figure 11 shows 10-2, 10-3 in Figure 10,
This is a modification of the amplifier 10-4. 1
Image signals 1-1 and 11-2 have substantially the same amplitude and opposite polarity.

The amplifier circuit on the upper side of the figure (transistor 11-3,
11-5) and the lower amplifier circuit (transistor 11
-13, 11-14) are designed to have the same circuit configuration and amplification characteristics. 11-4,1
Reference numeral 1-8 denotes a variable resistor for gain control of the amplification system, which adjusts the contrast of the liquid crystal display image. 11-
4, 11-8 are moved by 11-10 shown in broken lines and can be manually adjusted from the outside. 11-7,1
1-9 is a variable resistor that controls the output potential level, that is, changes the brightness of the liquid crystal image display, and the broken line 11-9
11, and can be manually adjusted from the outside. However, the potential levels of 11-7 and 11-9 operate in opposite directions, and their respective outputs are as shown in FIG. 9, 9-1 and 9.
-2, symmetry is maintained around level 9-6. 11-12 is an image signal polarity changeover switch circuit corresponding to FIG. 10 10-6. The present invention can be realized by a configuration other than the circuit mentioned as an example. Furthermore, contrast and brightness adjustments can be made by
It is naturally possible to perform manual control as described above, or to automatically control the gain or bias level by automatically detecting light by making the display degree of the liquid crystal correspond to the reference pattern display signal level.

In the description of the embodiment 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 constructed within the silicon substrate. Therefore, it can be realized by configuring each element on a glass substrate or by other methods. In Fig. 5, the transistor provided to switch each picture element is one MOS transistor, but two types, P-type and N-type, are used to improve the linearity, response speed, operating voltage, etc. of the element. Switching can also be performed by combining two MOSFETs in a complementary manner. Of course
It is also possible to configure it with elements other than MOSFETs.

In Figure 5, a capacitor is placed in parallel with each liquid crystal picture element, but in this case, as mentioned earlier, both electrodes of the capacitor are not connected completely in parallel with the liquid crystal picture element electrodes, but on the common electrode side. The potentials are set separately for each. This is because by adopting the structure shown in FIG. 6, the common 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 picture element are different from the bias potential of the liquid crystal picture element electrode, but the effective electrical characteristics related to display are shown in Figure 2. This has the same effect as the case shown in .

〔effect〕

As described above, the present invention provides an image display device in which a liquid crystal is sealed within a pair of substrates, and a plurality of pixel electrodes are arranged in a matrix on the substrates, and includes a preamplifying means for amplifying an input video signal; positive phase amplification means into which a video signal from the preamplification means is input; a positive phase amplification means which receives the video signal from the preamplification means and inverts and amplifies the video signal, and has the same gain as the positive phase amplification means; a negative phase amplification means having a characteristic, a DC bias means for applying the same DC bias to the positive phase amplification means and the negative phase amplification means, an output video signal from the positive phase amplification means or an output video signal from the negative phase video amplification means. Since the amplifier includes a switching means for selectively switching the output video signal at regular intervals, and a sampling means for sampling the output video signal from the switching means and supplying it to the pixel electrode, the gain characteristic of the amplifier is It is possible to obtain an ideal symmetrical AC video signal, and
An ideal symmetrical DC level can be achieved by the DC bias described above. Therefore, an ideal positive/negative symmetrical AC inversion signal can be obtained with a simple circuit configuration.

[Brief explanation of drawings]

Figure 1...Example of voltage-display characteristics of TN type liquid crystal, 2nd
FIG. 3: Another conventional display circuit example; FIG. 4: A block diagram showing an embodiment of the present invention; FIG. 5: An example of a display circuit diagram according to the present invention. Figure 6...Example of partial sectional view of display device, Figure 7...6
FIG. 8 shows a conventional image signal and sample clock, FIG. 9 shows a signal waveform diagram in an embodiment of the present invention, and FIGS. 10 and 11 show an example of an implementation circuit of the present invention. 4-12...Matrix display section, 6-1...Silicon substrate, 7-8a...Data line for driving matrix display, 7-5a...Clock line for driving matrix display, 7-5b...Capacitor electrode, 8 −
1,9-1,9-2...image signal, 10-2...
Image signal amplification bridge, 10-3, 10-4...differential amplifier.

Claims (1)

[Claims] 1. An image display device in which a liquid crystal is sealed within a pair of substrates, and a plurality of pixel electrodes are arranged in a matrix on the substrates, comprising: a first differential amplifying means; a second differential amplifying means; dynamic amplification means; preamplification means for amplifying and inputting an input video signal to the positive input terminal of the first differential amplification means and the negative input terminal of the second differential amplification means; DC bias means configured to apply a variable DC bias to the negative input terminal of the first differential amplification means and the positive input terminal of the second differential amplification means; switching means for selectively switching the output video signal or the output video signal from the second differential amplification means at regular intervals; sampling means for sampling the output video signal from the switching means and supplying it to the pixel electrode; An image display device comprising: