JP2823049B2 - 2D display - Google Patents

Description

The present invention relates to a two-dimensional display device, and more specifically, to a two-dimensional display device.
The present invention relates to a two-dimensional display device using a two-dimensional display element having a signal storage function. [Prior Art] Due to their features such as small size and low power consumption, liquid crystal elements have come to be used as display devices for video signals. As a TV image display device using a liquid crystal element, a matrix type display as shown in FIG. 5 is adopted because of a two-dimensional display.
There are a simple matrix address system and an active matrix address system. The matrix type display is shown in FIG.
A plurality of X-axis electrodes (scanning electrodes) and Y-axis electrodes (display electrodes) orthogonal to each other are provided on each of two substrates sandwiching the liquid crystal, and an image signal is applied to the Y-axis electrodes while sequentially applying a scanning voltage to the X-axis electrodes. An image is displayed by applying a voltage. In a simple matrix addressing scheme, simply the X and Y axes, for example,
A voltage is applied to the X ₂ axis and the Y ₂ axis to select a pixel (X ₂ , Y ₂ ). However, in this method, the intersection (X ₂ , Y ₂ ) in FIG.
Pixels in the shaded area other than (half-selected pixels)
A voltage of 2 is applied, which causes cross talk and deteriorates display characteristics. What was devised to improve this cross talk,
An active matrix addressing method, in which, as shown in FIG. 6, a capacitor is connected to an active element such as a transistor or FET or a switching element for each pixel, and the target pixel is continuously driven by the accumulated charge of the capacitor. To increase the contrast. FIG. 7 is a block diagram of a conventional system for displaying a reproduced video signal of a VTR as an image using the liquid crystal display element. In FIG. 7, the input signal to the tuner 10 is changed by the changeover switch 12 between the carrier television signal from the antenna 14 and the output signal of the RF converter 82 for converting the reproduced video signal of the VTR 80 into the form of the carrier television signal. Is switched between. The output of the tuner 10 is input to a video signal detection circuit 18 via a known intermediate frequency amplification and AGC circuit 16, and among the output signals of the circuit 18, an audio signal is voiced by an audio circuit 20 and a speaker 22. . The video signal of the output of the video signal detection circuit 18 is amplified by a video signal amplifier 24, converted into a digital signal by an A / D converter 26, and sequentially converted to a line memory 28 for each scanning line.
Is stored. Further, the synchronization separation circuit 30 separates the horizontal synchronization signal and the vertical synchronization signal from the output of the video signal detection circuit 18 and supplies them to the horizontal oscillation circuit 32 and the vertical oscillation circuit 34, respectively. The timing circuit 36 controls the A / D conversion in the A / D converter 26, the writing / reading to / from the line memory 28, and the clock for controlling the shift register 38, respectively, according to the outputs of the oscillation circuits 32 and 34. Form and output signals 36a, 36b, 36c. The shift register 38 applies a timing pulse to the scan drive circuit 40 so that the scan drive circuit 40 sequentially drives the scan electrodes of the liquid crystal display 42. In addition, line
The video information data read from the memory 28 is converted by the modulation drive circuit 44 into a signal suitable for driving the liquid crystal display 42, and drives the liquid crystal of the corresponding pixel. The VTR 80 receives the output signal of the video signal detection circuit 18 at a recording processing circuit 84, which converts the signal into a signal form suitable for recording, sends the signal to an electromagnetic conversion circuit 86, and records the signal on a magnetic tape. Let it. At the time of reproduction, the electromagnetic conversion circuit 86 sends the reproduced video signal reproduced from the magnetic tape to the reproduction processing circuit 88, and the reproduction processing circuit 88 returns the reproduced signal to the original signal form and sends it to the RF converter 82. Servo circuit 90
Is a circuit for controlling the motor for the transfer of the magnetic tape, the rotation of the head and the like in the electromagnetic conversion in the electromagnetic conversion circuit 86. The main control circuit 92, including the servo circuit 90,
Is a circuit for controlling the whole of the circuit. In recent years, even when playing back video from the VTR 80, special playback modes such as still image playback and high-speed search have been adopted. In the still image reproduction mode, the video signal of the target screen is stored in the field memory 94, and the stored signal is repeatedly sent to the RF converter 82, so that the moving image can be observed in a still state. In the high-speed search, the tape is run at a speed several times faster than usual, and the reproducing head traces across a plurality of video signal tracks, and the large and small portions of the reproduced output appear alternately within one field period. The larger part of the data is sequentially written to the field memory 94, and thereafter the RF converter 82
To send to. According to the high-speed search using such a field memory, a reproduced signal with less noise can be obtained. [Problems to be Solved by the Invention] Special reproduction of a recorded image of a VTR requires a large-scale field memory that operates at high speed, and the VTR must be expensive. Was. SUMMARY OF THE INVENTION It is an object of the present invention to provide a two-dimensional display device which can realize a special effect in a pseudo manner by using a signal storage characteristic of a display element without using another special effect memory. [Means for Solving the Problems] A two-dimensional display device according to the present invention has a plurality of scanning electrodes and a plurality of signal electrodes arranged in an intersecting manner, and has a signal storage function by maintaining the orientation of liquid crystal molecules. A predetermined display signal is applied to the two-dimensional display element and the plurality of intersecting scanning electrodes and the plurality of signal electrodes in accordance with an input video signal to be input, so that a display signal is written to a pixel at the intersecting position. Driving means for performing display, a detecting means for detecting a signal level of the input video signal, and a display of pixels by the driving means in a portion where the signal level is lower than a predetermined level according to a detection result of the detecting means. Control means for prohibiting rewriting and permitting the driving means to rewrite the display of pixels in other portions. [Operation] By selectively rewriting the two-dimensional display element having the signal storage function in connection with the special reproduction function of the reproduction apparatus, the display element itself can be used as a special effect memory. That is, at the time of high-speed search in the reproducing apparatus, since the head performs reproduction diagonally across the track, the signal level periodically decreases. Therefore, if this is displayed as it is, a noise bar will be displayed. However, in the first invention of the present application, the display signal is not rewritten in the portion where the signal level of the reproduced signal is reduced at the time of high-speed search. Not done. And in this part,
Since the previous image is still displayed, an image without a sense of incongruity is displayed on the screen. Further, according to the second invention of the present application, when performing the still image reproduction, only the video signal for one screen of the video signals that are continuously reproduced is made valid and supplied to the display element. The still image is displayed without change by the signal storage function of the display element. That is, the still image reproducing function can be easily realized. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a circuit for implementing the control method of the present invention. Members corresponding to those in FIG. 7 are denoted by the same reference numerals. The liquid crystal display 46 is a matrix type display having a memory (signal storage) function for holding a previous signal state unless a next signal input or reset scan is performed. Preferably, the liquid crystal display 46 is a chiral smectic phase (CS phase) described later. ) Liquid crystal. Reference numeral 100 denotes an envelope detection circuit that detects the envelope of the reproduction signal in the reproduction processing circuit 88, and performs an operation of detecting a small portion of the reproduction output during the high-speed search described above, and generates a detection signal indicating a corresponding area on the screen. The signal is sent to the mute pulse forming circuit 102. This mute pulse forming circuit 102 is used to output a still image.
In accordance with an instruction signal from the main control circuit 124, a mute pulse that enables only the video signal for one field is formed. The mute circuit 104 mutes the scan drive pulse applied by the scan drive circuit 40 to the display 46 according to the mute pulse from the mute pulse forming circuit 102.
As a result, the display 46 continues to display the contents displayed on the previous screen without resetting. That is, if only the necessary reproduced video signal portion is reset or cleared for writing, and the memory function of the liquid crystal itself is used, it is possible to obtain an output screen similar to high-speed search or still image reproduction in a VTR. An example of a liquid crystal having a memory function is a chiral liquid crystal.
There is a ferroelectric liquid crystal device having a smectic phase (CS phase), which is described in U.S. Pat. No. 4,367,924 and JP-A-59-193427. In addition to the memory function, the CS type liquid crystal with ferroelectricity is capable of high-speed optical switching, and is capable of displaying images without deterioration in image quality even if the number of time divisions increases. Because it has
It has been used in liquid crystal color televisions intended for multi-pixel, high-definition display without flicker.
In a normal TN type liquid crystal, it is difficult to increase the number of scanning lines because the threshold characteristic is not steep, and it is not suitable for a large screen or a high resolution display. The CS phase ferroelectric liquid crystal is characterized in that it has an asymmetric carbon atom in the molecule and has a dipole moment in a direction perpendicular to the long axis of the molecule. This molecular arrangement has a helical structure as shown in FIG. 2, and the direction of spontaneous polarization is rotating along the helical axis, so that the dipole moment is totally canceled. However, when the thickness of the liquid crystal cell is made smaller than the helical pitch, the helix is released and the spontaneous polarization is aligned upward (FIG. 3 (a)) or downward (FIG. 3 (b)) with respect to the paper surface. When a DC voltage is applied to the liquid crystal cell in such a state, the direction of spontaneous polarization can be aligned in one direction over the entire liquid crystal cell. The states shown in FIGS. 3A and 3B are maintained as they are even when the voltage is turned off, and the direction of the spontaneous polarization is reversed by applying a voltage of the opposite polarity. Since spontaneous polarization directly acts on an electric field, switching can be performed in an order of magnitude shorter than a nematic liquid crystal having no spontaneous polarization. By the way, while the switching time of a normal nematic liquid crystal cell is several tens of milliseconds,
With a chiral smectic liquid crystal, 0.5 μsec is possible, and high-speed operation about four orders of magnitude faster is possible. A driving method of a matrix type display using such a ferroelectric liquid crystal will be briefly described. FIG. 4A (a) is a schematic view of a cell 110 having a matrix electrode structure in which a ferroelectric liquid crystal compound is sandwiched. 1
Reference numeral 12 denotes a scanning electrode group, and 113 denotes a signal electrode group. 4A
FIG. 2B shows an electric signal applied to the selected scanning electrode 112 (s), and FIG. 2C shows an electric signal applied to the unselected scanning electrode 112 (n). (D)
Shows an electric signal applied to the selected (information-bearing) signal electrode 113 (s), and FIG. 3E shows an electric signal applied to the unselected (information-less) signal electrode 113 (n). Indicates a signal. The horizontal axis of (b), (c), (d), and (e) of FIG. 4A represents time, and the vertical axis represents voltage. When displaying a moving image, the scanning electrodes 112 are sequentially and periodically selected. The threshold voltage for providing the first stable state of the liquid crystal cell having bistability is V _th1 , the threshold value for providing the second stable state is −V _th2 , and the voltage value V is V <V _th1 < 2V and-
It is assumed that both V> −V _th2 > −2V are satisfied. Voltage applied to the selected scanning electrodes 112 (s), the first 4A 2V in the period t ₁ as shown in Figure (b), an alternating voltage such that -V during the period t _2. The voltage applied to the unselected scanning electrode 112 (n) is the fourth
A: It is 0 (earth) as shown in FIG. On the other hand, the voltage applied to the selected signal electrodes 113 (s) may, Figure 4A 0 in the period t ₁ as shown in (d), a V in the period t _2, applied to the non-selected signal electrodes 113 (n) The voltage is 0 (earth) as shown in FIG. 4A (e). FIG. 4B shows a waveform of a voltage applied to each pixel when such a voltage is applied to the scanning electrode 112 and the signal electrode 113. 4A, (a), (b), (c), and (d) correspond to the pixels A, B, C, and D in FIG. 4A (a), respectively. That is, as can be seen from Figure 4B, all of the pixels of the selected scan line, the voltage exceeding the threshold voltage -V _th2 in the first period t ₁ -2 V
Is applied, first, it is once set to the second stable state. Then, in the second period t _2, the pixel A corresponding to the information signal Yes, since the voltage of 2V exceeding the threshold voltage V _th1 is applied, shifts to the first stable state. However pixels B corresponding to the same scan line, the information-free, since the applied voltage in the second period t ₂ is V, remains stayed in the second stable state. On the other hand, pixels on non-selected scanning lines, such as pixels C and D,
The applied voltage is V or 0, neither of which exceeds the threshold.
Therefore, the liquid crystal molecules in each of the pixels C and D maintain the alignment of the signal state at the time of the previous scan, that is, store the signal of the previous screen. Therefore, even if the number of scanning electrodes increases, the substantial duty ratio does not change, and no reduction in contrast or crosstalk occurs. The value of the voltage V and the value of the signal writing period T (t ₁ + t ₂ ) to each pixel depend on the liquid crystal material used and the thickness of the cell, but usually 3 volts to 70 volts, 0.1 μsec.
The range is 2 μsec. When a liquid crystal display is used in color, a color filter layer or a color polarizer is arranged in a mosaic pattern for each pixel, and the transmittance of the three primary colors is individually controlled. 3, and the color display ability also decreases. High-speed driving is possible with ferroelectric liquid crystals.
The size of the display screen can be increased, and higher-definition images can be displayed compared to conventional TN liquid crystals. In the above description, the VTR is used as the input video signal to the display element.
However, the present invention can be similarly applied to other image recording / reproducing apparatuses, such as optical discs, compact discs, and fields of displaying image signals in computers. [Effects of the Invention] As can be easily understood from the above description, according to the present invention, a video signal can be displayed on a screen as intended without preparing a high-speed large-scale field memory or the like. And no noise is added. Further, image display can be further speeded up.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a circuit for implementing a method according to the present invention. FIG. 2 is a view showing a molecular arrangement of a ferroelectric liquid crystal having a chiral smectic phase, FIG. 3 is a view showing an arrangement of liquid crystal molecules when the thickness of the liquid crystal in FIG. 2 is reduced, and FIG. 4A. 4B are explanatory diagrams of a driving method and a driving state when the ferroelectric liquid crystal is matrix-driven, FIG. 5 is a simplified explanatory diagram of the outer surface of a general liquid crystal matrix display, and FIG. FIG. 7 is an explanatory diagram of a matrix drive system. FIG. 7 is a block diagram of a conventional image display circuit using a liquid crystal matrix type display. 10 Tuner, 12 Changeover switch, 14 Antenna, 16 Intermediate frequency amplification and AGC circuit, 18 Video detection circuit, 20 Audio circuit, 22 Speaker, 24
... video amplifier, 26 ... A / D converter, 28 ... line memory, 30 ... sync separation circuit, 32 ... horizontal oscillation circuit, 34 ...
Vertical oscillation circuit, 36 timing circuit, 38 shift
Register, 40: Scan drive circuit, 42, 46: Liquid crystal display, 44: Modulation drive circuit, 80: VTR device, 82: R
F converter, 84: Recording processing circuit, 86: Electromagnetic conversion circuit, 88: Reproduction processing circuit, 90: Servo circuit, 92: Main control circuit, 100: Envelope detection circuit, 102: Mute pulse Forming circuit, 104 Mute circuit

Continuation of front page    (72) Inventor Susumu Kozuki               770 Shimonoge, Takatsu-ku, Kawasaki-shi Canon               Tamagawa Works Co., Ltd.                (56) References JP-A-58-107782 (JP, A)                 JP-A-60-37890 (JP, A)                 JP-A-58-66477 (JP, A)                 JP-A-59-193427 (JP, A)

Claims (1)

(57) [Claims] A two-dimensional display element having a plurality of scanning electrodes and a plurality of signal electrodes arranged in an intersecting manner and having a signal storage function by maintaining the orientation of liquid crystal molecules; and the plurality of intersecting arrangements according to an input video signal inputted Driving means for applying a predetermined display signal to the scanning electrode and the plurality of signal electrodes to write a display signal to a pixel at an intersecting position to perform display, and detecting the signal level of the input video signal Means for inhibiting rewriting of pixel display by the driving means in a portion where the signal level is lower than a predetermined level, and rewriting of display of pixels by the driving means in other portions in accordance with a detection result of the detecting means. A two-dimensional display device, comprising: control means for permitting the display.