JPH0398085A - After-image canceling circuit of liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a reproduced image of good quality after an after-image is canceled even if there is variation in ambient temperature by adding a deformation difference signal which is deformed with a signal generated corresponding to temperature and outputting a difference signal which is at an interval of one frame period or one field period from an input video signal. CONSTITUTION:The difference signal of a video signal which is at the interval of one frame period or one field period of the video signal to be displayed is obtained through the loop of a subtracter 2, a memory 3, a subtracter 4 and a coefficient circuit 5. The coefficient circuit 5 generates a signal corresponding to the ambient temperature of a liquid crystal display element and a coefficient circuit 6 deforms the difference signal with the signal corresponding to the ambient temperature of the liquid crystal display element to generate the deformed difference signal. An adder 7 adds the deformed difference signal to the input video signal and outputs the resulting signal. Therefore, canceling operation for the after-image of a displayed image can be varied corresponding to variation in the transient response of liquid crystal due to temperature variation. Consequently, even when the ambient temperature varies, the reproduced image of good quality after the after-image is canceled is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an afterimage canceling circuit in a liquid crystal display device. (Prior Art) Liquid crystal display devices that display images using liquid crystal display elements have been widely used as image display devices for various electronic devices because the image display section can be constructed as a thin device. In addition, the Pji image projector, which uses a liquid crystal display element as a light valve to modulate the intensity of light from a light source using an image signal and projects it onto a screen via a projection optical system, has also come into practical use. Ta. (Problem to be solved by the invention) Now, the liquid crystal display element uses a thermo-opening liquid crystal,
For example, the alignment state of liquid crystal molecules in a nematic phase is changed by an electric field so that a display operation in a specific display mode is performed.

When the liquid crystal display mode is, for example, the twisted nematic field effect mode, the operation of the liquid crystal display element is such that the light propagation mode of the nematic liquid crystal molecules arranged in twisted nematic orientation between a pair of substrates is the so-called waveguide mode. This is done so that the conditions are satisfied. By the way, in liquid crystal display elements, due to the viscosity of the liquid crystal used therein, there is a delay in the change in orientation of liquid crystal molecules in response to changes in the electric field, so the rise time and fall time are long, that is, the transient response It is known to have poor characteristics. When displaying still images with a liquid crystal display element, the transient response characteristics of the liquid crystal described above do not pose a problem, but when displaying moving images with a liquid crystal display element, afterimages appear in the displayed image and playback problems occur. The problem is that the quality of the image deteriorates.

In particular, a situation in which the images for the right eye and the image for the left eye, which are displayed consecutively on the liquid crystal display screen on the time axis, are spatially shifted, such as in a frame-sequential 3D television image. When a fast-moving image is displayed, such as a so-called video game image, the above-mentioned problem of afterimage generation on the display screen becomes a big problem. By the way, the transient response characteristics of the liquid crystal described above change depending on the temperature of the liquid crystal, so if the effect of canceling the afterimage of the displayed image is performed regardless of the temperature, the surroundings may not be present in the displayed image. Because afterimages appear as the temperature changes and the quality of reproduced images deteriorates, a method to improve this problem was needed. (Means for Solving the Problems) The present invention provides a means for obtaining a difference signal between video signals to be displayed by a liquid crystal display device separated by one frame period or one field period, and a means for obtaining a difference signal between video signals to be displayed by a liquid crystal display device, means for generating a corresponding signal; means for changing the difference signal according to the signal corresponding to the temperature near the liquid crystal display element to obtain a deformation difference signal; and adding the deformation difference signal from the input video signal. The present invention provides an afterimage canceling circuit for a liquid crystal display device, comprising means for outputting afterimages. (Function) A difference signal between video signals to be displayed on a liquid crystal display device separated by one frame period or one field period is obtained. A deformed difference signal is generated by deforming the difference signal described above using a signal generated in response to temperature. The above-mentioned deformation difference signal is added to the input video signal to output a video signal in which afterimages are canceled regardless of changes in ambient temperature. (Example) Hereinafter, specific contents of the afterimage canceling circuit in the liquid crystal display device of the present invention will be explained in detail with reference to the accompanying drawings. 1 and 6 are block diagrams showing embodiments of the afterimage canceling circuit in the liquid crystal display device of the present invention, and FIGS. 2 and 3 show the coefficient circuits used in FIGS. 1 and 6. Examples of characteristic curves, FIGS. 4 and 5 are block diagrams showing examples of the structure of coefficient circuits, FIGS. 7 and 8 are block diagrams of a liquid crystal display device equipped with an afterimage canceling circuit, and FIG. 9 is an afterimage canceling circuit. It is a waveform diagram for explaining the principle of afterimage cancellation in the cancellation circuit.
First, the principle of afterimage cancellation performed in the afterimage cancellation circuit in the liquid crystal display device of the present invention will be explained with reference to FIG. In FIG. 9, Si is an input signal of a video signal to be displayed on a liquid crystal display device. Figure 9(a) shows that, as mentioned above, due to the viscosity of the liquid crystal used in liquid crystal display elements, changes in the orientation of liquid crystal molecules occur with a delay in response to changes in the electric field. For example, even if a step voltage input signal Si is input to the input signal Si, the display mode of the liquid crystal display element will not rise as shown by SO in FIG. 9(a) due to the transient response characteristics of the liquid crystal. (Although illustration is omitted, there is also a delay on the time axis at the falling edge.) In addition, (b) of FIG.
As shown by So in the figure, the display state of the liquid crystal display element shown in (.) in the figure is delayed by the amount of time that the input signal Si changes on the time axis due to the transient response characteristics of the liquid crystal. 9 is an explanatory diagram in the case where a correction signal Ss is added in advance to the step-like input signal Si so as to be in a substantially corrected state like So′ in FIG. 9(b), and the above-mentioned The signal Ss corresponds to So shown in (.) in FIG. 9 minus Si.

As can be seen from the explanation with reference to FIGS. 9(a) and (b) above, the display state of the liquid crystal display element changes depending on the transient response characteristics of the liquid crystal on the time axis of the incoming signal Si. A correction signal Ss is added in advance to the step-like input signal Si so that the delay with respect to the change mode is substantially corrected as shown in So' in FIG. 9(b). If this is done, there will be virtually no delay in the display on the liquid crystal display element on the time axis when the input signal changes, and no afterimage will occur in the image displayed on the liquid crystal display element. By the way, the above-described transient response characteristic of the liquid crystal is such that the viscosity of the liquid crystal changes depending on the temperature.
s must be made into an appropriate signal format depending on the ambient temperature of the liquid crystal display element. Therefore, the afterimage canceling circuit in the liquid crystal display device of the present invention generates a difference signal between video signals to be displayed by the liquid crystal display device separated by one frame period or one field period, and displays the difference signal on the liquid crystal display device. A deformation difference signal that is appropriately deformed according to the ambient temperature of the element is generated, and the deformation difference signal is added to the input video signal, so that afterimages can be effectively canceled regardless of the ambient temperature of the liquid crystal display element. A circuit for canceling afterimages in a liquid crystal display device is constructed. Figures 1 and 65! fL In the block diagram of an embodiment of the afterimage canceling circuit in the liquid crystal display device of the present invention, 1
is an input terminal for a video signal in the digital signal state; 3 is a field memory or frame memory (hereinafter also referred to as memory); 4 is a subtracter; 6 is a coefficient circuit; 7
is an adder, 8 is an output terminal, 35.36 is an input terminal for coefficient control signals, and in FIG.
is a coefficient circuit, 9 is an adder in Fig. 4, 10a, ↓o
b is a coefficient circuit. In the afterimage canceling circuit shown in FIG. 1, the video signal supplied to the input terminal 1 is supplied to the subtracters 2 and 4 as a minuend signal, and is also supplied to the adder 7. The output signal of the coefficient circuit 5 is supplied to the subtracter 2 as a subtraction signal, and the output signal of the subtracter 2 is stored in the memory 3. As memory 3, for example, FIFO
The current one field period (or one frame period) The video signal of one field period (or one frame period) earlier than the video signal of period) is read out from the memory 3 and supplied to the subtracter 4 as a subtraction signal. In the subtracter 4, the current video signal supplied from the input terminal 1 is used as the minuend signal, and the current video signal of one field period (or one frame period) read out from the memory 3 is shorter than the current video signal of one field period (or one frame period). (or one frame period) The difference signal obtained by subtracting the previous video signal is supplied to the coefficient circuits 5 and 6, and the coefficient circuit 5 is connected to the coefficient control signal input terminal 36.
A smaller coefficient {the input/output characteristics of the coefficient circuit N5 is shown in FIG. 2} set corresponding to the coefficient control signal supplied to is multiplied by , and supplied to subtractor 2 as a subtraction signal. So, subtracter 2 → memory 3 → subtracter 4 → coefficient circuit 5 →
Due to the loop operation of subtractor 2, subtracter 4 outputs
A difference signal (motion detection signal) between video signals separated by one frame period or one field period is output. The difference signal between the video signals output from the subtracter 4 that is separated by Y frame periods or one field period is supplied to a coefficient circuit 6 having input/output characteristics as illustrated in FIG. 3, for example. It will be done. The coefficient circuit 6 multiplies the difference signal output from the subtracter 4 by a coefficient set corresponding to the coefficient control signal supplied to the coefficient control signal input terminal 35 and supplies the result to the adder 7. .

The adder 7 outputs a video signal obtained by adding the above-mentioned difference signal to the input video signal to the output terminal 8. In this state, the output signal is one of the liquid crystal display elements. It is designed to be able to cancel the afterimage of the image displayed on the liquid crystal display element regardless of the ambient temperature. In the coefficient circuit 5, the coefficient control signal input terminal 36
In Figure 2, which shows an example of coefficients to be set in response to the coefficient control signal supplied to The coefficients for each case are shown for reference, and the solid lines in FIG. The plurality of coefficients described above are determined depending on the level of ambient temperature of the liquid crystal display element.

In addition, in FIG. 3, which shows an example of coefficients to be set corresponding to the coefficient control signal supplied to the input terminal 36 of the coefficient control signal in the coefficient circuit 6, the plurality of straight lines are A plurality of coefficients should be set depending on the level of the ambient temperature of the device, and the above-mentioned plurality of coefficients are respectively determined corresponding to the level of the ambient temperature of the liquid crystal display element. In addition, the coefficient control signal described above includes a temperature sensor (indicated by reference numeral 34 in FIGS. 4, 7, and 8) that is placed around the liquid crystal so as to detect the ambient temperature of the liquid crystal display element. A signal indicating temperature information emitted from a The coefficient circuit 5 (or coefficient circuit 6) can select and use one of the plurality of coefficients according to the coefficient control signal supplied to its coefficient control signal input terminal 36 (or 35). For example, a structure such as that illustrated in FIG. 4 or FIG. 5 can be used. The coefficient circuit illustrated in FIG.
7 as the upper address, and also the subtracter 4 mentioned above.
By giving the difference signal output from the temperature sensor 34 to the read-only memory 37 as a lower address, eight types of temperatures determined by the 3-bit signal generated from the temperature sensor 34 can be read as illustrated in FIG. 2 or 3. The coefficient circuit shown in FIG. The difference signals output from the data selector 38 and the subtracter 4 are multiplied by predetermined different coefficients. By doing so, eight multipliers 40, 41, 42, . use,
The data selector 38 to which the outputs of the eight multipliers 40, 41, 42, etc. described above is input selects and outputs output data corresponding to the ambient temperature of the liquid crystal display element. belongs to. In addition, Figures 2 and 3
The input/output characteristics of the coefficient circuit 6 shown in the figure are merely exemplary characteristics, and it goes without saying that coefficient circuits 5 and 6 having other input/output characteristics may be used in implementing the present invention. It is. Next, the embodiment of the afterimage canceling circuit in the liquid crystal display device of the present invention shown in FIG. 6 has a structure in which the coefficient circuit 5 in FIG. 1 is divided into a coefficient circuit 10a and a coefficient circuit 10b. Since the operation is exactly the same as that of the embodiment of the afterimage canceling circuit in the liquid crystal display device shown in the first figure, a detailed explanation of the operation will be omitted. 7 and 8 show an example of the structure of a liquid crystal display device to which the afterimage canceling circuit of the present invention is applied. First, in FIG. 7, 1l is an input terminal for a multiplexed signal of a luminance signal and a carrier color signal, 12 is an input terminal for a luminance signal, and 13 is an input terminal for a multiplexed signal of a luminance signal and a carrier color signal.
is an input terminal for the carrier color signal, ↓4 is a YC separation circuit, and 34 is a temperature sensor.The luminance signal output from the YC separation circuit 14 is supplied to the fixed contact a of the changeover switch SWI, and The carrier color signal output from the YC separation circuit 14 is supplied to the fixed contact a of the changeover switch SW2.

The fixed contact b of the changeover switch SW1 has terminal 1.
A luminance signal is supplied from the terminal 13, and a carrier color signal is supplied from the terminal 13 to the fixed contact b of the changeover switch SW2. And the above-mentioned double changeover switch SW
The movable contacts V of I and SW2 are configured to be switched to a fixed contact a and a fixed contact b in conjunction with each other, and a brightness signal is supplied from the movable contact V of the changeover switch SWI to an analog-to-digital converter l6. Further, the carrier color signal is supplied to the color demodulation circuit 5 from the movable contact V of the changeover switch SW2. The color difference signal R-Y output from the color demodulation circuit 15 is supplied to the analog-to-digital converter 17, and the color difference signal RY outputted from the color demodulation circuit 15 is
The color difference signal B-Y output from is supplied to the analog-to-digital converter 18. The digital signals outputted from each of the analog-to-digital converters 16 to 18 described above are supplied to input terminals in afterimage canceling circuits 19 to 21 having functions as described with reference to FIGS. 1 to 4. be done. Also, the terminal 3 in the afterimage canceling circuit 19 described above
6y, 35y, terminal 36r in afterimage canceling circuit 20,
35r, terminals 36b and 35b in the afterimage cancellation circuit 21
correspond to the input terminals 35 and 36 of the coefficient control signal in the coefficient circuits 5 and 6 described above (the same applies to FIG. 8), and the temperature sensor 34 is connected to each of the terminals described above. The transmitted number control signal is supplied to coefficient circuits 5 and 6 provided in each of the afterimage canceling circuits 19 to 21, respectively. The output signal of the luminance signal in a state where the afterimage has been canceled, which is output from the output terminal 8 of the afterimage canceling circuit 19, is supplied to the digital signal processing circuit 22, and the digital signal processing circuit 22 processes the luminance signal in a predetermined manner. After signal processing, the signal is converted into a luminance signal in an analog signal state by a digital-to-analog converter 24, and is supplied to a matrix circuit 27. Further, the output signal of the color difference signal RY in a state in which the afterimage has been canceled, which is output from the output terminal 8 of the afterimage canceling circuit 20, is supplied to the digital signal processing circuit 23. After being subjected to predetermined signal processing at step 23, the digital-to-analog converter 25 outputs the color difference signal RY in an analog signal state and supplies it to the matrix circuit 27. The output signal of the color difference signal B-Y in which the afterimage has been canceled, which is output from the output terminal 8 of the afterimage canceling circuit 21, is supplied to the digital signal processing circuit 23. [After predetermined signal processing is performed, the digital-to-analog converter 26 outputs the color difference signal RY in the analog signal state, and the matrix circuit 2
7 is supplied. The matrix circuit 27 generates three primary color signals R from the luminance signal Y and the two color difference signals R-Y and B-Y supplied thereto.
, G, and B, and supply the respective primary color signals R, G, and B to corresponding ones of the individual LCD drive circuits 28-30. The output signals from each of the LCD drive circuits 28 to 30 described above are transmitted to the liquid crystal display elements 31 to 33 to which they belong.
is supplied to Then, the above-mentioned liquid crystal display element 3 to 3
The image displayed in 3 is made without any afterimages despite changes in temperature. Next, FIG. 8 shows another example of the structure of a liquid crystal display device to which the afterimage canceling circuit of the present invention is applied, and the liquid crystal display device illustrated in FIG. The three primary color signals R, G,
After B is converted into a digital signal by each of the analog-to-digital converters 16 to 18, the digital signals output from each of the above-mentioned analog to digital converters 16 to 18 are as shown in FIGS. 1 to 6. The signal is supplied to the input terminal 1 of the afterimage canceling circuits 19 to 21 having the functions described above. The R signal outputted from the output terminal 8 of the afterimage canceling circuit 19, in which the afterimage has been cancelled, is converted into an R signal in the analog signal state by the digital-to-analog converter 24, and is used to drive the LCD. circuit 2
8, and the output signal from the LCD drive circuit 28 is supplied to the liquid crystal display element 3l. Further, the G signal output from the output terminal 8 of the afterimage canceling circuit 2o, in which the afterimage has been cancelled, is converted into a G signal in the analog signal state by the digital-to-analog converter 25, and then converted into the G signal in the analog signal state.
A D drive circuit 296 is supplied. The output signal from the LCD drive circuit 29 is supplied to the liquid crystal display element 32. Further, the B signal outputted from the output terminal 8 of the afterimage canceling circuit 21 and in which the afterimage has been cancelled, is converted into the B signal in the analog signal state by the digital-to-analog converter 26 to drive the LCD. The output signal from the LCD drive circuit 30 is supplied to the liquid crystal display element 33. The images displayed on the liquid crystal display elements 31 to 33 described above are free from afterimages despite changes in temperature. (Effects of the Invention) As is clear from the above detailed explanation, the present invention provides means for obtaining a difference signal between video signals separated by one frame period or one field period in video signals to be displayed by a liquid crystal display device. means for generating a signal corresponding to the temperature in the vicinity of the liquid crystal display element; means for changing the difference signal by the signal corresponding to the temperature in the vicinity of the liquid crystal display element to obtain a deformed difference signal; An afterimage canceling circuit in a liquid crystal display device, comprising means for adding the above-described deformation difference signal to a signal and outputting the resultant signal, the circuit comprising:
Even when a moving image is displayed using a liquid crystal display element, there is no afterimage in the displayed image, and it is possible to display a good quality image. When images for the right eye and images for the left eye that are displayed consecutively on the liquid crystal display screen on the time axis are displayed in a spatially shifted state, or as in the case of so-called video game images, Even when fast-moving images are displayed, good reproduced images can be obtained, and in addition, the afterimage of the displayed image can be canceled out in response to changes in the transient response characteristics of the liquid crystal due to temperature changes. , even if the ambient temperature changes, it is possible to always obtain a high-quality reproduced image in which afterimages are well canceled.

[Brief explanation of drawings]

1 and 6 are block diagrams showing an embodiment of the afterimage canceling circuit in the liquid crystal display device of the present invention, and FIGS. 2 and 3 show the coefficient circuit used in FIGS. 1 and 6. Examples of characteristic curves, Figures 4 and 5 are block diagrams showing an example of the structure of a coefficient circuit, Figures 7 and 8 are block diagrams of a liquid crystal display device equipped with an afterimage canceling circuit, and Figure 9 is an afterimage canceling circuit. It is a waveform diagram for explaining the principle of afterimage cancellation in the cancellation circuit.
1... Input terminal for video signal in digital signal state, 2
, 4... Subtractor, 3... Field memory or frame memory, 5, 6, 10a, lOb... Coefficient circuit, 7... Adder, 8... Output terminal, 11... Luminance Input terminal for multiplexed signal of signal and carrier color signal, 12...
・Input terminal for luminance signal. 13... Input terminal for carrier color signal, 14... YC separation circuit, 16-18... Analog-to-digital converter, 19-21... Afterimage cancellation circuit, 2
2, 23...Digital signal processing circuit, 24-26...
・Digital analog converter, 27... Matrix circuit, 28-30... LCD drive circuit, 31-33...
・Liquid crystal display element, 34...Temperature sensor, 35, 36,
35y, 36y, 35r, 36r, 35b, 36b...
・Terminals, S Wl, S W2...Changing switch, procedural amendment form (self-restraint 1. Indication of the incident, Patent Application No. 235235 of 2011 2. Name of the invention Afterimage canceling circuit in liquid crystal display device 3. Making corrections) Relationship with the patent case Patent Applicant address 3-12 Moriya-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Name (432) Victor Japan Co., Ltd. 4. Agent address 3-4-19-915 Higashi-Shinagawa, Shinagawa-ku, Tokyo No. 5. Date of amendment order (voluntary) 6. Column for detailed explanation of the invention in the specification to be amended 7. Contents of amendment 7th page of the specification, line 13

Claims (1)

[Claims] means for obtaining a difference signal between video signals to be displayed by a liquid crystal display device separated by one frame period or one field period; means for generating a signal corresponding to the temperature near the liquid crystal display element; A liquid crystal display comprising means for obtaining a deformed difference signal by changing the above-mentioned difference signal according to a signal corresponding to the temperature near the display element, and means for adding the above-described deformed difference signal to an input video signal and outputting the result. Afterimage cancellation circuit in equipment