JPH0752331B2 - Afterimage canceling circuit in liquid crystal display device - Google Patents

Description

The present invention relates to an afterimage canceling circuit in a liquid crystal display device.

(Prior Art) A liquid crystal display device configured to display an image by a liquid crystal display element has been widely used as an image display device for various electronic devices since the image display portion can be configured to be thin. In addition, an image projector in which a liquid crystal display element is used as a light valve and the intensity of light from a light source is intensity-modulated by an image signal and projected on a screen through a projection optical system has come into practical use. .

(Problems to be solved by the invention) Now, a liquid crystal display device uses a thermotropic liquid crystal,
For example, the state of alignment 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 in the twisted nematic alignment between the pair of substrates is the so-called waveguide mode. It is performed so as to satisfy the conditions.

By the way, in a liquid crystal display element, due to the viscosity of the liquid crystal used for it, there is a delay in the change in the orientation of the liquid crystal molecules with respect to the change in the electric field, so the rise time and fall time are large, that is, the transient response. It is known that the characteristics are poor.

When a still image is displayed by the liquid crystal display element, the transient response characteristics of the liquid crystal described above do not pose a problem, but when a moving image is displayed by the liquid crystal display element, a residual layer appears in the displayed image. The problem is that the quality of the reproduced image deteriorates.

In particular, for example, as in the case of a frame-sequential stereoscopic television image, a state in which the image for the right eye and the image for the left eye continuously displayed on the liquid crystal display surface on the time axis are spatially displaced from each other. In the case of being displayed in, or in the case of displaying a fast-moving image such as a so-called video game image, the above-mentioned problem of residual image generation on the display screen becomes a serious problem.

Further, when the video signal contains noise, the quality of the display screen is deteriorated, so that it is necessary to reduce the noise in the video signal in order to obtain a high quality display screen.

(Means for Solving the Problems) The present invention provides a means for obtaining a difference signal of video signals separated by one frame period or one field period in a video signal to be displayed by a liquid crystal display device, and the magnitude of the difference signal. When is smaller than a predetermined value, means for subtracting and outputting the difference signal from the input video signal,
An afterimage canceling circuit in a liquid crystal display device, comprising: a means for adding the difference signal to an input video signal and outputting when the magnitude of the difference signal is larger than a predetermined value, and a liquid crystal. Means for obtaining a difference signal of the video signals separated by one frame period or one field period in the video signal to be displayed by the display device, and inputting when the magnitude of the difference signal is smaller than a predetermined value. And a means for outputting the video signal as it is and a means for adding the difference signal to the input video signal and outputting it when the magnitude of the difference signal is larger than a predetermined value. An afterimage canceling circuit in a liquid crystal display device is provided.

(Operation) The difference signal of the video signals separated by one frame period or one field period in the video signal to be displayed by the liquid crystal display device is obtained.

If the magnitude of the difference signal is smaller than a predetermined value, it is regarded as noise and the difference signal is subtracted from the input video signal to output a video signal with reduced noise. Alternatively, the input video signal is output as it is, and if the magnitude of the difference signal is larger than a predetermined value, the difference signal of the input video signal is added to cancel the afterimage. The video signal of is output.

(Embodiment) Hereinafter, specific contents of the afterimage canceling circuit in the liquid crystal display device of the present invention will be described in detail with reference to the accompanying drawings.

1 and 4 are block diagrams showing an embodiment of an afterimage canceling circuit in a liquid crystal display device of the present invention, and FIGS. 2 and 3 show a coefficient circuit used in FIGS. 1 and 4. FIG. 5 is a block diagram of a liquid crystal display device having an afterimage canceling circuit, and FIG. 7 is a waveform diagram for explaining the principle of afterimage canceling in the afterimage canceling circuit.

First, the principle of afterimage cancellation performed by the afterimage cancellation circuit in the liquid crystal display device of the present invention will be described with reference to FIG. In FIG. 7, Si is an input signal of a video signal to be displayed by the liquid crystal display device.

As shown in FIG. 7A, the change in the orientation of the liquid crystal molecules occurs after the change in the electric field due to the viscosity of the liquid crystal used in the liquid crystal display element, as described above. For example, even when a step voltage input signal Si is input to the liquid crystal display element, the transient response characteristic of the liquid crystal causes the rise of the display mode of the liquid crystal display element as shown by So in FIG. FIG. 7 is a diagram explaining that there is a delay (although not shown, there is a delay on the time axis even for the fall), and FIG. 7 (b) is (a) of FIG. 7 described above. The display state of the liquid crystal display element shown in) is delayed by the transient response characteristics of the liquid crystal with respect to the mode of change of the input signal Si on the time axis, as shown by So in the figure.
FIG. 9 is an explanatory diagram of a case where a correction signal Ss is added in advance to the stepwise input signal Si so as to be in a substantially corrected state like So ′ in FIG. The signal Ss corresponds to the So minus the Si shown in FIG. 7 (a).

As can be seen from the description made with reference to FIGS. 7 (a) and 7 (b), the display state of the liquid crystal display element changes in the input signal Si on the time axis due to the transient response characteristics of the liquid crystal. The amount of delay with respect to
If a signal Ss for correction is added in advance to the stepwise input signal Si so as to be in a substantially corrected state like So ′, the display of the liquid crystal display element when the input signal changes The delay on the time axis is substantially eliminated, and an afterimage does not occur in the image displayed on the liquid crystal display element.

Therefore, the afterimage canceling circuit in the liquid crystal display device of the present invention generates a difference signal of video signals separated by one frame period or one field period in the video signal to be displayed by the liquid crystal display device, and the magnitude of the difference signal is generated. When the magnitude of the difference signal is larger than a predetermined value than a predetermined value, the difference signal is added to the input video signal as the signal Ss, and the liquid crystal display element is displayed. While preventing afterimage from occurring in the displayed image, when the magnitude of the difference signal is smaller than a predetermined value, the difference signal is regarded as noise,
It is possible to output the input video signal as it is without adding the difference signal to the input video signal, or to output the noise-reduced video signal by subtracting the difference signal from the input video signal. The afterimage canceling circuit in the liquid crystal display device is configured.

In the block diagram of the embodiment of the afterimage canceling circuit in the liquid crystal display device of the present invention shown in FIGS. 1 and 4, 1 is an input terminal of a video signal in a digital signal state, 3 is a field memory or a frame memory (hereinafter, Sometimes referred to as a memory), 4 is a subtractor, 6 is a coefficient circuit, 7 is an adder, 8 is an output terminal, and 2 is a subtractor in FIG. 1, 5 is a coefficient circuit, and 4th. In the figure, 9 is an adder, 10a,
10b 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 also to the adder 7.

The subtractor 2 is supplied with the output signal of the coefficient circuit 5 as a subtraction signal, and the output signal of the subtractor 2 is stored in the memory 3. As the memory 3, for example, a FIFO is used, or two memories configured to alternately perform writing and reading every one field period (or one frame period) are used. The video signal one field period (or one frame period) earlier than the video signal (or one frame period) is read from the memory 3 and supplied to the subtractor 4 as a subtraction signal.

In the subtracter 4, the current video signal supplied from the input terminal 1 is used as a subtracted signal, and the current video signal read from the memory 3 is one field period longer 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.

The coefficient circuit 5 described above multiplies the difference signal output from the subtracter 4 by a coefficient smaller than 1, for example, and supplies it to the subtracter 2 as a subtraction signal.

That is, subtracter 2 → memory 3 → subtractor 4 → coefficient circuit 5 →
Due to the operation of one loop of the subtractor 2,
A difference signal (motion detection signal) of the video signals separated by one frame period or one field period in the video signals is output.

The difference signal of the video signals output from the subtractor 4 separated by one frame period or one field period is a coefficient circuit 6 having an input / output characteristic as illustrated in FIG. 2 or 3, for example. Is supplied to.

Coefficient circuit 6 showing the input / output characteristics illustrated in FIG.
Is composed of, for example, a multiplier that multiplies the input signal by a predetermined coefficient, or can be composed by using a ROM table,
Further, the coefficient circuit 6 showing the input / output characteristics illustrated in FIG. 3 can be configured by using, for example, a ROM table.

Coefficient circuit 6 in the afterimage canceling circuit shown in FIG.
As an example, when the coefficient circuit 6 having the input / output characteristics as shown in the second diagram is used, the difference signal supplied from the subtractor 4 to the coefficient circuit 6 is 0 to + a, 0 to
If the magnitude is within the range of −a, that is, if it is smaller than the predetermined magnitude | a |, the output of the state in which the input signal is multiplied by the coefficient of the polarity opposite to the polarity of the input signal A signal is output and supplied to the adder 7. From the adder 7, a video signal obtained by subtracting the difference signal from the input video signal is output to the output terminal 8, and the output in this state is output. The signal is in a state where noise in the video signal is reduced.

In addition, the difference signal supplied from the subtractor 4 to the coefficient circuit 6 is out of the range of 0 to + a and 0 to -a, that is, a predetermined size | a | If it is also large, the output signal in a state in which the input signal is multiplied by the coefficient having the same polarity as the input signal is output and supplied to the adder 7, and the adder 7 outputs the input video signal to the input video signal. The video signal in the state where the difference signal is added is output to the output terminal 8, and the output signal in this state becomes a state in which the afterimage of the image displayed on the liquid crystal display element can be canceled.

Next, when the coefficient circuit 6 having the input / output characteristics as shown in FIG. 3 is used as the coefficient circuit 6 in the afterimage canceling circuit shown in FIG. The difference signal supplied from the instrument 4 is 0 to +
a, a size in the range of 0 to -a, that is,
When it is smaller than the predetermined size | a |, the output signal in the state where the difference is multiplied by 0 is supplied to the adder 7, and the input video signal is directly output from the adder 7. It is output to the terminal 8.

In addition, the difference signal supplied from the subtractor 4 to the coefficient circuit 6 is out of the range of 0 to + a and 0 to -a, that is, a predetermined size | a | If it is also large, the output signal in a state in which the input signal is multiplied by the coefficient having the same polarity as the input signal is output and supplied to the adder 7, and the adder 7 outputs the input video signal to the input video signal. The video signal in the state where the difference signal is added is output to the output terminal 8, and the output signal in this state becomes a state in which the afterimage of the image displayed on the liquid crystal display element can be canceled.

The input / output characteristics of the coefficient circuit 6 shown in FIGS. 2 and 3 are examples of characteristics, and coefficient circuits 6 having other input / output characteristics are used in implementing the present invention. Of course, it is okay.

Next, in the embodiment of the afterimage canceling circuit in the liquid crystal display device of the present invention shown in FIG. 4, the coefficient circuit 5 in FIG.
The operation is the same as that of the embodiment of the afterimage canceling circuit in the liquid crystal display device shown in FIG. 1 described above. The description will be omitted.

FIG. 5 and FIG. 6 show an example of the structure of a liquid crystal display device to which the afterimage canceling circuit in the liquid crystal display device of the present invention is applied.

First, in FIG. 5, 11 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, 13 is an input terminal for a carrier color signal, and 14 is a YC separation circuit. The luminance signal output from the separation circuit 14 is supplied to the fixed contact a of the changeover switch SW1, and the carrier color signal output from the YC separation circuit 14 is supplied to the fixed contact a of the changeover switch SW2.

A luminance signal is supplied from the terminal 12 to the fixed contact b of the changeover switch SW1 described above.
A carrier color signal is supplied from the terminal 13 to the fixed contact b of SW2.

The movable contacts v of the changeover switches SW1 and SW2 are interlocked to switch between the fixed contact a and the fixed contact b, and the luminance signal is converted from analog to digital from the movable contact v of the changeover switch SW1. Further, the carrier color signal is supplied to the color demodulation circuit 15 from the movable contact v of the changeover switch SW2.

The color difference signal RY output from the color demodulation circuit 15 is supplied to an analog-digital converter 17, and the color difference signal BY output from the color demodulation circuit 15 is an analog-digital converter 18.
Is supplied to.

The digital signals output from the analog-to-digital converters 16 to 18 are supplied to the input terminal 1 of the afterimage canceling circuits 19 to 21 having the functions described with reference to FIGS. 1 to 4. To be done.

The output signal of the luminance signal output from the output terminal 8 of the afterimage canceling circuit 19 in the state where the afterimage is canceled is supplied to the digital signal processing circuit 22, and the digital signal processing circuit 22 outputs a predetermined signal. After being processed, it is converted into a luminance signal in an analog signal state by the digital-analog converter 24 and supplied to the matrix circuit 27.

Further, the output signal of the color difference signal RY output from the output terminal 8 of the afterimage canceling circuit 20 in the state where the afterimage is canceled is supplied to the digital signal processing circuit 23, and this digital signal processing circuit After being subjected to a predetermined signal processing in 23, the digital-analog converter 25 outputs the color difference signal RY in the state of an analog signal and supplies it to the matrix circuit 27.

The output signal of the color-difference signal BY which is output from the output terminal 8 of the afterimage canceling circuit 21 in the state where the afterimage is canceled is supplied to the digital signal processing circuit 23, and in this digital signal processing circuit 23. After the predetermined signal processing is performed, the color-difference signal RY in the state of an analog signal is output by the digital-analog converter 26 and supplied to the matrix circuit 27.

In the matrix circuit 27, the luminance signal Y supplied to it
And three color difference signals R-Y, B-Y to generate three primary color signals R, G, B, and the respective primary color signals R, G, B correspond to the individual LCD drive circuits 28-30. Supply things.

The output signals from the above LCD drive circuits 28 to 30 are supplied to the liquid crystal display elements 31 to 33 to which they belong. Then, the images displayed on the liquid crystal display elements 31 to 33 described above can be displayed in a state in which there is no afterimage, and images can be displayed in a state in which noise is reduced.

Next, FIG. 6 shows another configuration example of a liquid crystal display device to which the afterimage canceling circuit in the liquid crystal display device of the present invention is applied. The liquid crystal display device illustrated in FIG. And the three primary color signals R, G, B output from the matrix circuit 27 to which the two color difference signals RY, BY are supplied are converted into digital signals by the analog-digital converters 16 to 18, respectively, Next, the digital signals respectively output from the analog-to-digital converters 16 to 18 described above are input to the input terminal 1 of the afterimage canceling circuits 19 to 21 having the functions described with reference to FIGS. 1 to 4. Supplied.

The output signal of the R signal output from the output terminal 8 of the afterimage canceling circuit 19 in the state where the afterimage is canceled is converted into the R signal in the analog signal state by the digital-analog converter 24, and the LCD driving circuit 28 And the output signal from the LCD drive circuit 28 is supplied to the liquid crystal display element 31.

Further, the output signal of the G signal output from the output terminal 8 of the afterimage canceling circuit 20 in the state in which the afterimage is canceled is converted into the G signal in the state of the analog signal by the digital-analog converter 25 to drive the LCD. The output signal supplied from the LCD drive circuit 29 to the circuit 29 is supplied to the liquid crystal display device 32.

Further, the output signal of the B signal in the state where the afterimage is canceled output from the output terminal 8 of the afterimage canceling circuit 21 is converted into the B signal in the state of the analog signal by the digital-analog converter 26 to drive the LCD. Supplied to the circuit 30, LCD drive circuit 30
The output signal from is supplied to the liquid crystal display element 33.

The images displayed on the liquid crystal display elements 31 to 33 described above can be displayed in a state where there is no afterimage, and images can be displayed in a state where noise is reduced.

(Effect of the Invention) As is clear from the above description, the present invention is a means for obtaining a difference signal of video signals separated by one frame period or one field period in a video signal to be displayed by a liquid crystal display device. And a means for subtracting the difference signal from the input video signal and outputting the subtracted signal when the magnitude of the difference signal is smaller than a predetermined value, and the magnitude of the difference signal is predetermined. If the value is larger than the above value, a residual image canceling circuit in the liquid crystal display device comprising means for adding the difference signal to the input video signal and outputting the result, and 1 in the video signal to be displayed by the liquid crystal display device. Means for obtaining a difference signal of video signals separated by a frame period or one field period, and an input image when the magnitude of the difference signal is smaller than a predetermined value. A liquid crystal comprising means for outputting the image signal as it is, and means for adding the difference signal to an input video signal and outputting it when the magnitude of the difference signal is larger than a predetermined value. An afterimage cancellation circuit in a display device,
In the afterimage canceling circuit in the liquid crystal display device of the present invention,
If the difference signal of the video signals separated by one frame period or one field period in the video signal to be displayed by the liquid crystal display device is obtained and the magnitude of the difference signal is smaller than a predetermined value, It is regarded as noise and the difference signal is subtracted from the input video signal to output a video signal with reduced noise, or the input video signal is output as it is. Is greater than a predetermined value, the difference signal is regarded as a motion detection signal, and the difference signal is added to the input video signal to output a video signal in a state where the afterimage is canceled. Therefore, even when a moving image is displayed by a liquid crystal display element, an afterimage does not appear in the displayed image, and a high quality image can be displayed. As three-dimensional television image,
When the image for the right eye and the image for the left eye that are continuously displayed on the liquid crystal display surface on the time axis are displayed in a spatially shifted state, or like a so-called video game image. Even when a fast-moving image is displayed, it is possible to obtain a good reproduced image. Also, since the afterimage cancellation circuit operates as a noise reduction circuit, high-quality images with reduced noise in the video signal. You can get the display screen of.

[Brief description of drawings]

1 and 4 are block diagrams showing an embodiment of an afterimage canceling circuit in a liquid crystal display device of the present invention, and FIGS. 2 and 3 show a coefficient circuit used in FIGS. 1 and 4. FIG. 5 is a block diagram of a liquid crystal display device having an afterimage canceling circuit, and FIG. 7 is a waveform diagram for explaining the principle of afterimage canceling in the afterimage canceling circuit. 1 …… Video signal input terminal in digital signal state, 2, 4
...... Subtractor, 3 …… Field memory or frame memory, 5,6,10a, 10b …… Coefficient circuit, 7 …… Adder, 8 ・ ・ ・
… Output terminal, 11 …… Input terminal for multiplexed signal of luminance 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 canceling circuit, 22,23
...... Digital signal processing circuit, 24 to 26 ...... Digital-to-analog converter, 27 ...... Matrix circuit, 28 to 30 ...... LCD drive circuit, 31 to 33 ...... Liquid crystal display element, SW1, SW2 ...... Changeover switch,

Claims (2)

[Claims] 1. A means for obtaining a difference signal of video signals which are separated by one frame period or one field period in a video signal to be displayed by a liquid crystal display device, and the magnitude of the difference signal is based on a predetermined value. Means for subtracting the difference signal from the input video signal and outputting the difference signal, and if the magnitude of the difference signal is larger than a predetermined value, the difference in the input video signal An afterimage canceling circuit in a liquid crystal display device comprising means for adding and outputting signals 2. A means for obtaining a difference signal of video signals separated by one frame period or one field period in a video signal to be displayed by a liquid crystal display device, and the magnitude of the difference signal is set to a predetermined value. Is smaller than the predetermined value, the means for outputting the input video signal as it is, and when the magnitude of the difference signal is larger than a predetermined value, the difference signal is added to the input video signal and output. Image canceling circuit in a liquid crystal display device including: