JPH02153688A - Liquid crystal driving device - Google Patents

Abstract

PURPOSE:To improve the response speed of only a required image area and to prevent an after image and a noise occurring by applying a signal processing to enhance change replying to every direction of the change when a large amount of change exists in an image signal. CONSTITUTION:A digital signal wn outputted from an A/D converter 11 and a signal wn-1 outputted from a one-frame delay circuit 12 are also sent to a motion detection circuit 31. The motion detection circuit 31 judges whether or not a large amount of change(motion) exists in the images of the picture elements of two signals wn and wn-1 having time difference of one frame by performing the subtraction of the two signals wn and wn-1. A judged result is sent to an ON/OFF direction detection circuit 32. The ON/OFF direction ditection circuit 32 judges the direction of the change of the image directing (darkness brightness) or (brightness darkness) by the code of a subtraction result between the signals wn and wn-1, and sends a constant K suitable for the transfer function of a liquid crystal display panel 18 to a multiplier 14 and a multiplier 15 according to the judged result. In such a way, it is possible to improve the response speed of only the required image area by necessary share and to prevent the after image and the noise occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal driving device for driving a dot matrix liquid crystal display panel.

[Prior Art] Conventionally, dot matrix liquid crystal display panels have generally been used in display units of small portable television receivers and the like. The TV image is 17 [mS] (-1/60 [s
Since the display must be displayed every 1), it is naturally desirable that the response speed of the liquid crystal display panel be sufficiently faster than 17 [aS]. However, the response speed of current liquid crystal display panels is about 50 [sS] to 100 [sS], and there is a drawback that afterimages are visible when displaying moving images.

Therefore, the following method was devised as a liquid crystal driving device that improves response speed and eliminates afterimages. That is,
When focusing on one pixel in the liquid crystal display panel, 1F (r frame referred to in this specification as frame 2) indicates a period in which all the pixels constituting one screen are scanned once, and for example, a TV signal. When displaying by scanning all the pictures constituting one screen for each field, one field of the TV signal is considered to be equal to one frame referred to in this application,
This does not necessarily correspond to a "frame" of a TV signal. ) is selected once and the image data is refreshed. It is well known that liquid crystal display panels have cumulative responsivity, but this cumulative responsivity can be expressed as a mathematical model: Vn-(1-K) : input image data yn : output image data (data to be displayed)). When this formula (1) is Z-transformed, Y(z)=(
1-K)X(z)+KZ-1Y(z)Y(z)=(1
-K)X(z)/(1-KZ-')...(2) (Z-1: delay operator for one frame). Therefore, the transfer function H(z) of the liquid crystal display panel is H(z)=(1-K)/(1-KZ-1)...(
3) It can be considered as follows. Here, if the signal is pre-processed using a transfer function opposite to that of the liquid crystal display panel, the response speed of the display can be improved.

That is, X(z)” (1-KZ-1)W(z)/ (1-KZ
-')...(4) If we inversely transform this equation (4), we get Xfi -(wl -Kwn-+) / (1-K)・
...(5) The following equation is obtained. Note that the signal Xfi obtained in this way has a large amplitude and cannot be displayed as is on a liquid crystal display panel, so it is necessary to equalize the amplitudes of Xyl and Wn using a limiter.

In addition, although the signal Xfi described above is effective in improving the responsiveness of fast-moving images, on the other hand, slight changes are emphasized for images with little movement and close to still images. Therefore, there is a problem that noise increases. Therefore, the processing of the signal Xfi as described above needs to be performed only on pixels and regions where the image changes to a certain extent or more.

FIG. 2 shows the circuit configuration for realizing the above equation (5). The analog video input signal is converted into two pixels in units of NXM dots by the A/D converter 11, and the digital signal w
It is sent to the 1-frame delay circuit 12 and the subtracter 13 as n. The one-frame delay circuit 12 delays the input signal Wl by one frame, 17 [mS], and outputs the delayed signal to the multiplier 14 as a signal W1-1. Multiplier 14
is the signal Wn multiplied by KW n-1, and the above subtraction 31
3. Send it to the first input blade end.

In the subtracter 13, the signal Wl from the A/D converter 11 and the signal Kw old from the subtracter 13 are used to subtract Wn - Kw.
1-1 and outputs the difference to the multiplier 15. Multiplier 15
is the input signal multiplied by 1/(1-K), and the limiter 16
Send to. The limiter 16 is used to limit the sent signal by calculation when it exceeds the amplitude of the output signal Wn of the A/D converter 11, and its output is sent to the segment driver 17 as a signal Xi. . Segment driver 17 drives segment electrodes of liquid crystal display panel (LCD) 1B according to signal Xfi. The common electrode of this liquid crystal display panel 18 is driven by a common driver 19, and these liquid crystal display panels 18,
Both the common driver 19 and the A/D converter 11 operate in synchronization with the timing signal sent from the timing signal generation circuit 20.

Therefore, the digital signal W output from the A/D converter 11
fi and the signal Wn output from the one frame delay circuit 12 are also sent to the motion detection circuit 21. This motion detection circuit 21
are two signals Wn, Wn with a time difference of one frame.
Based on the difference of -1, it is determined whether the change (movement) in the image of that pixel is large or not, and a constant K is output to the multiplier 14 and the multiplier 2H15 in accordance with the determination result.

For example, the digital signal WQ output from the A/D converter 11
and a signal W which is delayed by one frame by one frame delay circuit 12. -1 represents the luminance component of the video signal as data with a weight of m bits, so it is determined whether the change in the image is large based on whether the difference between them is greater than or equal to a certain predetermined bit. . The range of the constant output from the motion detection circuit 21 based on this judgment result is "0≦1". If it is determined that the change is small, the value of the constant becomes "0", and as a result, the output of the multiplier 14 is "0", and the multiplier 15 acts as a through noise (signal processing that emphasizes the image change). In addition, if it is determined that the change is large, the constant must have rO<
The value is set in advance within the range of ``K<1''.

The operation when it is determined that the change in image data is large will be described below.

Assume that the response speed of one pixel of the liquid crystal display panel 18 is, for example, 50 [S] (-3 frames).

In this case, the constant in equation (5) above is 1/2. Therefore, the multiplier 14 converts the signal w B4 delayed by the one-frame delay circuit 12 into W n-+ /2, and the subtracter 13 performs the subtraction Wn-Wn-1/2. Multiplier 15 doubles the input signal,
A signal "r2wn-w old" is sent to the limiter 16.

The limiter 16 performs an operation such as xl-(2wn wn-t)/3+1/3 on the received signal to obtain a signal X. is output to the segment driver 17 and displayed on the liquid crystal display panel 18.

With this circuit configuration, if there is a large change in the image, the liquid crystal display panel is driven using data that has been subjected to signal processing that emphasizes that change in advance, so there is no noise and no afterimages are generated. It becomes possible to remove the influencing components that result in , and it is possible to compensate for the low response speed of the liquid crystal display panel.

[Problems to be Solved by the Invention] The liquid crystal drive device configured as described above has an A/D converter 11.
The motion detection circuit 21 detects the magnitude of the change in the image signal from the absolute value of the difference between the image signal Wn which is the output of the image signal Wn and the signal Wn-1 which is delayed by one frame by the one frame delay circuit 12. , a constant K was output.

However, when the image signal changes, in reality, the direction of the change, that is, when the brightness changes from bright to dark, and when the brightness changes from dark to bright, the liquid crystal display panel as shown in equation (3) above actually changes. Since the values of the constants in the transfer function are different, if the constant of the transfer function is set uniformly regardless of the direction of change as described above, appropriate signal processing cannot be performed.

This invention was made in view of the above circumstances,
It is an object of the present invention to provide a liquid crystal driving device that can always perform image signal compensation in an appropriate state and improve response speed.

[Means and Effects for Solving the Problems] This invention is such that when there is a large change in an image signal, signal processing is performed to emphasize the change in each direction of the change. Changes in the image signal are emphasized and the response speed is adjusted to the required extent only in the necessary image areas.
No afterimage or noise occurs.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the circuit configuration of one embodiment, and since the basic configuration is the same as that in FIG. 2, the same parts are given the same reference numerals and the explanation thereof will be omitted.

Then, the digital signal wn output from the A/D converter 11
The signal W n-1 output from the one-frame delay circuit 12 is also sent to the motion detection circuit 31 . This motion detection circuit 3
1 indicates two signals W having a time difference of one frame. +
By subtracting wI)l, the change in the image of that pixel (
The judgment result is sent to the on/off direction detection circuit 32. The on/off direction detection circuit 32 receives the sent judgment results, that is, the signals Wn and W. It is determined from the sign of the subtraction result of -8 whether the direction of image change is on (dark → bright) or off (bright → dark), and the liquid crystal display panel 18
A constant K suitable for the transfer function of is sent to the multiplier 14 and the multiplier 15.

The motion detection circuit 31 receives, for example, an m-bit digital signal W (1 and 1 frame delay circuit I) output from the A/D converter 11.
Subtraction Wn Wn-1 is performed using the same m-bit signal W n-1 outputted by 2, and if the difference is more than a predetermined bit, the motion detection circuit 31 determines that the change in the image is large and calculates the difference. The judgment result is sent to the on/off direction detection circuit 32 along with information as to whether the sign is positive or negative. The on/off direction detection circuit 32 receives the determination result that the change is large from the motion detection circuit 31, and at the same time determines whether the difference between the subtracted signals wn and W old is positive or negative. If it is positive, the direction of change is on (dark→bright), and a constant value optimal for the transfer function of the liquid crystal display panel 18 in this state is sent to the multipliers 14 and 15.

Furthermore, if the difference between the subtracted signals Wn and Wn-+ is negative, the direction of change is off (bright→dark), and the optimum constant for the transfer function of the liquid crystal display panel 18 in this state is also determined. The value of is sent to the multiplier 14 and the multiplier 15.

In this way, by variably setting the value of the constant in the transfer function of the liquid crystal display panel 18 according to the direction of change in the image signal, the 1-frame delay circuit 12, subtracter 13, and multiplier 14
．． 15 and the limiter IB can optimize the degree of emphasis on changes in the image signal.

[Effects of the Invention] As detailed above, according to the present invention, when there is a large change in the image signal, signal processing is performed to emphasize the change in accordance with the direction of the change, so that the change is always maintained at an appropriate degree. Changes in the image signal are emphasized, and the response speed is improved only in the necessary image area by the necessary amount, so it is possible to provide a liquid crystal driving device that does not generate afterimages or noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing the circuit configuration of a conventional liquid crystal driving device. 11... A/D converter, 12... 1 frame delay circuit, 13... Subtractor, 14.15... Multiplier, 1B
...Limiter, I7...Segment driver, 18
...Liquid crystal display panel, 19...Common driver, 2
0...Timing signal generation circuit, 21, 31...Motion detection circuit, 32...ON◆OFF direction detection circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] Motion detection means for detecting when the amount of change in image data corresponding to a predetermined pixel exceeds a predetermined value; After subtracting K times the data of the n-1th frame from
/(1-K) multiplication processing means, and direction detection means for detecting the direction of change in image data based on the detected content of the motion detection means and variably setting the value of a constant K in the processing means, A liquid crystal driving device characterized in that a liquid crystal display panel is driven using data processed by the processing means.