JPH088671B2 - Liquid crystal drive - Google Patents

Description

The present invention relates to a liquid crystal drive device for driving a dot matrix liquid crystal display panel.

[Prior Art] Conventionally, a dot-matrix liquid crystal display panel is generally used for a display unit of a portable small television receiver, a small electronic calculator, or the like. FIG. 5 shows the structure of the drive circuit. 11 is a liquid crystal display panel (LCD) of a dot matrix of N × M dots, 12 is a segment driver for driving the segment electrodes of the liquid crystal display panel 11, and 13 is also a liquid crystal. A common driver that drives the common electrode of the display panel 11, 14 is an A / D converter that quantizes an analog video input signal in N × M pixel units, and 15 is the segment driver 12, common driver 13, A / D A timing signal generation circuit for sending a timing signal to each converter 14.

The analog video input signal is quantized by the A / D converter 14 by the timing signal from the timing signal generation circuit 15 in pixel units of N × M dots and sent to the segment driver 12. This segment driver 12 is the above A / D converter 1
4, timing signal generator 15 with common driver 13
It operates in synchronization with the timing signal from
The gradation waveform corresponding to the digital data from the converter 14 is displayed on the scanning line selected by the common driver 13.

In the liquid crystal driving device having the above structure, the television image must be displayed every 17 [mS] (= 1/60 [s]), so the response speed of the liquid crystal display panel is necessarily 17 [mS]. m
S] is expected to be sufficiently faster. However, the current response speed of liquid crystal display panels is 50 [mS] to 100 [m
However, the afterimage is visible when displaying a moving image.

Therefore, the following method has been conceived as a liquid crystal driving device that improves the response speed and eliminates the afterimage. That is, focusing on one pixel in the liquid crystal display panel, 1F (frame: “frame” in the specification of the present application indicates a period in which all the picture elements forming one screen are scanned in one way, for example, a TV signal). When all the picture elements that compose one screen for one field are scanned and displayed, one field of the TV signal and one frame in the present application are considered to be equal, and one frame of the TV signal does not necessarily match. No)), the image data is refreshed. It is well known that a liquid crystal display panel has a cumulative response, but when this cumulative response is expressed as a mathematical model, y _n = (1-K) x _n + Ky _n-1 (1) (where K: Constant x _n : Input image data y _n : Output image data (displayed data)). When Z-transforming this equation (1), Y (z) = (1-K) X (z) + KZ- ¹ Y (z) Y (z) = (1-K) X (z) / (1-KZ ^-1 ) (2) (However, Z ^-1 : delay operator for one frame).
Therefore, the transfer function H (z) of the liquid crystal display panel can be considered as H (z) = (1−K) / (1−KZ ⁻¹ ) (3). Here, if the signal is preprocessed with a transfer function opposite to the transfer function of the liquid crystal display panel, the display response speed can be improved. That is, X (z) = (1−KZ ⁻¹ ) W (z) / (1−K) (4) When this formula (4) is inversely Z-transformed, x _n = (w _n −Kw _n−1) ) / (1-K) (5) The signal obtained in this way
Since the amplitude of x _n becomes large and it is impossible to display it on the liquid crystal display panel as it is, it is necessary to make the amplitudes of x _n and w _n equal by a limiter.

FIG. 6 shows a circuit configuration for realizing the above formula (5). An analog video input signal is quantized by the A / D converter 21 pixel by pixel, and a 1-frame delay circuit is provided as a digital signal w _n. It is sent to the + input side of the subtractor 23 and the subtractor 23. The 1-frame delay circuit 22 receives the input signal w _n for 1 frame,
The signal is delayed by [mS] and output as a signal w _n-1 to the multiplier 24. The multiplier 24 multiplies the signal w _n-1 by K to obtain Kw _n-1, and sends it to the minus input side of the subtractor 23. A / D converter 2 in subtractor 23
Subtraction w _n −Kw _n−1 is performed by the signal w _n from ₁ and the signal Kw _n−1 from the subtractor 23, and the difference is output to the multiplier 25. The multiplier 25 multiplies the input signal by 1 / (1-K) and sends it to the limiter 26. The limiter 26 sends the received signal to the A / D converter 2 described above.
When the amplitude of the output signal w _n of 1 is exceeded, this is limited by calculation, and its output is sent to the segment driver 27 as the signal x _n . The segment driver 27 drives the segment electrodes of the liquid crystal display panel 28 according to the signal x _n . The common electrode of the liquid crystal display panel 28 is driven by a common driver 29. The liquid crystal display panel 28, the common driver 29 and the A / D converter 21 are all timing signals sent from the timing signal generating circuit 30. It operates in synchronization with.

In the above structure, the response speed in one pixel of the liquid crystal display panel 28 is, for example, 50 [mS] (≈3 frames).
Suppose In this case, the constant K in equation (5) K = 1/2
Becomes Therefore, in the multiplier 24, the 1-frame delay circuit
The signal w _n-1 delayed by 22 is set to w _n-1 / 2, and the subtractor 23 performs subtraction w _n −w _n-1 / 2. The multiplier 25 doubles the input signal and sends a signal "2w _n -w _n-1 " to the limiter 26. In the limiter 26, against sent signal, for example, _{x n = (2w n -w n} -1) / 3 + 1/3 becomes operational alms, resulting signal x _n segment driver
Output to 27 and display on liquid crystal display panel 28.

With such a circuit configuration, since the liquid crystal display panel is driven by using the data that has been subjected to the signal processing that emphasizes the image change in the time direction in advance, it is possible to remove the influence component that causes the afterimage. The low response speed of the liquid crystal display panel can be compensated.

[Problems to be Solved by the Invention] However, although the liquid crystal drive device having the above-described configuration has a great effect of improving the response speed, on the other hand, the change is emphasized excessively in an image region having a small amount of motion close to a still image. I will end up.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal drive device capable of displaying an image with significantly reduced afterimage and noise.

[Means and Actions for Solving the Problem] The present invention discriminates between a still image region with little motion and a moving image region with many motions, and performs signal processing for emphasizing image changes in the time direction only in the moving image region. Since the response speed is improved only in the necessary image area, afterimage and noise can be significantly reduced.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit structure of one embodiment, and since the basic structure is the same as that of FIG. 6, the same portions are denoted by the same reference numerals and the description thereof will be omitted.

The digital signal w _n output from the A / D converter 21 and the signal w _n-1 output from the 1-frame delay circuit 22 are also sent to the motion detection circuit 31. The motion detection circuit 31 determines whether the pixel is in the moving image area or the still image area based on the difference between the two signals w _n and w _n−1 having a time difference of one frame.
The constant K is output to the multiplier 24 and the multiplier 25 according to the result of the determination.

For example, a digital signal w _n output from the A / D converter 21 and a signal w _n-1 obtained by delaying the digital signal w _n by one frame by the one-frame delay circuit 22 have a luminance component of a video signal with a weight of m bits. Since it is represented by data, it is determined whether it is a moving image area or a still image area depending on whether these differences are equal to or more than a predetermined bit. The range of the constant K output from the motion detection circuit 31 based on the result of this determination is “0 ≦ K <1”. If it is determined to be the still image area, the value of the constant K becomes "0", and as a result, the multiplier 24
Is "0", and the multiplier 25 is a through-pass, so that it becomes a circuit which is functionally identical to the circuit shown in FIG. 7 and which does not perform signal processing for emphasizing image change. If it is determined that the area is a moving image area, the constant K is set to a preset value within the range of “0 <K <1”, for example, “1/2”. As shown, signal processing that emphasizes image changes is performed to improve the response speed. in this case,
The closer the value of the constant K is to “1”, the greater the degree of emphasis.

In FIG. 1 above, the signal w _n is delayed by one frame.
Although w _n-1 is used to detect whether or not there is motion, instead of this, it is also possible to detect motion in the same way using the signal w _n and the signal x _n output from the limiter 26. To be

FIG. 2 shows another configuration example in which this is realized. Since the basic configuration is the same as that shown in FIG. 6 as in FIG. 1, the same parts are designated by the same reference numerals. The description will be omitted.

Then, the digital signal w _n output from the A / D converter 21 is output to the motion detection circuit 32. The signal x _n, which is the output of the limiter 26, is delayed by one frame via the one-frame delay circuit 33 and is input to the motion detection circuit 32 as a signal x _n-1 . The motion detection circuit 32 determines whether the pixel is in the moving image area or the still image area from the difference between the two signals w _n and x _n−1 having the time difference of one frame, and the result of the determination is In response, the constant K is output to the multiplier 24 and the multiplier 25.

The operation itself of the motion detection circuit 32 is similar to that of the motion detection circuit 31 of FIG. 1, but the frequency characteristic of the motion detection circuit 31 is flat, and the image change is emphasized regardless of the frequency. The circuit 32 has a high-pass filter-like frequency characteristic, and the degree of emphasis increases as the frequency increases. This is the transfer function H of the liquid crystal display panel.
(Z) is as shown in the above formula (3). This (3)
Substituting Z ⁻¹ = e ^-jwT (6) into the equation, and looking at the frequency characteristics, Is obtained. FIG. 3 shows a frequency characteristic I for motion detection by the motion detection circuit 31 in FIG. 1 and a frequency characteristic II for motion detection by the motion detection circuit 32 in FIG. This means that it is possible to detect the motion (that is, the change in the image) more significantly than the above.

Further, the configuration shown in FIG. 2 may be further modified as shown in FIG. This is the (1) is the inverse function seek when _{x n = (y n -Ky n} -1) / (1-K) ... (8) becomes equation of Formula obtained. , Image input data y _n of this equation (8)
When the replaced by _{w n x n = (w n} -Ky n-1) / (1-K) ... (9) becomes equation is obtained, a circuit for realizing this A / D converter 21 and the segment driver If it is arranged between the two 27, the same effect as that of FIG. 1 can be obtained. Hereinafter, FIG. 4 will be described.

In the figure, the digital signal w _n sent from the A / D converter 21 (not shown) is sent to the motion detection circuit 34 and the subtractor 35. The subtraction result of the subtraction destination 35 is sent to the multiplier 36,
The multiplier 36 multiplies the received signal by 1 / (1-K) and outputs it to the limiter 37. The limiter 37 limits the calculated signal when the sent signal exceeds the amplitude of the output signal w _n of the A / D converter 21, and its output is the signal.
It is sent to the segment driver 27 (not shown) as x _n , and is also sent to the 1-frame delay circuit 38 and the multiplier 39. The multiplier 39 multiplies the input signal x _n by (1−K) and outputs the multiplication result to the adder 40. The adder 40 adds the signal from the multiplier 42 described later and the signal from the multiplier 39,
The signal y _n which is the addition result is sent to the 1-frame delay circuit 41. The signal delayed by one frame in the one-frame delay circuit 41 to become y _n-1 is multiplied by K in the multiplier 42, and then output to the-input side of the adder 40 and the subtractor 35. The 1-frame delay circuit 38 delays the signal x _n by 1 frame,
It is output to the motion detection circuit 34 as a signal x _n-1 . The motion detection circuit 34 uses two signals w _n and x having a time difference of 1 frame.
It is determined from the difference of _n-1 whether the pixel is in the moving image area or the still image area, and the multiplier 3 is used according to the determination result.
6. The constant K is output to the multiplier 39 and the multiplier 42.

The operation of this circuit is similar to that shown in FIG. 2, and the motion detection circuit 32 has a high-pass filter-like frequency characteristic, and the degree of emphasis increases as the frequency increases. Therefore, it is possible to detect the motion (that is, the change in the image) more remarkably than the motion detection circuit 31 of FIG. 1 [Effect of the invention] As described above in detail, according to the present invention, the motion is small. The still image area and the moving image area with a lot of movement are discriminated, and the signal processing that emphasizes the image change in the time direction is applied only to the moving image area. It is possible to provide a liquid crystal driving device in which the occurrence of

[Brief description of drawings]

1 to 4 show an embodiment of the present invention. FIG. 1 is a block diagram showing a circuit configuration of one embodiment, FIG. 2 is a block diagram showing another configuration example, and FIG. The figure which shows the frequency characteristic of FIG. 2, FIG. 4 is the block diagram which shows another structural example,
5 and 6 are block diagrams showing a circuit configuration of a conventional liquid crystal driving device. 11,28 …… Liquid crystal display panel, 12,27 …… Segment driver, 13,29 …… Common driver, 14,21 …… A / D converter, 1
5,30 …… Timing signal generator, 22,33,38,41 …… 1
Frame delay circuit, 23,35 ... Subtractor, 24,25,36,39,42
…… Multiplier, 26,37 …… Limiter, 31,32,34 …… Motion detection circuit, 40 …… Adder.

Claims (3)

[Claims] 1. A liquid crystal driving device for displaying a video signal on a liquid crystal display panel having a cumulative response, a video signal output means for outputting a video signal W _n (n is a frame), and a transfer function of the liquid crystal display panel. H (z) = (1−K) / (1−KZ ⁻¹ ) (K is a constant) and a transfer function having an inverse characteristic X (z) = (1−KZ ⁻¹ ) W (z) / (1− calculating means for processing the video signal W _n in K), compared with the video signal W _n and W _n-1, and setting means for setting the constant K in accordance with the magnitude of the difference, the operation A liquid crystal drive device comprising: a drive unit that displays on a liquid crystal display panel based on the processed video signal X _n . 2. A first delay means for delaying and outputting a video signal W _n (n is a frame) by one frame, and a video signal W _n-1 output from this delay means is multiplied by a constant K. A first multiplication means, a subtraction means for subtracting the video signal KW _n-1 output from the first multiplication means from the video signal W _n, and a video signal “W _n −KW _n-1 ” output from the subtraction means. Is multiplied by a multiplier "1 / (1-K)" using a constant K, and a video signal "(W _n -K
W _n-1 ) / (1-K) ”amplitude limiting means, second delay means for delaying the video signal x _n output from this limiting means by one frame, and outputting the delayed signal. The video signal x _n-1 output from the second delay means is compared with the video signal W _n, and the motion detection means sets the constant K in accordance with the magnitude of the difference, and the output from the limiting means. And a drive means for displaying on the liquid crystal display panel based on the video signal x _n . 3. A first subtracting means for subtracting the video signal Ky _n-1 from the video signal W _n (n is a frame), and a video signal "W _n -Ky _n-1 " output by the first subtracting means. "
Multiplication with the constant K with respect to "1 / (1-K)" and the first multiplying means for multiplying the video signal "W _n -Ky _n-1 output from the first multiplying means)
/ (1-K) "limiting means for limiting the amplitude and a constant K for the video signal x _n output from the limiting means.
And a video signal "(1-K)" output from the second multiplication means.
adding means for adding the video signal Ky _n-1 and x _n ", a first delay means for outputting a video signal y _n to be outputted from the adding means with a delay of one frame, the first delay A second multiplication means for multiplying the video signal y _n-1 output from the means by a constant K, and outputting a video signal Ky _n-1 which is the product output to the first addition means and the addition output. Second delay means for delaying and outputting the video signal x _n output from the limiting means by one frame, and the video signal x _n-1 output from the second delay means and the video signal W _n And a driving means for displaying on the liquid crystal display panel based on the video signal x _n output from the limiting means. A liquid crystal drive device characterized by the above.