JP2008287016A - Driving method for improving reaction time of tn type or stn type liquid crystal display device independent of graphic memory addition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method for improving reaction time of TN type or STN type liquid crystal display device independent of graphic memory addition. <P>SOLUTION: In the driving method for improving reaction time of TN type and STN type liquid crystal display device independent of graphic memory addition, three primary color data of an image are converted into YCbCr data and over-drive YCbCr data; then, storage bits of a part of the YCbCr data and over-drive YCbCr data are further reduced by performing the sampling and alignment according to the video compression standard; an over-drive compensation potential which is higher or lower than the conventional output potential is flexibly applied N times according to the over-drive YCbCr data within an updating time of each data bus via a frequency division multiple circuit and, as the result, the reaction time and the blurring of a moving image of the liquid crystal display device is improved independent of graphic memory addition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a kind of passive nematic liquid crystal display technology, in particular, a kind of twisted nematic type (TN) and super twisted nematic type (STN) passive nematic liquid crystal display (LCD) does not depend on the addition of graphic memory, and the liquid crystal reaction The present invention relates to a driving method that effectively shortens time and improves the blurring phenomenon of moving images.

  Conventional liquid crystal display devices can be classified into two types, passive nematic type (PM-LCD) and active nematic type (AM-LCD), depending on the driving display method. Among them, the drive display type of PM-LCD is provided with a horizontal transparent indium tin oxide (ITO) electrode on one of the two upper and lower glass panels, and vertically on the other panel. Oriented transparent indium tin oxide (ITO). After the two panels are pasted together (filled with liquid crystal in the middle layer), the grid-like locations where the electrodes cross over the upper and lower panels become the pixels of the display panel. The potential difference of the pixel controls the electrodes in both directions by a driving voltage provided externally, thereby realizing inversion of the liquid crystal of the pixel.

  Both twisted nematic type (TN) and super twisted nematic type (STN), which are often seen, are passive nematic liquid crystal displays (PM-LCDs). Since the device itself does not have the liquid crystal control operation of the pixel by a non-linear element (similar to the switch element), each pixel is formed from the overlapping area of the horizontal common electrode line and the vertical segment electrode line. To do. The basic operation principle uses the electro-optic effect generated from the root mean square value (RMS) of the voltage applied by the liquid crystal material. The reaction time of the liquid crystal material must be much larger than the operating period of the drive pulse, and if the frame rate is 60 hertz, one horizontal scan line (ie, a bipolar electrode) When the selected time interval is 16.67 ms, the required reaction time of the liquid crystal material is typically 200 ms, which is a prerequisite for the liquid crystal to react to the root mean square (RMS) value.

  However, in the conventional amplitude selection drive (Alt & Pleshko Therory, APT) system, when a moving image is displayed, the liquid crystal material has a slow reaction time, so that the moving image is blurred. On the other hand, when using a liquid crystal material that reacts quickly, it causes a severe flicker phenomenon on the screen, and the contrast of the screen is greatly reduced.

  FIG. 1 is a block schematic diagram of a normal over-driving electric circuit reference table. As a general solution to the above problem, different overdrive voltage V 'values are given to the respective image frames. In this method, the current image frame (Current Field) sent by the image image determination circuit 10 and the previous image frame (Previous Field) previously stored in the internal (or external) graphic memory 11 of the drive unit are compared by the comparison circuit 12. When the comparison is made and the data is different, it is regarded as a moving image. Usually, it is a well-known overdrive circuit operating principle that moving image data is sent through the reference table (LUT) arithmetic circuit 13 using a table reference method and corresponding output voltage interest value of the overdrive.

  The reference table (LUT) uses a new overdrive voltage V 'value table for reference distribution, and represents non-linear and complex operations consistently with constants. Increase processing efficiency. The output voltage value sent out is output as an overdrive voltage V ′ in accordance with the segment electrode, so that the amplitude selective drive (APT) used in conventional passive nematic liquid crystal display devices (TN type and STN type) is used. ) Reaction time can be reliably shortened, and the blurring phenomenon of the reproduced moving image can be suppressed.

  Since the passive nematic liquid crystal display device is a kind of passive configuration, it does not have a switching element inside each pixel. The charge stored in the liquid crystal after charging the capacitor cannot be locked. Therefore, after the voltage is output from the segment electrode, the charge in the liquid crystal capacitor leaks from the stray capacitance or its charging path, so that the liquid crystal capacitor cannot be maintained at a fixed level. For this reason, after the segment electrode is charged in one image frame time, the net effective potential of the liquid crystal pixel capacitor is much smaller than the output of the segment electrode, and the blurring phenomenon of the contour portion is displayed on the moving image display. It will cause.

  Further, the drive compensation method is necessary for comparing the data of the previous image frame with the current image frame data, and also needs to store the compensated image (compensation voltage) data after the comparison. Therefore, it is necessary to add a storage capacity of the graphic memory in order to save the compensated image (compensation voltage) data after the comparison. As a result, there is a shortage of memory inside the drive integrated circuit (IC), and it is necessary to add a double memory space. This increases the memory capacity of the product and increases production costs. It is forced to increase the die size of (IC).

  In order to solve the above-described drawbacks and to eliminate the disadvantages, the present invention performs amplitude selection driving of passive nematic liquid crystal display devices such as twisted nematic type (TN) and super twisted nematic type (STN). In addition to the high-frequency update rate method, the compensation method is added, and bit re-allocation of the stored data is performed, and the total of both the original and overdrive data before and after the odd number and even number and the conventional odd number and even number The response time of passive nematic liquid crystal display devices such as twisted nematic type (TN) and super twisted nematic type (STN) under the condition that the number of storage bits of the three primary colors (RGB) is the same and no graphic memory (GRAM) is added. To improve the blurring phenomenon of moving images.

  In order to realize the above-described object, the driving method for improving the reaction time of the TN type and STN type liquid crystal display device without adding the graphic memory according to the present invention uses the operation principle of overdrive to determine the current three primary colors as a moving image. When the data of the current image frame and the previous image frame differ depending on the function, the corresponding overdrive three primary color data is output using the table reference method of the reference table (LUT) arithmetic circuit. In order to reduce the storage space for graphic memory, the three primary color data of the current image frame is replaced with YCbCr data, and the output overdrive three primary color data of the current image frame is replaced with overdrive YCbCr, The overdrive YCbCr data is compressed according to the video compression standard, sampled and aligned, the CbCr storage bits of the YCbCr data are reduced, and the YCbCr storage bits of the overdrive YCbCr are reduced. The YCbCr data whose number of bits has been reduced due to the redistribution of data bits and the overdrive YCbCr data are stored together in the graphic memory, and the frequency division multiplex output circuit allows flexible overdrive within the update time of each data bus. YCbCr data is given to N times of overdrive compensation potential higher (or lower) than the conventional output potential. Wherein, N is an integer equal to or greater than 2, less than or equal to 8.

  Among them, the three primary color data output from the overdrive is calculated using a reference table, and the overdrive compensation potential corresponding to each image is specified and given. The overdrive compensation potential is greater than 0 or less than or equal to the highest voltage for driving the liquid crystal. On the other hand, sampling after compressing the three primary color data to YCbCr is Y: Cb: Cr = 4: 2: 2, Y: Cb: Cr = 4: 2: 0 and Y: Cb: Cr = 4: 1: 1 Any sampling operation rule is used.

  This usually outputs one data voltage for one frame time to charge the liquid crystal capacitor. However, the passive nematic liquid crystal display devices (TN type and STN type) do not have a switch element, so the charge inside the liquid crystal capacitor leaks from the stray capacitance or charging path, and after one image frame time has passed, the liquid crystal capacitor Will not meet the voltage level desired by the data bus. In addition to outputting N times (ie, charging the pixel capacitor N times in one image frame time) within one image frame time, the present invention outputs higher (or lower) overdrive. Due to the slow reaction time that occurs in passive nematic liquid crystal display devices such as twisted nematic type (TN) and super twisted nematic type (STN) by twisting the liquid crystal in a shorter time to give the compensation voltage and realizing the predetermined brightness The problem of blurring can be greatly improved.

  With the overdrive method, a desired luminance is realized by driving a plurality of times within one image frame time. Therefore, the effect of improving the reaction time is also obtained at a voltage of a few bits less or less accurate. Therefore, without adding a graphic memory, the previous image frame and the current image frame are stored in a single graphic memory inside the conventional driving integrated circuit (IC) by combining the data after the overdrive compensation processing. The purpose of improving the reaction time of twisted nematic and super twisted nematic (TN / STN) passive nematic liquid crystal displays can be realized.

In the invention of claim 1, the drive system includes the following items,
If the contents of the current image frame and previous image frame data are different by the moving image judgment function using the principle of driving operation and the current image frame and the previous image frame data contents are different, output the three primary color data of the current image frame and convert the three primary color data of the current image frame to YCbCr data. Replace the overdrive three primary color data with overdrive YCbCr data, and
Compress YCbCr data of current image frame and YCbCr data of overdrive according to video compression standard, perform sampling and alignment,
Decrease the CbCr storage bit of the current image frame YCbCr data, reduce the YCbCr storage bit number of the overdrive YCbCr, save the YCbCr data and the overdrive YCbCr data whose bits are reduced by redistribution in the graphic memory, and ,
A graphic characterized in that an overdrive compensation potential higher or lower than the conventional output potential is specified and given N times in accordance with overdrive YCbCr data within the update time of each data bus through a frequency division multiplex output circuit. This is a driving method for improving the reaction time of TN type and STN type liquid crystal display devices without adding memory.
According to a second aspect of the present invention, the overdrive three primary color data is output to the respective overdrive compensation potentials via the reference table arithmetic circuit, and the overdrive compensation potential is greater than or equal to 0. 2. The driving method for improving the reaction time of the TN type and STN type liquid crystal display device without adding a graphic memory according to claim 1, wherein the driving voltage is less than or equal to the maximum voltage of liquid crystal driving.
In the invention of claim 3, the compression sampling is any of Y: Cb: Cr = 4: 2: 2, Y: Cb: Cr = 4: 2: 0 and Y: Cb: Cr = 4: 1: 1. The driving method for improving the reaction time of the TN type and STN type liquid crystal display device without adding the graphic memory according to claim 1, wherein the sampling calculation rule is used.
The invention according to claim 4 is characterized in that the N is an integer greater than or equal to 2, less than or equal to 8, and a TN-type and STN-type liquid crystal display device without addition of graphic memory according to claim 1 This is a driving method for improving the reaction time.

  Amplitude selective driving of passive nematic liquid crystal display devices such as twisted nematic type (TN) and super twisted nematic type (STN) of the present invention is a method of high frequency update rate by adding inter-gamut data replacement and overdrive compensation means. In addition, bit re-allocation of stored data is performed, and the total number of original data and overdrive data before and after is the same as the total number of stored bits of the conventional odd and even three primary colors (RGB). Therefore, in the condition that no graphic memory (GRAM) is added, the reaction time of passive nematic liquid crystal display devices such as twisted nematic type (TN) and super twisted nematic type (STN) is improved, and the blurring phenomenon of moving images To improve.

  According to the driving system of passive nematic liquid crystal display devices such as twisted nematic type and super twisted nematic type (TN / STN), data of driving integrated circuit (IC), digital red, green and blue three primary color data input to each image frame, Convert to each grayscale output voltage. Twisted nematic type (TN) and super twisted nematic type (STN) have only two colors, white and black, while gray scale has a pulse width modulation (Pulse Width Modulation, PWM) for one line time. Colors are divided according to the method. FIG. 2 shows a schematic diagram of an output waveform within a scanning frame time in which one segment electrode is provided. In the case of m scanning lines (m × n nematic display device) within one image frame time, when one read / write (WR) cycle is set to one scanning line time (1 line time), from FIG. It can be seen that the electrodes output different pulse width modulation waveforms with different gray scale output voltages included in the data.

  As shown in FIG. 3, the charge time of one scanning line is divided into 16 equal parts, and the segment electrode signal SEG0 has 6/16 in all black equal parts in one line time. One line occupies 12/16, and the segment electrode SEG1 occupies 13/16 for all black in this one line time, and the next one line occupies 10/16. However, since there is no switching element inside the pixel of the passive nematic liquid crystal display device, after the voltage is output from the segment electrode, the charge in the liquid crystal capacitor leaks from the stray capacitance or the charging path, so that the liquid crystal capacitor has a certain level. Can't keep up. As a result, after the segment electrode is charged in one image frame time, the net effective potential of the liquid crystal pixel capacitor is much smaller than that output from the segment electrode.

  FIG. 4 shows a schematic diagram from the initial lighting of the liquid crystal to the desired luminance position in one pixel. The segment electrode is charged for several image frame times, and the liquid crystal inside the pixel reaches the effective voltage Veff from the initial position to the target position, which is the twisted nematic type (TN) and the super twisted nematic type (STN). ) And the like, which slows the reaction time of the passive nematic liquid crystal display device. The segment electrode of one image frame time has a charging voltage Vl for the liquid crystal capacitor, but since there is further stray capacitance or leakage voltage dl of the charging path, the segment electrode of the first image frame time is effective for the final liquid crystal capacitor The voltage is V1-d1 = Veff1. By analogizing this, the effective voltage for the liquid crystal capacitor of the segment electrode in the second frame time is V1-d1 = Veff2. If the desired luminance is realized by outputting the same voltage 12 times from the segment electrodes, the reaction time of the liquid crystal display device is one image frame time 16.67 ms × 12, which is approximately 200 ms.

  FIG. 5 shows a block schematic diagram of the overdrive circuit of the present invention. In the present invention, a different overdrive voltage V1 value is specified for each image frame using a normal overdrive operation principle, and the image determination circuit 20 preliminarily stores data of a current image frame (Current Field) to be newly introduced, The previous image frame (Previous Field) data in the graphic memory 21 stored inside (or outside) the drive device is compared by the comparison device 22, and if it is different, it is determined as a moving image. Usually, after the moving image data is referred to by the reference table (LUT) arithmetic circuit 23 using the table reference method, the corresponding overdrive voltage V ′ value is output.

  In the present invention, after the data is input to the three primary color (RGB) data bus and the data of the current image frame is different from the previous image frame by the moving image determination comparison device 22, the reference table (LUT) calculation circuit 23. The overdrive compensation potential V ′ higher (or lower) than the conventional output potential V is applied N times within the update time of each data bus via the frequency division multiple output circuit 24 provided after the N and the N value is 2 An integer greater than or equal to, less than or equal to 8 (2 ≦ N ≦ 8). Further, the compensation potential V ′ refers to the conventional output voltage V from the reference table (LUT) and outputs a corresponding overdrive output voltage value. The voltage range is 0 ≦ V ′ ≦ maximum voltage for driving the liquid crystal. Therefore, the rate of writing to the display panel from the segment electrode of the drive element is N times the update rate input to the three primary color (RGB) data bus.

  FIG. 6 is a schematic diagram in which the segment electrode of the drive element is N times (6 times) the update rate of the input data bus, and the comparison rate with the conventional update rate. On the right side, the segment electrode takes the same output voltage V1 over six image frame times until the liquid crystal in one pixel reaches the target voltage level (Target Voltage) from the initial zero level to the target brightness. The target brightness can be realized after sending out. Accordingly, the reaction time is the time 16.6 ms × 6 of each image frame (Frame), which is approximately 100 ms. Among them, dl represents a voltage level dragged by a pixel leakage path. 6 shows the output level V1 of the segment electrode according to the present invention within one data update time (that is, one image frame time) via the frequency division multiplex output circuit 24 according to the present invention. Repeat for 6 times. As a result, the target luminance desired for the liquid crystal can be realized in one image frame time, so that the reaction time can be shortened to one image frame time = 16.6 ms.

  FIG. 7 is a schematic diagram in which the segment electrodes of the drive elements are written to the panel by the overdrive voltage and the rate is N times (6 times) the update rate of the input data bus, compared with the conventional update rate. Refer to the left side of the figure. If the output voltage V1 of the segment electrode is replaced by the overdrive voltage V ', if the reaction time is further shortened (the reaction time is less than one image frame time), the twisted nematic type (TN) and the super twisted nematic The improvement effect on the slow reaction time of the passive nematic liquid crystal display device such as the type (STN) is even greater. Such a method can make the effective voltage output of the segment electrode larger (or smaller) than the conventional output potential V, and can output a plurality of times in one data update time. Therefore, the liquid crystal is twisted in a shorter time to achieve the desired target luminance of the present invention, and the passive nematic liquid crystal display device such as twisted nematic type (TN) and super twisted nematic type (STN) has a slow reaction time, so the movement It can greatly improve the problem that causes blurring on the screen.

  FIG. 8 shows a schematic diagram of an over-driving compensation segment electrode level waveform (output level overdrive in FIG. 3). In the segment electrode SEG0 after overdrive, in one line time, the all black equality occupies 13/16 of each scan line time (1 line time), and the next one line is 14/16. Occupy. In addition, in the time of one line with the segment electrode SEG1, the total black equality occupies 15/16, and the next one line occupies 12/16.

  In the present invention, the segment electrode is subjected to N overdrive compensations within each data update time, so that the liquid crystal inside the pixel is moved from the initial position in a shorter time (close to one image frame time). Since the target brightness of the effective voltage Veff up to the target position is reached or brought close to, the blur phenomenon of the moving screen can be greatly improved. The basic drive system of the twisted nematic type (TN) and the super twisted nematic type (STN) is amplitude selective drive (APT). The operation principle uses an electro-optic effect generated from the root mean square value (RMS) of the voltage applied from the liquid crystal material. Therefore, even when the overdrive voltage compensation method of the present invention is applied to the root mean square (RMS) value, severe flicker does not occur.

  Furthermore, in the storage of graphic data, the conventional overdrive voltage compensation method saves the data of the entire image frame after the comparison of the previous image frame and compares it with the image frame data captured at the present time. Must be added. The present invention replaces the three primary color (RGB) data of the image data with YCbCr, compresses it according to the video compression standard, and performs sampling and matching (shown in FIG. 5). For the data of the previous image frame, first, the first conversion unit 25 accepts the three primary color (RGB) image data of the previous image frame, and replaces the three primary color (RGB) data with YCbCr data. On the other hand, for moving images, after replacing the YCbCr data with the overdrive YCbCr, the YCbCr data and the overdrive YCbCr data are compressed according to the video compression standard, sampled and matched, and then the YCbCr data is stored inside the drive unit (or externally). ) In the graphic memory 21, and the second conversion unit 26 replaces the YCbCr data with the three primary color (RGB) data again and transmits the data to the comparison device 22. Among them, the compression sampling is any sampling rule of Y: Cb: Cr = 4: 2: 2, Y: Cb: Cr = 4: 2: 0 and Y: Cb: Cr = 4: 1: 1. Use. Y represents a luminance signal, and Cb and Cr represent color differences. The Y component that is most sensitive to human vision is proportionally sampled and compressed, and then stored in the graphic memory to reduce the required memory capacity of the drive unit.

  As shown in FIG. 9, if the format of the RGB data is 6 bits, before the inter-gamut data is replaced, the three primary color (RGB) data of the odd and even 18 bits in each set are totaled to 36 bits. In the present invention, data conversion between Y: Cb: Cr = 4: 2: 2 color gamut is performed for odd and even RGB, and the amount of stored data is reduced. Therefore, the data of the previous image frame after conversion is 24 bits, the data of the overdrive compensation screen is also 24 bits, 48 bits after adding both, which is 12 bits more than the conventional 36 bits. As a result, it is necessary to add 1/3 of the memory capacity. Therefore, inter-gamut data conversion is performed, and Y: Cb: Cr = 4: 2: 2. Also, by performing bit re-allocation with a reduced number of bits in Cb and Cr of the original YCbCr data after conversion, the original 6-bit storage is changed to 5-bit storage. The original YCbCr data occupies a total memory capacity of 20 bits. On the other hand, the odd and even overdrive YCbCr data Y ', Y' after conversion occupy a 5-bit memory capacity, and Cb 'and Cr' take only 3 bits of space. Therefore, the driving YCbCr data occupies a total of 16 bits. By converting data between gamuts and redistributing stored data bits, the total of both the original and overdrive data before and after the odd and even data is 36 bits. It is the same as the amount of data. Therefore, the present invention improves the reaction time of passive nematic liquid crystal display devices such as twisted nematic type (TN) and super twisted nematic type (STN) under the condition that no graphic memory is added, and blurring phenomenon of moving images. Can be improved.

  The fact that the number of stored bits can be reduced is because the response time of the passive nematic liquid crystal display device is slow, and the above-described method realizes a desired luminance by driving a plurality of times within one image frame time. Even with a small number of voltages or a less accurate voltage, the reaction time can be improved. For this reason, without adding graphic memory, the previous image frame and the current image frame are combined with the data after overdrive compensation processing and stored in one graphic memory inside the conventional driving integrated circuit (IC), and the twisted nematic type Realize the purpose of improving reaction time of super twisted nematic (TN / STN) passive nematic liquid crystal display.

It is a calculation block schematic diagram of a normal overdrive circuit. FIG. 6 is a schematic diagram of an output waveform within a scanning frame time when a segment electrode is one; The segment electrode signal is a schematic diagram of an output level and a waveform obtained by dividing one line time into 16 equal parts. FIG. 6 is a schematic view from the initial lighting of the liquid crystal in one pixel to the desired luminance position. It is a block schematic diagram of the overdrive circuit of the present invention. The write rate to the panel of the segment electrode of the drive element is N times (64 times) the update rate of the input data bus, and is a schematic diagram compared with the conventional update rate. The segment electrode of the drive element is written to the panel by the overdrive voltage, and its rate is N times (6 times) the update rate of the input data bus, and is a schematic diagram compared with the conventional update rate. The segment electrode signal (SEG) for overdrive compensation is a schematic diagram of output levels and waveforms obtained by dividing one line time into 16 equal parts. It is the schematic of YCbCr (4: 2: 2) conversion and bit number reduction of three primary color data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image image judgment circuit 11 Graphic memory 12 Comparison circuit 13 Reference table (LUT) arithmetic circuit 20 Image judgment circuit 22 Comparison apparatus 21 Graphic memory 23 Reference table (LUT) arithmetic circuit 24 Frequency division multiplexing circuit 25 1st conversion unit 26 2nd Conversion unit

Claims (4)

The drive system includes the following items:
If the contents of the current image frame and previous image frame data are different due to the moving image judgment function using the principle of driving operation and the current image frame and the previous image frame data contents are different, the three primary color data of the current image frame is output to YCbCr data. Replace the overdrive three primary color data with overdrive YCbCr data, and
Compress YCbCr data of current image frame and YCbCr data of overdrive according to video compression standard, perform sampling and alignment,
Decrease the CbCr storage bit of the current image frame YCbCr data, reduce the YCbCr storage bit number of the overdrive YCbCr, save the YCbCr data and the overdrive YCbCr data whose bits are reduced by redistribution in the graphic memory, and ,
A graphic characterized in that an overdrive compensation potential higher or lower than the conventional output potential is specified and given N times in accordance with overdrive YCbCr data within the update time of each data bus through a frequency division multiplex output circuit. Driving method for improving reaction time of TN type and STN type liquid crystal display devices without adding memory.   The overdrive three primary color data are output to the respective overdrive compensation potentials via the reference table arithmetic circuit, and the overdrive compensation potential is greater than or equal to 0 and less than the highest voltage for driving the liquid crystal. 2. The driving method for improving the reaction time of TN type and STN type liquid crystal display devices without adding a graphic memory according to claim 1, wherein the driving time is not equal to or equal to or equal in range.   The compression sampling should be set to any sampling calculation rule among Y: Cb: Cr = 4: 2: 2, Y: Cb: Cr = 4: 2: 0 and Y: Cb: Cr = 4: 1: 1. The driving method for improving the reaction time of the TN type and STN type liquid crystal display device without adding a graphic memory according to claim 1 or 2.   2. The driving method for improving the response time of TN type and STN type liquid crystal display devices without adding a graphic memory according to claim 1, wherein N is an integer greater than or equal to 2, less than or equal to 8.

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