KR101598219B1 - Display driver method and apparatus - Google Patents

Abstract

An image display system that provides an LCD overdrive drive scheme is disclosed. The method includes measuring a stable transmission level of an LCD display pixel corresponding to a target drive level. The overdrive transfer level is measured corresponding to the overdrive drive level. The measured overdrive transmission level is compared with the measured stable transmission level to determine whether the overdrive drive level is too high or too low. The iterative process then changes the overdrive drive level until an appropriate overdrive drive level is found. This is used to derive overdrive drive parameters stored in the memory of the LCD device. If an overdrive approach is determined during use of the device, the overdrive approach considers temperature and display aging without the effect of modeling temperature and display aging.

Description

DISPLAY DRIVER METHOD AND APPARATUS [0001]

This application claims priority to U.S. Provisional Application No. 61 / 017,809, filed December 31, 2007, the entire contents of which are incorporated herein by reference.

This application claims priority to European Patent No. 08163613.6, filed September 3, 2008, which is hereby incorporated by reference in its entirety.

The present invention relates to a driver for driving pixels of a display panel. The present invention also relates to a display module comprising such a driver, an apparatus comprising such a display module, and a method of providing an LCD overdrive drive scheme.

More and more LCD display modules are being used to display motion pictures and TV signals. Objects moving fast in a picture are a challenge for LCD display modules.

The reason is due to the response time of the pixels of the LCD display module to the changes required for luminance. Overdrive technology is known to improve response time.

Without overdrive, when a luminance change of a pixel is required, a driving voltage is finally applied to the pixel so as to reach a desired luminance. The luminance of the pixel gradually changes from the starting luminance to the desired luminance. When a moving image or a TV signal is to be displayed, the change required for luminance needs to be achieved within a short period called a so-called frame period. The frame period is a duration during which a single image of a moving image or a TV signal is supplied to the display module. During the frame period, all pixels of the display panel are processed once to receive the driving voltage.

When applying the required driving voltage to the pixel to achieve the desired luminance, the actual luminance of the pixel lags behind the desired luminance due to the inertia of the pixel. Several processing periods may be required until the desired brightness is achieved, which results in a blurred edge or ghost image.

In order to shorten the reaction time of the pixel, an overdrive voltage is applied. The level of the overdrive voltage ultimately exceeds the level of the driving voltage required to obtain the desired luminance, and thus aims at overdrive luminance exceeding the desired luminance. When applying an overdrive voltage, it usually takes some processing time to reach the overdrive luminance. However, when the overdrive voltage is carefully selected, the luminance achieved at the end of a single processing period is equal to the desired luminance.

When good motion fidelity is expected, overdrive is recognized as a basic requirement for the AMLCD. A single frame LC response at 60 Hz will not be sufficient in the future because many driving schemes aimed at removing sample-and-hold motion artefacts follow a high frame rate of 120 Hz or higher, Is increased.

Using the overdrive technique, the desired luminance is reached in one processing period, and therefore the reaction time of the pixel is artificially increased. The overdrive voltage required to achieve the desired brightness depends on the required brightness variation and onset brightness, and also on other variables, such as the type of display module and the frame rate at which the display operates. Therefore, the overdrive voltage is usually listed in the look-up table (LUT).

Typically, a unique look-up table for all AMLCD designs is required, possibly requiring batch to batch or even module-to-module tuning. Also, if overdrive accuracy is maintained, the LUT must vary with ambient temperature and display frame rate. Presently, it is unclear how much overdrive inaccuracies are acceptable in many applications, so it is not clear how much LUT data should be stored if a frame rate flexible system and / or a temperature compensation system is implemented.

A standard approach to implementing overdrive is to measure the LUT for each module design (batch, module) in the factory and store the measurements in the system's AMLCD module or elsewhere (EP) ROM. This forces the manufacturer to compromise performance because it creates significant logistical challenges for the manufacturer and also needs to reconcile the overdrive accuracy with the cost of ROM, temperature sensors, and so on. Thus, implementing overdrive as an integral part of an AMLCD module can be accomplished by designing each new module design, perhaps each new batch realizing a production line, or even a professional measurement that needs to be performed separately for each module This is a difficult logistical task for the module manufacturing that is caused. In addition, there is a challenge to store enough measurement data to ensure a sufficiently accurate overdrive for an application. The latter is more important in portable devices where the intended operating temperature range may cause a demand for temperature compensated overdrive.

According to the present invention there is provided a method of providing an LCD overdrive drive scheme comprising the steps of:

(i) measuring a stable transmission level of an LCD display pixel of an LCD device when the target driving level becomes a stable transmission level;

(ii) measuring an overdrive transmission level of the display pixel at the end of one frame after application of the overdrive drive level;

(iii) comparing the measured overdrive transmission level with the measured steady transmission level to determine whether the overdrive drive level is too high or too low;

(iv) if the overdrive drive level is too high or too low, change the overdrive drive level and repeat steps (ii) and (iii) until a proper overdrive drive level is found; And

(v) using the appropriate overdrive drive level found to derive the overdrive drive mode parameters, and storing the parameters in the memory of the LCD device.

This method allows the overdrive method to be determined during use of the device. Moreover, temperature and display aging can be considered without the effect that may be caused by temperature and display aging being modeled. Thus, the present invention allows the module manufacturer to fully understand the overdrive characteristic and avoid the need to maintain the LUT measurement function. You can avoid logistics efforts to supply each new product, product update, or product batch to the correct LUT. Overdrive accuracy is also provided automatically over temperature range and frame rate.

The measurements are compared, which reduces the accuracy requirement for the measurements.

This method can be implemented automatically and periodically or continuously as part of the normal operation of the AMLCD module in the background, using a robust and simple method. Thus, the logistics task is removed and a means for compensating for the temperature change is provided.

The transmission level may be measured by an optical sensor (i.e., a direct measurement) or may be derived from a measurement of an LC capacitance (i.e., an indirect measurement).

The LCD display pixels may comprise dummy pixels (or rows of pixels or a plurality of rows of pixels) of an LCD device. This means that the method of deriving the overdrive parameter can be implemented without affecting the normal display function. Thus, the method can be performed as a background function using the dummy pixel (s) during normal use of the display device.

The overdrive drive level may be determined to be too high if there is an overshoot of a transmission level greater than the threshold consisting of adding a predetermined amount to a stable transmission level. If the transmission level is below the threshold, the overdrive drive level is determined to be too low. This allows the simple iterative process to be defined to find the best overdrive level of a particular target drive level to be tested. For example, a suitable overdrive level may include a maximum overdrive drive level with no overshoot greater than the threshold. The overdrive drive type parameters may include LUT parameters.

The present invention also provides an LCD driver. The LCD driver includes a processor and a memory. The memory stores overdrive drive mode parameters. The processor,

(i) when the target drive level becomes a stable transmission level, measuring a stable transmission level of the display pixel;

(ii) after the application of the overdrive drive level, measure the overdrive transfer level of the display pixel at the end of one frame;

(iii) comparing the measured overdrive transmission level with the measured stable transmission level to determine whether the overdrive drive level is too high or too low;

(iv) if the overdrive drive level is too high or too low, change the overdrive drive level and repeat steps (ii) and (iii) until a proper overdrive drive level is found;

(v) to control the display pixels and measurement means to utilize the appropriate overdrive drive level found to derive overdrive drive parameters for storage in memory.

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Such a driver may be used in an LCD device that includes a display panel and means for measuring the transfer level of the LCD display pixels.

The method of the present invention can be implemented as a computer program.

The following detailed description is given with reference to the accompanying drawings.

The following description is the best considered mode for carrying out the invention. This description is intended to be illustrative of the general principles of the present invention and should not be construed in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

The present invention provides a method of providing an LCD overdrive drive scheme in which a suitable overdrive level is determined in use based on a comparison measurement between a desired transmit level of the LC pixel and a transmit level provided by a series of test overdrive levels . This provides an iterative process for determining an appropriate overdrive level and this process can compensate for these parameters without requiring detailed modeling of the effect of temperature and frame rate on the required overdrive scheme.

The present invention essentially provides overdrive drive type parameters, e.g., in the form of LUT values. The nature of the LUT measurement algorithm is described with reference to Figures 1 and 2.

Figure 1 shows the voltage profile of the pixel voltage drive level "DL " as applied to the pixel when the gate line is on.

The drive level starts at the start value DL_start indicating the drive level for the previous frame and is maintained at the overdrive level DL_overdrive before returning to the next target level DL_target.

The first step of the process is to measure the stable transmission level of the LCD display pixel when the target drive level DL_target is at a stable transmission level. The stable transmission level is shown as TL_target. For example, this stable transmission level can be measured after the target drive level DL_target is applied for a number of consecutive frames.

The overdrive transmission level of the display pixel is then measured at the end of one frame after application of the overdrive drive level DL_overdrive. The overdrive level is selected as the test overdrive value within the maximum possible overdrive range. Since this overdrive level may be too high, a considerable overshoot of the resulting pixel transmission may be as shown by the line 10, or because the overdrive level is not strong enough, Similarly, pixel transmission is still slow to respond. A good overdrive profile is shown in line 14, where the transmission level at the end of one frame period is close to the desired transmission level (TL-target). The measurement interval is shown as the area 16.

In order to determine whether the overdrive drive level is too high (leading 10) or too low (leading 12), the overdrive transmission level measured during time interval 16 is compared with the measured stable transmission level (TL_target) .

If there is an overshoot at a transmission level greater than the threshold 18 consisting of a stable transmission level (TL_target) plus a predetermined amount (TL_margin) (if it is desired that the achieved brightness never exceed the target brightness, the TL_margin value 0), it is determined that the overdrive drive level is too high. If the transmission level is less than the threshold value 18, it is determined that the overdrive drive level is too low. In this way, a simple binary comparison can be performed to determine whether the measured transmission level is too high or too low.

A suitable overdrive level may be determined to have a maximum overdrive level DL_overdrive without overshoot greater than the threshold value 18.

In order to find such an appropriate level, an iterative process in which the overdrive level changes, as described with reference to FIG. 2, may follow.

The left part 20 of FIG. 2 shows the first overdrive test after determining the target transmission level TL_target.

The applied overdrive is the value "OD test ", which may be any value in the allowable overdrive range" poss. Range "

If overshoot is detected, the sub-range of the overdrive range below the 0D test value becomes the new range. This is because the previous overdrive level was too high. This is shown by the line 22. The next overdrive test "New OD test" is the midpoint of the subrange of the range, as shown.

If no overshoot is detected in test 20, the upper range of the overdrive range becomes the new range as shown by the line 24.

This process is iteratively repeated until the final range can not be divided, and thus includes only the finest resolution of the one gray level, the overdrive signal DL_overdrive.

The end result is that a maximum override level DL_overdrive with no overshoot greater than the threshold 18 is found.

Overdrive values may be used to form the LUT, and then the LUT may be applied in a known manner. The LUT can provide overdrive levels for all starting and ending transmission levels (i.e., all variations in the transmission level). This modeling can be achieved by obtaining an overdrive level suitable for all combinations of the starting drive level (DL_start) and the target drive level (DL_target) or by performing extrapolating between smaller sets.

It is a preferred method to use the subset LUT obtained by overdrive measurement with interpolating. This is because measurements can be made very quickly. An overdrive LUT generally implements a smoothly varying surface function, so a simple linear interpolation is sufficient to extrapolate between values, which is low cost in the chip area. This also reduces the EEPROM or RAM requirement (thus, there are some LUTs in the EEPROM and the entire LUT is in the RAM), since only the subset LUT needs to be stored and the interpolation can be done with power on exist). Interpolation can even be provided in real time.

A dummy pixel may be used for the test method. One dummy pixel, preferably a plurality of pixels, can be used, for example one row of pixels or even a plurality of rows of pixels are used. This allows a plurality of overdrive repeat measurements to be acquired in parallel.

The above given technique relates to the most basic algorithm modification. This can be supplemented to achieve better efficiency, accuracy, and the like. For example, measurements may be averaged to increase accuracy, and previously recorded LUT values may be used to define a logical starting range, and so on. Thus, the algorithm can use already measured LUT values to arrive at the values that are still to be measured. This speeds up the remainder of the measurements made. In the simplest case, the possible range "poss. Range" can be narrowed further using information contained in a partially measured LUT or LUT subset. More advanced algorithms can also generate a better initial guess of the overdrive value, instead of simply selecting a value in the middle of the range.

The derived LUT can be either RAM (which is recreated each time the power is turned on) or RAM (for example, if the temperature at the last power-off was considerably different, ensuring that the incorrect LUT is not applied when the power is turned on, ) Can be stored in the EEPROM. Combination approaches are also possible depending on application requirements.

The method can be applied as a continuous background measurement. This results in an overdrive that continues to adapt to the ambient temperature, thus eliminating the need for other means for temperature compensation. Continually averaging the LUT values results in improved accuracy of the LUT over time.

Transmissions can be measured directly using photo sensing devices and backlights, or can be measured indirectly by measuring the liquid crystal capacitance associated with transmission in a known manner.

Figure 3 shows an AMLCD with a display panel 30 with direct or indirect transmission sensing elements 32 connected to the display driver integrated circuit 34 (x-Si, LTPS, etc.) via control and read lines Figure 2 illustrates a system 28 of the present invention. The display driver circuit includes circuits that implement overdrive, such as RAM and / or EEPROM memory 36 and circuitry 38 that implements the algorithm described above to derive the LUT to be stored in memory.

The transmission sensing element 32 is associated with a dummy row or rows of pixels in this example.

The algorithm may be executed by a processor running a computer program.

The algorithm may be implemented by routine hardware and software, and transmission measurements may also be implemented using known techniques, such as using a photodiode to measure the light level when known backlight brightness is applied. A backlight is partitioned so that the backlight portion behind the dummy pixel can be independently controlled. The light output from the dummy pixel can also be protected from the viewer.

It is also possible to continuously use the display normal pixels for the overdrive algorithm as an operation during drive or during use of the display.

The present invention relates in particular to mobile devices such as mobile phones, portable DVD players, MP4 players, screens for automotive applications, screens for laptops, and screens for LCD TVs.

Various modifications will be apparent to those skilled in the art.

While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. In contrast, it is intended to include various modifications and similar arrangements (as will be apparent to those skilled in the art). Accordingly, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

The invention may be more fully understood by reading the foregoing description and examples with reference to the accompanying drawings.

Figure 1 shows the pixel voltage and is used to illustrate the method of the present invention.

Figure 2 is used to illustrate the iterative processor of the method of the present invention.

3 shows a display driver and apparatus of the present invention.

Claims (9)

1. An image display system comprising a display driver, The display driver, A processor; And A memory for storing overdrive drive mode parameters, The processor comprising: (i) when the target drive level becomes a stable transmission level, measuring a stable transmission level of the display pixel; (ii) after the application of the overdrive drive level, measure the overdrive transfer level of the display pixel at the end of one frame; (iii) compare the measured overdrive transmission level with the measured steady transmission level; (iv) changing the overdrive drive level and repeating steps (ii) and (iii) until a suitable overdrive drive level is found; And (v) derive the overdrive drive type parameters for storage in the memory based on the appropriate overdrive drive level, A display pixel and a measuring means, Wherein the appropriate overdrive drive level includes a maximum overdrive drive level without overshoot greater than a threshold; And Wherein the threshold comprises adding a predetermined amount to the steady transmission level. The image display system according to claim 1, wherein the measurement means includes an optical sensor or an LC capacitance measurement device. delete delete 2. The image display system of claim 1, wherein the overdrive drive-type parameters form a look-up-table. 2. The image display system of claim 1, wherein the overdrive drive level applied in step (ii) is selected in consideration of existing overdrive drive mode parameters. 1. A liquid crystal display device (LCD) A display panel; Measuring means; And A display driver including a processor and a memory for storing overdrive drive mode parameters, The processor comprising: (i) when the target drive level becomes a stable transmission level, measuring a stable transmission level of the display pixel; (ii) after the application of the overdrive drive level, measure the overdrive transfer level of the display pixel at the end of one frame; (iii) compare the measured overdrive transmission level with the measured steady transmission level; (iv) changing the overdrive drive level and repeating steps (ii) and (iii) until a suitable overdrive drive level is found; And (v) derive the overdrive drive type parameters for storage in the memory based on the appropriate overdrive drive level, A display pixel and a measuring means, Wherein the appropriate overdrive drive level includes a maximum overdrive drive level without overshoot greater than a threshold; And Wherein the threshold comprises adding a predetermined amount to the stable transmission level. 8. The liquid crystal display of claim 7, wherein the display pixel is a dummy pixel of the LCD device. 9. The liquid crystal display of claim 8, wherein the processor derives the overdrive drive type parameters during normal use of the LCD device.

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