Line compensated overdriving circuit of color sequential display and line compensated overdriving method thereof

A line compensated overdriving circuit for use in a color sequential display is disclosed. The line compensated overdriving circuit comprises an overdrive unit, a line compensation generator, and a line compensated overdrive (LCO) processor. The overdrive unit receives previous data and present data to output overdrive data. The line compensated generator receives a line position of each pixel to output a line compensated factor, and the LCO processor receives the line compensated factor and the overdriven data to generate compensated data for the pixel. Thus, the line compensated overdriving circuit can eliminate the spatial intensity variations associated with the conventional color sequential displays.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to overdriving circuits of color sequential displays, and more particularly to line compensated overdriving circuits of color sequential liquid crystal displays (LCDs).

2. Description of the Related Art

In recent years, the flat panel display (FPD) industry has been focused on developing liquid crystal displays (LCDs), especially on developing thin film transistor (TFT) LCDs, and hoping to replace the role of cathode ray tube (CRT) displays in video applications. Each pixel on a TFT LCD is provided with a switching transistor for enabling image data to be written into a panel of the display.

One way of displaying the TFT LCD is to use color sequential technology. A typical frame for displaying a color image is divided into three subframes for the three primary colors of red, green and blue, and each subframe is further divided into a subframe writing period and a subframe illumination period. To display the color image, the TFT LCD is first addressed line by line by display drivers to write image data of the corresponding primary color into the pixels during the subframe writing period, in the meanwhile, capacitors located at each pixel are charged to set the liquid crystals in the pixels to their light transmittive states for displaying appropriate gray values of the corresponding primary color. Then, during the subframe illumination period, light sources, such as light emitting diode (LEDs), are turned on to display the corresponding primary color component of the color image, such that these three primary color components can be compositely perceived as a full-color image. However, the color sequential display is likely to suffer spatial intensity variations, which may cause the bottom portion of the TFT LCD to appear dimmer.

The spatial intensity variations associated with the conventional line addressing method is primarily due to insufficient pixel response times. Conventionally, during the subframe writing periods, the addressing of scan lines usually follows a unidirectional sequence such as from top to bottom or from bottom to top.FIG. 1illustrates the pixel response time associated with a conventional line addressing method during a subframe writing period of a subframe. Taking a red subframe writing period Tr′ for illustration, as shown inFIG. 1, suppose the line addressing sequence is from top to bottom, that is, the top line of the panel is addressed first, and the bottom line of the panel is addressed last. Since the pixels on the top line are first addressed, the pixels on the top line would have sufficient time to respond, that is, have a longest pixel response time of TR1that is substantially close to the red subframe writing period Tr′. In turn, the pixels on the next line would have a pixel response time of TR2that is a little shorter that TR1. Yet, the pixels on the following lines would have even shorter pixel response times than TR2. Since the pixels on the bottom line are addressed last and a substantial part of the red subframe writing period has elapsed; the pixels on the bottom line would have a shortest pixel response time of TRn. The response time TRn is significantly less than TR1. Therefore, the pixels on the bottom lines, in case the line addressing sequence is from top to bottom, often do not have sufficient response times to appropriately charge the capacitors that are positioned at each pixel to set liquid crystals in the pixels to their light transmittive states for displaying the appropriate gray value. Consequently, the bottom portion of the panel in the conventional color sequential display often appears dimmer.

Hence, there is a need to provide a novel line compensated overdriving circuit and line compensated overdriving method, such that the spatial intensity variations associated with color sequential display can be greatly eliminated.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a novel line compensated overdriving circuit and line compensated overdriving method for use in a color sequential display such that the spatial intensity variations can be greatly eliminated.

The invention achieves the above-identified object by providing an line compensated overdriving circuit for used in a color sequential display. The line compensated overdriving circuit includes an overdrive unit, a line compensation generator and a line compensated overdrive (LCO) processor. The overdrive unit receives previous data and present data to output overdrive data, wherein the previous data have been used to drive the pixels in a previous subframe. The line compensated generator receives a line position of each pixel to output a line compensated factor, and the LCO processor receives the line compensated factor and the overdrive data to generate a compensated data to drive the pixel.

The invention achieves the above-identified object by further providing a polarity checking unit in the overdrive unit. The polarity checking unit compares the previous data with the present data to output a polarity factor, such that the LCO processor generates the compensated data in response to the overdrive data, the line compensated factor, and the polarity factor.

Also, the invention achieves the above-mentioned object by providing a line compensated overdriving method of a color sequential display. The steps include: first, receiving previous data that have been used to drive the pixels in a previous subframe; then, receiving present data; next, determining an overdrive data in response to the previous data and the present data; then, receiving a line position of each pixel; then, determining a line compensated factor in response to the line position; and outputting, for the pixel, a compensated data in response to the line compensated factor and the overdrive data.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2shows a block diagram of a color sequential display according to a preferred embodiment of the invention. The color sequential display300, such as a color sequential liquid crystal display, includes an line compensated overdriving circuit310, a source driver250, a gate driver260, and a panel270. The line compensated overdriving circuit310outputs compensated data DATA″(t) to drive a pixel on panel270via the source driver250. The panel270includes pixels that are arranged in a matrix of rows and columns, and receives DATA″(t) from the source driver250for writing into the pixels. Preferably, the color sequential display is a color sequential liquid crystal display (LCD), such that the panel of the color sequential LCD has liquid crystals located at each pixel of the panel.

FIG. 3Ashows a block diagram of one example of the line compensated overdriving circuit300. The line compensated overdriving circuit300includes an overdrive unit310, a line compensated overdrive (LCO) processor320, and a line compensation generator330. The overdrive unit310includes a data comparator312receiving previous data DATA(t−1) and present data DATA(t). The previous data DATA(t−1) refers to data that have been used to drive the pixels during a previous subframe. The preset data DATA(t) refers to data that are about to drive the pixels during a present subframe. The previous data DATA(t−1) is typically being temporarily stored and retrieved from a buffer (not shown). Upon receiving, the data comparator312compares present data DATA(t) with the previous data DATA(t−1), and outputs an overdrive data DATA′(t), such as by means of a look-up table, in order to overdrive the pixels depending both on the present data DATA(t) and the previous data DATA(t−1).

Furthermore, the line compensation generator330is provided to receive a line position M of each pixel, for example, the line position M is obtained based on the horizontal synchronization signal. From the line position M of the pixel, the line compensation generator330outputs a line compensated factor α. The line compensated factor α, for instance, is derived according to a table look-up method, such that the compensated factor α for the pixels on the bottommost line is greatest in order to shorten pixel response time and the compensated factor α for the pixels on the topmost line is smallest. By this, the spatial intensity variations associated with the conventional line addressing method, for example, in case the line addressing sequence is from top to bottom, can be effectively compensated. The LCO processor320receives the line compensated factor α from the line compensation generator330, and the overdrive data DATA′(t) from the overdrive unit310, and generates a compensated data DATA″(t) to drive the pixel of the present data DATA(t). More specifically, the compensated data DATA″(t) is generated by multiplying the line compensated factor α and the original overdrive data DATA′(t), as shown in the following equation:
DATA″(t)=DATA′(t)*α  (1)

Consequently, based on equation (1), the compensated data DATA″(t) is generated by LCO processor320and written into the pixel, thereby driving the pixel of the present data DATA(t).

FIG. 3Bshows a block diagram of another example of the line compensated overdriving circuit300. In addition to the data comparator312, the overdrive unit310further includes a polarity checking unit314that compares the previous data DATA(t−1) with the present data DATA(t) to output a polarity factor Pol. Referring toFIG. 3B, the LCO processor320further receives the polarity factor in addition to the overdrive data Data′(t) and the line compensated factor α, and generates the compensated data Data″(t) in response to the overdrive data Data′(t), the line compensated factor α and the polarity factor POL. More specifically, the compensated data DATA″ (t) is generated by summing the overdriven data DATA′(t) and a product of the polarity factor POL and the line compensated factor α, as shown in the following equation:
DATA″(t)=DATA′(t)+POL*α(2)

Also, in equation (2), the polarity of the polarity factor POL is dependent of the preset data DATA(t) and the previous data DATA(t−1). Namely, the polarity factor POL is negative if the present data DATA(t) is smaller than the previous data DATA(t−1). Otherwise, the polarity factor POL is positive.

Consequently, based on equation (2), the compensated data DATA″(t) is generated by the LCO processor320and written into the pixel, thereby driving the pixels corresponding to the present data DATA(t).

With the line compensated overdriving circuit300as illustrated, the pixel response time required for the pixels on the bottom lines of the panel, in case the line addressing sequence is from top to bottom, can be effectively reduced due to the compensated data DATA″(t) generated by the LCO processor320. In this case, the pixels on the bottom lines can have sufficient time to properly charge the capacitors at each pixel to their light transmittive states, and thus display the appropriate gray value. Hence, the spatial intensity variations associated with the conventional color sequential display can be effectively reduced, and users are able to perceive color images on the panel as having evenly distributed brightness.

The invention also provides a line compensated overdriving method for a color sequential display, as shown inFIG. 4, in order to reduce the spatial intensity variations associated with the conventional line addressing method. First, step410is performed to receive previous data DATA(t−1) that have been used to drive the pixels during a previous subframe. Then, in step420, present data DATA(t) are received, which are about to drive the pixels in the coming subframe. Next, step430is performed to determine an overdrive data DATA′(t) in response to the previous data DATA(t−1) and the present data DATA(t). In step440, a line position M of each pixel is received. In step450, a line compensated factor α in response to the line position M is determined. Then, step460is performed to output a compensated data DATA″(t) in response to the line compensated factor α and the overdrive data DATA′(t), in order to drive the pixels of the present data DATA(t) in the coming subframe.

In one example of the invention, step460further comprises the steps of comparing the present data DATA(t) and the previous data DATA(t−1) to output a polarity factor POL; and generating the compensated data DATA″(t) in response to the polarity factor POL, the line compensated factor α and the overdrive data DATA′(t).