Abstract:
A display driving integrated circuit (IC) capable of reducing the number of transmission lines for transmitting gray-scale data from a memory. The display driving IC receives M-bit gray-scale data to represent the gray scale of one pixel and drives a panel including a plurality of pixels. The display driving IC includes a memory storing gray-scale data representing the gray scales of the plurality of pixels, a source driver receiving the gray-scale data from the memory through transmission lines and transmitting the received gray-scale data to the panel, and at least one multiplexer to transmit the M-bit gray-scale data representing the gray scale of one pixel through L transmission lines, wherein the value of L is smaller than the value of M.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
       [0001]     This application claims priority to Korean Patent Application No. 10-2005-0087856, filed on Sep. 21, 2005, the disclosure of which is herein incorporated by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field  
         [0003]     The present disclosure relates to an integrated circuit (IC) and method for driving a display and, more particularly, to a display driving IC capable of reducing the number of transmission lines for transmitting gray-scale data from a memory and a display driving method thereof.  
         [0004]     2. Discussion of the Related Art  
         [0005]     Liquid crystal display (LCD) devices are widely used for information processing devices such as notebook computers, PDAs and monitors. An LCD comprises a liquid crystal panel having a thin film transistor (TFT) substrate on which a TFT is formed, a color filter substrate on which a color filter layer is formed, and a liquid crystal layer interdisposed between the two substrates. An LCD device displays an image by applying a controlled electric field to the liquid crystal layer to control the alignment of the liquid crystal and the quantity of light transmitted.  
         [0006]     An LCD panel includes pixels formed at the intersections of a plurality of scan lines for transferring a gate select signal and a plurality of data lines for transferring color data or gray-scale data.  
         [0007]     Driving ICs for driving a display device such as an LCD commonly include a scan driver for driving the scan lines and a source driver for driving the data lines. The scan driver and the source driver can be integrated into a single chip. An example of a source driver circuit for an LCD is disclosed in U.S. Pat. No. 6,747,626. In the &#39;626 patent, a source driver circuit for driving an LCD includes a shift register, a plurality of data inputs connected to the source driver circuit for receiving input data indicative of an image to be displayed on the LCD, a plurality of sample registers coupled to the shift register, and hold registers coupled to the sample registers.  
         [0008]      FIG. 1A  is a block diagram of a conventional display driving IC  20 . Referring to  FIG. 1A , the driving IC  20  for driving a panel  10  includes a source driver  21   a  and a memory  22   a . The driving IC  20  receives a control signal CON from an external controller  30  and drives the panel  10 . The memory  22   a  stores gray-scale data corresponding to frames of images to be displayed on the panel  10 . The gray-scale data is transmitted to the source driver  21   a  through a scan port of the memory  22   a . In this case, all of the bits of the gray-scale data representing a gray scale of one pixel are transmitted in parallel.  
         [0009]     In general, the size of the memory  22   b  decreases as the LCD becomes smaller, but, as shown in  FIG. 1B , reduction in the size of the source driver  21   b  is limited, for example, due to the voltage applied to the source driver  21   b . The required wiring space increases the height of the chip in which the driving IC is formed, and an increase in height is often not an acceptable option.  
       SUMMARY OF THE INVENTION  
       [0010]     Exemplary embodiments of the present invention generally include display driving integrated circuits capable of reducing the number of transmission lines for transferring gray-scale data from a memory.  
         [0011]     According to an exemplary embodiment of the present invention, there is provided a display driving integrated circuit (IC) receiving M-bit gray-scale data to represent the gray scale of one pixel and driving a panel including a plurality of pixels. The display driving IC includes a memory storing gray-scale data representing the gray scales of the plurality of pixels, a source driver receiving the gray-scale data from the memory through transmission lines and transmitting the received gray-scale data to the panel, and at least one multiplexer to transmit the M-bit gray-scale data representing the gray scale of one pixel through L transmission lines, wherein the value of L is smaller than the value of M. The at least one multiplexer may be disposed between the memory and the transmission lines.  
         [0012]     The display driving IC may further include at least one demultiplexer receiving gray-scale data through the L transmission lines, demultiplexing the received gray-scale data into M-bit gray-scale data and transmitting the M-bit gray-scale data to the source driver. The at least one demultiplexer may be disposed between the transmission lines and the source driver.  
         [0013]     Each of the at least one multiplexer may receive M/L-bit gray-scale data and sequentially output the M/L-bit gray-scale data bit by bit through one transmission line, where M/L is an integer.  
         [0014]     Each of the at least one demultiplexer may sequentially receive the M/L-bit gray-scale data bit by bit through a transmission line and output the M/L-bit gray-scale data in parallel.  
         [0015]     Each of the at least one demultiplexer may include at least one latch for parallel outputting the gray-scale data.  
         [0016]     The display driving IC may further include a control signal generator generating signals controlling the multiplexer and the demultiplexer such that the multiplexer and the demultiplexer transmit and receive the gray-scale data.  
         [0017]     The control signals may include M/L signals respectively transmitted through M/L lines, where M/L is an integer. The control signal generator may generate the M/L control signals in synchronization with K input signals.  
         [0018]     According to an exemplary embodiment of the present invention, there is provided a display driving IC receiving M-bit gray-scale data to represent the gray scale of one pixel and driving a panel including a plurality of pixels. The display driving IC includes a memory storing gray-scale data representing the gray scales of the plurality of pixels, and a source driver receiving the gray-scale data from the memory through transmission lines and transmitting the received gray-scale data to the panel. The M-bit gray-scale data representing the gray scale of one pixel is transmitted through L transmission lines,. wherein the value of L is smaller than the value of M. The M/L-bit gray-scale data, from among the gray-scale data is time-divided and sequentially transmitted bit by bit through one of the L transmission lines, where M/L is an integer.  
         [0019]     According to an exemplary embodiment of the present invention, there is provided a method for receiving M-bit gray-scale data to represent the gray scale of one pixel and driving a panel including a plurality of pixels. The method comprises reading gray-scale data stored in a memory, multiplexing the read gray-scale data to transmit the M-bit gray-scale data representing the gray scale of one pixel through L transmission lines, the value of L being smaller than the value of M, transmitting the multiplexed gray-scale data through the L transmission lines, receiving the gray-scale data through the L transmission lines and demultiplexing the received gray-scale data into M-bit gray-scale data, and parallel transmitting the demultiplexed M-bit gray-scale data to a source driver.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The present invention will become readily apparent to those of ordinary skill in the art when descriptions of exemplary embodiments thereof are read with reference to the accompanying drawings.  
         [0021]      FIGS. 1A and 1B  are block diagrams of conventional display driving ICs.  
         [0022]      FIG. 2  is a block diagram of a display driving IC according to an exemplary embodiment of the present invention.  
         [0023]      FIG. 3  is a block diagram of the multiplexer and the demultiplexer shown in  FIG. 2 , according to an exemplary embodiment of the present invention.  
         [0024]      FIG. 4  is a circuit diagram of the multiplexer and the demultiplexer shown in  FIG. 2 , according to an exemplary embodiment of the present invention.  
         [0025]      FIG. 5  illustrates the waveforms of control signals for driving the circuit of  FIG. 4 , and transmitted gray-scale data.  
         [0026]      FIG. 6  is a flow chart showing a display driving method according to an exemplary embodiment of the present invention. 
     
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0027]     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals refer to similar or identical elements throughout the description of the figures.  
         [0028]      FIG. 2  is a block diagram of a display driving IC  200  according to an exemplary embodiment of the present invention. Referring to  FIG. 2 , the display driving IC  200  includes a source driver  210 , a memory  220 , a multiplexer  230 , and a demultiplexer  240 . The display driving IC  200  may further include a control signal generator  250  for controlling the multiplexer  230  and/or the demultiplexer  240 .  
         [0029]     The memory  220  stores data such as frames of gray-scale data indicative of an image to be displayed on a panel. An image can be generated from M-bit gray-scale data for each pixel included in the panel. The M-bit gray-scale data may comprise, for example, N-bit red gray-scale data R 1  through RN, N-bit green gray-scale data G 1  through GN, and N-bit blue gray-scale data B 1  through BN.  
         [0030]     The gray-scale data stored in the memory  220  is read and transmitted through a scan port included in the memory  220 .  FIG. 2  shows the transmission of the M-bit gray-scale data corresponding to one pixel.  
         [0031]     The M-bit gray-scale data read from the memory  220  is inputted to the multiplexer  230 . The multiplexer  230  receives the M-bit gray-scale data and transmits the M-bit gray-scale data through L transmission lines. In an exemplary embodiment of the present invention, the value of L is smaller than the value of M. To transmit the M-bit gray-scale data through the L transmission lines, L M/L-to-1 multiplexers can be used. For example, in the case when the M-bit gray-scale data is 18-bit gray-scale data comprising 6-bit red gray-scale data, 6-bit green gray-scale data and 6-bit blue gray-scale data, two 9-to-1 multiplexers can be used to transmit the 18-bit gray-scale data through two transmission lines.  
         [0032]     The gray-scale data transmitted through the L transmission lines is inputted to the demultiplexer  240 . As shown in  FIG. 2 , the demultiplexer  240  may be disposed between the transmission lines and the source driver  210 . The demultiplexer  240  demultiplexes the gray-scale data transmitted through the L transmission lines into M-bit gray scale data and transmits the demultiplexed M-bit gray-scale data to the source driver  210 . In an exemplary embodiment of the present invention, the demultiplexer  240  is operated in connection with the multiplexer  230 . For example, L 1-to-M/L demultiplexers are used when the L M/L-to-1 multiplexers are used.  
         [0033]     The M-bit gray-scale data transmitted to the source driver  210  is transmitted to pixels of the panel through a plurality of data lines to construct an image according to R, G and B data.  
         [0034]     The control signal generator  250  generates control signals MUX_SEL&lt; 0 :(M/L)- 1 &gt; and MUX_SELB&lt; 0 :(M/L)- 1 &gt; for controlling the multiplexer  230  and the demultiplexer  240 . The control signal MUX_SELB&lt; 0 :(M/L)- 1 &gt; can be obtained by inverting the control signal MUX_SEL&lt; 0 :(M/L)- 1 &gt;. For example, in the case when the M-bit gray-scale data is 18-bit data and is transmitted through two transmission lines, the multiplexer  230  and the demultiplexer  240  are controlled by nine control signals MUX_SEL&lt; 0 : 8 &gt; and nine inverted control signals MUX_SELB&lt; 0 : 8 &gt;.  
         [0035]     To ensure correct data transmission between the multiplexer  230  and the demultiplexer  240 , the control signal generator  250  receives K input signals D 1  through DK and generates the control signals MUX_SEL&lt; 0 :(M/L)- 1 &gt; and MUX_SELB&lt; 0 :(M/L)- 1 &gt; in synchronization with the input signals D 1  through DK. For example, when 18-bit gray-scale data is transmitted through two transmission lines, nine control signals MUX_SEL&lt; 0 : 8 &gt; and four input signals D 1  through D 4  are required.  
         [0036]     Operations of the multiplexer  230  and the demultiplexer  240  according to an exemplary embodiment of the present invention will now be explained in detail with reference to  FIG. 3 .  
         [0037]      FIG. 3  is a block diagram of the multiplexer  230  and the demultiplexer  240  shown in  FIG. 2 , according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , the multiplexer  230  multiplexes M (3N) bit gray-scale data and outputs the multiplexed data through L transmission. lines. In this case, the multiplexer  230  can include L M/L-to — 1 multiplexers.  
         [0038]     The multiplexer  230  includes a switching unit  231 . The switching unit  231  controls the transmission of the gray-scale data in response to the control signals MUX_SEL&lt; 0 :(M/L)- 1 &gt; and the inverted control signals MUX_SELB&lt; 0 :(M/L)- 1 &gt;. The switching unit  231  includes M switches (not shown) corresponding to the M-bit gray-scale data. A M/L-to-1 multiplexer includes M/L switches respectively controlled by the control signals MUX_SEL&lt; 0 :(M/L)- 1 &gt; and the inverted control signals MUX_SELB&lt; 0 :(M/L)- 1 &gt;.  
         [0039]     For example, when 18-bit gray-scale data representing the gray scale of one pixel is transmitted through two transmission lines, two 9-to-1 multiplexers are needed. Each of the 9-to-1 multiplexers may include nine switches which are sequentially switched by nine control signals MUX_SEL&lt; 0 &gt; through MUX_SEL&lt; 8 &gt; and nine inverted control signals MUX_SELB&lt; 0 &gt; through MUX_SELB&lt; 8 &gt;.  
         [0040]     As the switches are sequentially switched, the gray-scale data is time-divided and sequentially transmitted through the transmission lines. In the case of a 9-to-1 multiplexer, the nine switches respectively controlling the transmission of nine gray-scale data bits are sequentially switched such that the nine gray-scale data bits are sequentially transmitted through one transmission line.  
         [0041]     The multiplexer  230  can include a latch (not shown) for holding the gray-scale data. The M gray-scale data may be simultaneously input to the switching unit  231 .  
         [0042]     The demultiplexer  240  demultiplexes the gray-scale data transmitted through the transmission lines into M-bit gray-scale data: When the multiplexer  230  includes L M/L-to-1 multiplexers, the demultiplexer  240  is composed includes L 1-to-M/L demultiplexers.  
         [0043]     The demultiplexer  240  can include a switching unit  241  and a latch  242 . The gray-scale data transmitted through the transmission lines is inputted to the switching unit  241  included in the demultiplexer  240 .  
         [0044]     The switching unit  241  includes M switches (not shown) corresponding to the M-bit gray-scale data. The switching unit  241  controls the input of the M-bit gray-scale data in response to the control signals MUX_SEL&lt; 0 :(M/L)- 1 &gt; and the inverted control signals MUX_SELB&lt; 0 :(M/L)- 1 &gt;. The switches of the multiplexer  230  and the switches of the demultiplexer  240  are controlled by the control signals MUX_SEL&lt; 0 :(M/L)- 1 &gt; and the inverted control signals MUX_SELB&lt; 0 :(M/L)- 1 &gt;. The switches of the multiplexer  230  are sequentially switched to transmit the gray-scale data through the transmission lines, and the switches of the demultiplexer  240  are sequentially switched to receive the transmitted gray-scale data.  
         [0045]     In an exemplary embodiment of the present invention, the demultiplexer  240  includes two 1-to-9 demultiplexers when the multiplexer  230  includes two 9-to-1 multiplexers. Nine switches included in each of the 1-to-9 demultiplexers are sequentially switched as the nine switches included in each of the 9-to-1 multiplexers are sequentially switched.  
         [0046]     The gray-scale data input to the switching unit  241  is temporarily held in the latch  242 , restored into the M-bit gray-scale data and output to the source driver.  
         [0047]     Operations of the multiplexer and the demultiplexer according to an exemplary embodiment of the present invention will now be explained in detail with reference to  FIG. 4 .  
         [0048]      FIG. 4  is a circuit diagram of the multiplexer  230  and the demultiplexer  240  shown in  FIG. 2 , according to an exemplary embodiment of the present invention. Referring to  FIG. 4 , the gray scale of one pixel can be represented by 18-bit gray-scale data comprising 6-bit red gray-scale data, 6-bit green gray-scale data and 6-bit blue gray-scale data. Two transmission lines L 1  and L 2  can be used to time-divide the 18-bit gray-scale data and serially transmit the time-divided 18-bit gray-scale data.  
         [0049]     The 18-bit gray-scale data sdout&lt; 0 &gt; through sdout&lt; 17 &gt; read from a memory is inputted to the multiplexer  230 . The multiplexer  230  includes two 9-to-1 multiplexers. For example, 9-bit gray-scale data sdout&lt; 0 &gt; through sdout&lt; 8 &gt; is transmitted through one transmission line L 1  and the other 9-bit gray-scale data sdout&lt; 9 &gt; through sdout&lt; 17 &gt; is transmitted through the other transmission line L 2 .  
         [0050]     In  FIG. 4 , the two 9-to-1 multiplexers respectively include nine switching elements. For example, one of the 9-to-1 multiplexer includes nine transfer gates T 0  through T 8  and the other 9-to-1 multiplexer includes nine transfer gates T 9  through T 17 .  
         [0051]     Hereinafter, operations of the 9-to-1 multiplexer and the demultiplexer in accordance with an exemplary embodiment of the present invention will be explained.  
         [0052]     The nine gray-scale data bits sdout&lt; 0 &gt; through sdout&lt; 8 &gt; are respectively input to the transfer gates T 0  through T 8  of the 9-to-1 multiplexer. The transfer gates T 0  through T 8  are gated by the control signals MUX_SEL&lt; 0 : 8 &gt; and the inverted control signals MUX_SELB&lt; 0 : 8 &gt;.  
         [0053]     The transfer gates T 0  through T 8  receive the control signals MUX_SEL&lt; 0 : 8 &gt; and the inverted control signals MUX_SELB&lt; 0 : 8 &gt; through control signal lines (not shown). The control signal lines may include nine lines. The control signals MUX_SEL&lt; 0 &gt; through MUX_SEL&lt; 8 &gt; can be respectively input through the nine control signal lines. The control signal lines transmitting the inverted control signals may include nine lines. The inverted control signals MUX_SELB&lt; 0 &gt; through MUX_SELB&lt; 8 &gt; can be respectively input through the nine control signal lines.  
         [0054]     The control signals MUX_SEL&lt; 0 : 8 &gt; and the inverted control signals MUX_SELB&lt; 0 : 8 &gt; sequentially gate the nine transfer gates T 0  through T 8 . For example, the first transfer gate T 0  is gated to first transfer one gray-scale data bit sdout&lt; 0 &gt; to the demultiplexer  240  through the transmission line L 1 . Then, the first transfer gate T 0  is turned off and the second transfer gate T 1  is gated to transfer the next gray-scale data bit sdout&lt; 1 &gt; through the transmission line L 1 . Operation continues in this manner, until the final ninth transfer gate T 8  is gated to transfer the gray-scale data bit sdout&lt; 8 &gt;. The nine gray-scale data bits sdout&lt; 0 &gt; through sdout&lt; 8 &gt; are time-divided and serially transmitted through one transmission line L 1 .  
         [0055]     The demultiplexer  240 , according to an exemplary embodiment of the present invention, includes two 1-to-9 demultiplexers each having nine switching elements. For example, one of the 1-to-9 demultiplexer includes transfer gates T 20  through T 28  and the other 1-to-9 demultiplexer includes transfer gates T 29  through T 37 .  
         [0056]     One of the 1-to-9 demultiplexers includes the nine transfer gates T 20  through T 28  controlled by the control signals MUX_SEL&lt; 0 : 8 &gt; and the inverted control signals MUX_SELB&lt; 0 : 8 &gt;. The transfer gates T 20  through T 28  are gated in connection with the transfer gates T 0  through T 8  included in the multiplexer.  
         [0057]     When the transfer gate T 0  of the multiplexer is gated to transfer the first gray-scale data bit sdout&lt; 0 &gt;, the transfer gate T 20  of the demultiplexer  240  is gated to receive the first gray-scale data bit sdout&lt; 0 &gt;. The received gray-scale data bit sdout&lt; 0 &gt; is held by a latch Lat 0 . The latch Lat 0  is operated by the inverted control signal MUX_SEL&lt; 0 &gt; to hold the first gray-scale data bit sdout&lt; 0 &gt; while the other gray-scale data bits sdout&lt; 1 &gt; through sdout&lt; 8 &gt; are transmitted.  
         [0058]     Then, the transfer gate T 1  of the multiplexer  230  and the transfer gate T 21  of the demultiplexer  240  are gated by the control signals MUX_SEL&lt; 0 : 8 &gt; and the inverted control signals MUX_SELB&lt; 0 : 8 &gt;. The demultiplexer  240  receives the next gray-scale data bit sdout&lt; 1 &gt; and a latch Lat 1  holds the gray-scale data bit sdout&lt; 1 &gt;. The nine gray-scale data bits sdout&lt; 0 &gt; through sdout&lt; 8 &gt; can be output in parallel to the source driver.  
         [0059]      FIG. 5  illustrates the waveforms of control signals for driving the circuit of  FIG. 4 , and transmitted gray-scale data. The waveforms shown in  FIG. 5  will now be explained with reference to  FIG. 4 .  
         [0060]     When the control signal MUX_SEL&lt; 0 &gt; is shifted to a high level, the transfer gates T 0  and T 9  of the two 9-to-1 multiplexers are gated and the transfer gates T 20  and T 29  of the two 1-to-9 demultiplexers are gated. The first gray-scale data bits sdout&lt; 0 &gt; and sdout&lt; 9 &gt; input to the respective multiplexers are respectively transmitted to the demultiplexers through the two transmission lines L 1  and L 2 . Subsequently, as the control signals MUX_SEL&lt; 1 &gt; through MUX_SEL&lt; 8 &gt; are sequentially shifted to a high level, the-second gray-scale data bits sdout&lt; 1 &gt; and sdout&lt; 10 &gt; through the ninth gray-scale data bits sdout&lt; 8 &gt; and sdout&lt; 17 &gt; are sequentially transmitted.  
         [0061]     While the 18-bit gray-scale data is transmitted by two 9-to-1 multiplexers through two transmission lines in an exemplary embodiment of the present invention, it is to be understood that the invention may be embodied with any suitable number of multiplexers and transmission lines. For example, the 18-bit gray-scale data can be transmitted by three 6-to-1 multiplexers through three transmission lines. Furthermore, it is to be understood that the characteristics of the multiplexer and the demultiplexer can be varied to suit the number of bits of gray-scale data representing the gray scale of one pixel.  
         [0062]     A driving IC according to an exemplary embodiment of the present invention is constructed so that the area required for the transmission lines can be reduced when a scan port of the memory is used to transmit gray-scale data. Although the area required for the transmission lines is increased slightly when using the three 6-to-1 multiplexers compared to when using the two 9-to-1 multiplexers, power loss is reduced because the 18-bit gray-scale data can be transmitted by six driving operations. In accordance with exemplary embodiments of the present invention, a driving IC can be designed in consideration of the area required for the transmission lines and power loss by controlling the characteristics of the multiplexer and demultiplexer.  
         [0063]      FIG. 6  is a flow chart showing a display driving method according to an exemplary embodiment of the present invention. Referring to  FIG. 6 , in step S 1 , the M-bit gray-scale data stored in a memory is read. Then, the M-bit gray-scale data is multiplexed in the step S 2 . To transmit the M-bit gray-scale data through L transmission lines, the M-bit gray-scale data can be multiplexed using L M/L-to-1 multiplexers.  
         [0064]     The M-bit gray-scale data is transmitted through the L transmission lines according to the multiplexing operation in the step S 3 . In the case of the M/L-to-1 multiplexer, M/L-bit gray-scale data bits are sequentially transmitted through the transmission lines.  
         [0065]     The gray-scale data transmitted through the transmission lines is demultiplexed into M-bit gray-scale data in the step S 4 . In step S 5 , the demultiplexed M-bit gray-scale data is transmitted in parallel to the source driver.  
         [0066]     According to an exemplary embodiment of the present invention, the number of transmission lines for transmitting gray-scale data from a memory can be reduced to improve the integration of a driving IC. A driving IC, in accordance with exemplary embodiments of the present invention, can be designed in consideration of integration and power loss according to multiplexing and demultiplexing characteristics.  
         [0067]     Although the exemplary embodiments of the present invention have been described in detail with reference to the accompanying drawings for the purpose of illustration, it is to be understood that the that the inventive processes and apparatus are not be construed as limited thereby. It will be readily apparent to those of ordinary skill in the art that various modifications to the foregoing exemplary embodiments can be made without departing from scope of the invention as defined by the appended claims, with equivalents of the claims to be included therein.