1. Field of the Invention
The present invention relates to a display and a timing controller mounted thereon, and more particularly, to a signal transmission technology employing a differential signal transmission method.
2. Description of the Background Art
Displays such as liquid crystal displays are provided with a timing controller (hereinafter referred to as “T-CON”) for supplying a clock signal and image data signals synchronized with the clock signal to column drivers (CDs) for driving a display panel. For signal transmission from the T-CON to the column drivers, a transmission method using differential signals (hereinafter referred to as “a differential signal transmission method”) such as a mini-LVDS (Low Voltage Differential Signaling) or RSDS™ (Reduced Swing Differential Signaling) interface technology has widely been used for fewer traces and minimized Electro-magnetic Interference (hereinafter referred to as “EMI”).
A mini-LVDS interface is generally applied to a high resolution display exceeding SXGA resolution (1280×1024 pixels) intended for high frequencies. In this case, driving is usually conducted with a screen divided into left and right halves. More specifically, the T-CON divides image data of one horizontal line into former and latter halves of image data, to be supplied in parallel to two groups of column drivers, respectively. Accordingly, the T-CON is provided with dual output ports for outputting image data signals, one for the left half of the screen and the other for the right half (cf. Japanese Patent Application Laid-Open Nos. 2004-354567 and 2004-205901).
In comparison with the mini-LVDS interface, an RSDS™ interface is often applied to a display with resolution in a low-frequency band lower than the SXGA resolution, and is widely used particularly with XGA resolution (1024×768 pixels). In this case, driving is usually conducted on the whole screen at a time without dividing the screen (cf. Japanese Patent Application Laid-Open No. 2004-45985;
Differential lines for transmitting differential signals from the T-CON to column drivers are generally laid out in a T- or L-configuration depending on the T-CON's position.
Column drivers are arranged in a line on one side of a display panel as shown in, e.g., FIGS. 2 to 4, which will be discussed later. In the L-configuration, the T-CON is located at one end of a circuit board connected to the column drivers (near the first or eighth column driver in an 8 column driver system, for example), and differential lines are routed in one direction along the column drivers (see
In the T-configuration, the T-CON is located in the center of a circuit board connected to column drivers (near the fourth and fifth column drivers in an 8 column driver system, for example). Differential lines out of the T-CON branch out to left and right on the way, and are routed from the branch point in the opposite directions along the column drivers (see
As will be described later in detail, the L-configuration can flow less current into buses and produce less signal distortion than in the T-configuration, and is therefore more advantageous in minimizing EMI. However, it is often difficult to employ the L-configuration by placing the T-CON at one end of a circuit board. Accordingly, the T-configuration is popularly used even at present.
An object of the present invention is to provide a timing controller and a display capable of achieving improved signal waveform to minimize EMI even when it is difficult to place a T-CON at one end of a circuit board.
According to the present invention, the display includes a timing controller configured to output a clock signal and an image data signal synchronized with said clock signal by a differential signal transmission method, and a plurality of drivers configured to drive a display panel on the basis of said clock signal and said image data signal. The timing controller includes dual clock output ports, each being made up of a differential pair, and each configured to output said clock signal, and at least one data output port made up of a differential pair configured to output said image data signal. Each of said plurality of drivers is connected to one of said dual clock output ports. The at least one data output port is connected to all of said plurality of drivers.
The timing controller according to the present invention outputs a clock signal and an image data signal synchronized with said clock signal by a differential signal transmission method. The timing controller includes dual clock output ports, each being made up of a differential pair, and each configured to output said clock signal, and at least one data output port made up of a differential pair configured to output said image data signal of one complete horizontal or vertical line.
Since the timing controller has dual clock output ports, even when it is difficult to place the timing controller at one end of a board on which the drivers are mounted, clock signal transmission can be made only through an L-configuration without employing a T-configuration. This prevents degradation in clock signal waveform, which in turn minimizes an EMI component resulting from a clock signal. Further, since the data output port is not configured as dual ports, the number of ports (output pins) of the timing controller is prevented from extremely increasing. As will be described later in detail, in an RSDS™ system, for example, an image data signal does not present a critical signal waveform that toggles at the maximum frequency, and accordingly, makes less contribution to EMI than the clock signal. Therefore, when the EMI component resulting from the clock signal is reduced by employing the L-configuration for clock signal transmission, sufficient effects can be obtained.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
FIGS. 2 to 4 are diagrams each illustrating the structure of a conventional display;
Preferred embodiments of the present invention will now be described. In these preferred embodiments, a method of transmitting a clock signal and image data signals from a T-CON to column drivers in a display will be described referring to an RSDS™ system. However, the present invention is not limited to the application to the RSDS™ system, but is also widely applicable to signal transmission systems employing a differential signal transmission method such as a mini-LVDS interface.
For the sake of convenience, a conventional display will be described prior to discussing the present invention. FIGS. 2 to 4 are diagrams each illustrating a specific structure of a conventional display.
In the example shown in
In the example shown in
In both
In the above two examples, the column drivers 15 are each mounted on the TCP/COF 14, however, there has been created a mode of COG (Chip On Glass) in recent years in which the column drivers 15 are mounted directly on the display panel 11, as shown in
In the case where an FPC connector 17 connected to the circuit board 12 is provided near the center of the FPC 18 as shown in
Each of the displays shown in
Each of the eight column drivers CD1 to CD8 receives a clock signal and image data signals synchronized with the clock signal from a timing controller (hereinafter referred to as “a T-CON”) 10, and drives the display panel on the basis of the signals. A start pulse SP is output from the T-CON 10 with predetermined timing, and transmitted to the column drivers CD1, CD2, . . . and CD8 in this order via a bus which daisy-chains the eight column drivers CD together. Timing with which each of the column drivers CD reads serially-transmitted image data is thereby specified.
According to the present embodiment, transmission of a clock signal and image data signals from the T-CON 10 to the column drivers CD is conducted by the RSDS™ system. For transmission of these signals, differential lines, each made up of a pair of a positive (+) side line and a negative (−) side line (hereinafter also referred to as “a differential pair”), are employed. For ease of description, a differential pair for transmitting a clock signal is called “a clock line”, and a differential pair for transmitting an image data signal is called “a data line”.
In an RSDS™ display, image data signals are transmitted in parallel in a plurality of bits via a plurality of data lines in order to achieve high resolution while controlling operating frequencies. For instance,
In the conventional display shown in
More specifically, the clock line CLK and the respective N data lines DA(1) to DA(N) are routed in one direction from the T-CON 10 along the arrangement of the column drivers CD in the order of the column drivers CD1, CD2, . . . , and CD8. For current-to-voltage conversion and reduced signal reflections, the clock line CLK is terminated by a termination resistor RCLK, and the data lines DA(1) to DA(N) are terminated by termination resistors R(1) to R(N), respectively.
In the above-described L-configuration, the data lines DA and clock line CLK are routed in one direction from one side to the other side of the arrangement of the column drivers CD, and are terminated by the termination resistors, respectively, on the other side. In other words, in the L-configuration, the data lines DA and clock line CLK each have a first terminal connected to the T-CON 10, only one second terminal terminated by a termination resistor R and a third terminal branching out between the first and second terminals to be connected to the column drivers CD.
In the conventional display shown in
More specifically, each of the clock line CLK and N data lines DA(1) to DA(N) extending out from the T-CON 10 branches out between the column drivers CD4 and CD5 into the opposite directions toward the column drivers CD1 to CD4 and toward the column drivers CD5 to CD8. The branches of the clock line CLK and data lines DA extending toward the column drivers CD1 to CD4 are respectively routed to the column drivers CD4, CD3, CD2 and CD1 in this order in the direction away from the T-CON 10 along the arrangement of the column drivers CD1 to CD4, and are terminated by termination resistors RCLK1 and R1(1) to R1(N), respectively. On the other hand, the branches of the clock line CLK and data lines DA extending toward the column drivers CD5 to CD8 are respectively routed the column drivers CD5, CD6, CD7 and CD8 in this order in the direction away from the T-CON 10 along the arrangement of the column drivers CD5 to CD8, and are terminated by a termination resistors RCLK2 and R2(1) to R2(N), respectively.
In the above-described T-configuration, the data lines DA and clock line CLK are routed from the center to the opposite ends, and therefore, the opposite ends are terminated. In other words, the T-configuration has two “second terminals” mentioned in the case of the L-configuration.
Unlike the L-configuration, the T-configuration has branches, which tends to cause greater signal reflections, and hence, greater signal distortion. With respect to the aforementioned termination resistor for controlling reflections, the L-configuration requires one termination resistor per differential pair, while the T-configuration requires two termination resistors per differential pair.
In the RSDS™ display, the termination of a differential pair is 100 Ω. Since the T-configuration has two termination resistors on the opposite ends being connected in parallel, an effective impedance is 50 Ω on the RSDS™ outputs of the T-CON 10 (in practical use, the effective impedance decreases under the influence of input capacitance of the column drivers CD and the like, and therefore, a practical termination resistor is often set lower than a theoretical value). Accordingly, to obtain the same signal amplitude as in the L-configuration, an RSDS™ output current of the T-CON 10 needs to be nearly doubled in the T-configuration.
That is, in comparison with the L-configuration, the T-configuration is not very desirable because of its great signal distortion and a great amount of current flowing into buses, which tends to increase EMI. Accordingly, from an EMI reduction standpoint, it is preferable to employ the L-configuration where possible.
The reason why the T-configuration is popularly used even at present irrespective of the superiority of the L-configuration is that it is difficult to always place a T-CON at one end of a circuit board to form the L-configuration. The T-CON's position on a board needs to be determined considering the positional relationship with an external input terminal of a display, easiness of routing, and the like. Besides, an increased board space needs to be suppressed for reducing the cost of the display. Accordingly, the position of the T-CON is limited.
In the display shown in
In other words, the T-CON 10 according to the present embodiment has dual clock output ports, one connected to the clock line CLK1, and the other connected to the clock line CLK2. Each of these clock output ports is made up of a differential pair. In the present embodiment, these clock output ports each output the same clock signal (CLK P/N). Accordingly, each of the column drivers CD shall be connected to either of the clock lines CLK1 and CLK2. In the example shown in
As described, since the T-CON 10 has dual clock output ports, two L-configuration buses (clock lines CLK1 and CLK2) can be routed from the T-CON 10 to the opposite sides. Accordingly, even when the T-CON 10 is located near the center of a circuit board on which column drivers are mounted due to the difficulty of placing the T-CON 10 at one end of the board, clock signal transmission can be made only through the L-configuration without employing the T-configuration. Degradation in clock signal waveform is therefore prevented, which in turn minimizes an EMI component resulting from the clock signal.
On the other hand, the T-CON 10 does not have dual data output ports for outputting image data. That is, driving with the screen divided into left and right (or top and bottom) halves is not conducted, unlike the aforementioned mini-LVDS display higher than SXGA resolution. Therefore, the T-CON 10 transmits image data of one horizontal (or vertical) line to each of the column drivers CD without dividing the data. The image data signal of one complete horizontal or vertical line is thus output from each of the data output ports of the T-CON 10. Accordingly, when the T-CON 10 is located near the center of the arrangement of the column drivers CD, the T-configuration is employed for routing the data lines DA as shown in
However, in the RSDS™ system, for example, image data signals are serially transmitted by 2 bits from the least significant bit as shown in the data mapping in
That is, according to the present embodiment, the EMI component resulting from the image data signals is at almost the same level as in the conventional display, however, the EMI component resulting from the clock signal can be reduced, which allows EMI caused by the whole display to be effectively reduced.
In addition to the clock output ports of the T-CON, each data output port may also be configured as dual ports so that both the data lines and clock line can always be routed in the L-configuration. Generally, however, a plurality of data output ports need to be provided in order for parallel output of image data signals. As already described, in the RSDS™ system, for example, 6-bit color RGB data requires 9 pairs of ports, and 8-bit color RGB data requires 12 pairs of ports. Accordingly, configuring each data output port as dual ports will result in an extreme increase in the number of T-CON's ports (output pins), which disadvantageously increases the circuit scale and cost of the T-CON. In other words, the display according to the present embodiment can minimize EMI while controlling the increase in circuit scale and cost of the T-CON.
Further, in
In the case where the T-CON 10 can be located near the column driver CD1 in the present embodiment, a clock line (either of the clock lines CLK1 and CLK2) and data lines DA may be routed in the L-configuration as shown in
Further, in the present embodiment, the connection between the T-CON 10, column drivers CD and display panel may be made through TCP or COF as shown in
The above description has been directed to a display in which unidirectional scan is always made in the order of the column drivers CD1, CD2, . . . , and CD8, however, the present invention is not limited to such application. For instance, a modification of the present embodiment is shown in
In forward scan in the display shown in
In
As already described, the T- and L-configurations each have a different number of termination resistors. Therefore, to equalize the amplitude of a transmitted signal in the both configurations, the T-CON output current needs to be varied. More specifically, the T-configuration requires nearly twice the current in the L-configuration.
Further, an output current of T-CON output buffers directly affects the amplitude of a signal transmitted via the clock line and data line, and therefore, needs to be minimized to the extent possible within a range that satisfies input specifications for the column drivers in order to reduce EMI.
The T-CON 10 according to the first preferred embodiment is assumed to have its dual clock output ports connected to the L-configuration buses (clock lines CLK1, CLK2) and its data output ports connected to the T-configuration buses (data lines DA), as shown in
The output current from the clock output ports can therefore be set at a value suitable for the L-configuration (e.g., nearly half the output current from the data output ports) while maintaining the output current from the data output ports at a value suitable for the T-configuration.
This allows the amplitude of the clock signal greatly contributing to EMI to be set more suitably, which achieves more effective reduction of EMI. Further, the independent control of the output current from the data output ports and the output current from the clock output ports permits application to various circuit boards, which advantageously results in wide versatility.
When locating the T-CON 10 near the column driver CD1 to route a clock line (either of the clock lines CLK1 and CLK2) and the data lines DA in the L-configuration similarly to
As means of controlling the output currents from the output buffers of the T-CON 10, the T-CON 10 may be provided with, for example, external resistors, one for controlling the output current from the output buffers of the data output ports and the other for controlling the output current from the output buffers of the clock output ports, and the respective resistors are independently controlled in value, so that the output currents can be controlled.
While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
Number | Date | Country | Kind |
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2005-142245 | May 2005 | JP | national |