JP2005351963A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low cost display device with high accuracy of color reproducibility and high picture quality. <P>SOLUTION: The device is equipped with a switch controlling means (5) to simultaneously turn on a plurality of switches (11 to 13) at a predetermined timing in one scanning period for sequential scanning and turn off a selected switch among the plurality of switches after the lapse of a predetermined time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display device that performs drive control to improve color reproducibility of a display image.

  In recent years, an active matrix driving liquid crystal display is increasingly used as a portable display device. The reasons for this are that the liquid crystal display is capable of reflective display, and that low power consumption has been promoted due to the spread of compact LED backlights. This is because further improvement in image quality was desired.

  In an active matrix liquid crystal display, a source line and a gate line are driven to apply and hold a voltage to a pixel serving as a display unit, thereby realizing image display. In this image display, the voltage applied to the source wiring is the voltage applied to the liquid crystal as it is, and the output of the analog amplifier is connected as the voltage supply source. Since the number of analog amplifiers directly affects the cost of the circuit that drives the source wiring, a method has been devised in which the output of one analog amplifier is time-divided and connected to a plurality of signal lines to apply a voltage in a predetermined order. Has been implemented.

  Three switches are connected to the output of one analog amplifier, and these three switches are connected to the red, green, and blue signal lines, respectively. In this analog amplifier and switch, the switch output is switched to the red, green, and blue signal line potentials, and the switch connection is switched accordingly, so that one analog amplifier supplies voltage to the three signal lines. It has become. As a result, the number of necessary amplifiers is reduced to 1/3, and cost reduction is realized.

  FIG. 6 shows a timing chart for switching the connection from one amplifier to three switches to supply a voltage. The switch is a three-select switch that selects three signal lines of red (R), green (G), and blue (B). Here, red (R) is connected to the switch A, green (G) is connected to the switch B, and blue (B) is connected to the switch C. The analog amplifier output supplies a voltage in a predetermined period in the order of red (R), green (G), and blue (B).

  Here, the switch A is turned ON at timing (1), and a red (R) voltage is output from the analog amplifier in synchronization with the timing (1). Similarly, a green (G) voltage is output from the analog amplifier at timing (2), and a blue (B) voltage is output from the analog amplifier at timing (3).

As shown in FIG. 4, the signal lines connected to the analog amplifier 21, the switch A11, the switch B12, the switch C13 and the red (R), green (G), and blue (B) pixels are distributed among the surrounding lines. C1 excluding the capacitance between the signal lines, and C2 of the capacitance coupling between the signal lines and the signal lines (see Patent Document 1).
Japanese Patent Laid-Open No. 2004-093887

  However, as shown in FIG. 5, in a state where the signal line is not connected in a direct current state (the other two connected switches except for the switch 11 are OFF and not connected to the analog amplifier 21), The potentials of the surrounding signal lines are also changed by being affected by the potential change of the signal lines.

  That is, in a liquid crystal that requires AC driving, a potential change is large in a method in which electric charges are sequentially supplied to adjacent signal lines once (voltage is written). For this reason, the potential of the signal line written earlier is influenced by the voltage change of the signal line written later, and the voltage changes.

  This is a crosstalk between signal lines, and a phenomenon in which the colors of red (R), green (G), and blue (B) are affected by the gradation of other colors and the color changes. Appears as The RGB signal has a problem that the gradation of each primary color is handled independently of the gradation of other primary colors, and as a result, a color different from the intended color is displayed.

  The present invention has been made in view of the above, and an object thereof is to provide a display device with high color reproduction accuracy, low cost, and high image quality.

  The present invention described in claim 1 includes a plurality of scanning lines that are arranged in parallel to perform sequential scanning, a plurality of signal lines that are arranged in parallel so as to intersect the scanning lines, and the scanning lines, A pixel arranged at each intersection with the signal line to form an image, a variable voltage source circuit for controlling the pixel by applying a voltage to the signal line, and the signal from the variable voltage source circuit A switch for turning ON / OFF the output of the voltage applied to the line, and simultaneously turning on a plurality of the switches at a predetermined timing in one scanning period of the sequential scanning. The gist is to provide a switch control means for turning off a switch selected from the plurality of switches after the passage.

  According to a second aspect of the present invention, the switch according to the first aspect of the invention is characterized in that the switch is arranged in three light filters of three colors of red, green, and blue for expressing the color of the image. The gist is that each of the three switches is connected to the pixel and controlled by the switch control means.

  The gist of the present invention described in claim 3 is that, in claim 2, the switch control means turns on the three switches simultaneously.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the switch control unit is configured such that the switch control unit is a switch other than one switch after a first period in which the three switches are simultaneously turned on. A second period in which the switch is turned off, and any one of the switches other than the switch that is turned on in the second period after the second period has elapsed is turned on. The gist.

  According to a fifth aspect of the present invention, a plurality of scanning lines that are arranged in parallel with each other and sequentially scan, a plurality of signal lines that are arranged in parallel so as to intersect the scanning lines, and the scanning Pixels for composing an image in combination with optical filters of three colors of red, green and blue for expressing the color of the image arranged at the intersection of the line and the signal line, and the signal A display device comprising: a variable voltage source circuit for applying a voltage to a line to control the pixel; and a switch for turning ON / OFF the output of the voltage applied from the variable voltage source circuit to the signal line , The predetermined period of the sequential scanning is divided into two periods of a first period and a second period. In the first period, the three switches are sequentially turned on one by one, and the second period 2 in the period Switch is summarized as further comprising a switch control means for the ON one by one.

  According to a sixth aspect of the present invention, the two switches that are turned on in the second period are switches that are turned on first and second in the first period.

  According to the present invention, a display device with high color reproduction accuracy, low cost, and high image quality can be provided.

  Hereinafter, embodiments of a display device of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a configuration diagram for explaining the overall configuration of a display device according to a first embodiment of the present invention. This display device includes a plurality of three selection switches 1, a plurality of analog amplifiers 2, a plurality of D / A converters 3, a frame memory 4, a selection control circuit 5, a gate scanning circuit 6, and pixels. Group 7, switch A11, switch B12, switch C13, individual analog amplifier 21, individual D / A converter 31, thin film transistor 61, red (R) electrode 62, and green (G) electrode 63 And a blue (B) electrode 64.

  The pixel group 7 is an aggregate of pixels configured by a combination of a red (R) electrode 62, a green (G) electrode 63, a blue (B) electrode 64, and a thin film transistor 61. The number of pixels included in the pixel group 7 is 240 pixels indicated by [1] to [240] in the horizontal direction, 320 pixels indicated by [1] to [320] in the vertical direction, and in the horizontal direction. Three sub-pixels (red, green and blue) are provided.

  A thin film transistor 61 is connected to the pixel, and a gate of the thin film transistor 61 is operated by a gate line connected to the gate scanning circuit 6. A source electrode of the thin film transistor 61 of the pixel has a signal line connected to the 3 selection switch 1, and a pixel electrode for applying a voltage to the liquid crystal is connected to the drain electrode. This pixel electrode is composed of three electrodes, a red (R) electrode 62, a green (G) electrode 63, and a blue (B) electrode 64. When a pixel represents a color, the voltage applied to the electrodes of these three colors is set to a predetermined voltage value, and each color of the three colors corresponding to the three electrodes is controlled to generate the necessary colors. doing.

  One row of data in the frame memory 4 for storing image data is converted to an analog voltage by an A / D (digital / analog converter) converter 3 and output to the 3-select switch 1 by an analog amplifier 2.

  In the 3-select switch 1 and the D / A converter 3, red (R), green (G), and blue (B) are sequentially output from the analog amplifier 21 by the selection control circuit 5 as shown in FIG. During the period in which the red (R) voltage is output from the analog amplifier 21, all the three switches A11, B12, and C13 of the three selection switch 1 are closed and turned on.

  Next, when the green (G) voltage is output, only the signal line switch B12 connected to the green (G) pixel is closed.

  Finally, when the blue (B) voltage is output, only the signal line switch C13 connected to the blue (B) pixel is closed.

  When the first red (R) voltage is output, three analog signal lines are connected to the analog amplifier 21 as a load, and the load is heavy. The output period of the first red (R) voltage is wider than the other green (G) and blue (B). Therefore, even if the load is heavy, sufficient writing can be performed.

  By first writing the red (R) voltage to all the signal lines, crosstalk from the green (G) and blue (B) signal lines written later is reduced, and the color reproduction accuracy is improved. Improved.

  The above is a liquid crystal display and three selection examples have been shown, but it goes without saying that it can be applied to other voltage holding type displays.

<Second Embodiment>
In the second embodiment of the present invention, unlike the control of the 3-select switch 1 in the first embodiment already described, ON / OFF is executed a plurality of times in order to repeat the signal line writing a plurality of times. . By turning ON / OFF the 3-select switch 1 a plurality of times, the potential generated in the signal line can be converged to a desired original voltage. That is, the switch A11, the switch B12, and the switch C13 are not turned ON only once in order, but are turned ON for a plurality of times. By such control, the difference between the output voltage of the analog amplifier 21 and the potential of the signal line before writing is reduced.

  For example, when the ON of the 3-select switch 1 is performed twice by performing the operation of the 3-select switch 1 twice, the 3-select switch 1 is operated after charge injection into each signal line is completed. Further, the third and subsequent operations in which the 3 selection switch 1 is turned on are also operated after the charge injection into each signal line is completed.

  Note that the specific number of times of charge injection is preferably two times, for example. This requires time to switch the output voltage of the analog amplifier 21 and stabilize the voltage fluctuation caused by the operation of the 3 selection switch. For example, if the number of times of ON is increased by 3 times or more, a certain amount of time is required. This is to avoid reducing the total voltage writing time that can be secured in time.

  However, when a sufficient writing time can be ensured, the voltage accuracy can be increased by setting the number of times the 3 selection switch 1 is turned ON to 3 or 4 times, so that a preferable result can be obtained.

  In order to realize this driving, there are provided means for switching the output of the analog amplifier 21 a plurality of times and switching the operation between the image frame memory 4 (image line memory) and the analog amplifier 21, which are referred to in FIG.

  The above operation can be expressed by a simple equation. When the voltage before charge injection of the signal line is V− and the output voltage of the analog amplifier 21 is V +, the voltage of the adjacent signal line fluctuates in proportion to this voltage difference. Receive. When the proportionality coefficient is k, the voltage fluctuation ΔV1 is ΔV1 = k (V + −V−).

  In the second charge injection, ΔV1 is the difference between the output voltage of the analog amplifier 21 and the signal line, so the influence ΔV2 is ΔV2 = kΔV1 = k ^ 2 (V + −V−).

  The proportionality coefficient k indicates the influence of coupling between signal lines, but generally k <1, and ΔV2 is sufficiently smaller than ΔV1.

  That is, the difference ΔV from the output voltage of the analog amplifier 21 is reduced, and the voltage accuracy is improved. This means that the display color accuracy is improved.

  As shown in FIG. 3, the 3 selection switch 1 and the D / A converter 3 output red (R) and green (G) from the analog amplifier 21 twice in order, as shown in FIG. ) Is output only once, and the selection switch operates in synchronization with the output contents. By the writing operation by the combination of the two times and the one time, the crosstalk between red (R), green (G), and blue (B) is reduced, and the accuracy of color reproduction is improved.

  In this way, by taking the last period of the first three selections longer and omitting the second selection, the first writing of red (R) and green (G) in (a) and (b). Execute. Next, blue (B) writing is performed in (c). The voltage of the red (R) and green (G) signal lines is determined by the first writing, and a large voltage change occurs in the second writing. Therefore, one writing of blue (B) in FIG. 3 can be omitted.

  In this way, since the number of ON / OFF operations of the 3-select switch 1 is reduced, a single writing period can be made longer, so that the writing accuracy can be further improved. In the first embodiment and the second embodiment described above, the configuration including the liquid crystal display (display device) and the three selection switch 1 is used for the description. The main point is that it can be applied to other types of holding type displays.

The block diagram for demonstrating the whole structure of the display apparatus based on the 1st Embodiment of this invention is shown. The timing diagram for demonstrating control of ON / OFF of a switch based on the 1st Embodiment of this invention is shown. An explanatory view for explaining ON / OFF control of a switch concerning a 2nd embodiment of the present invention is shown. The equivalent circuit schematic of the capacity distribution in a prior art is shown. An explanatory view for explaining potential change resulting from capacity distribution in the prior art is shown. The timing diagram for demonstrating control of ON / OFF of the switch in a prior art is shown.

Explanation of symbols

1 3 Selection switch (switch)
2 Analog amplifier 3 D / A converter 4 Frame memory 5 Selection control circuit (selection control means)
6 Gate scanning circuit 7 Pixel group 11 Switch A
12 Switch B
13 Switch C

Claims (6)

A plurality of scanning lines arranged in parallel with each other and sequentially scanned, a plurality of signal lines arranged in parallel so as to cross the scanning lines, and an intersection of the scanning lines and the signal lines, respectively. A pixel for constituting an image, a variable voltage source circuit for controlling the pixel by applying a voltage to the signal line, and an output of the voltage applied from the variable voltage source circuit to the signal line. In a display device having an ON / OFF switch,
A switch control unit for simultaneously turning on the plurality of switches at a predetermined timing during one scanning period of the sequential scanning and turning off a switch selected from the plurality of switches after a predetermined time has elapsed; A display device. The switch is
The switch control means is connected to each of the three pixels arranged in each of red, green, and blue optical filters for expressing the color of the image, and the three switches as a set. The display device according to claim 1, wherein the display device is controlled by: The switch control means includes
The display device according to claim 2, wherein the three switches are simultaneously turned on. The switch control means includes
After the elapse of the first period in which the three switches are simultaneously turned on, a second period in which the other switches except for one switch are turned off is provided. After the elapse of the second period, the second period is established. The display device according to claim 3, wherein any one of the switches other than the switch that has been turned on for a period is turned on. A plurality of scanning lines that are arranged in parallel and sequentially scan, a plurality of signal lines that are arranged in parallel so as to cross the scanning lines, and an intersection of the scanning lines and the signal lines are arranged. In addition, a pixel for constituting an image combined with each of red, green, and blue optical filters for expressing the color of the image, and a voltage is applied to the signal line to control the pixel. And a switch for turning ON / OFF the output of the voltage applied from the variable voltage source circuit to the signal line.
The predetermined period of the sequential scanning is divided into two periods, a first period and a second period. In the first period, the three switches are sequentially turned on one by one, and in the second period, A display device comprising switch control means for sequentially turning on two switches one by one. In the second period,
The display device according to claim 5, wherein the two switches that are turned on are switches that are turned on first and second in the first period.

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