JP2005345910A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately arrange a wiring layout of a precharge signal line for supplying a precharge signal.
A precharge signal line for supplying a precharge signal supplied to a data line Dn to a plurality of data lines Dn extended from a horizontal drive circuit 3 at a timing preceding a timing for supplying an image signal to the data line Dn. 13, the precharge signal 13 is wired so as to pass through the horizontal drive circuit 3, and is connected to the plurality of data lines Dn, and the first precharge signal line 13a. Is connected to the first precharge signal line 13a that is wired on the substrate 11 in the vicinity of the horizontal drive circuit 3 and has both ends passed through the horizontal drive circuit 3 so that the impedance is lower than the impedance of the first precharge signal line 13a. This is realized by branching to the charge signal line 13b.
[Selection] Figure 5

Description

  The present invention relates to a wiring layout of predetermined wirings formed in a display device, and more specifically, a precharge signal line for supplying a precharge signal written to a data line before writing an image signal to a pixel capacitor via the data line. Related to the wiring layout.

  For display monitors of digital still cameras and digital cameras, active matrix type liquid crystal display devices driven by small and high-definition TFTs (Thin Film Transistors) are employed.

  In this liquid crystal display device, a TFT array substrate in which pixel cells are formed in a matrix and a counter substrate on which a transparent electrode is formed are opposed to the TFT array substrate, and liquid crystal is sealed between the TFT array substrate and the counter substrate. Have a structure.

  On the TFT array substrate, a plurality of scanning lines (gate lines) and signal lines (data lines) are wired in the horizontal and vertical directions of the display area, and pixel cells are formed at the intersections of these scanning lines and signal lines. ing. These scanning lines and signal lines are respectively driven by a vertical driving circuit and a horizontal driving circuit arranged outside the display area on the TFT array substrate, and a display image is formed by writing an image signal to the pixel capacity of the pixel cell. Will be.

  The signal lines of the liquid crystal display device have a timing preceding the timing at which the image signal is supplied for the purpose of improving the contrast ratio of the image to be displayed, stabilizing the potential level of the data line, and reducing the line unevenness on the display image. Thus, a precharge signal is supplied.

  This precharge signal is supplied for the purpose of reducing the load when the image signal is written to the data line by the horizontal drive circuit. In particular, in the 1H inversion driving method in which the voltage polarity of the data line is inverted and driven (AC driving) every horizontal scanning period in order to extend the life of the sealed liquid crystal, a precharge signal having a predetermined potential is used. Is written to the data line at the above-described timing, there is an advantage that the amount of charge required for writing the image signal to the data line can be greatly reduced.

JP-A-11-202296

  In general, the signal line that becomes the signal transmission path increases the wiring resistance when the wiring becomes long, and the wiring capacity is increased by crossing the wiring and the internal impedance becomes high, so that the signal to be transmitted is deteriorated. It will be. For example, the signal to be transmitted differs greatly between the input end and the output end of the signal line due to the influence as described above.

  In a liquid crystal display device, the above-described precharge signal is easily affected by a precharge signal line as a transmission path, and depending on the wiring layout of the precharge signal line, for example, it is unnecessary at the left end and the right end on the screen. It becomes a fatal problem that the displayed image deteriorates, such as the appearance of shading. This becomes particularly conspicuous when the number of pixel cells increases and the number of signal lines increases due to high definition of the liquid crystal display device, because the wiring capacity of the precharge signal lines increases.

  Therefore, the present invention has been devised in order to solve the above-described problems. By appropriately arranging the wiring layout of the precharge signal line for supplying the precharge signal, the display image by the precharge signal can be displayed. An object of the present invention is to provide a display device in which the influence of the above is suppressed.

  In order to achieve the above object, a display device according to the present invention includes a plurality of pixel cells each including a pixel switch and a pixel capacitor connected to the pixel switch and holding an image signal written via a data line. In a display device comprising: a substrate arranged in a matrix; a vertical drive circuit that sequentially drives a plurality of gate lines connected to the pixel switch; and a horizontal drive circuit that sequentially drives the plurality of data lines. A precharge signal line for supplying a precharge signal supplied to the data line at a timing preceding a timing for supplying the image signal to the data line to the plurality of data lines extending from the horizontal drive circuit; The precharge signal is wired so as to pass through the horizontal driving circuit, and is connected to the plurality of data lines. And the first precharge signal that is wired on the substrate in the vicinity of the horizontal drive circuit so that the impedance is lower than the impedance of the first precharge signal line, and both ends pass through the horizontal drive circuit. The second branch is branched to a second precharge signal line connected to the signal line.

  The display device according to the present invention includes a precharge signal line that supplies a precharge signal that is supplied to the data line at a timing that precedes a timing that supplies the image signal to the data line to a plurality of data lines that extend from the horizontal drive circuit. Prepare. The precharge signal line is wired so as to pass through the horizontal drive circuit, and the first precharge signal line connected to the plurality of data lines and the impedance of the first precharge signal line Branched to a second precharge signal line that is wired on the substrate in the vicinity of the horizontal drive circuit and has both ends connected to the first precharge signal line that has passed through the horizontal drive circuit so as to have a small impedance. ing.

  As a result, the influence of the impedance of the first precharge signal line wired in the horizontal drive circuit can be suppressed, so that the display device can display an image with good image quality without deterioration. .

  Further, since the branched second precharge signal line is wired on the substrate in the vicinity of the horizontal drive circuit, it is a peripheral region of the display area of the display device for wiring the precharge signal line. Since it is not necessary to secure a so-called frame area, an ideal display device having a large display area and a small frame area can be formed.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following examples, It cannot be overemphasized that it can change arbitrarily in the range which does not deviate from the summary of this invention.

  First, the configuration of an active matrix type liquid crystal display device driven by a TFT (Thin Film Transistor) to which the present invention is applied will be described with reference to FIG. Note that a precharge signal line for supplying a precharge signal is not shown in FIG.

  As shown in FIG. 1, an active matrix type liquid crystal display device 1 driven by a TFT has a plurality of pixel switches Svh (v and h are natural numbers) arranged in a matrix on a TFT array substrate, and a pixel capacitance. A pixel cell driving circuit including Cvh and the pixel electrode Pvh, and a vertical driving circuit 2 and a horizontal driving circuit 3 including a shift register are provided. The TFT array substrate is arranged so that a counter electrode having a transparent electrode to which a common potential Vcom is applied is opposed to the TFT array substrate. Then, the liquid crystal layer 5 is formed by sealing the liquid crystal between the TFT array substrate and the counter electrode arranged in the above-described positional relationship facing each other.

  In the liquid crystal display device 1 thus formed, the display area in the liquid crystal layer 5 corresponding to each pixel electrode Pvh becomes a pixel cell vh indicating one pixel.

  For example, an N-channel FET (Field Effect Transistor) is used for the pixel switch Svh. The source (S) of the pixel switch Svh is connected to the common electrode (or ground) via the pixel capacitor Cvh. In addition, a pixel electrode Pvh is connected to a connection point between the source of the pixel switch Svh and the pixel capacitor Cvh. Further, the gate line Gv drawn from the vertical drive circuit 2 is connected to the gate (G) of the pixel switch Svh, and the data line Dh drawn from the horizontal drive circuit 3 is connected to the drain (D). Is done.

  The vertical drive circuit 2 includes a shift register, and sequentially operates the gate lines G1, G2,... Gv that are drawn in the horizontal direction and are connected to the gates of the pixel switches Svh included in the pixel cells vh. The horizontal drive circuit 3 includes a shift register, and sequentially scans the data lines D1, D2, D3,... Dh that are drawn in the vertical direction and are connected to the drains of the pixel switches Svh included in the pixel cells vh. . The liquid crystal display device 1 as a whole has such a configuration.

  In the liquid crystal display device 1 having such a configuration, charges are written in the pixels as follows. First, when the gate line G1 rises by the vertical drive circuit 2, the pixel switches S11 to Svh in the first row are turned on. When the data line D1 is driven by the horizontal drive circuit 3 after the pixel switches S11 to Svh are turned on, data (image signal) is written to the pixel capacitor C11 via the pixel switch S11.

  Next, the horizontal drive circuit 3 stops driving the data line D1, turns off the pixel switch S11, further drives the data line D2, and turns on the pixel switch S12. Thereby, the data written in the pixel capacitor C11 is held, and the data is written in the pixel capacitor C12 via the pixel switch S12. By repeating this process up to the data line Dh, data can be written to the pixels in the first row in the horizontal direction.

  When the data writing to the pixels in the first row in the horizontal direction is completed, the vertical drive circuit 2 lowers the gate line G1 and raises the gate line G2. The horizontal drive circuit 3 sequentially drives the data lines D1 to Dh according to the rise of the gate line G2, and executes data writing to the pixels in the horizontal direction as described above. By repeating this operation up to the gate line Gv, data writing to all the pixels of the liquid crystal display device 1 is executed.

  In this way, the image signal is written to all the pixels of the liquid crystal display device 1, but the precharge signal is written to the data line Dn at a timing preceding the timing at which the image signal is written. Become.

  As described in the related art, the precharge signal is generally supplied for the purpose of reducing the load when the image signal is written to the data line by the horizontal drive circuit. In particular, in the 1H inversion driving method in which the voltage polarity of the data line is inverted and driven (AC driving) every horizontal scanning period in order to extend the life of the enclosed liquid crystal, a precharge signal having a predetermined potential is used. Is written to the data line at the timing described above, which has the advantage that the amount of charge required to write the image signal to the data line can be greatly reduced.

  As shown in FIGS. 2A and 2B, the precharge signal is transmitted via a precharge signal line 13 wired on a so-called frame region GF, which is a peripheral region of the display region DF of the TFT array substrate 11. Thus, it is supplied to the data line Dn (not shown) drawn from the horizontal drive circuit 3. FIG. 2A shows a liquid crystal display device 1 of a type in which a flexible printed wiring board (FPC) 12 for supplying an external signal into the liquid crystal display device 1 is provided below the TFT array substrate 11. FIG. 2B is a diagram showing a liquid crystal display device 1 of a type in which the flexible printed wiring board 12 is provided on the left side of the TFT array substrate 11. The liquid crystal display device 1 shown in FIGS. 2A and 2B is functionally different only in the arrangement of the flexible printed wiring board 12 and the horizontal drive circuit 3.

  As shown in FIGS. 2A and 2B, the precharge signal line 13 is connected to the flexible printed wiring board 12, wired on the frame region GF of the TFT array substrate 11, and further in the horizontal drive circuit 3. Are connected to a data line Dn (not shown). The precharge signal line 13 is branched at a branch point X when being wired from the frame region GF to the horizontal drive circuit 3. One branched precharge signal line 13 passes through the horizontal drive circuit 3 so as to be connected to the data line Dn, and the other branched precharge signal line 13 is applied to the TFT array substrate 11. In order not to be affected by various wirings, the upper part of the horizontal drive circuit 3, that is, the vicinity of the horizontal drive circuit 3, is routed and further connected to the precharge signal line 13 that has passed through the horizontal drive circuit 3. Wired in a loop shape. In other words, both ends of the other branched precharge signal line are connected to one precharge signal line branched and passed through the horizontal drive circuit 3.

  Conventionally, for example, as shown in FIGS. 3A and 3B, unlike the case where the present invention is applied, the precharge signal line 13 is wired in the horizontal drive circuit 3 without branching. . When the precharge signal line 13 is wired in the horizontal drive circuit 3 as shown in FIGS. 3A and 3B, the precharge signal line 13 is suspended from the wiring in the horizontal drive circuit 3 or the data line Dn. Under the influence of the shift register cell, an impedance is added.

  FIG. 4 is a diagram equivalently showing the impedance added to the precharge signal line 13 in the liquid crystal display device 1 shown in FIGS. 3A and 3B using the wiring resistance r and the wiring capacitance c. It is. The wiring resistance r increases when the precharge signal line 13 is lengthened or the wiring is thinned to reduce the cross-sectional area of the wiring. Further, the wiring capacitance c increases as the precharge signal line 13 is lengthened or the number of intersections between the wirings increases.

  Therefore, as shown in FIG. 4, when the precharge signal line 13 is wired to the horizontal drive circuit 3, the precharge signal line 13 at the point A that is the entrance side and the point B that is the exit side of the horizontal drive circuit 3. Will cause an impedance difference corresponding to the impedance in the horizontal drive circuit 3. Thus, when an impedance difference occurs in the precharge signal line 13, a difference in charge / discharge capability occurs between the point A side and the point B side, and a potential difference finally occurs. Accordingly, since the precharge signal is not properly written to the pixel capacitor Cuv of the pixel cell uv via the data line Dn on the A point side and the data line Dn on the B point side, the image signal is written after the precharge signal is supplied. As a result, the image displayed on the liquid crystal display device 1 is an image in which the image quality is deteriorated.

  In particular, when the liquid crystal display device 1 has a higher definition and the number of register cells in the horizontal drive circuit 3 is increased or the display area is increased, the wiring resistance r and the wiring capacitance c are increased. For this reason, the impedance difference between the two points described above becomes large, and the image quality deterioration appears remarkably.

  FIG. 5 is an equivalent diagram showing the impedance added to the precharge signal line 13 in the liquid crystal display device 1 shown in FIGS. 2A and 2B using the wiring resistance r and the wiring capacitance c. It is. As shown in FIG. 5, the precharge signal line 13b branched at the branch point X and routed to the top of the horizontal drive circuit 3 has a wiring resistance R and a wiring capacitance C. Since there is no intersection, the impedance is lower than the impedance of the precharge signal line 13a wired in the horizontal drive circuit 3. Since the precharge signal line 13a and the precharge signal line 13b branched at one end at the point X are looped and connected on the point B side, the impedance of the precharge signal line 13a wired in the horizontal drive circuit 3 is reached. The potential difference due to the minute can be reduced.

  FIG. 7 shows the result of measuring the potential at points A and B when the precharge signal is supplied when the precharge signal line 13 is wired in the horizontal drive circuit 3 as shown in FIG. . As shown in FIG. 7, it can be seen that the waveform indicating the potential at point A and the waveform indicating the potential at point B do not overlap and there is a large potential difference. That is, when the precharge signal line 13 is wired in the horizontal driving circuit 3 as shown in FIG. 6, it is affected by the impedance as described above.

  On the other hand, when a precharge signal is supplied in FIG. 9 when the precharge signal line 13 is routed so as to pass through the horizontal drive circuit 3 and loop over the horizontal drive circuit 3 as shown in FIG. The result of having measured the electric potential in A point and B point of is shown. As shown in FIG. 9, it can be seen that the waveform indicating the potential at the point A and the waveform indicating the potential at the point B almost overlap each other, and there is almost no potential difference. That is, as shown in FIG. 8, when the precharge signal line 13 is wired in a loop with respect to the horizontal drive circuit 3, it is not affected by the impedance in the horizontal drive circuit 3.

  As shown in FIGS. 10A and 10B, the precharge signal line 13 extending from the flexible printed wiring board 12 is routed in the horizontal drive circuit 3 and loops around the frame region GF of the TFT array substrate 11. In the case where the wiring is performed as shown in FIGS. 2A and 2B, the influence of the impedance in the horizontal drive circuit 3 can be reduced as in the case where the wiring is performed as shown in FIGS.

  However, as shown in FIGS. 2A and 2B, when the precharge signal line 13 is wired so as to pass through the horizontal drive circuit 3 and loop over the horizontal drive circuit 3, Since the frame area GF of the TFT array substrate 11 is small, there is an advantage that the liquid crystal display device 1 can be made a narrow frame.

  The present invention is not limited to a liquid crystal display device, and can be widely applied to, for example, an organic EL (Electro Luminescence) display, an inorganic EL display, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a configuration of a liquid crystal display device shown as the best mode for carrying out the present invention. It is the figure which showed a mode that the pre-charge signal line was wired to the liquid crystal display device. It is the figure which showed a mode that the pre-charge signal line was wired to the conventional liquid crystal display device. It is the figure which equivalently showed the impedance added to the precharge signal line wired by the conventional liquid crystal display device. It is the figure which equivalently showed the impedance added to the precharge signal line wired by the liquid crystal display device of this invention. It is the figure which showed the position of the precharge signal line which performs an electrical potential measurement in the conventional liquid crystal display device. FIG. 7 is a diagram showing a result of measuring potential at a predetermined position of the precharge signal line shown in FIG. 6. In the liquid crystal display device of this invention, it is the figure which showed the position of the precharge signal line which performs an electric potential measurement. It is the figure which showed the result of having measured the electric potential in the predetermined position of the precharge signal line shown in FIG. It is the figure which showed another example of the wiring layout of the precharge signal line which reduces the impedance difference in a horizontal drive circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 2 Vertical drive circuit, 3 Horizontal drive circuit, 11 TFT (Thin Film Transistor) array board | substrate, 12 Flexible printed wiring board (FPC), 13 Precharge signal line, DF display area, GF frame area

Claims (1)

A substrate in which a plurality of pixel cells each including a pixel switch and a pixel capacitor connected to the pixel switch and holding an image signal written via a data line are arranged in a matrix, and a plurality of pixels connected to the pixel switch In a display device comprising a vertical drive circuit for sequentially driving the gate lines and a horizontal drive circuit for sequentially driving the plurality of data lines,
A precharge signal line for supplying a precharge signal supplied to the data line at a timing preceding the timing for supplying the image signal to the data line to the plurality of data lines extending from the horizontal drive circuit;
The precharge signal is wired to pass through the horizontal driving circuit, and is connected to the plurality of data lines, and a first precharge signal line;
The first precharge signal line that is wired on the substrate in the vicinity of the horizontal drive circuit so that the impedance is lower than the impedance of the first precharge signal line, and both ends pass through the horizontal drive circuit. Branching to a second precharge signal line connected to the display device.

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