JPH043552B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active matrix type liquid crystal display device, and particularly to a drive circuit for an active matrix type liquid crystal image display device.

An active matrix type liquid crystal display device is an active matrix substrate consisting of a plurality of gate lines, a plurality of data lines perpendicular to the gate lines, and a plurality of MOS transistors formed near each intersection of the gate lines and the data lines. A liquid crystal is interposed between the active matrix substrate and a common electrode facing the active matrix substrate. Examples of active matrix substrates include those in which a MOS transistor array is formed on a single-crystal silicon substrate, or those in which a thin film MOS transistor array is formed on a transparent substrate. In recent years, many attempts have been made to manufacture active matrix type liquid crystal image display devices.

The plurality of gate lines are connected to a gate side drive circuit, and the plurality of data lines are connected to a data side drive circuit. Conventionally, when wiring data lines using a material with low resistivity such as aluminum or aluminum alloy, there was no need to add a capacitor to the data side drive circuit because the time constant for charging and discharging the data lines was small.

An example is shown in FIG. In the figure, 101 is an active matrix liquid crystal display device composed of gate lines, data lines, and a pixel array.
102, 103, 104 etc. are gate lines, 105,
106, 107 etc. are data lines, 111, 112,
113, etc. are pixels. Further, 114 is a gate side drive circuit consisting of a shift register, 121, 12
2, 123, 124, 125, etc. are analog switches; 126 is an input terminal for a video signal applied to the data line; 131 is a shift register for controlling opening/closing of the analog switches; the analog switches 121 to 125, etc. and the shift register 131 constitute a data side drive circuit. The analog switches 121 to 125 and the like function to sample and hold video signals, and the time that one analog switch is conductive is limited to about 1 μsec at maximum.

FIG. 2 shows one pixel. In the figure, 201 is a liquid crystal, 202 is a MOS transistor,
203 is a gate line, and 204 is a data line.

By the way, as the specific resistance of the data line increases,
The time constant when charging and discharging charges to the data line also increases. For this reason, if you try to drive a data line with a large resistivity using the drive response shown in Figure 1, the data line will not be completely charged or discharged within the conduction time of the analog switch, making it extremely difficult to display images. . For example, since the voltage drop in the data line is significant, the potential difference between the electrodes of the liquid crystal 201 in FIG. 2 becomes small, and what should appear black appears whitish gray.

In that case, one possibility is to add a capacitor immediately after each analog switch 121 to 125, etc.
Even after the analog switch is opened, the data line is charged by discharging the capacitance to prevent voltage drop. However, if a capacitance is added to each data line, the same number of capacitances as the number of data lines is required, which increases the number of elements in the data side drive circuit. When a data-side drive circuit with an increased number of elements is formed into an integrated circuit, the area of the integrated circuit increases significantly. Since the main application of liquid crystal display devices is for small-sized, low-power consumption electronic devices, the aforementioned increase in the number of elements in the drive circuit, that is, a significant increase in the area of the integrated circuit, is a fatal drawback. In fact, the area per unit of capacity is
Assuming 0.07 mm ² , if there are 100 capacitors, the area of the capacitor group alone will be 7 mm ² , which is not suitable for practical use in terms of integrated circuit production costs. Moreover, as a matter of course, the above-mentioned miniaturization is not satisfactory.

An object of the present invention is to efficiently utilize the capacitance added to the data-side drive circuit, thereby making it possible to drive a data line with high specific resistance with a drive circuit with a small number of elements, and to provide a compact and high-performance active circuit. The object of the present invention is to realize a driving circuit for a matrix type liquid crystal display device.

The gist of the present invention is to use materials with high specific resistance, such as P.
By switching the front and rear terminals of the added capacitor with an appropriate clock signal, the capacitor is The key point is that a large amount of data is used in a time-division manner so that a single capacitor can drive multiple data lines.

Hereinafter, the present invention will be explained in detail based on Examples.

Fig. 3 shows an embodiment of the present invention, and Fig. 4 shows a third embodiment of the present invention.
The waveforms applied to each part of the drive circuit shown in the figure are shown. FIG. 3 shows an example in which all data lines are driven by four capacitors in the data side drive circuit, 300 is an active matrix liquid crystal display device composed of a gate line data line and a pixel array, and 301 306 to 306 are gate lines, 307 to 318 are data lines formed of a material with a resistivity higher than aluminum (for example, a diffusion layer, a transparent conductive film, a silicon thin film, etc.), and 319 to 323 are pixels shown in FIG. ,
331 is a gate side drive circuit consisting of a shift register, and 332 is an analog switch 341 to 352.
333 is a shift register that controls opening and closing of analog switches 381 to 384, 334 to 337 are added capacitors, 501 to 504 are at least two or more of the analog switches 341 to 352, 334 to 337 and a first connection line connecting the analog switches 381 to 384, a capacitance and a second analog switch connected to each of the first connection lines, and 338 applied to the data line. Video signal input terminals 361 to 372 are output terminals of the shift register 332, 391 to 394
is the output terminal of the shift register 333. 33
2 to 394 constitute a data side drive circuit. 401, 402, 403, 404 in Figure 4
are each output terminal 3 of the shift register 333, respectively.
91, 392, 393, 394 output signals are shown, and 405, 406, 407, 408, 40
9, 410, 411, 412 are output terminals 361, 362, 36 of the shift register 332, respectively.
3,364,365,366,367,368 output signals are shown. When the output signal is high, the analog switch is conductive, and when the output signal is low, the analog switch is non-conductive. The video signal input from the input terminal 338 is
At time t ₁ to t ₂ in FIG.
1, the capacitor 334 is charged, and the data line 307 is driven by discharging the capacitor 334 even after t ₂ . At time t ₃ , output terminal 3
The output signal 405 of the switch 61 becomes low, the analog switch 341 becomes non-conductive, and the driving of the data line 307 by the capacitor 334 ends. At the same time, output signals 401 and 40 of output terminals 391 and 365
9 goes high, analog switches 381 and 3
45 becomes conductive. The video signal sampled by the analog switch 381 from time t ₃ to t ₄ charges the capacitor 334 and the analog switch 34
The data line 311 is driven from time t ₃ to t ₅ when the line 5 is conductive.

By repeating the operations described above, the capacitor 334 connects the data lines 307, 311, . . ., and the capacitor 335 connects the data lines 308, 312, .
The capacitor 336 connects the data lines 309, 313......
Capacitor 337 drives data lines 310, 314, . . . , respectively. From FIG. 4, it can be seen that by using four capacitors, the time for driving one data line is four times as long as when no capacitors are used. If the number of capacitors to be added is increased, the time required to drive one data line increases, but the area of the integrated circuit of the data side drive circuit will also inevitably increase. Therefore, by appropriately determining the number of additional capacitors depending on the amount of time required to charge and discharge charges on one data line, the capacitance can be used most efficiently and a high-performance, compact data side can be achieved. An integrated circuit of the drive circuit is realized. By using this data side drive circuit, even if a material with high resistivity is used for the data line,
There is sufficient time to drive the data lines, and the voltage drop in the data lines is reduced, so that the display performance of the active matrix liquid crystal display device is significantly improved. In fact, in Fig. 3, the capacity is 334 to 33
7 to 40PF, analog switch 3381 to 38
4, the sampling time of the video signal is 1μsec,
If the sheet resistance of the data line is 100Ω, the data line repeatedly charges and discharges, and the time it takes for the signal to reach the end of the data line is about 3.4 μsec, and the voltage drop rate in the data line is about 10%, which is sufficient for practical use. Not only that, but it has become extremely high-performance.

As described above, in the drive circuit for an active matrix liquid crystal display device of the present invention, a liquid crystal is sandwiched between a pair of substrates, and one of the pair of substrates has a plurality of data lines arranged in a matrix. A gate-side drive circuit connected to the plurality of data lines of an active matrix liquid crystal display device including a plurality of gate lines, MOS transistors arranged at the intersections of the data lines and the gate lines, and pixels. and a gate-side drive circuit connected to the plurality of gate lines, the data-side drive circuit comprising at least one capacitor, the capacitor being It is connected to the video signal terminal through a first analog switch, and connected to the plurality of data lines through a plurality of second analog switches, and the capacity and the number of the first analog switches are Since the data line and the second analog switch are smaller than each other, a video signal can be sufficiently applied to the data line of the active matrix liquid crystal display device, and Si, which is a high resistance material, can also be used as the wiring material for the data line and gate line. It made it possible to do so. High-strength wiring materials are used for the data lines and gate lines mentioned above.
The fact that Si can be used prevents the wiring material from being damaged by rubbing when rubbing the alignment film formed on the data lines and gate lines. Note that even when low-resistance Al or the like is used for the data lines and gate lines of an active matrix liquid crystal display device, if the drive circuit of the present invention is used, the video signal can be more fully applied to the data lines, and display unevenness can be reduced. This makes it possible to provide a liquid crystal display device that does not have a conventional liquid crystal display device.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a conventional active matrix liquid crystal display device and its driving circuit. FIG. 2 is a diagram showing the configuration of one pixel of an active matrix liquid crystal display device. FIG. 3 and FIG. 4 are diagrams for explaining an embodiment of the present invention.

Claims (1)

[Claims] 1. A liquid crystal is sandwiched between a pair of substrates, and one of the pair of substrates has a plurality of data lines and a plurality of gate lines arranged in a matrix, and a plurality of data lines and a plurality of gate lines are arranged in a matrix at the intersections of the data lines and the gate lines. A data side drive circuit connected to the plurality of data lines of an active matrix type liquid crystal display device including arranged MOS transistors and pixels, and a gate side drive circuit connected to the plurality of gate lines. In the drive circuit for an active matrix liquid crystal display device, the data side drive circuit includes a first analog switch connected to each of the plurality of data lines, and at least two of the first analog switches. a first connection line connecting two or more devices; a capacitor connected to each of the first connection lines; and a second analog switch, a video signal input connected to each of the second analog switches. a terminal, a first shift register that controls the first analog switch, and a second shift register that controls the second analog switch, and the video signal input to the video signal input terminal is The signal from the first shift register operates the first analog switch, and the signal from the second shift register operates the first analog switch, and the signal is supplied to the data line. The signals from the first and first shift registers operate the second analog switch and the first analog switch, respectively, for a certain period of time and at a certain period. The time at which the first and second analog switches start operating for a certain period of time is synchronous, and the time at which the first analog switch is turned on for a certain period of time by a signal from the first shift register is the same as the time at which the first and second analog switches start operating for a certain period of time. 1. A drive circuit for an active matrix liquid crystal display device, characterized in that the second analog switch is turned on for a certain period of time by a signal from a second shift register.