JP3842884B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a TFT (Thin Film Transistor) dot matrix type liquid crystal display device, and more particularly to a technique for relieving a disconnected source bus.
[0002]
[Prior art]
As shown in FIG. 5, a conventional liquid crystal display device 100 of this type is called an LCD panel 1, a plurality of source drive IC substrates (also referred to as source drivers) 2 called flexible TABs, and a plurality of flexible TABs. A gate driving IC substrate (also referred to as a gate driver) 3 and an auxiliary wiring substrate 4 are included. In the LCD panel 1, a column-shaped source bus 5 and a row-shaped gate bus 6 are formed, and one pixel is formed corresponding to the mesh surrounded by the source bus 5 and the gate bus 6. At one corner of the mesh, a TFT (not shown) is formed as a switching element that is connected to the corresponding source bus and gate bus and turns on / off the connection between the pixel and the corresponding source bus.
[0003]
One end of the source driver 2 is connected to the A side 1a on one end side of the source bus 5 of the LCD panel 1, and one end of the gate driver 3 is connected to the B side 1b orthogonal to the A side 1a. Connected to the other end of the disconnected source bus 5 by, for example, laser trimming, and a plurality of (several) rescue lines 7 for relieving the disconnected source bus cross the source bus 5 and face the A side. It is formed along the C side 1c.
[0004]
In the LCD panel 1, a short rescue line 7 ′ is formed so as to cross the source bus 5 along one end on the output side of each source driver 2. The other end of the source driver 2 and the gate driver 3 is connected to the auxiliary wiring substrate 4 arranged along the A side 1a and the B side 1b of the LCD panel 1, and a plurality of units for relieving the disconnected source bus. An auxiliary rescue line 8 is formed. One end side of the auxiliary rescue line 8 is connected to one end of the source bus 5 which is disconnected through the solder strap terminal (land) 9, the source driver 2 and the rescue line 7 ′, for example, by laser trimming. The other end side of the auxiliary rescue line 8 is connected to the rescue line 7 via the gate driver 3 near the C side 1c.
[0005]
The auxiliary wiring board 4 is generally divided into a plurality of parts, and the divided boards are connected to each other by an FPC (flexible printed circuit). Although not shown in the figure, the auxiliary wiring board 4 is mounted with a common voltage generation circuit, a power supply circuit, a timing circuit, a gate voltage generation circuit, and the like.
An insulating layer is formed between the source bus 5 and the rescue lines 7, 7 ′ that intersect each other on the LCD panel 1. However, if the source bus 5 is disconnected at the point P in FIG. 1, in order to relieve it, the intersection Q2 between the other end of the disconnected source bus 5 and the rescue line 7 and the disconnected source bus 5 The crossing point Q1 between the one end and the rescue line 7 'is irradiated with a laser beam to break the insulating layer, and the crossing points are welded.
[0006]
The rescue line 7 ′ is connected to the terminal 9 of the auxiliary wiring substrate 4 through the source driver 2, and is connected to the auxiliary rescue line 8 by a solder bridge (solder connection) of the terminal 9. The auxiliary rescue line 8 is connected to the rescue line 7 and extended, and is connected to the source bus that is disconnected at the point Q2. The disconnected source bus 5 is directly driven by the source driver 2 in the section from the source driver 2 to the point P of the disconnection, but the section far from the point P is the rescue line 7'-source driver 2-terminal 9 -Auxiliary rescue line 8-Gate driver 3-Rescue line 7-Driven via point Q2.
[0007]
[Problems to be solved by the invention]
The output circuit of the source driver 2 is a constant voltage circuit with a small internal impedance. By the way, the load impedance ZL of the output circuit that drives the disconnected source bus is the impedance Za as viewed from the Q1 point of the source bus from the Q1 point to the P point, the rescue line 7 'and the auxiliary rescue line 8 from the Q1 point The impedance Zb of the line extending from the Q2 point of the source bus to the P point via the path of the rescue line 7 (hereinafter referred to as a detour) is connected in parallel at the Q1 point.
[0008]
Since the auxiliary rescue line 8 and the rescue line 7 are longer than the source bus and have a large capacity to ground, the impedance Zb on the bypass side is small, so that the load impedance ZL is lowered and affects the operation of the output circuit. For this reason, the output circuit cannot maintain constant voltage characteristics, and the rising edge of the source driver output waveform is lost as shown by the characteristic (2) in FIGS. In the figure, (1) is a waveform of a normal source driver output when the source bus is not disconnected. FIG. 0-No. No. 63 out of 63 gradations. This is a case where black, which is 0 gradation, is displayed on one side. This is a case where 46 gray levels are displayed on one side.
[0009]
When the source driver output waveform when the disconnection of the source bus is relieved as shown in (2), the charge accumulated in the pixel capacitance of the pixel connected to the disconnected source bus via the TFT is reduced. There is a problem that the brightness of the corresponding vertical line is lower than that of a normal vertical line and the display quality is lowered.
An object of the present invention is to prevent a decrease in luminance of a vertical line corresponding to a source bus whose wire breakage has been repaired by simple means.
[0010]
[Means for Solving the Problems]
(1) In the invention of claim 1, a buffer circuit for driving the disconnected source bus from the C side is inserted into the auxiliary rescue line of the auxiliary wiring board.
(2) In the invention of claim 2, the buffer circuit is constituted by a voltage follower circuit.
(3) In the invention of claim 3, the voltage follower circuit is constituted by one operational amplifier.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
It is conceivable to increase the output current capacity of the output circuit of the source driver 2 in order to eliminate the rounding of the source driver output when the disconnection of the source bus 5 is remedied. Since it is necessary to drive several tens to several hundreds of source buses with one source driver, the source driver is large and expensive, and power consumption increases.
[0012]
Therefore, in the present invention, without increasing the output current capacity of the source driver, the buffer circuit 11 (11a, 11b) is inserted into the auxiliary rescue line 8 near the right side of the rightmost terminal 9 in the figure as shown in FIG. The buffer circuit 11 drives the far end side (between P and Q2) of the disconnected source bus. In this way, since the impedance Zb of the detour seen from the point Q1 has a sufficiently high input impedance of the buffer circuit 11, the impedance of the line up to the buffer circuit insertion position of the auxiliary rescue line 8 can be seen mainly. This line is considerably shorter than in the conventional case of FIG. 5, the ground capacity is reduced, and Zb is higher than in the conventional case. Therefore, the impedance drop due to Zb on the detour side of the load impedance ZL of the source driver is alleviated and the influence on the output circuit is reduced, and the source driver output has a rounded waveform as shown by (3) in FIGS. Is greatly improved. Although the output waveform of the buffer circuit 11 is not shown, the waveform is almost the same as the source driver output waveform {circle around (3)} and has less rounding. As a result, the decrease in luminance of the vertical line corresponding to the disconnected source bus cannot be visually observed, and the display quality is prevented from deteriorating.
[0013]
As the buffer circuit 11, a voltage follower circuit using an operational amplifier 12 as shown in FIG. 2 can be used. As is well known, a voltage follower circuit has a very high input impedance (ideally infinite), an extremely low output impedance (ideally zero), and constant voltage characteristics. The input voltage and the output voltage are almost equal, and the voltage drop between the input terminal IN and the output terminal OUT is almost zero.
[0014]
The current consumption of the liquid crystal display device of FIG. 1 is shown in FIG. 3 together with the conventional device of FIG. 5 in which the buffer circuit 11 is not inserted. The increase in current was difficult to measure with a measurement error (about 1 mA) or less. The current consumption is measured by (A) character display, (B) 64 gray scale, (C) 2 dot vertical stripe, (D) 2 sub pixel vertical stripe, (E) 2 dot checkered, ( F) For each display of 2 sub pixel checkers. From this measurement, it was found that the increase in power consumption due to the insertion of the buffer circuit 11 is extremely small and does not cause a problem.
[0015]
【The invention's effect】
(1) As described above, since the buffer circuit 11 is inserted in the middle of the auxiliary rescue line 8 in the present invention, the output waveform of the source driver that drives the disconnected source bus is almost eliminated and the output of the buffer circuit 11 is eliminated. Similarly, the waveform is a waveform with less rounding. As a result, the decrease in the electric charge accumulated in the pixel capacitor connected to the disconnected source bus due to the rounding of the waveform is almost eliminated, the decrease in the luminance of the disconnection can be prevented, and the display quality can be improved.
[0016]
(2) The number of rescue lines and therefore the number of buffer circuits 11 may be several, and the buffer circuit 11 can be easily configured using an inexpensive operational amplifier or the like. be able to.
(3) Since several buffer circuits 11 are required, the increase in power consumption of the liquid crystal display device due to the insertion of the buffer circuit 11 is almost negligible compared with the case where the output current capacity of the source driver is increased. Does not affect capacity.
[Brief description of the drawings]
FIG. 1 is a wiring diagram showing a main part of an embodiment of the present invention.
FIG. 2 is a circuit diagram of the buffer circuit 11 of FIG.
FIG. 3 is a diagram showing current consumption of the device of the present invention (FIG. 1) in comparison with a conventional device (FIG. 5).
4 is a diagram showing a display image when the current consumption of FIG. 4 is measured.
FIG. 5 is a wiring diagram showing a main part of a conventional liquid phase display device.
6 is a waveform diagram showing an example of the source driver output voltage and the gate driver output voltage of FIGS. 5 and 1. FIG.
7 is a waveform diagram showing another example of the source driver output voltage and the gate driver output voltage shown in FIGS. 5 and 1. FIG.

Claims (3)

A TFT (thin film transistor) dot-matrix type liquid crystal display panel (hereinafter referred to as an LCD panel) is formed with a column-shaped source bus and a row-shaped gate bus. One end on the output side of the source driving IC substrate is connected to the other side (referred to as the B side) orthogonal to the side A, and one end on the output side of the gate driving IC substrate is connected to the disconnected source bus. A rescue line connected to the other end and relieving the disconnected source bus is formed along one side (referred to as C side) facing the A side,
The other end of the source driving IC substrate and the gate driving IC substrate is connected to the auxiliary wiring substrate arranged along the A side and the B side of the LCD panel, and the auxiliary for repairing the disconnected source bus A rescue line is formed,
One end side of the auxiliary rescue line is connected to one end of the source bus that is disconnected through the source driving IC substrate, and the other end side is a liquid crystal display device connected to the rescue line through the gate driving IC substrate. There,
A liquid crystal display device, wherein a buffer circuit for driving a disconnected source bus from the C side is inserted into an auxiliary rescue line of the auxiliary wiring board. 2. The liquid crystal display device according to claim 1, wherein the buffer circuit is a voltage follower circuit. 3. The liquid crystal display device according to claim 2, wherein the voltage follower circuit is composed of one operational amplifier.

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