The present invention relates to liquid crystal display devices and, for example, to a liquid crystal display device of the so called chiponglass (COG) type.
Liquid crystal display devices have a pair of transparent substrates spatially stacked so as to oppose each other with a layer of liquid crystals being sealed therebetween, so as to have multiple pixels (picture elements) formed in the expansion direction of such liquid crystals. Each pixel independently controls the optical transmissivity of light passing there through with respect to an electric field applied to the liquid crystal (LC) material thereof For this purpose, electrodes for generating electric fields in the respective pixels and image signal lines for supplying an image signal to the electrodes are formed on a surface of one of the transparent substrates which confronts the liquid crystal material.
Typically, an image signal is supplied from an image signal drive circuit which is composed of a semiconductor integrated circuit (IC) chip for the image signal line, and the semiconductor integrated circuit is mounted on a region of the one of the transparent substrates other than the display area thereof. Since the image signal is applied to one of a source electrode and a drain electrode of a thin film transistor in the pixel in order to generate an electric field in the pixel, the image signal is called a drain signal or a video signal, the image signal line is called a drain signal line or a video signal line, and the image signal driver circuit is called a drain signal driver circuit or a video signal driver circuit. In this case, logic signals, reference voltages (reference voltage signals), and electric power are supplied from a controller circuit board disposed in the vicinity of one of the peripheral sides of the transparent substrate to the image signal drive circuit through a flexible printed circuit board having a wiring pattern. Therefore, wiring layers connected both to input electrodes of the image signal drive circuit and to output terminals of the flexible printed circuit board are formed on the aforementioned transparent substrate.
As the screen size of the liquid crystal display device having the aforementioned structure becomes larger, the density of the aforementioned wiring layers connected to the image signal drive circuit becomes higher, and thus some disadvantages in the liquid crystal display device caused thereby have arisen.
Since the input side of the image signal drive circuit is high in impedance, the electrical resistivity of the respective wiring lines may be up to a certain value, but should be substantially uniform for each of the wiring lines. This is based on the fact that a deviation in signal waveform delay arises among a plurality of the wiring lines when the resistivity is not uniform, which makes the image signal drive circuit unstable in operation.
A power supply input section is disposed on the input side of the image signal drive circuit, and the electrical resistance of the wiring layer therebetween should be reduced to less than a certain amount to avoid a significant reduction of the operating voltage of the image signal drive circuit. In this case, it may be desirable to balance the resistance values of the wiring layers, other than the wiring layer between the power supply input section and the image signal drive circuit, with the resistance of the wiring layer therebetween, but this can hardly be applied to wiring layers arranged in high density.
The present invention has been made in view of the technical background mentioned above, and an object of the invention is to provide a liquid crystal display device with image signal drive circuitry which exhibits an enhanced operation stability.
Some representative aspects of the invention as disclosed and claimed herein will be briefly summarized as follows.
In a liquid crystal display device, there is provided a pair of substrates disposed to oppose one another, a liquid crystal layer sealed between the pair of substrates, an image signal driver circuit disposed on a surface of one of the pair of substrates which confronts the liquid crystal layer, and a plurality of wiring layers formed on the surface of one of the pair of substrates so as to connect the image signal driver circuit electrically to external circuitry, at least two of the plurality of wiring layers being provided as a first group used for a connection to input electrodes of the image signal driver circuit for receiving logic signals. At least two of the plurality of the wiring layers other than those of the first group are provided as a second group used for a connection to input electrodes of the image signal driver circuit other than those for receiving logic signals. Thus, the input electrodes related to the second group are electrically connected to a voltage supply. Moreover, at least one of the groups of wiring layers belonging to the first group and belonging to the second group are substantially similar to each other in the group thereof.
The liquid crystal display device thus arranged maintains the resistance values of the wiring layers connected to the logic signal input electrodes in a designated range even if the resistivity values thereof are increased, or keeps the resistance values of the wiring layer connected to the reference power supply electrodes in a designated range even if the resistivity values thereof are increased. Both of the wiring layers are conductive films or stripes formed on the substrate on which the image signal drive circuit (IC) chip is mounted. The wiring layer is formed of a material such as a metal, an alloy, an impurity doped semiconductor, or the like.
Keeping the resistance values among the wiring layers connected to the logic input electrodes in a designated range so that the resistance values are similar to each other preferably ensures that a deviation will no longer take place in the delay of the signal waveforms, and thereby enhances the operation stability of the image signal drive circuitry.
On the other hand, keeping the resistance values among the wiring layers connected to the reference power supply electrodes in a designated range so that the resistance values are similar to each other also preferably reduces any deviation in voltage potential drop of the reference power supply.
By adjusting nothing but the electrical resistance of the aforementioned wiring layers of concern, at least one of the advantages mentioned above can be obtained even if the wiring layers are arranged densely on the substrate.
In the aforementioned liquid crystal display device, certain numbers of the input electrodes of the image signal driver circuit are divided for the logic signal input electrodes and the reference voltage supply electrodes, respectively, the input electrodes used as logic signal input electrodes being disposed adjacent to each other, and the input electrodes used as reference voltage supply electrodes being disposed adjacent to each other.
In this liquid crystal display device, the wiring layers connected to the logic input electrodes are arranged in proximity to one another, and the wiring layers connected to the reference power supply electrodes are arranged in proximity to one another, respectively. Therefore, the wiring design and the arrangement of the wiring layer for unifying substantially the electrical resistance of the wiring layer of concern are simplified.
Based on the several reasons mentioned above, it is recommended that in a liquid crystal display device having a pair of substrates disposed so as to confront one another, a liquid crystal layer being sealed between the pair of substrates, and an image signal driver circuit element disposed on a main surface of one of the pair of substrates and a plurality of input terminals arranged along an edge of the one of the pair of substrates close to the image signal driver circuit element, the plurality of input terminals are divided into groups relative to the functions thereof and are arranged with respect to the groups.