Drive circuit of TFTLCD

A drive circuit of a thin-film transistor type liquid crystal display. A plurality of source drivers is connected in series. Each of the source drives has a charge pump therein to compensate the voltage drop caused by the metal wires for connecting the neighboring source drivers. The charge pump is preferably disposed at an input of the power line. A capacitor is further connected to each of the power lines for rectifying and filtering the power source transmitted by the power lines. The drive circuit also has a plurality of gate drivers. When the voltage drop caused by the power transmission line between the gate drivers is significant enough to affect a normal operation of the gate drivers, the charge pump is installed in each of the gate drivers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Taiwan application serial no. 91112054, filed on Jun. 05, 2002.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates in general to a drive circuit of a thin-film transistor type liquid crystal display (TFTLCD), and more particularly, to a drive circuit that maintains a sufficient voltage to provide a normal operation of such drive circuit.

2. Description of the Related Art

Recently, the conventional widely used cathode ray tube (CRT) display has been gradually replaced by the flat panel display in small volume and light weight. Currently, the most popular flat panel display includes the liquid crystal display. The application of the liquid crystal display includes the low power products such as calculator, cellular phone, palm pilot, and the notebook computer, desktop computer, and even the wall television. To obtain an optimum display area of a liquid crystal display and to form a thinnest module, the technique of applying a drive integrated circuit (drive IC) has been intensively developed and studied.

There are two commonly used technique for applying the drive IC to the liquid crystal display. One is to connect a printed circuit board mounted with a drive IC to a liquid crystal panel, the other is to install a drive IC on a liquid crystal panel directly. The latter method is also called a chip on glass method (COG).

The former method has the disadvantages including the usage of expensive wiring board (normally polyamide), requirement of large amount of devices, and the need of additional equipment to complete the connection between the drive circuit and the liquid crystal panel. Moreover, when the terminal has a minute pitch, it further restricts the tape carrier pattern and the connection to the electrodes of the liquid crystal panel.

The chip on glass method is a technique for forming a compact display. The electrodes of pixels are formed on the thin-film transistor glass of the liquid crystal panel directly. The liquid crystal panel is patterned to install the drive circuit. The drive circuit is then connected to the liquid crystal panel. This method provides an improved yield and stability and the advantages of small volume and low cost.

However, in the conventional chip on glass structure, metal wires are used to the drivers. The resistance of the metal wires causes a significant voltage drop from one driver to the other. The voltage drop seriously affects the normal operation of the drivers. Therefore, a long strip flexible printed circuit board (FPC) is provided to directly connect each source driver. Therefore, the voltage drop caused by the connection via the metal wires can be obviated. This method requires a large area of the flexible printed circuit board. In addition, as the drive circuits include data lines and power lines, a multiple layer structure is required for the flexible printed circuit board. This method does not only increase the fabrication complexity of the flexible printed circuit board, but also increase the cost and the overall volume of the liquid crystal display. Moreover, as the fabrication process is more complex, the reliability is decreased.

SUMMARY OF INVENTION

The invention provides a drive circuit, in which each source driver comprises a charge pump to compensate the voltage drop caused by the metal wire for power transmission. The large area flexible printed circuit board used in the prior art is not required, so that the increased volume of the liquid crystal display is obviated. In addition, the drive circuit provided by the invention has a simple fabrication process, such that the reliability is increased.

The drive circuit provided by the invention comprises a plurality of source drivers connected in series. The neighboring source drivers are connected with data lines and source lines. The charge pump is disposed at the inputs of the power lines, such that the voltage pump caused by the resistance of the metal wires is compensated. The power is maintained at a certain level to provide a normal operation of the drive circuit. The drive circuit further comprises a capacitor connected to each of the power lines, such that the wave of the power transmitted by the power lines can be filtered and rectified.

The drive circuit further comprises a plurality of gate drivers, preferably connected in series. When similar problem of voltage drop occur to the gate drivers, each of the gate drivers may also comprise a charge pump to resolve such problem. The capacitors for rectifying and filtering the power can be formed on the thin-film transistor glass, such that the overall volume of the liquid crystal display is not increased thereby. In addition, the source drivers and the gate drivers are connected to the liquid display panel via a flexible printed circuit board with a small area to achieve its driving function.

DETAILED DESCRIPTION

InFIG. 1, a typical chip on glass type liquid crystal display with multiple chips is shown. The liquid crystal display comprises a liquid crystal panel100, a drive circuit (referred as10as shown inFIG. 2), and a flexible printed circuit board12to connect the liquid crystal panel and the drive circuit. The liquid crystal panel100further comprises a circuit array substrate, that is, the thin-film transistor substrate104, a counter substrate102and a liquid crystal material filling the space between these two substrates102and104. The connection between the flexible printed circuit board12and the liquid crystal panel100is typically achieved using an electrically anisotropic conductive thin film106, for example.

As mentioned above, in the conventional drive circuit, the power transmission between the source drivers are performed by the metal lines. Such metal lines have a resistance that generates a significant voltage drop, so that the drive circuit cannot operate properly. The prior art provides a structure to resolve such problem. That is, using a long strip flexible printed circuit board to connect each source driver directly. Therefore, the power transmission between the source drivers is achieved without using the metal wires, and consequently, the problem of voltage drop is resolved. However, this structure requires a flexible printed circuit board with a large area that increase a great amount of fabrication cost, and further increase the overall volume of the liquid crystal display. Therefore, instead of using a flexible printed circuit board with a large area, the invention applies a flexible printed circuit board connected to one source driver and one gate driver only. The power transmission is executed with the metal wires, while the voltage drop caused thereby is compensated by pumping up the power source with a charge pump installed in each source driver. Therefore, the space occupied by the flexible printed circuit board is greatly saved, and the cost is reduced. It is appreciated that people of ordinary skill in the art may modify the size and the connection between to the printed circuit board according to specific requirement. For example, the flexible printed circuit board may be connected to more than one source driver and/or more than one gate driver.

FIG. 2shows an embodiment of a drive circuit of a thin-film transistor type liquid crystal display provided by the invention, andFIG. 3shows an enlarged view of two neighboring source drivers as shown inFIG. 2.

Referring toFIGS. 2 and 3, the invention provides a drive circuit10using a flexible printed circuit board12to connect the drive circuit10to the liquid crystal panel (100as shown inFIG. 1). Between two neighboring source drivers14, there are a data line and a power line for power transmission. When a power is transmitted from one source driver14to the next source driver14, a voltage drop is inevitably caused by the resistance of the metal for forming the power line. This voltage drop is more and more significant for the later source drivers14such that the normal operation is affected. Therefore, from the second source driver14, that is, the source driver14right after the one connected to the flexibility printed circuit board12directly, a charge pump24is installed therein. The charge pump24is preferably located at an input of the power line22to compensate the voltage drop. Thereby, the voltage is pumped up to a certain level to provide a normal operation of each of the source drivers14.

In addition, the drive circuit10further comprises a capacitor18connected to each of the power lines22for rectifying and filtering the power transmitted thereby. The capacitors18are preferably formed on the thin-film transistor substrate106to save the space, so as to reduce the volume of the liquid crystal display.

The drive circuit10further comprises a plurality of gate drivers16connected to the flexible printed circuit board12in series. When similar problem of voltage drop occurs to these gate drivers16, the charge pumps24may also be installed in the gate drivers16to compensate the voltage drop and to maintain a normal operation.

Constructed as above, that is, by installing a charge pump in each of the source drivers that are not directly connected to the flexible printed circuit board, the voltage drop caused by the resistance of the power lines can be compensated. As a result, the power of each source driver is maintained at a certain level to provide a normal operation of the drive circuit. Therefore, without a large area of the flexible printed circuit board, the liquid crystal display can be operated normally. Furthermore, additional discrete capacitors used in other conventional method are also avoided. The invention thus provides a drive circuit in small volume, low cost and with high reliability.