Discharge circuit and liquid crystal display using the same

An exemplary discharge circuit (220) includes a first input terminal (2202); a transistor (2204) having a gate electrode, a drain electrode, and a source electrode; a resistance (2205); and a control circuit (2203) provided to control a voltage applied to the gate electrode of the transistor. The source electrode of the transistor is connected to the first input terminal, and the drain electrode of the transistor is grounded via the resistance. Electric charge from the first input terminal is discharged through the transistor and the resistance under control of the control circuit. A liquid crystal display (LCD) (2) employing the discharge circuit exhibits few or no residual images.

FIELD OF THE INVENTION

The present invention relates to discharge circuits such as those used in liquid crystal displays (LCDs); and particularly to a discharge circuit used for eliminating residual images, and an LCD incorporating the discharge circuit.

GENERAL BACKGROUND

An LCD has the advantages of portability, low power consumption, and low radiation. Therefore, the LCD has been widely used in various portable information products, such as notebooks, personal digital assistant (PDA), video cameras, and the like. Furthermore, the LCD is considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.

In general, an LCD includes a gate driver and a data driver. The gate and data drivers drive thin film transistors (TFTs) of an LCD panel of the LCD to display images on a display screen of the LCD panel. Usually, an external power supply provides an operating voltage to enable the gate driver and the data driver to function. When the LCD operates, much electric charge is stored at the gate driver and the data driver. When the LCD is powered off, the electric charge stored at the gate driver and the data driver cannot discharge quickly. That is, the voltage at the gate driver and the data driver only drops slowly. As a result, it is difficult to rapidly shut off the TFTs. Therefore when the LCD is powered off, a voltage from the data driver is still applied to source electrodes of the TFTs, and this produces a so-called residual image on the display screen of the LCD panel.

For the purpose of eliminating residual images, it is common to provide a resistance between a power supply terminal of the gate driver and ground. When the LCD is powered off, the electric charge stored at the gate driver can be discharged quickly through the resistance. That is, the voltage on the gate driver drops quickly and the TFTs connected to the gate driver are shut off as soon as the LCD is powered off. Therefore the voltage from the data driver is not applied to the drain electrodes of the TFTs, and residual images are reduced or eliminated.

However, when the gate driver operates, there is current flowing through the resistance. This increases the power consumption of the LCD.

What is needed, therefore, is a discharge circuit and a liquid crystal display employing the discharge circuit that can overcome the above-described deficiencies.

SUMMARY

A discharge circuit includes a first input terminal; a transistor having a gate electrode, a drain electrode, and a source electrode; a resistance; and a control circuit provided to control a voltage applied to the gate electrode of the transistor. The source electrode of the transistor is connected to the first input terminal, and the drain electrode of the transistor is grounded via the resistance. Electric charge from the first input terminal is discharged through the transistor and the resistance under the control of control circuit.

A liquid crystal display includes a driving circuit provided to drive the liquid crystal display, and a discharge circuit. The discharge circuit includes a first input terminal; a transistor having a gate electrode, a drain electrode, and a source electrode; a resistance; and a control circuit provided to control a voltage applied to the gate electrode of the transistor. The source electrode of the transistor is connected to the first input terminal, and the drain electrode of the transistor is grounded via the resistance. Electric charge stored on the driving circuit is discharged through the first input terminal, the transistor, and the resistance under control of the control circuit.

Other novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe the preferred embodiments in detail.

FIG. 1is a schematic, abbreviated diagram of certain components of a TFT substrate of an LCD according to an exemplary embodiment of the present invention. The LCD2typically includes a color filter substrate (not shown), the TFT substrate which is positioned generally opposite to the color filter substrate, and a liquid crystal layer (not shown) sandwiched between the two substrates. The TFT substrate includes a plurality of data lines211that are parallel to each other and that each extend along a first direction; a plurality of gate lines221that are parallel to each other and that each extend along a second direction orthogonal to the first direction; a plurality of pixel units (not labeled) defined by the intersecting gate lines221and data lines211; a data driver21provided to drive the data lines211; and a gate driver22provided to drive the gate lines221.

Each pixel unit includes a TFT201, a liquid crystal capacitance202, and a storage capacitance203. In each pixel unit, a gate electrode (not labeled) of the TFT201is electrically connected to a corresponding gate line221, a source electrode (not labeled) of the TFT201is electrically connected to a corresponding data line211, and a drain electrode (not labeled) of the TFT201is electrically connected to a corresponding pixel electrode (not shown). The pixel electrode, a common electrode204, and liquid crystal (not shown) sandwiched between the pixel electrode and common electrode204cooperatively define the liquid crystal capacitance202. The pixel electrode, a common line205electrically connected with the common electrode204, and an insulating layer (not shown) sandwiched between the pixel electrode and the common line205cooperatively define the storage capacitance203.

The gate driver22includes a discharge circuit220.FIG. 2is a diagram of the discharge circuit220. The discharge circuit220includes a first input terminal2202, a second input terminal2201, a transistor2204used as a switch, a resistance2205, and a control circuit2203provided to control the voltage on a gate electrode (not labeled) of the transistor2204.

The first input terminal2202of the discharge circuit220is electrically connected to a power input terminal (not shown) of the gate driver22. The second input terminal2201of the discharge circuit220is electrically connected to the control circuit2203. A drain electrode (not labeled) of the transistor2204is electrically connected to the first input terminal2202of the discharge circuit220. A source electrode (not labeled) of the transistor2204is grounded via the resistance2205. A gate electrode of the transistor2204is electrically connected to an output terminal (not labeled) of the control circuit2203.

FIG. 3is a diagram of the control circuit2203. The control circuit2203includes a first inverter2206, a second inverter2207, and a D flip-flop2208. The second input terminal2201of the discharge circuit220is electrically connected to a D input terminal and a CLK input terminal of the D flip-flop2208via the first inverter2206and the second inverter2207, respectively. A Q output terminal of the D flip-flop2208is the output terminal of the control circuit2203.

In use of the LCD2, when the gate driver22operates, the LCD2generates an “OFF” signal, and supplies the “OFF” signal to the second input terminal2201of the discharge circuit220. Then the control circuit2203outputs a low voltage (0V) to turn off the transistor2204. Thereby, there is no current flowing through the resistance2205. When the gate driver22is powered off, the LCD2generates an “ON” signal, and supplies the “ON” signal to the second input terminal2201of the discharge circuit220. Then the control circuit2203outputs a high voltage (3.3V) to turn on the transistor2204. Therefore, the power input terminal of the gate driver22is grounded via the transistor2204and the resistance2205. The electric charge stored on the gate driver22can be discharged quickly through the first input terminal2202, the transistor2204, and the resistance2205. Thereby, the voltage on the gate driver22drops quickly and the TFTs201connected to the gate driver22are shut off as soon as the gate driver22is powered off. Thus, a voltage from the data driver21is not applied to the drain electrodes of the TFTs201.

When the gate driver22operates, the transistor2204is turned off, and there is no current flowing through the resistance2205. This minimizes the power consumption of the LCD2. Moreover, when the gate driver22is powered off, the electric charge stored on the gate driver22can be discharged quickly through the first input terminal2202, the transistor2204, and the resistance2205. Thereby, the voltage on the gate driver22drops quickly and the TFTs201connected to the gate driver22are shut off as soon as the gate driver22is powered off. Thus, the voltage from the data driver21is not applied to the drain electrodes of the TFTs201. Accordingly, a display screen of the LCD2exhibits few or no residual images.

Various modifications and alterations of the exemplary embodiment are possible, as are various alternative embodiments. For example, the gate driver22and the data driver21can cooperatively define a driving circuit, and the discharge circuit220can be provided in the data driver21of the driving circuit.