KR20080016048A - Panel driving circuit driving the panel using an active pre-charge voltage - Google Patents

Abstract

A panel driving circuit driving a panel by using an active precharge voltage is provided to decrease a power consumption of an LCD(Liquid Crystal Display) device by varying a voltage according to a data signal. A panel driving circuit includes buffers(111,112), a precharge unit(131), and precharge voltage generators(121,122). The buffers receive data signals, buffer the received data signals, and output the buffered data signals. The precharge unit performs a precharge process on a channel line which delivers the data signal to respective pixels. The precharge voltage generators generate a precharge voltage having different levels according to the data signal. The precharge voltage generator includes a voltage divider which divides a voltage between a first signal and a reference voltage. The first voltage corresponds to the data signal. The voltage divider supplies the divided voltage as the precharge voltage.

Description

Panel Driving Circuit driving the panel using an active pre-charge voltage}

1 is a graph illustrating a change in voltage of a channel line according to a conventional precharge operation.

2 is a graph showing a change in voltage of a channel line to indicate energy loss caused by a fixed precharge voltage.

3 is a circuit diagram illustrating a panel driving circuit according to an embodiment of the present invention.

4A and 4B are circuit diagrams illustrating an exemplary embodiment of the precharge voltage generator of FIG. 3.

5 is a graph illustrating a change in voltage of a channel line according to the panel driving circuit of FIG. 3.

6A and 6B are graphs showing the voltage change of the channel line during the precharge operation in the conventional and the present invention, respectively.

Explanation of symbols on the main parts of the drawings

10: panel driving circuit 111, 112: buffer unit

121,122: precharge voltage generator 131,132: precharge unit

133: charge sharing unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a panel driving circuit, and more particularly, to a panel driving circuit capable of reducing energy loss that may occur during a precharge operation since the panel is driven using an active precharge voltage.

Among the display devices, liquid crystal displays (LCDs), which are rapidly growing in the display market, are rapidly replacing CRTs due to various advantages such as low power consumption, thinness, and excellent image quality. LCDs are used in various fields from small LCDs used in mobile phones to large LCDs applied to laptops, desktop monitors and digital TVs.

Recently, since LCDs are used in 20-inch or larger digital TVs, the driving capability for driving such large LCD panels should be increased. In addition, the number of channels is increased to drive a large LCD panel, and in order to achieve high resolution and large size of the LCD panel, the number of data that can be processed by the panel driving circuit must be increased. As the driving capability required in the LCD driving circuit must be increased, the increased driving capability increases the power consumed in the panel driving circuit.

However, as the power consumed increases, the temperature inside the chip where the panel driving circuit is implemented is increased. Increasing the temperature inside the chip causes a problem of deteriorating the performance of the panel driving circuit and causing an error in the output signal.

On the other hand, as a means for suppressing the temperature rise inside the chip as described above, the panel driving circuit may include a precharge means and a charge sharing means. In the precharging operation, the panel driving circuit may be precharged by applying a predetermined voltage to the channel line in advance before delivering the output voltage according to the data signal, thereby reducing the burden on the driving of the panel driving circuit.

In general, the voltage applied to the channel line during the precharge operation (hereinafter, the precharge voltage) is a positive voltage and a negative value based on a voltage VCOM that determines the liquid crystal rotation direction of the LCD panel. Use voltage. However, there is a problem of excessive energy consumption in the entire circuit when using a voltage having a constant magnitude consisting of a predetermined positive voltage and a negative voltage as described above.

1 is a graph illustrating a change in voltage of a channel line according to a conventional precharge operation. In the illustrated section A, the charge sharing period is shown. When charge sharing is performed while the voltage VOL.ch of the initial channel line is at a low level, the voltage VOL.ch of the channel line increases during the period.

The illustrated section B represents a precharge section. As an example, the precharge is performed with the high level precharge voltage VHC with respect to the voltage VOL.ch of the channel line. Thereafter, a buffer output operation period C is provided to provide a voltage according to the data signal to the panel. For example, when the voltage level of the data signal for realizing the gray level of the panel is 14V and the high level precharge voltage VHC is set to 3/4 of the general driving voltage, the channel line during the buffer output operation period C The voltage VOL.ch rises. After that, the A to C sections are repeated again, and the voltage VOL.ch of the channel line is changed according to the input data signal and the fixed precharge voltage.

On the other hand, Figure 2 is a graph showing the voltage change of the channel line to represent the energy loss caused by the fixed precharge voltage. As shown in FIG. 2, the voltage VOL.ch of the channel line is changed during the charge sharing period A, and the precharge voltage at which the voltage VOL.ch of the channel line is fixed in the precharge period B is fixed. For example, the voltage reaches the high level of the precharge voltage VHC. However, when the voltage of the data signal output in the buffer output operation period C has a value similar to the voltage VCOM, the voltage VOL.ch of the channel line falls back to a low value during the buffer output operation period C. .

In addition, as shown in the following A through C periods, the voltage VOL.ch of the channel line is unnecessarily lowered to the precharge voltage VLC of a low level. As a result, the voltage VOL.ch of the channel line is unnecessarily changed during the precharge operation, thereby increasing the amount of current consumed in the circuit as a whole. If the current flows more than necessary, the result is a waste of the circuit's energy as a whole, and also raises the temperature of the system. However, in the conventional case, since there is no means for improving the above-described problems, there is a problem of consuming unnecessary energy due to the precharge operation.

The technical problem to be solved by the present invention is to use an active precharge technique that varies the level of the precharge voltage according to the input data signal, thereby reducing the problem of unnecessary energy consumption during the precharge operation. In providing the furnace.

According to another aspect of the present invention, a panel driving circuit includes a buffer unit for receiving a data signal and buffering and outputting a data signal, and a precharge operation with respect to a channel line for transmitting the data signal to each pixel. And a precharge voltage generator for generating a precharge voltage having different levels according to the input data signal.

Preferably, the precharge voltage generator includes a voltage divider configured to divide a voltage between the voltage corresponding to the data signal and a reference voltage to provide the divided voltage as the precharge voltage.

Also preferably, the voltage divider may include a first resistor for generating a first precharge voltage and a second resistor for generating a second precharge voltage.

The precharge voltage generator may be electrically connected to an input terminal of the buffer unit to generate a precharge voltage according to a data signal before the buffering operation is performed.

The precharge voltage generator may be electrically connected to an output terminal of the buffer unit to generate a precharge voltage according to a data signal in which the buffering operation is performed.

Meanwhile, preferably, the panel driving circuit may be applied to a liquid crystal display (LCD).

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

3 is a circuit diagram illustrating a panel driving circuit according to an embodiment of the present invention. As shown in the drawing, the panel driving circuit 10 includes buffer units 111 and 112 for receiving data signals Vin1 and Vin2 and buffering and outputting the data signals Vin1 and Vin2, and channels for transmitting the data signals Vin1 and Vin2 to each pixel. The precharge units 131 and 132 for performing the precharge operation on the lines CL1 and CL2 and the precharge voltages VHC1, VLC1, VHC2, which have different levels according to the input data signals Vin1 and Vin2. Precharge voltage generators 121 and 122 that generate VLC2 may be provided.

The configuration of the panel driving circuit 10 according to each channel line CL1 and CL2 is as follows.

The panel driving circuit 10 includes buffer units BUF1 and 111 for buffering the data signal Vin1 transmitted through the channel line CL1. A precharge unit 131 may be provided to perform a precharge operation on the channel line CL1 that transmits the data signal Vin1. In addition, a precharge voltage generator 121 for generating precharge voltages VHC1 and VLC1 having different levels according to the input data signal Vin1 is provided.

The precharge unit 131 may include a switch for applying a high level precharge voltage VHC1 to the channel line 1 CL1 according to a predetermined control signal C1, and the predetermined control signal C2. ), A switch for applying a low level precharge voltage VLC1 to the channel line CL1 may be provided. In FIG. 3, as an example, the first PMOS transistor MP1 is applied as a switch for controlling the application of the high level precharge voltage VHC1, and the application of the low level precharge voltage VLC1 is controlled. The first NMOS transistor MN1 is applied as a switch for the following.

In addition, the panel driving circuit 10 is for driving the channel line CL2 according to the input data signal Vin2, and includes the buffer units BUF2 and 112, the precharge voltage generator 122, and the precharge unit. 132. The precharge voltage generator 122 generates precharge voltages VHC2 and VLC2 having different levels according to the input data signal Vin2.

The precharge unit 132 may include at least one switch for controlling the transfer of the precharge voltages VHC2 and VLC2 to the channel line CL2. For example, the precharge voltage of the high level precharge voltage ( As a switch for controlling the application of the VHC2, a second PMOS transistor MP2 gated by the control signal C3 is applied, and a switch for controlling the application of the low-level precharge voltage VLC2 to the control signal C4. The second NMOS transistor MN2 gated by is shown applied.

Among the non-described reference numerals, the reference voltage Vr may be provided to the precharge voltage generators 121 and 122 to generate the precharge voltages VHC1, VLC1, VHC2, and VLC2. As the reference voltage Vr, the ground voltage GND may be applied, and the reference voltage VCOM for determining the liquid crystal rotation direction may be applied.

In addition, the switches S1 and S2 are turned off during the precharge period, and are turned on after the precharge operation is completed, so that the data signals Vin1 and Vin2 buffered by the buffer units 111 and 112 are transferred through the pads PAD1 and PAD2. Transfer to the liquid crystal panel. In addition, the illustrated switches (for example, MN3 and 113) are for charge sharing and are turned on by the control signal C5 before performing the precharge operation, thereby sharing the charges between the channel lines 1 and 2.

In addition, each of the illustrated resistors R and capacitor C represents an equivalent resistance and a capacitor of one liquid crystal pixel, and implements an image as a gray level corresponding to the voltage levels of the input data signals Vin1 and Vin2.

The operation of the panel driving circuit configured as described above will be described with reference to FIGS. 4A and 4B. In particular, the operation of the panel driving circuit for channel line CL1 will be described.

4A and 4B are circuit diagrams illustrating an exemplary embodiment of the precharge voltage generator of FIG. 3. 4A illustrates that the precharge voltage generator 121 is electrically connected to an input terminal of the buffer 111 and generates precharge voltages VHC1 and VLC1 according to the data signal Vin1 before the buffering operation is performed.

When the image data DATA is input through the video signal input terminal, the decoder 141 decodes the image data DATA and outputs a data signal Vin1 having a predetermined voltage level. The data signal Vin1 is buffered by the buffer unit 111 and provided to the pixel of the liquid crystal panel through the channel line CL1.

The precharge voltage generator 121 divides a voltage between the voltage corresponding to the data signal Vin1 and the reference voltage Vr, and uses the divided voltage as the precharge voltages VHC1 and VLC1. To provide. The precharge voltage generator 121 may include at least one resistor R1 to R4 connected between the voltage corresponding to the data signal Vin1 and the reference voltage Vr to distribute the voltage. As described above, the reference voltage Vr may be applied with the ground voltage GND, and the reference voltage VCOM for determining the liquid crystal rotation direction may be applied.

In general, in order to prevent degradation of the liquid crystal panel when the decoder 141 outputs the data signal Vin1, the positive voltage and the negative voltage are alternated with respect to the reference voltage VCOM, which determines the liquid crystal rotation direction. To print. When the positive data signal Vin1 is transmitted through the channel line CL1, the precharge voltage generator 121 may supply a voltage between the positive data signal Vin1 and the reference voltage Vr. Is divided to generate precharge voltages VHC1 and VLC1. In addition, during the precharge operation, the first PMOS transistor MP1 is turned on by the control signal C1, and the precharge unit 131 performs the precharge operation with the high level precharge voltage VHC1 with respect to the channel line CL1. Perform.

After completion of the precharge operation, the switch S1 is turned on so that a positive data signal Vin1 is transmitted to the panel through the channel line CL1.

After that, the negative data signal Vin1 is transmitted, and the precharge voltage generator 121 divides the voltage between the negative data signal Vin1 and the reference voltage Vr to precharge the voltage VHC1. , VLC1). In addition, during the precharge operation, the first NMOS transistor MN1 is turned on by the control signal C2, and the precharge unit 131 performs the precharge operation with the low level precharge voltage VLC1 with respect to the channel line CL1. Perform.

In the case of FIG. 4A, the precharge voltage generator 121 generates resistors R1 and R2 for generating a high level precharge voltage VHC1 and a low level precharge voltage VLC1. Although the resistors R3 and R4 are provided separately, the present invention is not limited thereto. The voltage distributed through one resistor unit may be provided to one electrode of the first PMOS transistor MP1 and the first NMOS transistor MN1 as a precharge voltage. In addition, the resistors R1 to R4 included in the precharge voltage generation unit 121 may be implemented as passive devices or active devices using transistor devices.

Meanwhile, the panel driving circuit according to an embodiment of the present invention may be implemented as shown in FIG. 4B. In FIG. 4B, the precharge voltage generator 121 is electrically connected to the output terminal of the buffer unit 111 and generates the precharge voltages VHC1 and VLC1 according to the data signal Vin1 in which the buffering operation is performed.

As the size of the liquid crystal panel increases, the number of pixels driven by the data signal Vin1 increases, so that the load value applied by the pixels increases. In response to this, the data signal Vin1 is buffered to improve driving capability. Accordingly, since the precharge voltages VHC1 and VLC1 are generated using the buffered data signal Vin1, the performance of performing the precharge operation can be improved.

The operation of the panel driving circuit that can be configured as described above will be described with reference to FIG. 5.

5 is a graph illustrating a change in voltage of a channel line according to the panel driving circuit of FIG. 3. 5 illustrates a change in voltage of the channel line when the data signal implements a low gray level near VCOM. The illustrated VHC and VLC represent a precharge voltage having a conventional fixed value, and the Active VHC and VLC represent an active precharge voltage having a value that varies with the data signal.

The voltage VOL.ch of the initial channel line increases by the charge sharing period A, and then the precharge period B proceeds. In performing the precharge operation, precharge voltages having different levels are generated according to input data signals. The active precharge voltages (Active VHC, Active VLC) generated thereby have a constant level of level compared to the voltage level of the data signal. Therefore, during the precharge period B, the voltage VOL.ch of the channel line rises as shown.

Thereafter, a buffer output operation period C for providing a voltage according to the data signal to the panel is performed. In the period, the voltage VOL.ch of the channel line rises to a voltage level corresponding to the data signal. In this case, since the precharge operation is performed by the precharge voltage having a predetermined ratio according to the voltage level of the data signal, the voltage VOL.ch of the channel line can reach the voltage level of the data signal faster. have. Accordingly, the response speed of the liquid crystal panel can be shortened, and a better contrast ratio can be obtained than in the related art. In particular, by not excessively raising the voltage VOL.ch of the channel line to the precharge voltages VHC and VLC having a fixed value, it is possible to prevent unnecessary energy from being consumed.

6A and 6B are graphs showing the voltage change of the channel line during the precharge operation in the conventional and the present invention, respectively. In particular, the voltage change in the precharge section and the buffer output operation section is shown.

As shown in FIG. 6A, in the conventional precharge operation, the channel line is excessively precharged during the precharge period B as compared to the voltage change caused by the data signal during the actual buffer output operation period C. FIG. Therefore, since the swing width of the voltage is increased over the intervals, excessive voltage is used throughout the system and unnecessary energy is consumed.

However, as shown in FIG. 6B, in the precharge operation according to an embodiment of the present invention, the channel line is precharged during the precharge period B at a value corresponding to a predetermined ratio according to the voltage level of the data signal. . As a result, since the swing width of the voltage becomes smaller over the sections, not only a quick response speed but also a good contrast ratio can be obtained. In addition, since the channel line is precharged by a precharge voltage which is changed to an appropriate value according to the data signal, unnecessary energy consumption can be improved.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the panel driving circuit according to the exemplary embodiment of the present invention may not only obtain a fast response speed but also reduce unnecessary energy consumption by performing a precharge operation by varying a voltage according to a data signal. It can be effective.

Claims (6)

A buffer unit which receives a data signal and buffers and outputs the data signal; A precharge unit for performing a precharge operation on the channel line transferring the data signal to each pixel; And And a precharge voltage generator configured to generate precharge voltages having different levels according to the input data signal. The method of claim 1, wherein the precharge voltage generator, And a voltage divider for dividing a voltage between the voltage corresponding to the data signal and a reference voltage to provide the divided voltage as the precharge voltage. The method of claim 2, wherein the voltage divider, And a first resistor portion for generating a first precharge voltage and a second resistor portion for generating a second precharge voltage. The method of claim 1, wherein the precharge voltage generator, And a precharge voltage electrically connected to an input terminal of the buffer unit to generate a precharge voltage according to a data signal before the buffering operation is performed. The method of claim 1, wherein the precharge voltage generator, And a precharge voltage electrically connected to an output terminal of the buffer unit to generate a precharge voltage according to a data signal in which the buffering operation is performed. The method of claim 1, The panel driving circuit is applied to a liquid crystal display (LCD) panel driving circuit.

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