1. Field of the Invention
The present invention relates to a source driver integrated circuit, and more particularly, to a source driver integrated circuit with an improved slew rate wherein a switching unit operating as a resistance component in a procedure of transferring an output signal of an output buffer to a panel load is disposed in a feedback line loop of the output buffer, and thus the slew rate of the output signal can be improved.
2. Description of the Related Art
FIG. 1 is a view illustrating a connection structure of a panel and a conventional source driver IC in a liquid crystal display.
As illustrated in FIG. 1, a conventional source driver IC 100 of a liquid crystal display includes a digital-to-analog converter (DAC) unit 110 configured to convert digital data including an RGB signal into analog data and to output the analog data, an output buffer unit (e.g. amplifier) 120 configured to transfer the output of the DAC unit 110, and a pad unit 130 configured to output analog data which is outputted from the output buffer unit 120.
Meanwhile, the analog data outputted from the output buffer unit 120 passes through the pad unit 130, and then is transferred to a panel 200 via data lines 140.
In this case, digital data including an R signal is inputted through a first data line DL1, is converted into analog data by a first digital-to-analog converter 111, and then passes through a first output buffer 121 and a first pad 131, so that the analog data including the R signal is inputted to a first panel load 210 of the panel 200, and thus the panel 200 is driven with R data.
In the same sequence as described above, G analog data is inputted to a second data line DL2, and B analog data is inputted to a third data line DL3, so that data lines are driven in the RGB sequence.
FIG. 2 is a detailed view of a part of the conventional source driver IC in a liquid crystal display, illustrated in FIG. 1.
As illustrated in FIG. 2, the outputs of a first output buffer 121 and a second output buffer 122 in the conventional source driver IC of the liquid crystal display pass through a switching unit 150, and are outputted to a first panel load 210 and a second panel load 220 through data lines DL1 and DL2, respectively.
In a first driving mode, the first digital-to-analog converter 111 outputs and transfers a first polarity voltage having a positive polarity to the first output buffer 121, and a second digital-to-analog converter 112 outputs and transfers a second polarity voltage having a negative polarity to the second output buffer 122.
Subsequently, a 1-1st switch SW1-1 and a 2-1st switch SW2-1 in the switching unit 150 are turned on, while a 1-2nd switch SW1-2, a 2-2nd switch SW2-2, and a charge-sharing switch SW3 are turned off. Accordingly, the output signal of the first output buffer 121 is transferred to the first panel load 210 through the 1-1st switch SW1-1 and the first data line DL1, and the output signal of the second output buffer 122 is transferred to the second panel load 220 through the 2-1st switch SW2-1 and the second data line DL2.
In a first charge-sharing mode, a charge-sharing process is performed to reduce power consumption caused when the polarity is reversed between the data lines DL1 and DL2. In this case, the 1-1st switch SW1-1, the 1-2nd switch SW1-2, the 2-1st switch SW2-1, and the 2-2nd switch SW2-2 are turned off, while the charge-sharing switch SW3 is turned on. Accordingly, the first panel load 210 receiving the output signal of the first output buffer 121 and the second panel load 220 receiving the output signal of the second output buffer 122 share charges, which are accumulated in the respective panel loads 210 and 220, through the charge-sharing switch SW3.
In a second driving mode, the 1-1st switch SW1-1, the 2-1st switch SW2-1, and the charge-sharing switch SW3 in the switching unit 150 are turned off, while the 1-2nd switch SW1-2 and the 2-2nd switch SW2-2 are turned on.
Accordingly, the output signal of the first output buffer 121 is transferred to the second panel load 220 through the 1-2nd switch SW1-2 and the second data line DL2, and the output signal of the second output buffer 122 is transferred to the first panel load 210 through the 2-2nd switch SW2-2 and the first data line DL1.
In a second charge-sharing mode, charges accumulated in the respective panel loads 210 and 220 are again shared. That is to say, the 1-1st switch SW1-1, the 1-2nd switch SW1-2, the 2-1st switch SW2-1, and the 2-2nd switch SW2-2 are turned off, while the charge-sharing switch SW3 is turned on. Accordingly, the first panel load 210 and the second panel load 220 share charges, which are accumulated in the respective panel loads 210 and 220, through the charge-sharing switch SW3.
The source driver IC drives the liquid crystal display while repeating the operations from the first driving mode to the second charge-sharing mode, as described above.
FIG. 3 is a view explaining a problem in the feedback structure of the conventional source driver IC.
Generally, in a source driver IC, the switching unit 150 performing a switching operation for an output signal operates as a resistance component when transferring an output signal from the output buffers 121 and 122 to the panel loads 210 and 220. Therefore, the feedback structure of the source driver IC illustrated in FIG. 3(a) may be simplified and expressed as FIG. 3(b).
Referring to FIGS. 3(a) and 3(b), it can be understood that, in the feedback structure of the conventional source driver IC, the switching unit 150 operating as a resistance component is disposed outside the feedback line (FL) loop of the output buffers 121 and 122.
Accordingly, the switching unit biased toward the panel load operates as a resistor, so that the slow rate of an output signal transferred to the panel load is reduced. In addition, the reduced slew rate makes it impossible to easily implement an image through the display.