Amplifier and source driver utilizing the amplifier

A source driver includes an amplifier, and the amplifier includes an input stage, an output stage, a first current source, a second current source, a third current source, and a switch module. The first current source is utilized to provide a first bias current to the input stage, the second current source is utilized to provide a second bias current to the output stage, and the third current source is utilized to provide a third bias current. The switch module is utilized for selectively connecting the third current source to the input stage or the output stage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an amplifier, and more particularly, to an amplifier of a source driver.

2. Description of the Prior Art

For the resolution and the frame rate of the liquid crystal display (LCD) are getting greater, it is more difficult for charging pixel electrodes to achieve target voltage levels in time. To reduce the charging time, the driving current of an output buffer in a source driver of the LCD is increased to enhance the driving capability of the output buffer. However, increasing currents of the output buffers results in higher power consumption, and the power saving is therefore becomes an important issue.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide an output buffer with enhanced driving capability without wasting power.

According to one embodiment of the present invention, a source driver comprises an amplifier, and the amplifier comprises an input stage, an output stage, a first current source, a second current source, a third current source, and a switch module. The first current source is utilized to provide a first bias current to the input stage, the second current source is utilized to provide a second bias current to the output stage, and the third current source is utilized to provide a third bias current. The switch module is utilized for selectively connecting the third current source to the input stage or the output stage.

According to another embodiment of the present invention, an amplifier comprises an input stage, an output stage, a first current source, a second current source, a third current source, and a switch module. The first current source is utilized to provide a first bias current to the input stage, the second current source is utilized to provide a second bias current to the output stage, and the third current source is utilized to provide a third bias current. The switch module is utilized for selectively connecting the third current source to the input stage or the output stage.

DETAILED DESCRIPTION

Please refer toFIG. 1.FIG. 1is a diagram illustrating an output buffer100of a source driver of a display. As shown inFIG. 1, the output buffer100is an amplifier, which includes an input stage110, an output stage120, a switch module130, a first current source M6, a second current source M7, and a third current source M8. The input stage110includes four transistors M1-M4, the output stage120includes a transistor M5, and the switch module130includes a first switch132and a second switch134. In this embodiment, the first current source M6is used for providing a first bias current I1to the input stage110, the second current source M7is used for providing a second bias current I2to the output stage120, and a third current source M8is used for providing a third bias current I3. In addition, the first current source M6, the second current source M7and the third current source M8are implemented utilizing current mirrors. Furthermore, the switch module130is used for selectively connecting the third current source M8to the input stage110or the output stage120, where the first switch132selectively connects the third current source M8to the input stage110, and the second switch134selectively connects the third current source M8to the output stage120.

In the operations of the amplifier100, the switch module130is controlled by a control signal HDR generated according to a transfer pulse signal TP, where the transfer pulse signal TP is used to trigger the source driver to output display data. The first switch132is controlled by the control signal HDR and the second switch134is controlled by an inverted control signal HDRB, where the control signal HDR and the inverted control signal HDRB are phase-inverted.FIG. 2is a diagram illustrating a relationship between the control signal HDR and the transfer pulse signal TP according to a first embodiment of the present invention. As shown inFIG. 2, at a first line period T1, the transfer pulse signal TP is activated for the source driver to drive a row of pixels, and the control signal HDR is activated accordingly. In this embodiment, the activation time of the control signal HDR is longer than that of the transfer pulse signal TP. Then, at a second line period T2, the transfer pulse signal TP is activated for the source driver to drive a next row of pixels, and the control signal HDR is activated accordingly

During the activation time of the control signal HDR, the first switch132connects the third current source M8to the input stage110, and the bias current of the input stage110is a summation of the first bias current I1and the third bias current I3. Therefore, the driving ability of the input stage110is enhanced and a slew rate of a signal carrying display data is improved. In detail, in the embodiment shown inFIG. 2, the source driver outputs the display data at a falling edge of a pulse of the transfer pulse signal TP. During the activation time of the control signal HDR, first, a capacitor C in the output stage120is fast charged by the current provided by the input stage110, and when the source driver starts to output the signal carrying display data, an LC (liquid crystal) capacitor in a pixel is fast charged. When the control signal HDR is deactivated, the second switch134connects the third current source M8to the output stage120to stabilize the amplifier100. At this time, the bias current of the output stage120is a summation of the second bias current I2and the third bias current I3.

It is noted that, inFIG. 2, the activation time of the control signal HDR is a smaller part of a period of the control signal HDR; that is, for the majority of the time, the second switch134connects the third current source M8to the output stage120to make the amplifier100stable.

FIG. 3andFIG. 4are diagrams illustrating relationships between the control signal HDR and the transfer pulse signal TP according to other embodiments of the present invention. InFIG. 3, the control signal HDR is activated after the transfer pulse signal TP is deactivated. InFIG. 4, the control signal HDR is substantially synchronized with the transfer pulse signal TP.

Additionally, in the embodiment shown inFIG. 1, the third bias current I3is much greater than the first bias current I1and the second bias current I3. Therefore, when the capacitor C in the output stage or the LC capacitor in the pixel starts to be charged, the third current source M8provides the third bias current I3to the input stage110to increase the slew rate; and then the third current source M8provides the third bias current I3to the output stage120to stabilize the amplifier100.

It should be noted that the input stage110and the output stage120shown inFIG. 1are examples. In other embodiments of the present invention, the input stage110and the output stage can be a rail-to-rail operation amplifier or other amplifiers. These alternative designs are all within the scope of the present invention.

Briefly summarized, the amplifier in the source driver includes an input stage, an output stage, a first current source, a second current source, a third current source, and a switch module. The switch module is utilized for selectively connecting the third current source to the input stage or the output stage. For the majority of the time, the switch module connects the third current source to the output stage to stabilize the amplifier, and when the driving ability needs to be enhanced, the switch module connects the third current source to the input stage. Therefore, additional current is not needed to enhance the driving ability of the amplifier, and the power consumption is reduced.