Patent Application
20100321370
1. Field of Invention
The present invention relates to a source driver. More particularly, the present invention relates to a source driver of a display system.
2. Description of Related Art
A liquid crystal display (LCD) is a device which displays images by controlling transmittance of incident light emitted from a light source using optical anisotropy of liquid crystal molecules and polarization characteristics of a polarizer. Recently, the application of LCD has expanded since lightweight, slim size, high resolution and large screen size can be implemented in LCD which have low power consumption.
In general, LCD have a narrow viewing angle as compared to other display devices because light is transmitted only along a light transmitting axis of liquid crystal molecules to display images. Various technologies to improve the viewing angle of an LCD have been studied. One of the technologies is aligning liquid crystal molecules perpendicular to a substrate, forming a cutout or protrusion pattern respectively on a pixel electrode and a common electrode facing the pixel electrode, in which distorting an electric field between the two electrodes forms multi-domain structure and improves the viewing angle.
Although such method shows better contrast, however, the visibility, the viewing angle, the cross talk phenomenon, and particularly the side-visibility is still unacceptable.
According to one embodiment of the present invention, a source driver is disclosed. The source driver includes a gamma voltage generator and a digital to analog converter. The gamma voltage generator includes a first gamma resistor string, a second gamma resistor string, and a switch circuit. The first gamma resistor string receives a first gamma reference voltage and generates a plurality of first gamma voltages for driving at least one first pixel region of the sub-pixel. The second gamma resistor string receives a second gamma reference voltage and generates a plurality of second gamma voltages for driving at least one second pixel region of the sub-pixel, in which the second gamma voltages have different voltage values from the first gamma voltages. The switch circuit selects the first gamma voltages or the second gamma voltages as output gamma voltages according to a timing control signal. The digital to analog converter selects one of the output gamma voltages as a driving voltage corresponding to a received digital pixel data.
According to another embodiment of the present invention, a display system is disclosed. The display system includes a display panel and a source driver. The display panel includes a plurality of sub-pixels driven by driving 20. voltages on the data lines. The source driver includes a gamma voltage generator and a digital to analog converter. The gamma voltage generator includes a first gamma resistor string, a second gamma resistor string, and a switch circuit. The first gamma resistor string receives a first gamma reference voltage and generates a plurality of first gamma voltages for driving at least one first pixel region of the sub-pixel. The second gamma resistor string receives a second gamma reference voltage and generates a plurality of second gamma voltages for driving at least one second pixel region of the sub-pixel, in which the second gamma voltages have different voltage values from the first gamma voltages. The switch circuit selects the first gamma voltages or the second gamma voltages as output gamma voltages according to a timing control signal. The digital to analog converter selects one of the output gamma voltages as a driving voltage corresponding to a received digital pixel data.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
To improve the visibility, the viewing angle, the color shift, the cross talk phenomenon, and particularly the side-visibility of the LCD, some method such as 1 G-2 D, 1 G-1 D is utilized. These methods form a plurality of pixel regions in a sub-pixel, drive them independently, and apply different voltage to the respective divided pixel regions. Thereby, the viewing angle, the color shift, the cross talk phenomenon, and the side-visibility can be improved, since pixel regions are charged with different levels of voltage and the light transmitting axis of the liquid crystal molecule is controlled in various directions. Therefore, a gamma voltage generator is required for generating gamma voltages with different levels.
The first gamma resistor string 101 receives a first gamma reference voltage GRV1 and generates plenty of first gamma voltages VG1 for driving at least one first pixel region of the sub-pixel, while the second gamma resistor string 103 also receives the first gamma reference voltage GRV1 and generates plenty of second gamma voltages VG2 for driving at least one second pixel region of the sub-pixel.
The first gamma resistor string 101 includes plenty of first resistors 105, and the second gamma resistor string 103 includes plenty of second resistors 107 with resistance different from those of the first resistors 105. To make the first gamma voltages VG1 have voltage levels different from the voltage levels of the second gamma voltages VG2, the serially connected first resistors 105 have resistances different from each other. For example, the serially connected first resistors 105 might have resistances such as 1Ω, 2Ω, 3Ω . . . respectively. As a result of the current flowing through the first resistors 105 and second resistors 107, the first gamma voltages VG1 and the second gamma voltages VG2 have different voltage values. The switch circuit 109 then alternatively selects the first gamma voltages VG1 or the second gamma voltages VG2 as the output gamma voltages according to the timing control signal 115. For example, the first gamma voltages VG1 are selected before the second gamma voltages are selected, that is, the switch circuit 109 first select the first gamma voltages VG1, then select the second gamma voltages VG2 sequentially.
In more detail, if the gamma reference voltage GRV1 is a 110 V and the reference voltage is 0V, on the condition that there are ten serially connected first resistors 105 with 1Ω, 2Ω, 3Ω . . . 10Ω resistance respectively, and the ten second resistors 107 all have 2Ω resistance, then the first gamma voltages VG1 are 108 V, 104 V, 98 V . . . 20V respectively, while the gamma voltages VG2 are 99 V, 88 V, 77 V . . . 11 V respectively. In other words, the first gamma voltages VG1 and the second gamma voltages VG2 have different voltage values.
The switch circuit 109, having a lot of switches 109a, selects the first gamma voltages VG1 or the second gamma voltages VG2 as output gamma voltages according to the timing control signal 115, in which all the switches 109a select the first gamma voltages VG1 or the second gamma voltage VG2 uniformly. That is, either all the switches 109a select the first gamma voltages VG1, or all the switches 109a select the second gamma voltages VG2. Then the digital to analog converter 113 selects one of the output gamma voltages as a driving voltage corresponding to the received digital pixel data. In this source driver, the number of the first gamma voltages VG1, the second gamma voltage VG2 is corresponding to the bit number of a display channel.
The first gamma resistor string 101 includes a lot of first resistors 105 connected serially for dividing the first gamma reference voltage GRV1 into the first gamma voltages VG1, and the second gamma resistor string 103 includes a lot of second resistors 107 connected serially for dividing the second gamma reference voltage GRV2 into second gamma voltages VG2, in which the resistance of the first resistors 105 can be different from the resistance of the second resistors 107, such that the voltage value of each gamma voltage VG1 is different form the voltage value of the corresponding gamma voltage VG2. For example, the first gamma reference voltage GRV1 and the second gamma reference voltage GRV2 can be 20 V and 10V respectively, and the first resistors are 1Ω while the second resistors are 2Ω. If there are ten first resistors 105 and ten second resistors 107, as a result, the first gamma voltages are 18 V, 16 V . . . 2V, and the second gamma voltages are 9 V, 8V . . . 1V, which are different from the first gamma voltages.
On the other hand, because the second gamma reference voltage GRV2 has voltage different from the first gamma reference voltage GRV1, the resistance of the first resistors 105 can also be same to the resistance of the second resistors 107, and the voltage value of each gamma voltage VG1 is still different form the voltage value of the corresponding gamma voltage VG2.
The source driver 201 includes the gamma voltage generator 111 and a digital to analog converter 209. The gamma voltage generator 111 generates a lot of gamma voltages according to the timing control signal TC. Then the digital to analog converter 209 selects some of the gamma voltages as the driving voltages for driving the first pixel regions A or the second pixel regions B of the sub-pixels 215 alternatively based on received digital pixel data. The source driver 201 further includes a latch circuit 207 and a buffer 211. The latch circuit 207 is electrically connected to the digital to analog converter 209, in which the latch circuit 207 stores and passes the digital pixel data for the digital to analog converter 207. The buffers 211 enhance the driving capability of the data line 217 to drive the sub-pixels 215.
The display panel 213 includes lots of sub-pixels 215 driven by driving voltages on data lines 217. The sub-pixels 213 can be red light sub-pixels, green light sub-pixels, or blue light sub-pixels. The sub-pixels 215 of the display panel 213 include a lot of first pixel regions A driven by the driving voltages corresponding to the first gamma voltages, and a lot of second pixel regions B driven by the driving voltages corresponding to the second gamma voltages. Therefore, the pixel region A and the pixel region B of each sub-pixel 215 can be driven by voltage with different voltage value alternatively, which improves the visibility, particularly the side-visibility of the LCD.
According to the above embodiment, each of the sub-pixels is divided as at least two pixel regions, and the source driver can drive the pixel regions with different voltages alternatively according to the timing control signal, which improves the visibility, particularly the side-visibility of the LCD.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
