Patent Application
20100052964
1. Field of Invention
The present invention relates to a source driver. More particularly, the present invention relates to a digital to analog converter of the source driver.
2. Description of Related Art
A liquid crystal display (LCD) has many advantages over other types of displays, and is widely used in various applications such as televisions, mobile phones, video camcorders, personal computers and so on. Image data of the LCD are provided through one or more source drivers.
The digital pixel data on the data bus 118 is stored in the latch units 133, and moreover, the digital pixel data is stored first in the first latch 124 and then stored in the second latch 126. The DAC 130 receives the level-shifted digital pixel data and generates driving voltage based on the level-shifted digital pixel data.
However, due to the process variation, the DACs of the channels in the same source driver may generate different analog gamma voltages even if they receive the same level-shifted digital pixel data. As a result, the source drivers may generate different driving voltages even if they receive the same level-shifted digital pixel data, which causes the image noise (band mura) on the display.
Therefore, there is a need for a source driver with improved digital to analog converters to reduce the display image noise.
According to one embodiment of the present invention, a digital to analog converter of a source driver including a gamma voltage generator and a data decoder is disclosed. The data decoder receives digital pixel data and selects one analog gamma voltage from the gamma voltage generator as a driving voltage based on the digital pixel data.
The gamma voltage generator receives a gamma code to generate an analog gamma voltage. The gamma voltage generator includes a register, a reference decoder, and a calibrator. The register stores the gamma code. The reference decoder converts the gamma code from the register into the analog gamma voltage. The calibrator receives a reference gamma voltage in a calibration mode. The calibrator includes a comparator and a counter, in which the counter tunes the gamma code according to the control signal generated by the comparator comparing the analog gamma voltage and the reference gamma voltage.
According to another embodiment of the present invention, a display driving system includes a timing controller and a source driver. The timing controller outputs a digital pixel data and a gamma code. The source driver receives the digital pixel data and the gamma code, and generates a driving voltage to drive a display accordingly. The source driver includes a digital to analog converter, in which the digital to analog converter includes a gamma voltage generator and a data decoder. The data decoder receives digital pixel data and selects one analog gamma voltage as the driving voltage based on the digital pixel data.
The gamma voltage generator receives the gamma code to generate the analog gamma voltage. The gamma voltage generator includes a register, a reference decoder, and a calibrator. The register stores the gamma code. The reference decoder converts the gamma code from the register into the analog gamma voltage. The calibrator receives a reference gamma voltage in a calibration mode. The calibrator includes a comparator and a counter, in which the counter tunes the gamma code according to the control signal generated by the comparator comparing the analog gamma voltage and the reference gamma voltage.
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.
The calibrator of the source driver in the following embodiment eliminates the analog gamma voltage offset between the source drivers due to the process variation, such that source drivers can output the same driving voltage while receiving the same digital pixel data, which reduces the image noises (band mura) of the display.
The gamma voltage generator 315a includes plural gamma units 310a (1˜N), each generates a gamma voltage based on a corresponding gamma code. The gamma unit 310a (1) is used as an example in the following description. The gamma unit 310a (1) receives the gamma code 1 to generate the analog gamma voltage VG1. The gamma unit 310a (1) includes a reference decoder 301 and a calibrator 309a. The reference decoder 301 converts the gamma code 1 from the counter 307 into the analog gamma voltage VG1. The calibrator 309a includes a comparator 303 and a counter 307.
While in the calibration mode, the calibrator 309a receives a reference gamma voltage Gref, and the control signal is the result of comparing the analog gamma voltage VG1 and the reference gamma voltage Gref by the comparator 303. The counter 307, usually implemented as an adder or subtractor to increase or decrease the gamma code stored therein, receives the gamma code 1 from the data bus in the beginning. The counter 307 also tunes the gamma code according to the control signal generated by the comparator 303. Therefore, the gamma code is calibrated by the calibrator 309a based on the reference gamma voltage Gref, and the gamma voltage VG1 outputted by the reference decoder is thus calibrated.
The gamma voltage generator 315b includes plural gamma units 310b (1˜N), each generates a gamma voltage based on a corresponding gamma code. The gamma unit 310b (1) is used as an example in the following description.
The gamma unit 310b (1) receives the gamma code 1 to generate the analog gamma voltage VG1. Similar to the gamma unit 310a (1) shown in
Different to the calibrator 309a shown in
If every bit of the series binary bits and its adjacent bit have different logic value, such as 10101010 or 01010101 (which is so called as the up-dn value), it means that the analog gamma voltage VG1 is sufficiently equal to the reference gamma voltage Gref. In such case, the finite state machine 305 locks the counter 307, such that the counter 307 stops tuning the gamma code, and the calibration mode is ended.
Instead of stop tuning, the finite state machine 305 can also decrease the tuning scale of the counter 307 in order to tune the gamma code more precisely when every binary bit and its adjacent bit have different logic value. Thus, the analog gamma voltage VG1 can be tuned even close to the reference gamma voltage Gref.
The gamma voltage generator 415 includes the calibrator 419 and the reference decoder 301 (1˜N). In addition to the comparator 303, the counter 307, and the finite state machine 305, the calibrator 419 of the gamma voltage generator 415 in
The comparator 303 receives the gamma reference voltage Gref as a comparing basis, which is from the timing controller or from other standard source driver. The I/O multiplexer 409 outputs the gamma voltage if the source driver is used as a standard source driver, else receives reference gamma voltage from the bus to the comparator 303.
In order to convert the digital gamma code into the analog gamma voltage, the gamma voltage generator 415 also includes register 403 (1˜N), input switch 411 (1˜N), and output switch 413 (1˜N). The input switches 411 control the connections between the counter 307 and the registers 403. In detail, the input switches 411 pass the gamma code from the counter 307 to the corresponding register 403 sequentially in the calibration mode. On the contrary, the input switches 411 disconnect the connections between the counter 307 and the registers 403 when out of the calibration mode. The registers 403 store the gamma code, and the reference decoders 301 converts the gamma code from the registers 403 into the analog gamma voltage VG1-VGN.
Different to the digital to analog converter shown in
The F.S.M 305 controls the counter 307 to tune the gamma code according to the control signal generated by the comparator 303. If the control signal memorized by the F.S.M 305 equals the up-down value, the F.S.M 305 locks the counter 307 and disconnects the input switch 411 (1), and the reference decoder 301 (1) adapts the gamma code stored in the register 403 (1) for generating the analog gamma voltage VG1. After the analog gamma voltage VG1 had been calibrated, the gamma voltage generator 415 continues to repeat the calibration process in order to generate and calibrate another analog gamma voltage VG2. The calibration process needs to repeat as many times as the number of the reference gamma voltage (N times in this embodiment).
After all analog gamma voltages of the respective source driver, called the standard source driver, had been corrected, the gamma voltage generator 415 of the respective source driver runs out of the calibration, and all the analog gamma voltages of the standard source driver are close enough to the corresponding reference gamma voltages Gref. Other source drivers receive the corrected analog gamma voltage from the standard source driver as their reference gamma voltage, and tune the analog gamma voltages of their own simultaneously, such that the all the analog gamma voltages generated by various source drivers can be equalized.
According to the above embodiments of the present invention, the driving system of the display can equalize the analog gamma voltages generated by various source drivers, such that the gamma voltage offset between the source drivers can be reduced, thus the band mura on the display can also be reduced.
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.
