Circuitry for independent gamma adjustment points

• US 8,854,294 B2
• Filed: 03/06/2009
• Issued: 10/07/2014
• Est. Priority Date: 03/06/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Sakariya, Kapil V.
• Primary Examiner(s): Wang, Quan-Zhen
• Assistant Examiner(s): Runkle, III, Nelson D
• Application Number:
  US12/399,526
• Publication Number:
  US 20100225571A1
• Time in Patent Office: 2,041 Days
• Field of Search: 345/87
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

A display architecture providing independent adjustment of gamma with respect to each color channel of a display is provided. In one embodiment, gamma adjustment circuitry may utilize separate resistor strings for each color channel of the display. Gamma adjustment voltage taps for each resistor string may each be coupled to a respective switching logic block that includes a plurality of switches, each of which may be coupled to different respective locations of the resistor string. Based upon a gamma correction profile defining optimal gamma adjustment points for a particular color channel based at least partially upon its transmittance sensitivity characteristics, appropriate control signals may be provided to each of the switching logic blocks to facilitate the connection of the gamma adjustment voltage taps to desired adjustment points on a respective resistor string in order to optimize gamma correction and provide for increased accuracy in color output.

Claims

1. A display device, comprising

a display panel comprising a plurality of unit pixels defining a viewable region of the display device and having a plurality of color channels, each of the plurality of color channels having an associated gamma correction profile;

and

a source driver integrated circuit (IC) configured to process an image data stream and to transmit the processed image data to the display panel, wherein the source driver IC comprises;

gamma adjustment circuitry comprising;

a plurality of resistor strings, each corresponding to a respective one of the plurality of color channels, wherein each resistor string is configured to provide a plurality of output voltage levels corresponding to a respective color channel;

a plurality of sets of gamma adjustment voltage taps, each set of voltage taps corresponding to a respective one of the plurality of resistor strings, wherein each gamma adjustment voltage tap within a set is configured to be adjustably coupled to a respective location on a respective resistor string based upon a gamma correction profile configured to define a set of gamma adjustment locations along the respective resistor string to which each of a corresponding set of gamma adjustment voltage taps are coupled, wherein each respective set of gamma adjustment locations is determined based at least in part on transmittance sensitivity characteristics that corresponds to a transmittance versus voltage curve for the respective color channel, and wherein each respective set of gamma adjustment locations along the respective resistor string is determined by substantially optimizing a portion of the set of gamma adjustment locations to concentrate in a voltage range that corresponds to an area comprising a maximum absolute value of the transmittance sensitivity characteristics for the respective color channel; and

a selection circuit configured to receive the plurality of output voltage levels provided by each of the resistor strings, to select one of the output voltage levels based upon one or more selection signals, and to output the selected voltage level to the display panel.

2. The display device of claim 1, wherein each gamma adjustment voltage tap is provided as an input to a respective switching logic block, wherein each switching logic block comprises a plurality of switches, each switch being coupled to a respective location on the respective resistor string, and wherein each switching logic block is configured to select one of its respective plurality of switches based upon a respective control signal provided based upon the gamma correction profile associated with the color channel corresponding to the respective resistor string.

3. The display device of claim 1, wherein a number of the plurality of output voltage levels provided by each resistor string is 2^N, wherein N is the number of bits used to express a digital level for each color channel of the image data stream.

4. The display device of claim 1, wherein a number of voltage taps in each set of the plurality of sets of gamma adjustment voltage taps are adjustably coupled to the respective location on the respective resistor string vary based at least partially upon a range of voltages that corresponds to a range of maximum absolute values along the transmittance sensitivity characteristics of its corresponding color channel.

5. The display device of claim 1, wherein the unit pixels of the display panel are arranged in groups of three unit pixels, wherein each unit pixel within a group has an associated color characteristic based upon a respective color filter element, wherein each group of three unit pixels comprises a first unit pixel having a red color filter, a second unit pixel having a green color filter, and a third unit pixel having a blue color filter.

6. The display device of claim 1, wherein the set of gamma adjustment locations is adjustably coupled to the plurality of sets of gamma adjustment voltage taps at any node along the respective resistor string.

7. The display device of claim 6, wherein each node along the resistor string is positioned between two respective resistors of a plurality of resistors along the resistor string.

8. An integrated circuit, comprising:

an input bus for receiving an image data stream having image data corresponding to a plurality of color channels; and

a gamma processing block comprising;

gamma adjustment circuitry comprising;

a resistor string defining a plurality of voltage level outputs;

a switching matrix comprising a first set of conductors coupled to each of the voltage level outputs from the resistor string, a second set of conductors coupled to each of a plurality of gamma adjustment voltage taps, and a plurality of switches comprising a switch located at each intersection of a conductor from the first set and a conductor from the second set, wherein each switch, when operating in a closed state, is configured to couple a gamma adjustment voltage corresponding to the wire from the second set to a voltage level output of the resistor string output coupled to the wire from the first set; and

a selection circuit configured to receive and select one of the voltage level outputs from the resistor string based upon a selection signal comprising a digital level representation of the image data being processed and to output the selected voltage level output from the gamma processing block;

gamma control logic comprising;

a memory configured to store a gamma correction profile for each color channel, wherein each gamma correction profile defines a set of switches within the switching matrix corresponding to desired gamma adjustment locations for its respective color channel, the desired gamma adjustment points being determined based at least in part on a range of voltages that corresponds to a range of maximum values along a transmittance sensitivity curve for each respective color channel, wherein the desired gamma adjustment points are substantially optimized to concentrate a portion of the gamma adjustment points in the range of maximum values along the transmittance sensitivity curve for each respective color channel;

time division logic configured to implement a time division multiplexing scheme in which image data corresponding to each of the color channels is selected and processed in consecutive discrete timeslots, wherein during each timeslot, gamma adjustment points corresponding to a selected color channel are determined by selecting one or more switches within the switching matrix based upon the gamma correction profile associated with the selected color channel, wherein the discrete timeslots repeat in an alternating manner.

9. The integrated circuit of claim 8, wherein the color channels comprise first, second, and third channels, wherein a first set of switches defining a first set of gamma adjustment locations on the resistor string is selected based upon a first gamma correction profile corresponding to the first color channel during a first timeslot, wherein a second set of switches defining a second set of gamma adjustment locations on the resistor string is selected based upon a second gamma correction profile corresponding to the second color channel during a second timeslot, and wherein a third set of switches defining a third set of gamma adjustment locations on the resistor string is selected based upon a third gamma correction profile corresponding to the third color channel during a third timeslot.

10. The integrated circuit of claim 9, further comprising a fourth color channel, wherein a fourth set of switches defining a fourth set of gamma adjustment locations on the resistor string is selected based upon a fourth gamma correction profile corresponding to the fourth color channel during a fourth timeslot.

11. The integrated circuit of claim 8, comprising a timing generator block configured to supply timing signals to a gate driver integrated circuit configured to provide scanning signals to an addressed row of unit pixels of a display panel.

12. The integrated circuit of claim 11, comprising a frame buffer configured to receive the selected voltage level output from the gamma processing block and to provide the selected voltage level output to the display panel via a set of source lines.

13. A method for manufacturing a display device, comprising:

providing a display panel having a plurality of unit pixels arranged in columns and rows defined by source lines and gate lines, respectively, wherein each unit pixel is coupled to an intersection of a source line and a gate line, and wherein the display panel comprises a plurality of color channels;

coupling a source driver integrated circuit (IC) to the display panel, wherein the source driver IC is configured to receive image data corresponding to each of the plurality of color channels and to drive the display panel for displaying images, the source driver IC comprising;

gamma control logic configured to store a gamma correction profile for each of the plurality of color channels;

gamma adjustment circuitry configured to select for each color channel, a respective set of gamma adjustment points for providing a respective set of gamma adjustment voltages to a digital-to-analog converter configured to provide a plurality of output voltage levels, wherein the selection of the respective set of gamma adjustment points is based upon a respective gamma correction profile for a corresponding color channel; and

a selection circuit configured to select one of the output voltage levels based upon a selection signal;

wherein each respective gamma correction profile defines a respective one of a set of gamma adjustment points determined based upon transmittance sensitivity characteristics associated with a transmittance versus voltage curve of a respective color channel, wherein the respective one of the set of gamma adjustment points is configured to substantially optimize a portion of respective one of the set of gamma adjustment points to concentrate in a voltage range that corresponds to an area comprising a maximum absolute value of the transmittance sensitivity characteristics of the respective color channel; and

coupling a gate driver IC to the display panel, wherein the gate driver IC is configured to sequentially activate rows of unit pixels based upon timing signals provided by the source driver IC.

14. The method of claim 13, wherein the digital-to-analog converter comprises one or more resistor strings comprising a plurality of resistors.

15. The method of claim 14, wherein the one or more resistor strings comprises a single resistor string, and wherein the output voltage levels for each color channel are provided by the single resistor string using a time division multiplexing scheme.

16. The method of claim 13, wherein providing the display panel comprises providing one of a normally-black or a normally-white liquid crystal display (LCD).

17. A method, comprising:

providing a gamma correction profile for each of a plurality of color channels in a display device;

applying a respective gamma correction profile to a gamma adjustment circuit associated with each color channel, wherein the gamma correction profile for each color channel comprises data representative of locations of gamma adjustment points to be applied to a particular color channel to compensate for gamma inaccuracies of the display device, wherein the locations of the gamma adjustment points are determined by substantially optimizing a portion of the gamma adjustment points to concentrate in a voltage range that corresponds to the maximum transmittance sensitivity characteristics of the particular color channel;

applying for each gamma adjustment circuit a respective set of gamma adjustment voltages to respective gamma adjustment points corresponding to a respective applied gamma correction profile;

providing from each gamma adjustment circuit a plurality of adjusted voltage outputs, the voltage outputs having been adjusted based upon the respectively applied set of gamma adjustment voltages;

selecting one of the plurality of voltage outputs using a selection circuit; and

outputting the selected voltage output to a display panel.

18. The method of claim 17, wherein each gamma adjustment circuit comprises a resistor string having a plurality of resistors, and wherein each of a respective set of gamma adjustment points corresponds to a respective location along the resistor string.

19. The method of claim 18, wherein each of a set of gamma adjustment voltages is supplied to a switching logic block coupled to a respective resistor string by way of a plurality of switches, wherein each of the plurality of switches is coupled to different voltage outputs on the respective resistor string, and wherein determining a respective set of gamma adjustment points based upon the respectively applied gamma correction profile comprises:

transmitting respective control signals from a control circuit to each of the switching logic blocks; and

selecting a switch within each switching block based upon a respective control signal, wherein the selection of the switch couples the gamma adjustment voltage signal received by the switching block to a location on the respective resistor string that corresponds to the selected switch.

20. The method of claim 17, wherein digital level values of the image data are represented by N bits, and wherein a number of the voltage outputs for each gamma adjustment circuit comprises 2^N output voltages.

21. The method of claim 17, wherein a number of the gamma adjustment points for each color channel increases proportionately as the sensitivity transmittance of the color channel increases.

22. One or more non-transitory tangible computer-readable storage media comprising a computer program product, the computer program product comprising:

code to determine a maximum and minimum voltage value at which to apply gamma adjustment voltages for a color channel of a display device based at least partially upon a transmittance sensitivity curve for the color channel and a desired white balance and to select gamma adjustment points corresponding to each of the determined maximum and minimum voltage values, wherein the transmittance sensitivity curve is determined based at least in part on a transmittance versus voltage curve for the channel;

code to determine a first voltage range corresponding to a region over which the color channel exhibits a highest degree of sensitivity and to select one or more gamma adjustment points along a resistor string that corresponds to the color channel such that the resistor string outputs a plurality of voltages generally distributed within the first voltage range, wherein the code to select the one or more gamma adjustment points comprises substantially optimizing a portion of the one or more gamma adjustment points to concentrate in the first voltage range; and

code to store the selected gamma adjustment points as a gamma correction profile.

23. The one or more non-transitory tangible, computer-readable storage media of claim 22, comprising:

code to determine a second voltage range corresponding to a region of the transmittance sensitivity curve between the region of the highest degree of sensitivity and one of the minimum or the maximum applied voltages; and

code to select at least one gamma adjustment point within the second voltage range.

24. The one or more non-transitory tangible, computer-readable storage media of claim 22, wherein the gamma adjustment points are selected based at least partially upon empirical data.

25. The one or more non-transitory tangible, computer-readable storage media of claim 22, comprising code to determine, based upon the gamma correction profile, values corresponding to control signals to be transmitted to switching circuitry configured to select gamma adjustment points in a gamma adjustment circuit, such that the gamma adjustment points selected within the gamma adjustment circuit correspond to the gamma adjustment points defined in the stored the gamma correction profile.