Gamma voltage generator and display device having the same

1. A gamma voltage generator, comprising:

a reference gamma selector to receive a first reference voltage and a second reference voltage and to select a top reference gamma voltage and a bottom reference gamma voltage between the first and second reference voltages;

a reference gamma converter to convert the bottom reference gamma voltage to a conversion reference gamma voltage based on the top reference gamma voltage; and

a gamma curve adjuster to generate a plurality of grayscale gamma voltages based on the conversion reference gamma voltage and the top reference gamma voltage.

2. The gamma voltage generator as claimed in claim 1 , wherein the reference gamma selector is to select the top reference gamma voltage such that the top reference gamma voltage increases as a dimming level increases.

3. The gamma voltage generator as claimed in claim 1 , wherein the reference gamma converter is to adjust the conversion reference gamma voltage such that the conversion reference gamma voltage decreases as the top reference gamma voltage increases.

4. The gamma voltage generator as claimed in claim 3 , wherein the conversion reference gamma voltage is to linearly decrease as the top reference gamma voltage increases.

5. The gamma voltage generator as claimed in claim 1 , wherein the reference gamma selector includes:

a reference resistance string to distribute the first reference voltage and the second reference voltage;

a first reference selector to select one of the voltages distributed by the reference resistance string as the bottom reference gamma voltage based on a bottom selection signal; and

a second reference selector to select one of the voltages distributed by the reference resistance string as the top reference gamma voltage based on a top selection signal.

6. The gamma voltage generator as claimed in claim 1 , wherein the gamma curve adjuster includes:

a first median gamma selector to receive the conversion reference gamma voltage and the top reference gamma voltage and to select a plurality of median gamma voltages between the conversion reference voltage and the top reference voltage; and

a grayscale gamma output to output the grayscale gamma voltages by distributing the median gamma voltages.

7. The gamma voltage generator as claimed in claim 6 , wherein:

the first median gamma selector includes third through (N)th stages that are dependently connected, where N is an integer greater than 3, and

a (K)th stage includes:

a (K)th median resistance string is to distribute the conversion reference gamma voltage and a (K+1)th median gamma voltage output by a (K+1)th stage; and

a (K)th selector to select one of the voltages distributed by the (K)th median resistance string as a (K)th median gamma voltage based on a (K)th median selection signal, where K is an integer between 3 and (N−1).

8. The gamma voltage generator as claimed in claim 7 , wherein the gamma curve adjuster includes:

a second median gamma selector to receive the first reference voltage and a third median gamma voltage output by the third stage and to select at least one of the voltages between the first reference voltage and the third median gamma voltage as a median gamma voltage.

9. The gamma voltage generator as claimed in claim 8 , wherein:

the second median gamma selector includes a first stage and a second stage,

the first stage includes a first median resistance string to distribute the first reference voltage and a second median gamma voltage output by the second stage, and a first median selector to select one of the voltages distributed by the first median resistance string as a first median gamma voltage based on a first median selection signal, and

the second stage includes a second median resistance string to distribute the maximum reference voltage and the third median gamma voltage, and a second median selector to select one of voltages distributed by the second median resistance string as a second median gamma voltage based on a second median selection signal.

10. A display device, comprising:

a display panel including a plurality of pixels;

a scan driver to provide a scan signal to the pixels;

a gamma voltage generator to output a plurality of grayscale gamma voltages corresponding to a dimming level;

a data driver to generate a data signal based on the grayscale gamma voltages and to provide the data signal to the pixels; and

a controller to control the scan driver, the gamma voltage generator, and the data driver, wherein the gamma voltage generator includes:

a reference gamma selector to receive a first reference voltage and a second reference voltage and to select a top reference gamma voltage and a bottom reference gamma voltage between the first and second reference voltages;

a reference gamma converter to convert the bottom reference gamma voltage to a conversion reference gamma voltage based on the top reference gamma voltage; and

a gamma curve adjuster to generate the grayscale gamma voltages based on the conversion reference gamma voltage and the top reference gamma voltage.

11. The display device as claimed in claim 10 , wherein the reference gamma selector is to select the top reference gamma voltage such that the top reference gamma voltage increases as a dimming level increases.

12. The display device as claimed in claim 10 , wherein the reference gamma converter is to adjust the conversion reference gamma voltage such that the conversion reference gamma voltage decreases as the top reference gamma voltage increases.

13. The display device as claimed in claim 12 , wherein the conversion reference gamma voltage is to linearly decrease as the top reference gamma voltage increases.

14. The display device as claimed in claim 10 , wherein the reference gamma selector includes:

a reference resistance string to distribute the first reference voltage and the second reference voltage;

a first reference selector to select one of the voltages distributed by the reference resistance string as the bottom reference gamma voltage based on a bottom selection signal; and

a second reference selector to select one of the voltages distributed by the reference resistance string as the top reference gamma voltage based on a top selection signal.

15. The display device as claimed in claim 14 , wherein the controller is to adjust the top selection signal such that the top reference gamma voltage increases as a dimming level increases.

16. The display device as claimed in claim 10 , wherein the gamma curve adjuster includes:

a first median gamma selector to receive the conversion reference gamma voltage and the top reference gamma voltage and to select a plurality of median gamma voltages between the conversion reference voltage and the top reference voltage; and

a grayscale gamma output to output the grayscale gamma voltages by distributing the median gamma voltages.

17. The display device as claimed in claim 16 , wherein:

the first median gamma selector includes third through (N)th stages that are dependently connected, where N is an integer greater than 3, and

a (K)th stage includes:

a (K)th median resistance string to distribute the conversion reference gamma voltage and a (K+1)th median gamma voltage outputted by a (K+1)th stage; and

a (K)th selector to select one of the voltages by distributed the (K)th median resistance string as a (K)th median gamma voltage based on a (K)th median selection signal, where K is an integer between 3 and (N−1).

18. The display device as claimed in claim 17 , wherein the controller is to adjust the (K)th median selection signal when the dimming level is changed.

19. The display device as claimed in claim 17 , wherein the gamma curve adjuster includes:

a second median gamma selector to receive the first reference voltage and a third median gamma voltage output by the third stage and to select at least one of the voltages between the first reference voltage and the third median gamma voltage as a median gamma voltage.

20. The display device as claimed in claim 19 , wherein:

the second median gamma selector includes a first stage and a second stage,

the first stage includes a first median resistance string to distribute the first reference voltage and a second median gamma voltage output by the second stage, and a first median selector to select one of the voltages distributed by the first median resistance string as a first median gamma voltage based on a first median selection signal, and

the second stage includes a second median resistance string to distribute the first reference voltage and the third median gamma voltage, and a second median selector to select one of the voltages distributed by the second median resistance string as a second median gamma voltage based on a second median selection signal.