Apparatus for controlling data voltage of liquid crystal display unit to achieve multiple gray-scale

• US 6,222,515 B1
• Filed: 10/31/1991
• Issued: 04/24/2001
• Est. Priority Date: 10/31/1990
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Fujitsu Limited
• Inventors: Yamaguchi, Tadahisa, Yamaguchi, Hisashi, Takahara, Kazuhiro, Oda, Masami
• Primary Examiner(s): Mengistu, Amare
• Application Number:
  US07/786,251
• Time in Patent Office: 3,463 Days
• Field of Search: 245/89, 245/94, 245/96, 245/100
• US Class Current: 345/89
• 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 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

In a driving device of an active matrix type liquid crystal display unit including a liquid crystal display panel, a scan driver, and a data driver, a data voltage controlling apparatus is provided to achieve digital multiple gray-scale levels with little flickering. The data voltage controlling apparatus supplies the data driver with a combination of two different data voltages picked up from a plurality of digital data voltages previously set. The combination of two different data voltages are, for example, a combination of different waveforms, a combination of negative level and positive level, and a combination of two different voltages having at least a voltage difference. Further, a division of T-V characteristics and an exchange of data voltages are carried out to reduce the flickering.

Claims

1. An apparatus controlling data voltage of a liquid crystal display unit having an active matrix liquid crystal display panel, a scan driver, and a data bus driver to display an image of one frame, comprising:

a timing signal generating portion generating at least timing signals for the scan driver and the data bus driver; and

a data signal generating part coupled to the timing signal generating portion and dividing said image of one frame into a plurality of fields and outputting same to the data bus driver, said data bus driver applying different data voltage levels to each of the plurality of fields in the active matrix liquid crystal display panel and assigning a gray-scale level to the one frame according to a mean effective voltage of the voltage levels applied to each of the plurality of fields of the one frame, to obtain one of a plurality of gray-scale levels.

2. An apparatus as set forth in claim 1, wherein:

the one frame is formed of a first field and a second field;

said apparatus further comprises a voltage applying part generating voltage levels for the first field and the second field separately;

said timing signal generating portion generating a timing signal for switching each field;

the voltage applied to the data bus driver from the voltage applying part is switched from the first field voltage to the second field voltage and vice versa at every field by the timing signal for switching the field; and

a plurality of voltage levels that are relative to a one-value common level are making voltage levels in an odd frame equal to those in an even frame.

3. An apparatus as set forth in claim 2, wherein the data signal generating part includes at least one frame memory, and a reading speed of the data signal from the frame memory is faster than a writing speed of the data signal to the frame memory.

4. An apparatus as set forth in claim 2, wherein one frame is formed of a first field and a second field;

the voltage applying part generates a binary common voltage level, and a plurality of voltage levels that are relative to the binary common voltage level is switched from one to another for every field such that an absolute voltage value in a positive frame is equal to that in a negative frame, the common voltage level and display data is inverted for every frame or line.

5. An apparatus as set forth in claim 1, wherein the data signal generating part includes a data conversion table, thereby the voltage levels applied by the voltage applying part are converted into preset gray-scale levels with use of a conversion table in order not to generate deviations in the displayed gray-scale levels.

6. An apparatus as set forth in claim 5, wherein the conversion table comprises a ROM.

7. An apparatus as set forth in claim 5, wherein the data signal generating part includes at least one frame memory and the reading speed of the data signal from the frame memory is faster than the writing speed of the data signal to the frame memory.

8. An apparatus as set forth in claim 7, wherein the conversion table comprises a ROM.

9. An apparatus as set forth in claim 2, wherein the voltage applying part generates a plurality of data voltage levels for each of the voltage ranges which are set by dividing the transmissivity-voltage characteristics of the liquid crystal pixels without overlapping;

and

the data signal generating part generates the data voltage selecting signal so as to select data voltage levels from each voltage range.

10. An apparatus as set forth in claim 9, wherein the data signal generating part generates the data voltage selecting signal from which the combination of the voltage levels is changed between adjacent pixels.

11. An apparatus as set forth in claim 9, wherein the data signal generating part generates the data voltage selecting signal from which the phase of the voltage levels is changed between adjacent pixels.

12. An apparatus as set forth in claim 9, wherein the data signal generating part generates the data voltage selecting signal from which the combination and phase of the voltage levels are changed between adjacent pixels.

13. An apparatus as set forth in claim 9, wherein the data signal generating part generates the data voltage selecting signal from which the polarity of the voltage levels is changed between adjacent pixels.

14. An apparatus as set forth in claim 9, wherein the data signal generating part includes at least one frame memory and the reading speed of the data signal from the frame memory is faster than the writing speed of the data signal to the frame memory.

15. An apparatus as set forth in claim 14, wherein the selecting signal generating part generates the data voltage selecting signal from which the combination of the voltage levels is changed between adjacent pixels.

16. An apparatus as set forth in claim 14, wherein the data signal generating part generates the data voltage selecting signal from which the phase of the voltage levels is changed between adjacent pixels.

17. An apparatus as set forth in claim 14, wherein the data signal generating part generates the data voltage selecting signal from which the combination and phase of the voltage levels are changed between adjacent pixels.

18. An apparatus as set forth in claim 14, wherein the data signal generating part generates the data voltage selecting signal from which the polarity of the voltage levels is changed between adjacent pixels.

19. An apparatus as set forth in claim 1, wherein the data signal generating part generates the data voltage selecting signal from which a combination of the applied voltages is determined such that a difference between the voltages applied to the fields respectively is below a predetermined value at least on the white level side.

20. An apparatus as set forth in claim 1, wherein the data signal generating part generates the data voltage selecting signal in order that averages of groups of the voltage levels prepared for a plurality of the fields may substantially be equal to one another between the fields, thereby the voltages applied to the liquid crystal pixels are set according to transmissivity-voltage characteristics of the liquid crystal pixels such that transmissivity changes at substantially equal intervals.

21. An apparatus as set forth in claim 20, wherein the voltage applying part generates the plurality of data voltage levels for each of the voltage ranges which are set by dividing the transmissivity-voltage characteristics of the liquid crystal pixels without overlapping;

and

the data signal generating part generates the data voltage selecting signal so as to select data voltage levels from each voltage range.

22. An apparatus as set forth in claim 21, wherein one frame is formed of two fields, and the same number of voltage levels V1m and V2m (m being 0, 1, . . . ,(n1/2−

1)) are set for the fields, respectively, as follows;

23. An apparatus as set forth in claim 22, wherein the voltage applying part generates the plurality of data voltage levels for each of the voltage ranges which are set by dividing the transmissivity-voltage characteristics of the liquid crystal pixels without overlapping;

and

the data signal generating part generates the data voltage selecting signal so as to select data voltage levels from each voltage range.

24. An apparatus as set forth in claim 1, wherein one frame is formed of a first field and a second field;

the voltage applying part generates a binary common voltage level, and a plurality of voltage levels that are relative to the binary common voltage level being switched from one to another for every field such that an absolute voltage value in a positive frame is equal to that in a negative frame, the common voltage level and display data being inverted for every field or line.