LIQUID CRYSTAL DISPLAY APPARATUS, DRIVING METHOD THEREFOR, AND DISPLAY SYSTEM

• US 20020145602A1
• Filed: 09/14/1998
• Published: 10/10/2002
• Est. Priority Date: 02/21/1995
• Status: Active Grant

• Current Assignee: BOE Technology Group Co., Ltd.
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: MATSUEDA, YOJIRO
• Granted Patent: US 6,873,312 B2
• Time in Patent Office: Days
• US Class Current: 345/213
• 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 2310/0283 Arrangement of drivers for different directions of scanning
• 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 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

An n-bit digital image data is converted to (n+m)-bit data with a g-correction table, and displayed by the use of a (n+m)-bit D/A converter. A peripheral-driver logic section is driven with a low-voltage common power source and countermeasures to noise are taken. Data input to the D/A converter is not reversed and the power to the D/A converter is made alternating to apply an AC voltage to aligned crystal layer. A circuit is provided in order to compensate for a delay time in the driver. With this configuration, the image quality of a liquid crystal display apparatus in which the D/A converter is built is improved.

Claims

1. ) a liquid crystal display apparatus including a pair of substrates on which electrodes are formed respectively and which are disposed such that the electrode surfaces oppose each other, and a liquid crystal material held between said pair of substrates, wherein displaying is conducted at an illuminance according to the effective value of an ac voltage applied between the opposing electrodes, said liquid crystal display apparatus characterized by comprising a data conversion circuit in which n-bit digital input image data is converted to (n+m)-bit digital image data, and an (n+m)-bit digital data driver.

2. ) A liquid crystal display apparatus according to claim 1, characterized in that said data conversion circuit is provided with a ROM in which a conversion table for compensating for the g characteristic of the liquid crystal is written.

3. ) A liquid crystal display apparatus according to claim 1 or claim 2, characterized in that said digital data driver includes an (n+m)-bit D/A converter.

4. ) A liquid crystal display apparatus according to any of claims 1 to 3, characterized in that said liquid crystal display apparatus is an active-matrix liquid crystal display apparatus in which a thin-film transistor or a thin-film nonlinear device is used as a switching device.

5. ) A liquid crystal display apparatus according to any of claims 1 to 4, characterized in that a poly-silicon thin-film transistor for a pixel and a poly-silicon thin-film transistor for said digital data driver are formed on one substrate of said pair of substrates.

6. ) A liquid crystal display apparatus according to any of claims 1 to 5, characterized in that said (n+m)-bit digital data driver includes a D/A converter circuit in which (n+m) capacitors having the capacitance ratio of 1:

2;

4;

. . . ;

2<sup>n+m−

1</sup> and (n+m) analog switches are combined.

7. ) A liquid crystal display apparatus according to any of claims 1 to 6, characterized in that said (n+m) capacitors are formed by connecting in parallel a pattern having the same shape by the required number, respectively, one, two, four, . . . , and 2^n+m−

1.

8. ) A liquid crystal display apparatus according to any of claims 1 to 5, characterized in that said (n+m)-bit digital data driver is formed by a constant-current binary attenuation-type D/A converter circuit in which (n+m) constant-current circuits and (n+m) resister circuit networks having R and 2R are combined.

9. ) A driving method for a liquid crystal display apparatus which includes a pair of substrates on which electrodes are formed respectively and which are disposed such that the electrode surfaces oppose each other, and a liquid crystal material held between said pair of substrates, wherein displaying is conducted at an illuminance according to the effective value of an AC voltage applied between the opposing electrodes, said driving method characterized by comprising the steps of sequentially converting an n-bit digital input signal to (n+m)-bit digital data according to the g characteristic of the liquid crystal, and displaying in n-bit gray scale by the use of an (n+m)-bit digital data driver.

10. ) A driving method for a liquid crystal display apparatus according to claim 9, characterized in that after all signal lines are reset to the same voltage during the blanking period in a horizontal scanning period, an (n+m)-bit D/A-converted voltage is applied to each signal line.

11. ) A liquid crystal display apparatus including (a) a first substrate having a plurality of scanning lines;

a plurality of signal lines;

pixel electrodes disposed correspondingly to the intersections of said scanning lines and said signal lines; and

thin-film transistors for pixels, disposed correspondingly to said pixel electrodes, (b) a second substrate disposed oppositely to said first substrate and having a common electrode, and (c) a liquid crystal layer held between said first substrate and said second substrate, wherein said signal lines are driven by a data driver having a shift register, a level shifter, and a D/A converter, and said scanning lines are driven by a scanning driver having a shift register, a level shifter, and a buffer, said liquid crystal display apparatus characterized in that the shift register in said data driver and the shift register in said scanning driver are connected to a common power source, and

the voltage of said common power source is lower than the voltage of a power source for said D/A converter and said buffer.

12. ) A liquid crystal display apparatus according to claim 11, characterized in that said data driver has a thin-film transistor for a data driver, formed on said first substrate;

said scanning driver has a thin-film transistor for a scanning driver, formed on said first substrate; and

said thin-film transistors for pixels, said thin-film transistor for a data driver, and said thin-film transistor for a scanning driver are poly-silicon thin-film transistors.

13. ) A liquid crystal display apparatus according to claim 11 or claim 12, characterized in that said data driver includes a D/A converter circuit in which n capacitors having the capacitance ratio of 1:

2;

4;

. . . ;

2<sup>n−

1</sup> and n analog switches are combined.

14. ) A liquid crystal display apparatus according to claim 11 or claim 12, characterized in that the input section of each of said level shifters is connected to n-channel and p-channel two transistors connected in parallel.

17. ) A driving method for a liquid crystal display apparatus according to claim 15 or claim 16, characterized in that said D/A converter is divided into a plurality of systems and driven, and image signals having reverse polarities are always applied to adjacent signal lines.

15. ) A driving method for a liquid crystal display apparatus which includes (a) a first substrate having a plurality of scanning lines;

a plurality of signal lines;

pixel electrodes disposed correspondingly to the intersections of said scanning lines and said signal lines; and

thin-film transistors for pixels, disposed correspondingly to said pixel electrodes, (b) a second substrate disposed oppositely to said first substrate and having a common electrode, and (c) a liquid crystal layer held between said first substrate and said second substrate, wherein said signal lines are driven by a data driver having a shift register, a level shifter, and a D/A converter; and

said scanning lines are driven by a scanning driver having a shift register and a level shifter, said driving method characterized in that an image signal input to said D/A converter and a timing signal input to said shift register have the same amplitude, and the power level of said D/A converter is switched alternately in every field to apply an AC voltage to said liquid crystal layer.

18. ) A driving method for a liquid crystal display apparatus according to any of claims 15 to 17, characterized in that the voltage of said common electrode is switched alternately in every field.

19. ) A driving method for a liquid crystal display apparatus according to any of claims 15 to 17, characterized in that the voltage of said common electrode is switched in every horizontal scanning period.

20. ) A driving method for a liquid crystal display apparatus according to any of claims 15 to 19, characterized in that a scanning signal sent to said scanning lines has four voltage levels, and a case in which said scanning signal holds a non-selection voltage or more for a certain period before it changes from a selection voltage to the non-selection voltage immediately after the selection period, and a case in which said scanning signal holds the non-selection voltage or less in the same situation are switched in every field.

21. ) A driving method for a liquid crystal display apparatus according to any of claims 15 to 19, characterized in that a scanning signal sent to said scanning lines has four voltage levels, and a case in which said scanning signal holds a non-selection voltage or more for a certain period before it changes from a selection voltage to the non-selection voltage immediately after the selection period and a case in which said scanning signal holds the non-selection voltage or less in the same situation are switched in every horizontal scanning period.

22. ) A driving method for a liquid crystal display apparatus according to any of claims 15 to 21, characterized in that a capacitor-coupling D/A converter is used as said D/A converter, and a digital signal in which black and white levels are not reversed is input to said D/A converter.

24. ) A liquid crystal display apparatus according to claim 23, characterized in that said delay circuit has a delay-time detecting circuit for detecting a delay time in said shift register and a delay-time compensation circuit for delaying image signal data by the time detected by said delay-time detecting circuit.

25. ) A liquid crystal display apparatus according to claim 23 or claim 24, characterized in that said data driver has a thin-film transistor for a data driver, formed on said first substrate;

said scanning driver has a thin-film transistor for a scanning driver, formed on said first substrate; and

said thin-film transistors for pixels, said thin-film transistor for a data driver, and said thin-film transistor for a scanning driver are poly-silicon thin-film transistors.

27. ) A driving method for a liquid crystal display apparatus according to claim 26, characterized in that said delay circuit detects a delay time from a clock signal for said shift register to an output signal for controlling said latch and feeds back the detected delay time to a circuit for delaying image signal data to automatically compensate for the delay time.

29. ) A display system according to claim 28, characterized in that the output signal of said A/D converter, the input and output signals of said g-correction circuit, the output signal of said timing controller, and the input signal of said data driver have the same voltage amplitude.

30. ) A display system according to claim 28 or claim 29, characterized by comprising a delay circuit for delaying the output data of said g-correction circuit, and characterized in that the delay time of said delay circuit is set such that the sum of the delay time of said A/D converter, the delay time of said g-correction circuit, and the delay time of said delay circuit is equal to a delay time from the clock signal for said data driver to when image signal data is latched.

16. ) A driving method for a liquid crystal display apparatus which includes (a) a first substrate having a plurality of scanning lines;

a plurality of signal lines;

pixel electrodes disposed correspondingly to the intersections of said scanning lines and said signal lines; and

thin-film transistors for pixels, disposed correspondingly to said pixel electrodes, (b) a second substrate disposed oppositely to said first substrate and having a common electrode, and (c) a liquid crystal layer held between said first substrate and said second substrate, wherein said signal lines are driven by a data driver having a shift register, a level shifter, and a D/A converter; and

said scanning lines are driven by a scanning driver having a shift register and a level shifter, said driving method characterized in that an image signal input to said D/A converter and a timing signal input to said shift register have the same amplitude, and the power level of said D/A converter is switched alternately in every horizontal scanning period to apply an AC voltage to said liquid crystal layer.

23. ) A liquid crystal display apparatus including (a) a first substrate having a plurality of scanning lines;

a plurality of signal lines;

pixel electrodes disposed correspondingly to the intersections of said scanning lines and said signal lines; and

thin-film transistors for pixels, disposed correspondingly to said pixel electrodes, (b) a second substrate disposed oppositely to said first substrate and having a common electrode, (c) a liquid crystal layer held between said first substrate and said second substrate, a data driver for driving said signal lines, and a scanning driver for driving said scanning lines, said liquid crystal display apparatus characterized in that said data driver includes a shift register, a latch, and a delay circuit for delaying the timing of image signal data according to a delay time in said shift register.

26. ) A driving method for a liquid crystal display apparatus which includes (a) a first substrate having a plurality of scanning lines;

a plurality of signal lines;

pixel electrodes disposed correspondingly to the intersections of said scanning lines and said signal lines; and

thin-film transistors for pixels, disposed correspondingly to said pixel electrodes, (b) a second substrate disposed oppositely to said first substrate and having a common electrode, (c) a liquid crystal layer held between said first substrate and said second substrate, a data driver for driving said signal lines, and a scanning driver for driving said scanning lines, said driving method characterized in that said data driver delays the timing of image signal data according to a delay time in a shift register, a delay time in a latch, and a delay time from a clock signal for said shift register to an output signal for controlling said latch.

28. ) A display system characterized by comprising:

(a) an active-matrix liquid crystal display panel;

(b) a data driver having an A/D converter for converting an analog image signal to n-bit digital data, a g-correction circuit for converting said n-bit digital data to (n+m)-bit digital data according to the g characteristic of the liquid crystal, and a D/A converter for converting said (n+m)-bit digital data to an analog signal; and

(c) a timing controller for controlling the operation timing of these circuits.

31. ) A display system according to any of claims 28 to 30, characterized in that said data driver has a thin-film transistor for a data driver, formed on said first substrate;

said scanning driver has a thin-film transistor for a scanning driver, formed on said first substrate; and

said thin-film transistors for pixels and said thin-film transistor for a data driver are poly-silicon thin-film transistors.