Liquid crystal display driving circuit

• US 6,137,462 A
• Filed: 05/01/1997
• Issued: 10/24/2000
• Est. Priority Date: 05/02/1996
• Status: Expired due to Term

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Electronics, Inc. (LG Corporation)
• Inventors: Kim, Jun-Hee
• Primary Examiner(s): Shankar, Vijay
• Application Number:
  US08/850,099
• Time in Patent Office: 1,272 Days
• Field of Search: 345/94, 345/95, 345/100, 345/89, 345/50, 345/53, 345/87, 345/99, 340/784
• US Class Current: 345/94
• CPC Class Codes: G09G 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• 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 3/3688 suitable for active matrices only

Abstract

Liquid crystal display (LCD) driving circuit in which a small number of voltage sources enable multi-gradation display and gamma correction without extra gamma correction circuits is disclosed. The LCD driving circuit includes a ramp wave generator for generating a plurality of ramp waves each having an appropriate tilt for each section along a T axis of a T-V (transmission-voltage) curve representing the light transmittivity of an LCD according to an applied voltage, a ramp wave selector for selecting one of the plurality of ramp waves according to input data, and a counter for adjusting the time the ramp wave outputted by the ramp wave selector is applied.

Claims

1. A liquid crystal display (LCD) driving circuit comprising:

a ramp wave generating means for generating a plurality of ramp waves each having an appropriate tilt for each section along a T axis of a T-V (transmission-voltage) curve representing the light transmittivity of an LCD according to an applied voltage;

a ramp wave selecting means for selecting one of the plurality of ramp waves according to input data; and

,

a count means for adjusting the time the ramp wave outputted by the ramp wave selecting means is applied.

2. The LCD driving circuit as claimed in claim 1, wherein the count means comprises:

a counter for counting the input data in sequence;

a switching part responsive to the counter for outputting the ramp wave selected by the ramp wave selecting means; and

,

a buffer for maintaining the ramp wave outputted by the switching part for a predetermined time after the switching part is turned off.

3. A liquid crystal display (LCD) driving circuit comprising:

a voltage generating means for generating voltage sources each corresponding to sections along a T axis of a T-V (transmissivity-voltage) curve representing the light transmittivity of an LCD according to an applied voltage;

a ramp wave generating means for generating ramp waves each having an appropriate tilt for each of the sections;

an adding means for adding the voltage source and ramp wave generated from the voltage generating means and the ramp wave generating means, respectively, for a corresponding section; and

,

a count means for adjusting the time an adding result of the adding means is applied.

4. The LCD driving circuit as claimed in claim 3, wherein the voltage generating means comprises:

a voltage generating part for generating a voltage source for each section along the a T axis of the T-V curve; and

,

a selecting part for outputting one of the plurality of voltage sources according to input data.

5. The LCD driving circuit as claimed in claim 3, wherein the ramp wave generating means comprises:

a ramp wave generating part for generating a plurality of ramp waves having appropriate tilts at the sections set by the voltage generating means; and

,

a selecting part for selecting one of the plurality of ramp waves according to the input data.

6. The LCD driving circuit as claimed in claim 3, wherein each of the tilts of the ramp waves generated by the ramp wave generating means is ((V_i+1 +V_i)×

1 H), in which V_i+1 is a voltage of a section right after a predetermined number of the sections, and V_i is a voltage of a section just prior to the section, and 1 H is a selecting time of line 1.

7. The LCD driving circuit as claimed in claim 3, wherein the adding means inlcudes an adder using an operational amplifier.

8. The LCD driving circuit as claimed in claim 3, wherein the count means comprises:

a counter for counting a predetermined number of as many as predetermined steps between the sections set according to the input data;

a switching means for outputting an adding result of the adding means when activated by the counter; and

,

a latch for maintaining the adding result of the adding means for a predetermined time after the switching means is turned off by the count means.

9. The LCD driving circuit as claimed in claim 8, wherein the time for counting by the counter plus the time for maintaining by the latch equals the selecting time 1 H of line 1.

10. The LCD driving circuit as claimed in claim 8, wherein while the counter is counting, an output of the adding means is increased from the selected voltage source to the selected ramp wave form.

11. A method for driving a liquid crystal display (LCD) comprising the steps of:

generating a plurality of ramp waves each having an appropriate tilt for each section along a T axis of a T-V (transmission-voltage) curve representing the light transmittivity of an LCD according to an applied voltage;

selecting one of the plurality of ramp waves according to input data; and

,

adjusting a time the ramp wave outputted by the ramp wave selecting means is applied.

12. A method for driving an LCD comprising the steps of:

generating voltage sources each corresponding to sections along a T axis of a T-V (transmissivity-voltage) curve representing the light transmittivity of an LCD according to an applied voltage;

generating ramp waves each having an appropriate tilt for each of the sections;

adding the voltage source and ramp wave generated from the voltage generating means and the ramp wave generating means, respectively, for a corresponding section; and

,

adjusting the time an adding result of the adding means is applied.

13. A liquid crystal display (LCD) driving circuit comprising:

a ramp wave generator producing a plurality of ramp waves, the ramp waves having different tilts;

a ramp wave selector receiving the plurality of ramp waves and selecting one ramp wave corresponding to a first digital data; and

a switching part applying the selected ramp wave to a panel of the LCD for a predetermined time, the predetermined time being determined by a second digital data.

14. The liquid crystal display (LCD) driving circuit in claim 13, the circuit further including a counter receiving the second digital data and controlling the switching part.

15. The liquid crystal display (LCD) driving circuit in claim 13, the circuit further including:

a voltage generator producing a plurality of DC voltages;

a voltage selector receiving the plurality of DC voltages and selecting one DC voltage corresponding to the first digital data; and

an adder adding the selected ramp wave and the selected DC voltage.

16. The liquid crystal display (LCD) driving circuit in claim 15, wherein the first digital data and second digital data comprise all bits of display data.

17. The liquid crystal display (LCD) driving circuit in claim 15, the circuit further including a counter receiving the second digital data and controlling the switching part.

18. The liquid crystal display (LCD) driving circuit in claim 13, wherein the first digital data and second digital data comprise all bits of display data.

19. The liquid crystal display (LCD) driving circuit in claim 13, the circuit further including a buffer between the switching part and the panel.

20. The liquid crystal display (LCD) driving circuit in claim 13, wherein the second digital data includes the first digital data.