Electro-optical device and method of driving the same

• US 6,326,941 B1
• Filed: 10/07/1992
• Issued: 12/04/2001
• Est. Priority Date: 10/08/1991
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Hiroki, Masaaki, Takemura, Yasuhiko, Yamazaki, Shunpei
• Primary Examiner(s): NGUYEN, CHANH DUY
• Application Number:
  US07/957,106
• Time in Patent Office: 3,345 Days
• Field of Search: 340/784, 340/805, 340/793, 345/94, 345/95, 345/208, 345/209, 345/210, 345/89, 345/87, 345/77, 345/63
• US Class Current: 345/95
• CPC Class Codes: G09G 2300/08 Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2029 the sub-frames having non-binary weights
• CPC Class Codes: G09G 3/2081 with combination of amplitude modulation and time modulation space and time error diffusion G09G3/2066
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

For a gradation displaying operation of an electro-optical device, a gradation display method and an electro-optical device therefor which can be controlled with a digital signal, and which is hard to be affected by variation in characteristics between elements and can achieve high gradation display are provided. In the active matrix type of electro-optical device and method, the input analog signal is converted to a numerical value of N-radix notation, and pulses whose pulse height and width correspond to the numerical value. By applying these plural pulses to each picture element electrode, an average voltage of one frame of an image can be made an arbitrary value to finally display an intermediate color tone or gradation. The display device comprises a device for converting an input analog signal to a digital signal, a device for converting the digital signal to a numerical value of N-radix notation or a digital signal corresponding thereto (including digital signal), and a device for inputting this signal to an active matrix type device.

Claims

1. A method of driving an electro-optical device of an active matrix structure comprising the steps of:

converting an input analog signal into a numerical value of N-radix notation where N≧

3 or a signal corresponding to said numerical value of N-radix notation where N≧

3; and

applying a plurality of voltage pulses having pulse heights and pulse widths based on said numerical value or said signal corresponding to said numerical value of N-Radix notation where N≧

3 to a pixel of said elect-optical device,

wherein an average effective voltage of said voltage pulses is close to an arbitrary voltage; and

wherein both the said pulse widths and said pulse heights are varied so that the minimum width of said pulses can be increased.

2. The method of claim 1 wherein said electro-optical device is a display and an intermediate brightness can be displayed on said display by said voltage pulses.

3. The method of claim 1 wherein said pulse heights are four heights.

4. The method of claim 3 wherein said pulse widths are two widths.

5. The method of claim 4 wherein said pulse widths are a width of a unit period and a width four times as long as said unit period.

6. The method of claim 3 wherein said pulse widths are three widths.

7. The method of claim 6 wherein said pulse widths are a width of a unit period and a width four times as long as said unit period and a width sixteen times as long as said unit period.

8. The method of claim 1 wherein said N-radix notation is a ternary notation.

9. The method of claim 1 wherein said N-radix notation is a quinary notation.

10. The method of claim 1 wherein said pulse widths are a width of a unit period and a width three times as long as said unit period.

11. The method of claim 1 wherein said pulse widths are a width of a unit period and a width twenty-five times as long as said unit period.

12. The method of claim 1 wherein said electro-optical device is a liquid crystal display, a plasma display or a vacuum microelectro display.

13. The method of claim 1 wherein said plurality of voltage pulses have “

N”

levels.

14. The method of claim 1 further comprising the step of converting said analog signal into a binary digital data and converting said binary digital data into said numerical value of N-radix notation.

15. An electro-optical device of an active matrix structure comprising:

a device for converting an input analog signal into a digital signal;

a device for converting said digital signal into a numerical value of N-radix notation where N≧

3 or a digital signal corresponding to said numerical value of N-radix notation where N24; and

a device for generating N-stage voltages having pulse heights and pulse widths on the basis of said digital signal corresponding to said numerical value of N-radix notation where N≧

3; and

wherein both the said pulse widths and said pulse heights are varied so that the minimum width of said pulses can be increased.

16. The device of claim 15 wherein said device for converting an input analog signal into a digital signal is A/D converter.

17. The device of claim 15 wherein said electro-optical device is a liquid crystal display, a plasma display or a vacuum microelectro display.