Electro-optical device, gray scale display method, and electronic apparatus

• US 7,075,507 B2
• Filed: 12/05/2001
• Issued: 07/11/2006
• Est. Priority Date: 12/05/2000
• Status: Active Grant

• Current Assignee: Intellectuals High-Tech KFT
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Ishiguro, Hideto, Ozawa, Tokuro
• Primary Examiner(s): Awad, Amr A.
• Assistant Examiner(s): SHENG, TOM V
• Application Number:
  US10/002,121
• Publication Number:
  US 20020067327A1
• Time in Patent Office: 1,679 Days
• Field of Search: 345/89, 345/90, 345/94, 345/98, 345/99
• US Class Current: 345/89
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0857 Static memory circuit, e.g. flip-flop
• 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 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3659 the addressing of the pixel involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependant on signal of two data electrodes

Abstract

The invention produces a high-quality display, in which the occurrence of display variations is reduced, with low power consumption. One field is divided into subfields corresponding to the bits of gray scale data, and the period of each subfield is set in such a manner as to correspond to the weight of each bit. A pixel includes memories that store bits of the gray scale data, a selector that selects a memory that stores the bit corresponding to the subfield from among these memories, a closed loop of inverters, and a TFT that reads and latches the bits stored in the selected memory and that rewrites into the selected memory, and complementary switches that select, with respect to a pixel electrode, a voltage corresponding to an ON display signal or an OFF display signal in accordance with the bit read from the selected memory.

Claims

1. A gray scale display method for providing memories that respectively store each bit of gray scale data which indicates gray shade and that cause pixels arranged in a matrix in the row direction and in the column direction to produce a gray scale display, said gray scale display method comprising the steps of:

dividing one field into subfields corresponding to bits of said gray scale data;

setting a period of each subfield in such a manner as to correspond to a weight of each of said bits;

in each subfield and with respect to each pixel having a plurality of bit memories and a self-rewritable memory,

reading, from one of the said memories, a bit corresponding to the subfield within the gray scale data corresponding to the pixel,

latching the bit,

producing at least one of an ON display and an OFF display according to the bit, and

writing the latched bit to the one of the memories via said self-rewritable memory.

2. An electro-optical device which has pixels arranged in a matrix in a row direction and in a column direction, which divides one field into subfields corresponding to bits of gray scale data, which sets a period of each subfield in such a manner as to correspond to a weight of each of said bits, and which causes each of said pixels to produce at least one of an ON display and an OFF display according to the corresponding bits within said gray scale data, said electro-optical device comprising for each of said pixels:

a plurality of memories, each storing a respective bit of said gray scale data;

a self-rewritable memory;

a selector that selects a memory, that stores a bit corresponding to a subfield, from among said plurality of memories;

a latch circuit that reads and latches the bit stored in the memory selected by said selector, and that rewrites in the memory via the self-rewritable memory;

an on/off selection switch that selects a voltage corresponding to an ON display or an OFF display in accordance with the bit read from the memory selected by said selector; and

a pixel electrode to which the voltage selected by said on/off selection switch is applied.

3. The electro-optical device according to claim 2, said memory including:

a first transfer switch that transfers the bits of said gray scale data when a writing control signal indicating a bit writing timing switches to an active level; and

a holding element that holds a voltage corresponding to the bits transferred by said transfer switch.

4. The electro-optical device according to claim 2, further comprising a rewriting prohibition switch that prohibits rewriting to a memory until said latch circuit reads the bits stored in the memory selected by said selector and latches the bits.

5. The electro-optical device according to claim 2, further comprising a second transfer switch that transfers a writing permission signal which permits rewriting when a writing control signal indicating a bit writing timing switches to an active level,

said memory writing the bits of said gray scale data only when the writing permission signal transferred by said second transfer switch is at an active level.

6. The electro-optical device according to claim 2, the selection by said on/off selection switch being performed simultaneously in all the pixels in each subfield.

7. The electro-optical device according to claim 2, the selection by said on/off selection switch being performed sequentially for each row in each subfield.

8. The electro-optical device according to claim 2, said selector including switching elements which are interposed between each of said memories and said latch circuit and which are turned on in accordance with a subfield selection signal in which only one of the switching elements exclusively switches to an active level for each subfield.

9. The electro-optical device according to claim 2, said selector including a plurality of switching elements which cause only one of paths within the paths between each of said memories and said latch circuit to be exclusively turned on in accordance with data which specifies the subfield.

10. The electro-optical device according to claim 2, further comprising an opposing electrode which opposes said pixel electrode via an electro-optical material, a voltage corresponding to said OFF display being made to be substantially the same as the applied voltage of said opposing electrode,

a voltage corresponding to said ON display being inverted with respect to the voltage corresponding to said OFF display and is supplied for one or more fields.

11. The electro-optical device according to claim 2, further comprising an opposing electrode which opposes said pixel electrode via an electro-optical material,

a voltage corresponding to said OFF display being made to be substantially the same as the applied voltage of said opposing electrode,

said on/off selection switch alternately selecting, for one or more fields, a positive-polarity-side voltage and a negative-polarity-side voltage, in which the voltage differences with respect to the voltage corresponding to said OFF display are nearly equal, in accordance with a polarity signal indicating a writing polarity when the voltage corresponding to said ON display is selected.

12. An electronic apparatus, comprising:

the electro-optical device according to claim 2.