Matrix type liquid crystal display device with data electrode driving circuit in which display information for one screen is written into and read out from display memory at mutually different frequencies

• US 5,764,212 A
• Filed: 02/21/1995
• Issued: 06/09/1998
• Est. Priority Date: 02/21/1994
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Tsunekawa, Satoru, Kudo, Yasuyuki, Furuhashi, Tsutomu, Mano, Hiroyuki, Nishitani, Shigeyuki, Futami, Toshio, Inuzuka, Tatsuhiro
• Primary Examiner(s): NGUYEN, CHANH DUY
• Application Number:
  US08/391,599
• Time in Patent Office: 1,204 Days
• Field of Search: 345/87, 345/89, 345/92, 345/94, 345/95, 345/97, 345/98, 345/99, 345/200, 345/3, 345/1, 345/210, 345/211, 359/54, 359/56, 359/59, 349/33, 349/34, 349/36, 349/41, 349/42
• US Class Current: 345/98
• CPC Class Codes: G09G 2310/0289 Details of voltage level shifters arranged for use in a driving circuit
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3622 using a passive matrix G09G3/3674 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3625 using active addressing
• CPC Class Codes: G09G 3/3681 suitable for passive matrices only
• CPC Class Codes: G09G 3/3692 suitable for passive matrices only
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

A liquid crystal display device includes N (N is a positive integer except zero) data electrodes, M (M is a positive integer except zero) scan electrodes, a liquid crystal display panel having pixels located at crosspoints between said data electrodes and said scan electrodes, and a data electrode driving circuit. The data electrode circuit has a memory unit from or into which the information information is read or written, a write control circuit for controlling a write of the display information into a memory area of the memory unit, a read control circuit for simultaneously reading the display information corresponding to N data electrodes from the memory area at a different period of the writing period, and an output circuit for converting the display information read from the memory unit into the corresponding voltage and feeding the display voltage to the data electrode.

Claims

1. A data electrode driving circuit provided in a matrix type liquid crystal display device, said matrix type liquid crystal display device including N (N is a positive integer except zero) data electrodes, M (M is a positive integer except zero) scan electrodes, and a matrix type liquid crystal display panel having pixels located at crosspoints between said data electrodes and said scan electrodes, said data electrode driving circuit comprising:

a memory unit from or into which display information may be read or written;

control means for controlling a write of said display information into a memory area of said memory unit;

read control means for reading the display information corresponding to said N data electrodes from said memory area at a time, said display information for one screen being written in said memory area at a first frequency and said display information being read from said memory area at a second frequency different from said first frequency; and

an output circuit for converting the display information read out of said memory unit into a display voltage, and feeding said display voltage to said data electrodes.

2. A data electrode driving circuit as claimed in claim 1, wherein said memory area has a corresponding area to said pixels;

wherein said display information is sequentially inputted to said driving circuit at each n (n=N) pixels in one horizontal interval when all the pixels located on one scan electrode are driven;

wherein said write control means includes a write latch circuit for latching the inputted display information at each n (n=N) pixels, and writing in said memory area said display information read after the display information for n pixels is written therein.

3. A data electrode driving circuit as claimed in claim 2, wherein said write information is inputted in said data electrode driving circuit in response to an inputted horizontal clock signal having said first frequency;

wherein the display information for n pixels is read out of said memory area in response to a read horizontal clock signal having said second frequency.

4. A data electrode driving circuit as claimed in claim 3, further comprising a memory access control circuit for controlling said write and read control means so that said write and read control means operates to perform a reading operation first and a writing operation thereafter if a competition takes place between the operations of writing and reading the display information to and from said memory unit, and maintains constant a period at which said display information is read out of said memory area.

5. A data electrode driving circuit as claimed in any one of claims 1 to 4, wherein said read control means includes a read latch circuit for reading the display information read from said memory area;

wherein said data electrode driving circuit further comprises a decoder circuit for converting the display information latched by said read latch circuit into a voltage selecting signal for selecting said display voltage based on an ac signal; and

wherein said output circuit selects one voltage from plural variable voltages based on said voltage selecting signal as said display voltage.

6. A matrix type liquid crystal display device comprising:

N (N is a positive integer except zero) data electrodes;

M (M is a positive integer except zero) scan electrodes;

a matrix type liquid crystal display panel having pixels located at crosspoints between said data electrodes and said scan electrodes;

a data electrode driving circuit as claimed in claim 5;

a scan electrode driving circuit for selectively feeding a scan selecting voltage and a non-scan selecting voltage to said scan electrodes, said scan electrode driving circuit serving to output any one of a first scan selecting voltage and a second scan selecting voltage different from one another according to said ac signal; and

a voltage generator for generating plural variable display voltages, said scan selecting voltage, and said non-scan selecting voltage.

7. A matrix type liquid crystal display device as claimed in claim 6, wherein said scan electrode driving circuit operates to output according to said ac signal any one of said first and second scan selecting voltages to the scan electrode corresponding to the pixel to which said display voltage outputted from said data electrode driving circuit is fed, and to output said non-scan selecting voltage to the other scan electrodes.

8. A matrix type liquid crystal display device as claimed in claim 6, wherein said voltage generator includes:

a dc voltage generator for generating a predetermined reference voltage as said non-scan selecting voltage, and a plus voltage and a minus voltage about said reference voltage; and

a voltage divider for dividing said plus and minus voltages and generating said first and second scan selecting voltages.

9. A matrix type liquid crystal display device as claimed in claim 8, wherein said dc voltage generator operates to convert a predetermined dc voltage to be fed to said liquid crystal display device into said plus and minus voltages.

10. A data electrode driving circuit as claimed in any one of claims 1 to 4, wherein said read control means includes m (m is a positive integer of 2 or more) read latch circuits for reading the display information read out of said memory area;

wherein said data electrode driving circuit further comprises an operating unit for converting the display information latched in said read latch circuits into a voltage selecting signal for selecting said display voltage based on operation data; and

wherein said output circuit includes a voltage selector for selecting one of plural variable voltages based on said voltage selecting signal, and feeding said selected voltage as said display voltage to said data electrodes.

11. A matrix type liquid crystal display device comprising:

N (N is a positive integer except zero) data electrodes;

M (M is a positive integer except zero) scan electrodes;

a matrix type liquid crystal display panel having pixels located at crosspoints between said data electrodes and said scan electrodes;

a data electrode driving circuit as claimed in claim 10;

a scan electrode driving circuit for selectively feeding a scan selecting voltage and a non-scan selecting voltage to said scan electrodes, said scan electrode driving circuit serving to generate a first scan selecting voltage and a second scan selecting voltage different from one another based on said non-scan selecting voltage and predetermined operation data, and to output any one of said first and second scan selecting voltages; and

a voltage generator for generating plural variable display voltages, said scan selecting voltages and said non-scan selecting voltage.

12. A matrix type liquid crystal display device as claimed in claim 11, wherein said scan electrode driving circuit operates to output according to said operation data said first and second scan selecting voltages to the scan electrodes corresponding to the pixels to which the display information read in said m read latch circuits is fed, and to output said non-scan selecting voltage to the other scan electrodes.

13. A matrix type liquid crystal display device comprising:

N (N is a positive integer except zero) data electrodes;

M (M is a positive integer except zero) scan electrodes;

a matrix type liquid crystal display panel having pixels located at crosspoints between said data electrodes and said scan electrodes;

a data electrode driving circuit as claimed in any one of claims 1 to 4;

a scan electrode driving circuit for selectively outputting a scan selecting voltage and a non-scan selecting voltage to said scan electrodes; and

a voltage generator for generating plural variable display voltages, said scan selecting voltage, and said non-scan selecting voltage.

14. An information processing apparatus comprising:

a matrix type liquid crystal display device as claimed in claim 13; and

another image display device;

wherein a frame frequency at which the display information for one screen is inputted to said matrix type liquid crystal display device is equal to a frame frequency of said another image display device.