Liquid crystal display device which regulates display of frame image data and operation of backlight unit to reduce power consumption

• US 5,812,149 A
• Filed: 05/23/1995
• Issued: 09/22/1998
• Est. Priority Date: 05/24/1994
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Koyama, Jun, Kawasaki, Yuji
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): Miller, John W.
• Application Number:
  US08/447,932
• Time in Patent Office: 1,218 Days
• Field of Search: 345/190, 345/200, 345/102, 345/201, 348/553, 348/559, 348/560, 348/567, 348/563-566, 348/571, 348/725, 348/728, 348/722, 348/714-717, 348/739, 348/790, 348/791
• US Class Current: 345/98
• CPC Class Codes: G06F 1/3218 of display devices
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/022 in absence of operation, e.g. no data being entered during a predetermined time
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: H04N 5/63 Generation or supply of power specially adapted for television receivers
• CPC Class Codes: H04N 5/66 Transforming electric information into light information scanning details H04N3/00

Abstract

In a liquid crystal display (LCD) device, two continuous frame image data to be displayed on a display unit are compared with each other by a comparator circuit, and horizontal and vertical synchronizing signals are regulated in accordance with a comparison result. That is, when the two frame image data coincide with each other, the horizontal and vertical synchronizing signals are not output to the display unit through the controller, in order to decrease the number of scannings of frames to be displayed. Also, when the LCD device has a backlight unit and two frame image data coincide with each other, the backlight unit is turned off.

Claims

1. A liquid crystal display device comprising:

a display portion;

memory means for storing at least continuous first and second frame image data;

comparing means for comparing the first frame image data with the second frame image data;

output means for selectively outputting at least a vertical synchronizing signal in accordance with a comparison result of the comparing means; and

control means for reading out the frame image data from the memory means and controlling the display portion in accordance with the selectively output vertical synchronizing signal, to display the read out frame image data on the display portion.

2. The device of claim 1 wherein the memory means includes a video random access memory (VRAM).

3. The device of claim 1 further comprising a timer for outputting an interrupting signal to the comparing means when a count value reaches a desired value to be set, wherein when the second frame image data coincides with the first frame image data, counting of the count value is started.

4. The device of claim 3 further comprising a backlight unit, wherein when the second frame image data coincides with the first frame image data, the timer turns off the backlight unit.

5. The device of claim 4 wherein when the second frame image data is different from the first frame image data, the timer turns on the backlight unit.

6. A liquid crystal display device comprising:

a display portion;

memory means for storing at least continuous first and second frame image data;

comparing means for comparing the first frame image data with the second frame image data when the first frame image data is displayed on the display portion;

output means for selectively outputting at least a vertical synchronizing signal in accordance with a comparison result of the comparing means; and

control means for reading out the frame image data from the memory means and controlling the display portion in accordance with the selectively output vertical synchronizing signal,

wherein the second frame image data is displayed on the display portion when the second frame image data is different from the first frame image data.

7. A liquid crystal display device comprising:

a display portion;

memory means for storing at least continuous first and second frame image data;

comparing means for comparing the first frame image data with the second frame image data when the first frame image data is displayed on the display portion;

output means for selectively outputting at least a vertical synchronizing signal in accordance with a comparison result of the comparing means; and

control means for reading out the frame image data from the memory means and controlling the display portion in accordance with the selectively output vertical synchronizing signal,

wherein the comparing means outputs a level signal when the second frame image data is different from the first frame image data, and the output means outputs the vertical synchronizing signal in accordance with the output level signal.

8. A liquid crystal display device comprising:

a display portion;

memory means for storing at least continuous first and second frame image data;

comparing means for comparing the first frame image data with the second frame image data when the first frame image data is displayed on the display portion and outputting a level signal when the second frame image data is different from the first frame image data;

output means for outputting at least a vertical synchronizing signal in accordance with the output level signal;

control means for reading out the frame image data from the memory means and controlling the display portion in accordance with the output vertical synchronizing signal; and

a timer, including a counter, for outputting an interrupting signal to the comparing means when a count value reaches a desired value to be set, wherein when the second frame image data coincides with the first frame image data, counting of the count value is started, and when the comparing means receives the interrupting signal, the comparing means outputs the level signal and the count value of the timer is reset.

9. The device of claim 8 wherein the display portion further includes a liquid crystal, and the desired value is set in accordance with a characteristic of the liquid crystal without applying an alternating voltage to the liquid crystal.

10. The device of claim 8 wherein the display portion further includes an analog memory, and the desired value is set to a time shorter than a refreshing time of the analog memory.

11. A liquid crystal display device comprising:

a display portion including a matrix circuit and a liquid crystal;

a driver circuit for driving the display portion; and

a control portion for controlling a driver circuit,

wherein the control portion comprises,

at least one memory for storing at least continuous first and second frame image data;

a comparator for comparing the first frame image data with the second frame image data;

a generator for selectively outputting at least vertical synchronizing signal in accordance with a comparison result of the comparator; and

a controller for reading out the frame image data from the memory, receiving the selectively output vertical synchronizing signal from the generator, and outputting the frame image data and the received vertical synchronizing signal to the driver circuit, to display the frame image data on the display portion.

12. The device of claim 11 wherein when the second frame image data is different from the first frame image data, the generator outputs the vertical synchronizing signal.

13. The device of claim 11 further comprising a timer for outputting an interrupting signal to the comparator when a count value reaches a desired value to be set, wherein when the second frame image data coincides with the first frame image data, counting of the count value is started.

14. The device of claim 11 further comprising a backlight unit, wherein when the second frame image data coincides with the first frame image data, the timer turns off the backlight unit.

15. The device of claim 11 wherein when the second frame image data is different from the first frame image data, the timer turns on the backlight unit.

16. The device of claim 11 wherein the display portion further includes an analog memory, and the desired value is set to a time shorter than a refreshing time of the analog memory.

17. A liquid crystal display device comprising:

a display portion including a matrix circuit and a liquid crystal;

a driver circuit for driving the display portion; and

a control portion for controlling a driver circuit,

wherein the control portion comprises,

at least one memory for storing at least continuous first and second frame image data;

a comparator for comparing the first frame image data with the second frame image data and outputting a level signal when the second frame image data is different from the first frame image data;

a generator for outputting at least vertical synchronizing signal in accordance with the output level signal;

a controller for reading out the frame image data from the memory, receiving the output vertical synchronizing signal from the generator, and outputting the frame image data and the received vertical synchronizing signal to the driver circuit, to display the frame image data on the display portion; and

a timer, including a counter, for outputting an interrupting signal to the comparator when a count value reaches a desired value to be set,

wherein when the second frame image data coincides with the first frame image data, counting of the count value is started, and when the comparator receives the interrupting signal, the comparator outputs the level signal and the count value of the timer is reset.

18. The device of claim 17 wherein the desired value is set in accordance with a characteristic of the liquid crystal without applying an alternating voltage to the liquid crystal.

19. A liquid crystal display device comprising:

a display portion including a liquid crystal;

image data memory means for storing first and second frame image data representing currently displayed image data and image data to be displayed, respectively;

control means connected to said image data memory means for reading out the frame image data from the image data memory means and for controlling the display portion in response to a synchronizing signal input to display the read out frame image data on the liquid crystal;

image data arranging means connected to the image data memory means for providing an arrangement of the first and second frame image data facilitating comparisons between the first and second frame image data;

timing means for generating a refresh signal at a preset interval representing a desired maximum period between updates of the display portion;

image data comparing means, connected to the image data arranging means and the timing means, for accessing the image frame data, performing a comparison between the first frame image data and the second frame image data, and generating a control signal when (1) the first frame image data is different from the second frame image data or (2) when said refresh signal is received from the timing means;

synchronizing signal generating means for periodically generating at least a vertical synchronizing signal output;

synchronizing signal regulating means connected to said synchronizing signal generating means, said image data comparing means, and said control means for receiving said synchronizing signal output of the synchronizing signal generating means and said control signal of said image data comparing means, and for selectively transmitting said synchronizing signal output to said synchronizing signal input of said control means when said control signal indicates that either (1) the first frame image data is different from the second frame image data or (2) the desired maximum period between updates of the display portion has elapsed,

whereby power consumption of the display device is reduced at times when no change is desired in the currently displayed image data, by dynamically increasing a period between consecutive scans of the liquid crystal to said desired maximum period.