Display apparatus and method for driving the display apparatus

• US 6,169,532 B1
• Filed: 02/02/1998
• Issued: 01/02/2001
• Est. Priority Date: 02/03/1997
• Status: Expired due to Fees

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Sumi, Shinobu, Kanbara, Minoru
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Marc-Coleman, Marthe Y.
• Application Number:
  US09/017,653
• Time in Patent Office: 1,065 Days
• Field of Search: 345/98, 345/97, 345/99, 345/212, 345/211, 345/100, 345/205
• US Class Current: 345/98
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2330/022 in absence of operation, e.g. no data being entered during a predetermined time
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

A display apparatus comprises a liquid crystal display panel, gate driver circuit for scanning gate lines of the display panel, drain driver circuit for supplying the display data to drain lines of the display panel, level modulator circuit coupled to the display panel and control circuit. The control circuit determines that video data represents a still image data, stoped the operation of the drain driver circuit and activates the level modulator circuit. The level modulator circuit reads out from display signals from the display panel and re-writes display signals to the display panel in order to display the still image on the display panel. In this manner, the electric power consumed by the drain circuit can be conserved when the display apparatus displays the still image.

Claims

1. A display apparatus which is supplied with display data, said display apparatus comprising:

a display panel having a plurality of picture elements which are arranged in a matrix having rows and columns;

signal processing means for producing image signals corresponding to the display data and for outputting the image signals;

scanning means for sequentially selecting each row of said display panel;

display signal supplying means for selecting each column of a next row in the sequence, producing display signals corresponding to the image signals for that row and supplying the display signals to the picture elements in that row in response to the scanning means;

determining means for determining whether the display data represents a still image;

control means for stopping the operation of said display signal supplying means including the selection of each column in the next row in the sequence after the display signals representing the still image are supplied to all picture elements unless and until said determining means determines that the display data no longer represents the same still image;

read-out means for reading out the display signals retained in the picture elements when said control means stops the operation of said display supplying means;

modulating means for modulating the display signals read out from the picture elements by said read-out means in order to obtain appropriate display signals to maintain displaying the still image on said display panel; and

re-writing means for writing the modulated display signals into the picture elements from which the display signals were read out by said read-out means.

2. A display apparatus according to claim 1, wherein said modulating means comprises a plurality of modulating units, each of which is coupled to each column of said display panel, for modulating the display signal read out from the picture element in the coupled column.

3. A display apparatus according to claim 2, wherein said read-out means comprises means for simultaneously reading out the display signals retained in every picture element in one row of said display panel which is selected by said scanning means, and said re-writing means comprises means for simultaneously writing the modulated display signals into every picture element in the selected row.

4. A display apparatus according to claim 1, wherein said modulating means comprises amplifying means for amplifying the display signals read out from the picture elements by said read-out means.

5. A display apparatus according to claim 1, wherein said modulating means comprises detecting means for detecting the voltage of the display signal read out from the picture element by said read-out means, and means for determining an appropriate voltage based on the detected voltage and outputting a modulated display signal with the appropriate voltage.

6. A display apparatus according to claim 5, wherein said detecting means comprises comparator for comparing the voltage of the display signal read out from the picture element with a reference voltage.

7. A display apparatus according to claim 1, further comprising

a signal line electrically coupled to the picture element and said read-out means for providing the display signal retained in the picture element to said modulating means through said read-out means; and

a reset circuit for providing said signal line with a reset voltage to eliminate residual potential on said signal line before the display signal retained in the picture element is supplied to said modulating means through said read-out means.

8. A display apparatus according to claim 1, wherein said display signal supplying means comprises a shift register for selecting each column of the next row in the sequence, and said control means comprises means for controlling a clock signal into the shift register wherein the shift register operates when it receives the clock signal and stops operation when it does not receive the clock signal.

9. A display apparatus according to claim 8, wherein said data signal supplying means further comprises storing means for temporarily storing the display signals for the picture elements in one row.

10. A display apparatus according to claim 1, wherein said display panel comprises a liquid crystal display panel.

11. A display apparatus according to claim 10, wherein said modulating means comprises amplifying means for amplifying the display signals read out by said read-out means, and inverting means for inverting the polarity of the display signals.

12. A display apparatus according to claim 11, wherein said liquid crystal display panel comprises a switching element for connecting the picture element to either said display signal supplying means or said read-out means and the rewriting means, and said amplifying means comprises means for amplifying read-out display signals to compensate for a voltage drop caused by parasitic capacitance of said switching element.

13. A display apparatus according to claim 10, wherein said modulating means comprises detecting means for detecting the voltage of the display signal read out from the picture element, and means for determining an appropriate voltage based on the detected voltage and having an opposite polarity to the detected voltage, and outputting a modulated display signal with the determined voltage.

14. A display apparatus according to claim 13, wherein said detecting means comprises a comparator for comparing the voltage of the display signal read out from the picture element with a reference voltage.

15. A display apparatus according to claim 1, wherein said display panel comprises an organic electroluminescent display panel.

16. A display apparatus according to claim 15, wherein said modulating means comprises amplifying means for amplifying the display signals read out from the picture elements by said read-out means.

17. A display apparatus according to claim 16, wherein said organic electroluminescent display panel comprises a switching element for connecting said picture element to either said display signal supplying means or said read-out means and the rewriting means, and said amplifying means comprises means for amplifying read-out display signals to compensate for a voltage drop caused by a parasitic capacitance of said switching element.

18. A display apparatus according to claim 15, wherein said organic electroluminescent display panel comprises a data storing capacitor for storing the display singal.

19. A display apparatus according to claim 15, wherein said organic electroluminescent display panel comprises a thin film transistor for storing the display signal.

20. A method for driving a display apparatus which is supplied with display data and comprises a display panel having a plurality of picture elements which are arranged in a matrix having rows and columns, the method comprising the steps of:

producing image signals corresponding to the display data and outputting the image signals;

selecting each row of said display panel;

selecting each column of a next row in the sequence, producing display signals corresponding to the image signals for that row and supplying the display signals to the picture elements in that row;

determining whether the display data represents a still image;

stopping the selection of each column and production and supply of display signals after the display signals representing the still image are supplied to all picture elements unless and until the display data no longer represents the same still image;

reading out the display signals retained in the picture elements when the selection of each column and production and supply of display signals are stopped;

modulating the read out display signals in order to obtain appropriate display signals to maintain the still image displayed by said display panel; and

re-writing the modulated display signals into the picture elements from which the display signals were read out.

21. The method of claim 20, wherein the step of modulating the read out display signals comprises amplifying the read out display signals.

22. The method of claim 20, wherein the step of modulating the read out display signals comprises detecting for each read out display signal the voltage of the read out display signal and determining an appropriate voltage based on the detected voltage and outputting a modulated display signal with the appropriate voltage.

23. The method of claim 22, wherein the step of detecting comprises comparing the voltage of the read out display signal with a reference voltage.

24. The method of claim 20, wherein the step of reading out the display signals comprises a step of simultaneously reading out the display signals retained in every picture element in a currently selected row of said display panel, and the step of re-writing comprises a step of simultaneously re-writing the modulated display signals into every picture element in a currently selected row of said display panel.