Scan inversion symmetric drive

• US 4,975,691 A
• Filed: 06/16/1987
• Issued: 12/04/1990
• Est. Priority Date: 06/16/1987
• Status: Expired due to Fees

• Current Assignee: Interstate Electronics Corp. (L3Harris Technologies, Inc.)
• Original Assignee: Interstate Electronics Corp. (L3Harris Technologies, Inc.)
• Inventors: Lee, James Y.
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): Hjerpe, Richard
• Application Number:
  US07/063,179
• Time in Patent Office: 1,267 Days
• Field of Search: 340/825.81, 340/781, 340/805, 340/811, 340/812, 340/802, 340/718, 340/719, 340/727, 340/753, 340/754, 340/784, 340/792, 315/169.3
• US Class Current: 345/79
• CPC Class Codes: G09G 2310/0267 Details of drivers for scan electrodes, other than drivers for liquid crystal, plasma or OLED displays
• CPC Class Codes: G09G 2310/0275 Details of drivers for data electrodes, other than drivers for liquid crystal, plasma or OLED displays, not related to handling digital grey scale data or to communication of data to the pixels by means of a current
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 3/30 using electroluminescent panels

Abstract

A thin-film electroluminescent display panel system has a plurality of vertical column electrodes driven by column driver circuits and a plurality of horizontal row electrodes driven by row driver circuits. The system includes a row driver control circuit that enables the row drivers in a first sequence during a first display frame so that write voltage pulses are applied to the row electrodes in order from the top to the bottom of the display panel. The row driver control circuit enables the row drivers in a second sequence during a second display frame so that the write voltages are applied to the row electrodes in the reverse order from the bottom of the display panel to the top of the display panel. The alternating sequences of application of the write voltages to the row electrodes cause the average residual dc voltage across each of the pixel elements of the display panel to be substantially reduced towards zero so that latent image problems caused by the residual dc voltage is substantially reduced or eliminated.

Claims

1. In an electroluminescent display system having a display panel, said display panel having a plurality of column electrodes and having a plurality of row electrodes, a plurality of light-emitting pixel elements at the intersections of said column electrodes and said row electrodes, said pixel elements responsive to write pulses having a first polarity voltage applied to said row electrodes and refresh pulses having a second polarity voltage applied to said row electrodes, a method of applying said write pulses and said refresh pulses to said row electrodes comprising the steps of:

applying first, second and third refresh pulses to said row electrodes at fixed time intervals, the time interval between said first refresh pulse and said second refresh pulse comprising a first display frame, the time interval between said second refresh pulse and said third refresh pulse comprising a second display frame;

applying a first sequence of write pulses to said plurality of row electrodes, one at a time, during said first display frame between said first refresh pulse and said second refresh pulse, each of said write pulses in said first sequence applied at respective first time intervals after said first refresh pulse, said first time interval for each of said row electrodes proportional to the position of said row electrode with respect to the top of said display panel;

applying a second sequence of said write pulses to said row electrodes, one at a time, during said second display frame after said second refresh pulse, each of said write pulses in said second sequence applied at respective second time intervals with respect to said second refresh pulse, the second time interval for each of said row electrodes different from the corresponding first time interval for each of said row electrodes, such that the second time interval for each of said row electrodes is proportional to the position of said row electrode with respect to the bottom of said display panel.

2. The method as defined in claim 1, wherein said first sequence of write pulses comprises write pulses applied to said row electrodes in order from the top of said display panel to the bottom of said display panel during said first display frame and said second sequence of write pulses comprises write pulses applied to said row electrodes in reverse order from the bottom of said display panel to the top of said display panel during said second display frame.

3. The method as defined in claim 1, wherein the application of a refresh pulse to one of said pixel elements causes a residual dc voltage of a first polarity across said pixel element that remains until the next write pulse, and the application of a write pulse to said pixel element causes a residual dc voltage of a second polarity across said pixel element that remains until the application of the next refresh pulse to said pixel element, and wherein said first and second sequences cause the amount of time that said residual dc voltage of said first polarity remains across said pixel element during the total time of said first and second frames to be substantially equal to the amount of time that said residual dc voltage of said second polarity remains across said pixel element during the total time of said first and second frames.

4. An electroluminescent display system, comprising:

a thin-film electroluminescent display panel having an electroluminescent phosphor layer and a plurality of row electrodes and column electrodes that define pixel cells on said display panel;

a plurality of column drivers that apply column voltages to said column electrodes;

a plurality of row drivers that apply row voltages to said row electrodes;

a column driver control circuit that controls the application of said column voltages to said column electrodes by said column drivers; and

a row driver control circuit that controls the application of said row voltages to said row electrodes by said row drivers, said row driver control circuit comprising;

a first circuit that generates a plurality of refresh pulses having a first voltage polarity and spaced apart in time by fixed time intervals, the time interval between a first refresh pulse and a second refresh pulse comprising a first display frame, the time interval between said second refresh pulse and a third refresh pulse comprising a second display frame, said refresh pulses applied to said plurality of row electrodes; and

a second circuit that enables said row drivers to apply write voltage pulses to each of said row electrodes, one at a time, said second circuit enabling said row drivers in a first sequence during said first display frame so that said row electrodes are enabled in a first order during said first display frame and so that said row electrodes are enabled in a second order during said second display frame, said first and second orders selected so that for any one of a plurality of row electrodes, the amount of time between the occurrence of a write pulse on said any one row electrode in said first display frame and the occurrence of said second refresh pulse is substantially equal to the amount of time between the occurrence of said second refresh pulse and the occurrence of a write pulse on said any one electrode in said second display frame;

wherein said write voltage pulses are applied to said row electrodes in order from the top of the display panel to the bottom of the display panel during said first display frame and said write voltage pulses are applied to said row electrodes in order from the bottom of said display panel to the top of said display panel during said second display frame.

5. In an electroluminescent display system having a display panel that includes thin, electroluminescent phosphor layer and a plurality of row electrodes and column electrodes defining pixel elements on said display panel, a method of reducing the residual dc voltages across said pixel elements comprising the steps of:

applying a sequence of refresh pulses having a first voltage polarity to said row electrodes at fixed, spaced-apart intervals;

between a first of said refresh pulses and a second of said refresh pulses, applying a first sequence to write voltages having a second voltage polarity to said row electrodes in a first order from the top of said display panel to the bottom of said display panel; and

between said second of said refresh pulses and a third of said refresh pulses, applying a second sequence of write voltages to said row electrodes in a second order from the bottom of said display panel to the top of said display panel, said first order and said second order selected so that the sum of the amount of time between said first refresh pulse and the write voltage applied to any one of said row electrodes in said first sequence added to the amount of time between the second refresh pulse and the write voltage applied to said any one of said row electrodes in said second sequence is substantially equal to the amount of time between said first refresh pulse and said second refresh pulse.

6. A method of reducing the residual dc voltages across the pixel elements of a thin-film electroluminescent display panel, said display including a plurality of row electrodes and a plurality of column electrodes, said row electrodes and said column electrodes crossing to define said pixel elements, said row electrodes driven by a plurality of row drivers, said method comprising the steps of:

applying a sequence of refresh pulses to said plurality of row electrodes, said refresh pulses each comprising a voltage of a first polarity, each said refresh pulse applied to all of said plurality of row electrodes at substantially the same time, adjacent ones of said refresh pulses spaced apart in time from each other by a fixed amount of time, the fixed amount of time between adjacent refresh pulses defining a display frame;

applying a plurality of sequences of write pulses, one at a time, to said plurality of row electrodes during each said display frame, said write pulses comprising a voltage of a second polarity different from said first plurality, said plurality of sequences of write pulses repeating after a like plurality of display frames, said plurality of sequences selected so that over said plurality of display frames, for each row electrode the total time from the refresh pulses in the display frames to the next adjacent write pulses is substantially equal to the total time from the write pulses in the display frame to the next adjacent refresh pulses, the number of sequences in said plurality of sequences substantially less than the number of said plurality of row electrodes;

wherein said number of sequences is equal to two.

7. The method as defined in claim 6, wherein said number of row electrodes is equal to 256.