Electroluminescent display device

• US 6,271,812 B1
• Filed: 09/08/1998
• Issued: 08/07/2001
• Est. Priority Date: 09/25/1997
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Saito, Hideki, Nishioka, Ken, Kishita, Hiroyuki, Osada, Masahiko, Ninoyu, Toshinori
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): ZAMANI, ALI A
• Application Number:
  US09/149,076
• Time in Patent Office: 1,064 Days
• Field of Search: 345/76, 345/55, 345/98, 345/212, 345/213, 345/206, 345/211, 345/214, 345/77, 345/208, 345/210, 345/204, 340/455, 340/461, 340/462, 315/169.1, 315/169.2, 315/169.4
• US Class Current: 345/76
• CPC Class Codes: G09G 2310/0245 Clearing or presetting the whole screen independently of waveforms, e.g. on power-on G09G2310/063 takes precedence
• 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 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/30 using electroluminescent panels

Abstract

An Electroluminescent display device is designed not to display residual images due to electric charges stored in electroluminescent pixels or to make them invisible, when the device is turned on again. The stored charges are eliminated at the time a normal display on the panel is turned off at an end of an operation, by scanning pixels at least one time while giving a non-activating data voltage thereto. Alternatively, upon turning on the panel, pixels which were activated in a previous use are all lit at least one time, thereby making the residual images invisible. Thus, the residual images stored in a previous operation are not shown or made invisible when the electroluminescent display device is turned on next time.

Claims

1. An electroluminescent display device comprising:

an electroluminescent panel having electroluminescent elements and being powered by a DC power source;

driver means for selectively activating the electroluminescent elements to emit light therefrom;

a power source circuit for supplying electric power to the driver means;

switching means connected between the DC power source and the power source circuit; and

a controller for controlling operation of the driver means and the switching means, wherein;

the driver means continues to apply after termination of a display operation, for at least one period of the electroluminescent panel, a voltage having a value in a vicinity of a threshold voltage used to activate the electroluminescent elements on at least all of the electroluminescent elements which were activated in a previous display operation, whereby the applied voltage eliminates residual charges stored in the electroluminescent elements in the previous display operation, which cause a momentary image display upon re-starting the display operation; and

wherein

the switching means shuts off power from the DC power source to the power source circuit after the application of the voltage to eliminate residual charge.

5. The electroluminescent display device as in claim 1, wherein:

the voltage having a value in the vicinity of the threshold voltage applied after termination of the display operation is a pulse voltage having a width which is wider than that of a pulse voltage applied to activate the electroluminescent elements.

16. The electroluminescent display device as in claim 1, wherein the momentary image display is a combination of an image due to the residual charges and an image appearing upon re-starting the display operation.

2. An electroluminescent display device mounted on a vehicle and powered by an on-board battery comprising:

an electroluminescent panel having electroluminescent elements;

driver means for selectively activating the electroluminescent elements to emit light therefrom;

a power source circuit for supplying electric power to the driver means;

switching means for controlling power supply from the battery to power source circuit, operation of the switching means being triggered by a key switch of the vehicle; and

a controller for controlling operation of the driver means and the switching means, wherein;

the driver means continues to apply termination of a display operation, for at least one period of the electroluminescent panel, a voltage having a value in a vicinity of a threshold voltage used to activate the electroluminescent elements on at least all of the electroluminescent elements which were activated in a previous display operation, whereby the applied voltage eliminates residual charges stored in the electroluminescent elements in the previous display operation, which cause a momentary image display upon re-starting the display operation; and

wherein

the switching means shuts off the power supply from the battery to the power source circuit after the application of the voltage to eliminate residual charge.

3. The electroluminescent display device as in claim 2, wherein:

the controller generates a signal indicating the driver means to continue to apply the voltage upon turning off the key switch; and

the switching means allows power from the battery to the power source circuit either when the key switch is kept turned on or when the indicating signal exists.

4. The electroluminescent display device as in claim 3, wherein:

the switching means includes switching elements;

the battery supplies power to the power source circuit through the switching elements when the indicating signal exists; and

a signal indicating that the key switch is kept turned on is fed to the switching means.

6. An electroluminescent display device powered by a DC power source comprising:

an electroluminescent panel including a plurality of scanning electrodes, a plurality of data electrodes, and an electroluminescent layer interposed between the scanning and data electrodes, the scanning and data electrodes constituting a matrix, each intersection of the scanning and data electrodes and the electroluminescent layer constituting a plurality of pixels;

a scanning electrode driving circuit for sequentially applying scanning voltages on the scanning electrodes, polarities of the scanning voltages being alternately switched every positive and negative field;

a data electrode driving circuit for applying data voltages on the data electrodes;

a power source circuit for supplying voltages to the scanning and data electrode driving circuits;

a switching circuit for allowing and shutting off power from the DC power source to the power source circuit; and

a control circuit for controlling the scanning electrode driving circuit to apply a voltage to eliminate residual charges and has a value in a vicinity of a threshold voltage used to activate the pixels on the scanning electrodes for a period at least covering one field after a termination of display on the panel, the control circuit controlling the data electrode driving circuit to apply a data voltage which inactivates the pixels so that the pixels do not emit light on the data electrodes for the same period in which the scanning voltage is applied on the scanning electrodes after termination of display on the panel, and for controlling the switching circuit to shut off the voltage supply from the DC power source to the power source circuit.

7. The electroluminescent display device as in claim 6, wherein:

the voltage having the value in the vicinity of the threshold voltage and applied on the scanning electrodes for the period at least covering one field is the same voltage as the scanning voltage applied for a normal display.

8. An electroluminescent display device comprising:

an electroluminescent panel having electroluminescent elements;

driver means for selectively activate the electroluminescent elements to emit light therefrom;

power source means for supplying electric power to the driver means; and

a controller for controlling operation of the driver means and the power source means, wherein;

substantially all the electroluminescent elements are activated to emit light causing an image due to residual charges to be invisible, and displaying an initial display on the panel, upon turning on the electroluminescent display device.

9. The electroluminescent display device as in claim 8, wherein:

the electroluminescent elements constitute pixels which display images on the panel; and

the controller causes substantially all the pixels to emit light upon turning on the electroluminescent display device.

10. The electroluminescent display device as in claim 8, wherein:

the electroluminescent elements constitute pixels which display images on the panel; and

the controller causes the pixels scattered at random on the panel to emit light upon turning on the electroluminescent display device.

11. The electroluminescent display device as in claim 8, wherein:

the electroluminescent panel starts to display the initial display when the power source circuit establishes a predetermined voltage level after the power source is turned on.

14. The electroluminescent display device as in claim 9, wherein:

the electroluminescent panel starts to display the initial display when the power source circuit establishes a predetermined voltage level after the power source circuit is turned on.

15. The electroluminescent display device as in claim 10, wherein:

the electroluminescent panel starts to display the initial display when the power source circuit establishes a predetermined voltage level after the power source circuit is turned on.

12. A method of driving an electroluminescent display panel having picture elements, the method comprising steps of:

displaying images on the electroluminescent panel by applying to the picture elements scanning voltages and data voltages in synchronized relation;

discontinuing image display by changing the data voltages to a voltage level which displays no image while continuing to supply the scanning voltages for a period sufficient to scan all the picture elements at least one time, thereby eliminating electric charges stored in the picture elements, which cause a momentary image upon re-starting the image display; and

shutting off power for driving the electroluminescent display panel.

13. A method of driving an electroluminescent display panel having picture elements, the method comprising steps of:

starting a power supply for driving the electroluminescent display panel;

activating substantially all the picture elements so that the picture elements emit light at least one time, thereby making residual images invisible, which are momentarily displayed upon starting the power supply; and

displaying images on the electroluminescent display panel by imposing scanning voltages and data voltages on the picture elements.