Display driver circuits

• US 7,834,824 B2
• Filed: 06/11/2003
• Issued: 11/16/2010
• Est. Priority Date: 06/18/2002
• Status: Expired due to Fees

• Current Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Original Assignee: Cambridge Display Technology Limited (Sumitomo Chemical Company Limited)
• Inventors: Smith, Euan C., Routley, Paul R.
• Primary Examiner(s): Eisen; Alexander
• Assistant Examiner(s): MANDEVILLE, JASON M
• Application Number:
  US10/518,182
• Publication Number:
  US 20060038758A1
• Time in Patent Office: 2,715 Days
• Field of Search: 345/30, 345/36, 345/39, 345 44- 46, 345/55, 345 76- 83, 345204-207, 345211-212, 345214-215, 345/690, 345/697, 315/169.3
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/325 the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

This disclosure generally relates to display driver circuits for electro-optic displays, and more particularly relates to circuits and methods for driving active matrix organic light emitting diode displays with greater efficiency. A display driver for an electroluminescent display, the display including a plurality of electroluminescent display elements each associated with a display element driver circuit, each display element driver circuit including a drive transistor having a control connection for driving the associated display element in accordance with a voltage on the control connection, the display driver including at least one display element brightness controller to provide an output to drive a control connection to control the electroluminescent output from a display element; a voltage sensor to sense the voltage on a control connection; and a power controller for controlling an adjustable power supply for providing an adjustable voltage to the electroluminescent display to power said drive transistors for driving said display elements, the power controller being configured to provide a control signal to adjust said power supply voltage in response to said sensed voltage.

Claims

1. A display driver for an active matrix electroluminescent display, the display comprising a plurality of electroluminescent pixels each pixel comprising a pixel driver circuit and a display element, each said pixel driver circuit including a drive field effect transistor having a gate connection for driving the associated display element in accordance with a voltage on the gate connection to produce a driving current through said display element, the display driver comprising:

a display element brightness controller configured to provide an output to drive a said gate connection to control the electroluminescent output from a said pixel;

a voltage sensor to sense a said voltage on said gate connection; and

a power controller coupled to said voltage sensor for controlling an adjustable voltage power supply to each of said plurality of electroluminescent pixels, said power controller configured to read a sensed voltage on each said pixel gate connection within a predetermined period to identify a display element having a maximum brightness relative to others of said display elements within said predetermined period, wherein

said display element brightness controller and said power controller are configured to, respectively and concurrently within a period, increase said voltage on said gate connection of said pixel having said identified display element and to reduce said power supply voltage, to a point where the voltage of said adjustable voltage power supply is just sufficient to maintain a current to said identified display element substantially equal to a predetermined current corresponding to a current that is produced in said identified display element prior to said increasing of said voltage on said gate connection and said reducing of said power supply voltage, said increasing and said reducing in response to a said sensed voltage on said gate connection of said pixel having said identified display element, wherein said increasing and said reducing are performed as long as said sensed voltage on said gate connection is determined to be less than a maximum available voltage for outputting from said brightness controller to said display element and until said voltage on said gate connection substantially reaches said maximum available voltage.

2. A display driver as claimed in claim 1 wherein said voltage sensor is configured to sense the voltage on a said gate connection by sensing the voltage on an electrode of said display.

3. A display driver as claimed in claim 1 wherein a said pixel includes a photodiode, and wherein a photocurrent through said photodiode is determined by a said adjustable constant current to determine a brightness of said pixel.

4. A display driver as claimed in claim 1 wherein said power controller is further configured to increase said power supply voltage when said gate connection voltage of said brightest pixel has not reduced to less than a threshold value after a predetermined interval.

5. A display driver as claimed in claim 1 further comprising said adjustable voltage power supply.

9. A display driver as claimed in claim 1 wherein said electroluminescent display comprises an organic light emitting diode display.

6. A method of operating an active matrix electroluminescent display, the display comprising a plurality of electroluminescent pixels each pixel comprising an associated pixel driver and a display element, each said pixel driver including a drive field effect transistor having a gate connection for driving the associated display element in accordance with a voltage on the gate connection to produce a driving current through said display element, the display having an adjustable voltage power supply coupled to provide a power supply voltage to each of said plurality of electroluminescent pixels, and a plurality of control lines corresponding to said gate connections for setting the brightness of each pixel, the method comprising:

setting the brightness of pixels of the display using said control lines to drive said gate connections;

monitoring said control lines of the display to sense said voltages on said gate connections, and controlling said adjustable voltage power supply to each of said plurality of electroluminescent pixels by reading a sensed voltage on each said gate connection within a predetermined period to identify a display element having a maximum brightness relative to others of said display elements within said predetermined period; and

concurrently within a period, reducing said power supply voltage and increasing said voltage on said gate connection of said pixel having said identified display element, responsive to said monitoring to a point where a voltage of said adjustable voltage power supply is just sufficient to maintain a current to said identified display element substantially equal to a predetermined current corresponding to a current that is produced in said identified display element prior to said increasing of said voltage on said gate connection and said reducing of said power supply voltage, said increasing and said reducing in response to a said sensed voltage on said gate connection of said pixel having said identified display element, wherein said increasing and said reducing are performed as long as said sensed voltage on said gate connection is determined to be less than a maximum available voltage for outputting to said display element and until said voltage on said gate connection substantially reaches said maximum available voltage.

7. A method as claimed in claim 6 wherein a said pixel includes a photodiode and wherein a current through said photodiode is determined by an adjustable constant current.

8. An active matrix display driver configured to operate in accordance with the method of claim 6.

10. A method as claimed in claim 6 wherein said electroluminescent display comprises an organic light emitting diode display.