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Method and system for programming and driving active matrix light emitting device pixel having a controllable supply voltage

  • US 8,378,938 B2
  • Filed: 09/23/2011
  • Issued: 02/19/2013
  • Est. Priority Date: 12/07/2004
  • Status: Active Grant
First Claim
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1. A display system comprising:

  • a pixel circuit including a drive transistor, a storage capacitor, one or more switch transistors, and a light emitting device, the drive transistor having a terminal connected to the light emitting device, the drive transistor having a threshold voltage that shifts during operation of the drive transistor;

    a controllable power supply connected to a terminal of the drive transistor other than the one connected to the light emitting device for supplying the pixel circuit with a compensating voltage or with an operating voltage;

    a voltage driver for supplying a programming voltage to the pixel circuit via the one or more switch transistors along a data line so as to program the pixel circuit to emit light according to display information; and

    a controller configured to operate the controllable power supply, the voltage driver, and one or more select lines that control the one or more switch transistors, such that;

    in response to one of the one or more select lines being activated, the compensating voltage is applied to the light emitting device, via the drive transistor, to turn off the light emitting device,in response to applying the compensation voltage, setting the data line to a nonzero reference voltage,responsive to setting the data line to the nonzero reference voltage, the storage capacitor is allowed to charge or discharge, through the drive transistor, until the drive transistor turns off, while the one of the one or more select lines remain activated such that the threshold voltage of the drive transistor is established across the drive transistor,the programming voltage is applied to the pixel circuit, thereby establishing a fixed voltage across the drive transistor that accounts for instabilities in the threshold voltage of the drive transistor, andwherein the controller is configured to operate the pixel circuit to maintain the fixed voltage across the drive transistor on the storage capacitor while turning on the operating voltage during a driving cycle of the pixel circuit, the driving cycle being separate from a programming cycle during which the fixed voltage is established on the storage capacitor.

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