Circuit and method for driving an organic light emitting diode (O-LED) display
First Claim
1. A circuit, coupled to a current source, for driving a plurality of active organic light emitting diodes (O-LEDs) arranged in a column at a desired brightness comprising:
- an input leg of a current mirror for establishing a reference current for driving an active O-LED;
a plurality of selecting means, responsive to a row select signal, for respectively selecting an O-LED from the plurality of active O-LEDs;
an output leg of a current mirror for supplying a mirror of the established reference current to the selected O-LED;
a plurality of charging means for respectively storing a voltage differential which is related to the established reference current in order to continuously drive the selected O-LED.
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Accused Products
Abstract
Disclosed is a technique for driving a column of pixels implemented using O-LEDs. The technique includes separate, digitally adjustable current sources on each column conductor of the array. For each column, the digitally-programmed current flow terminates with a reference O-LED and a series NMOS transistor forming the input leg of a novel, distributed current mirror. The current is "mirrored" to the output leg of the distributed current mirror which can service any one of a plurality of active O-LEDs in the column based on a row select signal. In this way, a transistor on the output leg of the current mirror couples its respective O-LED to a source of operational power. The mirrored charge on the gate of the output leg transistor causes it to apply the same current to the active O-LED as was applied to the reference O-LED through the input leg transistor. Additionally, the voltage drop across the NMOS transistor and the reference O-LED is used to charge a capacitor associated with the selected O-LED. The charging of the capacitor, as a result of the digitally-programmed current supplied through the NMOS transistor to the reference O-LED, allows for continuous driving of the active O-LED during a cycle through. Thus, a reference O-LED in conjunction with an NMOS transistor, services all of a plurality of sequentially-loaded rows within each column.
195 Citations
15 Claims
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1. A circuit, coupled to a current source, for driving a plurality of active organic light emitting diodes (O-LEDs) arranged in a column at a desired brightness comprising:
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an input leg of a current mirror for establishing a reference current for driving an active O-LED; a plurality of selecting means, responsive to a row select signal, for respectively selecting an O-LED from the plurality of active O-LEDs; an output leg of a current mirror for supplying a mirror of the established reference current to the selected O-LED; a plurality of charging means for respectively storing a voltage differential which is related to the established reference current in order to continuously drive the selected O-LED. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An array of organic light emitting diodes (O-LEDs), having improved driving circuitry comprising:
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a plurality of rows and a plurality of columns of active O-LEDs; an adjustable current source coupled to one of the plurality of columns for providing a reference current to the column of active O-LEDs, the reference current level being configured to produce a desired brightness level in a selected one of the O-LEDs in the column; reference means, coupled to the one of the plurality of columns, for establishing the reference current level in a reference O-LED; selecting means, responsive to a row select signal, for selecting the selected O-LED in the column; converting means, responsive to the selecting means, for converting the established reference current in the reference O-LED into a corresponding voltage level and for storing the corresponding voltage level; and means, responsive to the stored voltage level for driving the selected O-LED with a current substantially equal to the reference current to produce the desired brightness level in the selected O-LED. - View Dependent Claims (9, 10)
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11. An array of organic light emitting diodes (O-LEDs), coupled to a digital current source, having improved driving circuitry comprising:
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a plurality of rows and a plurality of columns of active O-LEDs; reference means, coupled to each of the plurality of columns, for establishing a reference current for driving each active O-LED in every row of the respective column; a plurality of selecting means, responsive to a row select signal, for respectively selecting an active O-LED; a plurality of converting means, responsive to the selecting means, for converting the established reference current into a predetermined voltage; a plurality of means, responsive to the means for converting, for allowing a respectively selected O-LED to be driven at the desired brightness, wherein the reference means includes a reference O-LED, wherein the reference means includes an input leg of a current mirror including the reference O-LED.
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12. A method of driving a plurality of active organic light emitting diodes (O-LEDs) arranged in a column at a desired brightness, the method comprising the steps of:
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driving the column with a reference current level configured to produce a desired brightness level in a selected one of the O-LEDs; establishing the reference current level in a reference O-LED; selecting one of the O-LEDs in the column; converting the established reference current in the reference O-LED into a corresponding voltage level; transmitting the voltage level to the selected O-LED; storing the corresponding voltage level; converting the stored voltage level into a current substantially equal to the reference current; and driving the selected O-LED with the current substantially equal to the reference current to produce the desired brightness level in the selected O-LED. - View Dependent Claims (13, 14, 15)
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Specification