Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1999-07-21
2001-02-20
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S077000
Reexamination Certificate
active
06191534
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention pertains to circuitry for driving light emitting devices and pertains particularly to the low current drive of organic light emitting diodes.
2. Related Information
The organic light emitting diode (OLED) technology provides a low current emissive display technology. However, a large array of OLEDs contains a large amount of capacitance. This capacitance must be charged and discharged during multiplexed operation.
An equivalent circuit for an OLED pixel is a capacitor in parallel with the emitting diode. Typically the anodes of each OLED is driven by a current source since the pixel Vf may vary for individual OLEDs across an OLED array.
A typical implementation of circuitry which drives an array of OLEDs is using current sources to drive a column line for each column of an OLED array. The anode of each OLED is connected to a corresponding column line. The cathodes of each OLED is connected to a corresponding row line of the OLED matrix. Each row line has a switch. The switches enable one row at a time.
For background information on circuitry for driving OLEDs, see for example, U.S. Pat. No. 5,828,181 issued to Yohiyuki Okuda on Oct. 27, 1998 for DRIVING CIRCUIT FOR AN ORGANIC ELECTROLUMINESCENT ELEMENT USED IN A DISPLAY.
SUMMARY OF THE INVENTION
In accordance with the preferred embodiment of the present invention, control circuitry for an array of light emitting devices includes a first column line connected to each light emitting device in a column of light emitting devices. First column circuitry includes a first current source and a second current source. The first current source is connected to the first column line. The second current source is connected to the first column line. When a first light emitting device from the column of light emitting devices is to be turned on, the first current source is turned on until a voltage on the first column line is equal to a predetermined voltage. Then the first current source is turned off and the second current source supplies current sufficient to cause the first light emitting device to emit light to a first brightness level.
The present invention provides low power operation of a row of light emitting devices. Various embodiments of the invention also allow for reduced complexity when implementing control circuitry for the row of light emitting devices.
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Brummer John
Schuler Jeffrey A.
Zhao Yang
Infineon Technologies North America Corp.
Tran Thuy Vinh
Wong Don
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