ACTIVE MATRIX ORGANIC LIGHT EMITTING DIODE DISPLAY

摘要

An improved AM OLED pixel circuit and method of wide dynamic range dimming for AM OLED displays are disclosed that maintain color balance throughout the dimming range, and also maintain the uniformity of the luminance and chromaticity of the display at low gray-levels as the display is dimmed to lower luminance values. As such, AM OLED displays can meet the stringent color/dimming specifications required for existing and future avionics, cockpit, and hand-held military device display applications. Essentially, the OLED pixel circuit and method of dimming that are disclosed use Pulse Width Modulation (PWM) of the OLED pixel current to achieve the desired display luminance. Two example circuits are disclosed that externally PW modulate the common cathode voltage or common power supply voltage to modulate the OLED current in order to achieve the desired display luminance. Three example circuits are disclosed that incorporate additional transistor switches in the pixel circuit to modulate the OLED current during the frame time. By PWM of the OLED current, in combination with data voltage (or current) modulation, wide dynamic range dimming can be achieved while maintaining the color balance and the luminance and chromaticity uniformity required over the surface of the display involved.

主权项

1. An Organic Light Emitting Diode display, comprising:
a plurality of rows of Organic Light Emitting Diodes coupled to a power supply; a plurality of Pulse Width Modulation signal generators; at least one circuit comprising:
a first transistor, said first transistor coupled to a row address bus of said display and a column address bus of said display;a second transistor, said second transistor coupled to said first transistor and coupled directly to one Organic Light Emitting Diode of said plurality of rows of Organic Light Emitting Diodes;a storage capacitor, said storage capacitor coupled to said first transistor and said second transistor;a third transistor, said third transistor coupled to the one Organic Light Emitting Diode of said plurality of rows of Organic Light Emitting Diodes and to one of said Pulse Width Modulation signal generators such that the third transistor is configured to Pulse Width Modulate a current through a selected one of said rows of Organic Light Emitting Diodes and control a light emission thereof, said third transistor further coupled to a common cathode configuration in said display, anda fourth transistor, said fourth transistor directly coupled to said third transistor, said second transistor, the one of said Organic Light Emitting Diodes, and the one of said Pulse Width Modulation signal generators, wherein a gate of said fourth transistor is directly coupled to a gate of the third transistor, said fourth transistor operable to further control said light emission of said Organic Light Emitting Diode in cooperation with the third transistor.