Low power active matrix display
AssigneeStore Electronic Systems
InventorCharles F. Neugebauer
Life of this patent
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Abstract
Described herein are systems and methods for stress avoidance and stress compensation in low power Liquid Crystal Displays (LCDs). In an exemplary embodiment, two or more transistors in series are used to hold charge on an LCD pixel. To avoid negative stress on the transistors, the transistors are alternately driven to an “off” state so that no one transistor sees a long “off” time. In another embodiment, stress on transistors of a display circuit are measured and controlled negative stress is applied to the transistors to compensate for the measured stress.
Claims12
A method of operating a display circuit, wherein the display circuit comprises a plurality of pixel circuits, each pixel circuit comprising at least two transistors in series connected to a pixel of a Liquid Crystal Display (LCD), the method comprising:
- performing frame loading operations, wherein each frame loading operation updates a display image of the LCD;
- and
- between frame loading operations, for each pixel circuit, holding a charge of the corresponding LCD pixel,
- wherein to hold a charge of a LCD pixel of a pixel circuit between frame loading operations a negative gate bias voltage is alternately applied to the transistors of said transistors in series of the pixel circuit, and when the negative gate bias voltage is applied to a least one transistor of said transistors in series of the pixel circuit, a positive gate bias voltage is applied to the at least one other transistor of said transistors in series of the pixel circuit, thereby applying a positive stress to compensate for negative stress accumulated on said at least one other transistor of said transistors in series when the negative gate bias is applied,
- wherein said negative gate bias voltage and positive gate bias voltage are alternately applied between frame loading operations to each one of said transistors in series.
A display circuit for a pixel array, comprising:
- a row and column driver;
- and
- a plurality of pixel circuits coupled to the row and column driver, wherein each pixel circuit comprises at least two transistors in series connected to a pixel of a Liquid Crystal Display (LCD);
- wherein the row and column driver is configured to load a frame onto the LCD by applying positive voltages to the transistors of said transistors in series of the pixel circuits to form conduction paths to the pixels of the LCD and sending charges to the pixels through the conduction paths, and
- between frame load operations, for each pixel circuit, to alternately apply a negative gate bias voltage to one of the transistors of said transistors in series of the pixel circuit to hold the charge of the corresponding LCD pixel, and when the negative gate bias voltage is applied to a least one transistor of said transistors in series of the pixel circuit, a positive gate bias voltage is applied to the at least one other transistor of the pixel circuit, thereby applying a stress reducing voltage to the at least one other transistor of said transistors in series of the pixel circuit,
- wherein said negative gate bias voltage and positive gate bias voltage are alternately applied between frame loading operations to each one of said transistors in series.
Dependencies are inferred from the claim text.