Auto-calibrating Gamma Correction Circuit for AMOLED Displays
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Solution Overview
Problem
Existing OLED microdisplay driver circuits face challenges in miniaturization due to nonlinear voltage to luminance behavior caused by manufacturing variability and operational conditions, such as temperature changes, which affect gamma correction and pixel uniformity.
Innovation Solution
An adaptive gamma correction circuit using a spare OLED diode as a reference device, operating in reverse mode, replicates the inverse IV characteristic to generate an output voltage signal that compensates for temperature and process variability, ensuring a linear input signal to output current relationship.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If voltage mode driving is used to miniaturize pixel cells, then pixel area is reduced and manufacturing cost decreases, but gamma correction accuracy deteriorates due to nonlinear voltage to luminance behavior
Solution Approach 1:
The patent dynamically adjusts the gamma correction parameters based on detected temperature and process variability conditions. The circuit modifies the voltage to luminance transfer characteristics in real-time to compensate for environmental changes, maintaining accurate gamma correction while operating in voltage mode with miniaturized pixels.
Solution Approach 2:
The patent uses a reference OLED pixel that replicates the electrical and thermal characteristics of the display pixels. This reference pixel serves as a template for measuring and compensating gamma variations across the display, enabling accurate correction without requiring larger pixel structures.
2Stability of the object's composition
If long channel transistors are used to generate output current in current mode, then pixel to pixel uniformity improves, but pixel cell area increases and manufacturing cost increases
Solution Approach 1:
The patent inverts the traditional driving approach by using voltage mode instead of current mode, and employs a reference pixel that operates in reverse mode to characterize the OLED response. This inversion allows compact transistor design while maintaining uniformity through dynamic compensation algorithms.
Solution Approach 2:
The patent replaces the mechanical approach of using physically large long-channel transistors with an electrical/electronic solution involving dynamic voltage adjustment and reference-based compensation. This substitution enables uniformity control through software/firmware algorithms rather than relying on large transistor geometries.
3Device complexity
If voltage mode operation is implemented to reduce pixel size, then device complexity decreases and manufacturing simplifies, but gamma curve variability increases due to temperature and process changes
Solution Approach 1:
The patent implements a feedback mechanism where the reference OLED pixel continuously measures the actual voltage to luminance response under current operating conditions. This measurement feeds back to adjust the gamma correction parameters, automatically compensating for temperature and process variability without increasing pixel circuit complexity.
Solution Approach 2:
The patent performs preliminary characterization of the OLED response using the reference pixel before actual display operation. This preliminary measurement establishes the baseline gamma curve for the current conditions, allowing pre-computation of correction parameters that are then applied during normal operation to maintain stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate gamma function correction independent of manufacturing and operational conditions, allowing for miniaturization of pixel structures and improved image quality, reducing costs and variability across OLED microdisplays.
Implementation Method 1
The relationship between the current in an OLED diode and the voltage across the diode is known as its IV characteristic. The OLED current, I, is equal to a non-linear function of the voltage across the diode, V, and can be expressed in general as I=f(V).
Implementation Method 2
The processing means includes an operational amplifier having first and second inputs and an output. The first input of the operational amplifier is connected to receive the input voltage signal.
Implementation Method 3
A first transistor with a control electrode and an output circuit is included as part of the first processing means. The control electrode of the first transistor is connected to the output of the operational amplifier.
Data Source
AI summary
A drive circuit is provided for an OLED in a pixel array. The circuit includes input voltage signal receiving means. Output voltage signal generating means are operably connected to the pixel diode. Means are provided for processing the input voltage signal to replicate the inverse IV characteristic of the pixel diode, to form the output voltage signal.