OLED Data Driving Circuit Brightness Compensation
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Solution Overview
Problem
Light emitting displays face challenges in achieving uniform brightness due to variations in transistor threshold voltage and electron mobility, which affect the consistency of image display.
Innovation Solution
A data driving circuit that includes a current sink, voltage generator, digital-analog converter, and switching unit to set gray scale voltages based on a compensation voltage, ensuring that each pixel receives a current equal to or greater than the minimum required for maximum brightness, thereby compensating for variations in threshold voltage and electron mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard pixel circuits are used without compensation, then device complexity is low, but brightness uniformity deteriorates due to transistor characteristic variations
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the threshold voltage of the driving transistor is detected and stored in a storage capacitor. This stored threshold voltage is then fed back to compensate for variations in subsequent operations, ensuring uniform brightness across all pixels despite manufacturing variations in transistor characteristics.
Solution Approach 2:
The invention changes the operating parameters of the pixel circuit by dynamically adjusting the gate voltage based on the detected threshold voltage. By modifying the voltage parameters in response to measured transistor characteristics, the circuit compensates for variations and maintains consistent brightness output across different pixels.
2Manufacturing precision
If compensation for threshold voltage variations is implemented, then brightness uniformity improves, but measurement and control complexity increases
Solution Approach 1:
The pixel circuit performs self-measurement of its own threshold voltage using dedicated test transistors and measurement circuits. The circuit automatically detects its characteristic parameters and stores this information without external intervention, enabling automatic compensation while minimizing the complexity of external measurement systems.
Solution Approach 2:
The invention introduces intermediary measurement transistors and test circuits that facilitate the detection of threshold voltage variations. These intermediary components act as mediators between the main driving transistors and the measurement system, simplifying the overall measurement and control process while enabling precise compensation.
3Measurement precision
If multiple test modes are implemented for different scan directions, then measurement accuracy improves, but device complexity and operation time increase
Solution Approach 1:
The pixel circuit performs preliminary measurements of threshold voltage in both scan directions during manufacturing or initialization. These pre-measured values are stored and used for compensation in subsequent operations, eliminating the need for repeated time-consuming measurements during normal display operation while maintaining high measurement accuracy.
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
The solution enables the display of images with uniform brightness by compensating for variations in transistor characteristics, ensuring consistent light emission across all pixels.
Implementation Method 1
Light emitting displays may display images using organic light emitting diodes (OLEDs) that generate light when electrons and holes re-combine
Data Source
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AI summary
A data driving circuit for driving pixels of a light emitting display to display images with uniform brightness may include a current sink that is capable of receiving, via a data line, a predetermined current from a pixel to enable the data driving circuit to generate a compensation voltage for the pixel. The compensation voltage may compensate for variations among the pixels of the display. Variations among the pixels may result from different electron mobilities and/or threshold voltages of transistors included in the pixels. The value of the predetermined current may be equal to or higher than a value of a minimum current employable by the pixel to emit light of maximum brightness. The maximum brightness of the pixel may correspond to a brightness emitted by the pixel when a highest one of a plurality of set gray scale voltages is applied to the pixel.