Active Matrix Display Device Transistor Characteristic Compensation
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Solution Overview
Problem
Display brightness non-uniformity in active matrix organic electroluminescence (EL) displays due to initial variation and fluctuation of driving transistor characteristics over time, leading to inconsistent luminance across the display surface.
Innovation Solution
A display device with a measurement circuit that calculates and stores data on electron mobility and threshold values for each pixel circuit, using a constant current supply and A/D conversion to generate a gradation voltage that compensates for transistor characteristic changes, ensuring consistent current flow through emissive elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If active matrix driving with basic pixel circuits is used, then driving efficiency and response speed are improved, but display brightness non-uniformity occurs due to transistor characteristic variation
Solution Approach 1:
The patent applies preliminary action by measuring and storing the threshold voltage characteristics of each driving transistor before normal display operation. The measurement circuit quantizes the threshold voltage during a calibration period, and this pre-acquired data is then used to correct display brightness non-uniformity during actual operation, thereby eliminating the need for real-time adjustments while maintaining uniformity.
Solution Approach 2:
The patent implements feedback by using the measured threshold voltage characteristics of each transistor to generate corrected display data. The measurement circuit provides feedback information about transistor variations, and this feedback is used to adjust the driving signals accordingly, compensating for individual transistor differences and achieving uniform display brightness across all pixels.
2Device complexity
If transistor characteristics are not compensated, then device complexity is reduced, but display brightness non-uniformity increases
Solution Approach 1:
The patent applies segmentation by separating the display system into two functional parts: a measurement circuit for characterizing transistor properties and a normal display circuit for image output. The measurement circuit is used only during calibration to acquire threshold voltage data, which is then stored and applied during normal operation, allowing the main display circuit to remain simple while achieving brightness uniformity.
Solution Approach 2:
The patent implements self-service by enabling each pixel's driving transistor to be individually characterized and compensated. The measurement circuit automatically measures and stores the threshold voltage of each transistor, and this self-acquired information is used to correct display non-uniformity without requiring external calibration equipment or complex real-time control systems.
3Manufacturing precision
If threshold voltage measurement and compensation is implemented, then display brightness uniformity is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies merging by integrating the measurement circuit functionality into the existing pixel circuit structure. The measurement circuit uses the same transistor and capacitor elements already present in the pixel, combining the characterization and display functions in a unified circuit design, thereby minimizing additional complexity while achieving brightness uniformity compensation.
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
Significantly reduces display brightness non-uniformity by correcting for initial variations and long-term fluctuations in transistor characteristics, maintaining consistent luminance across the display.
Implementation Method 1
an A/D converter to which there is inputted an output voltage of the constant current supplying circuit and that A/D-converts the voltage
Data Source
AI summary
A display device of active matrix type allows reducing display brightness non-uniformity that is caused by initial variation and fluctuation over time in a driving transistor for emissive elements in pixel circuits. The display device includes pixel circuits, a measurement circuit and a gradation voltage supplying circuit. Each pixel circuit includes the driving transistor and an input circuit. The measurement circuit includes a constant current supplying circuit for generating and supplying one or more constant currents to the input circuit of the pixel circuits in a time division manner. The measurement circuit A/D-converts output voltages of the constant current supplying circuit and calculates data relating to electron mobility and threshold value of the driving transistor. The gradation voltage supplying circuit supplies to the pixel circuits a corrected gradation voltage, which is data corrected on the basis of data calculated from the measurement circuit.