P-type TFT OLED Pixel Circuit Hybrid Compensation
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Solution Overview
Problem
Current organic light emitting displays face luminance deviations due to non-uniform electrical properties of P-type driving Thin Film Transistors (TFTs), which existing compensation methods have not adequately addressed, particularly for P-type TFTs.
Innovation Solution
A hybrid compensation method for P-type TFTs is implemented, using a specific pixel structure with P-type TFTs and a driving method that includes initialization, programming, compensation, and emission periods to adjust voltage signals and connect/disconnect components to compensate for threshold voltage and mobility deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an internal compensation method is used to compensate for electrical property deviation of driving TFTs, then the compensation process is simple and tact time is short, but the pixel circuit becomes complicated
Solution Approach 1:
The pixel circuit uses dynamic control of switch TFTs (first, second, and third switch TFTs) to enable different connection configurations during different time periods (initialization, programming, compensation, emission). This dynamic switching allows the same circuit to perform multiple functions without requiring permanently complex circuitry, resolving the contradiction between simple compensation process and short tact time versus complicated pixel circuit
2Device complexity
If an external compensation method is used to measure sensing voltage and modulate image data, then the pixel circuit is simple, but the compensation process is complicated and tact time is long
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the driving TFT's electrical properties are sensed through the connection of gate node and drain node via the second switch TFT. The sensed information (sensing voltage) is used to adjust the gate-source voltage of the driving TFT through the storage capacitor, compensating for threshold voltage and mobility deviations. This internal feedback loop simplifies the overall system by eliminating external compensation circuits while maintaining short tact time
3Manufacturing precision
If a hybrid compensation method is implemented for P-type driving TFTs, then both threshold voltage and mobility deviations can be compensated, but a suitable pixel structure must be developed
Solution Approach 1:
The pixel circuit is segmented into distinct functional blocks: a driving TFT for current control, a storage capacitor for voltage holding, and three switch TFTs for different operational phases. This segmentation allows each component to perform its specific function efficiently - the driving TFT controls luminance, the storage capacitor maintains gate voltage, and the switch TFTs enable sequential operations. The segmented structure achieves hybrid compensation capability without requiring overly complex integrated circuits
4Measurement precision
If the gate node and drain node are connected to compensate for electrical property deviation, then compensation accuracy is improved, but the connection control becomes more complex
Solution Approach 1:
The connection between gate node and drain node is performed periodically through the second switch TFT during specific time periods (initialization period and compensation period) rather than continuously. This periodic connection allows sensing voltage measurement and compensation to occur at predetermined moments in the display refresh cycle, achieving accurate electrical property compensation without requiring complex continuous control mechanisms. The periodic action is synchronized with the display timing to ensure proper 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
This approach effectively compensates for luminance deviations by accurately adjusting driving currents, improving luminance uniformity and reducing compensation time, while maintaining a streamlined process.
Implementation Method 1
When a driving voltage is applied to the anode electrode and the cathode electrode, holes passing through the hole transport layer HTL and electrons passing through the electron transport layer ETL move to the light emitting layer EML and form excitons. As a result, the light emitting layer EML generates visible light.
Data Source
AI summary
Disclosed is an organic light emitting display including: a display panel on which a plurality of gate lines, a plurality of data lines, and a plurality of pixels are arranged, each pixel including an organic light emitting diode (OLED); a gate driving circuit connected to the pixels through the gate lines; and a data driving circuit connected to the pixels through the data lines, wherein each of the pixels comprises: a driving thin film transistor (TFT); a first switch TFT; a second switch TFT; a third switch TFT; and a storage capacitor, and wherein the first to third TFTs and the driving TFT are P-type TFTs.