Pixel Driver Circuit Threshold Voltage Compensation for AMOLED Uniformity
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Solution Overview
Problem
AMOLED displays face non-uniformity in luminance due to variances in threshold voltage of driving transistors, leading to the Mura phenomenon and image sticking, which complicates manufacturing and affects display quality.
Innovation Solution
A pixel driving circuit with a data line, gate line, power supply lines, reference signal line, storage capacitor, reset unit, data writing unit, compensating unit, and light emitting control unit, where the threshold voltage of the driving transistor is compensated by loading the first power supply voltage and threshold voltage into the storage capacitor, allowing the driving transistor to control current amplitude based on data voltage, threshold voltage, and reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LTPS TFTs or Oxide TFTs are used to achieve higher mobility and stable characteristics, then the driving capability and display quality are improved, but non-uniformity in electrical parameters (threshold voltage, mobility) occurs due to crystallization process limitations, resulting in Mura phenomenon
Solution Approach 1:
The patent applies preliminary action by compensating for the threshold voltage of the driving transistor before the light emitting device is driven. The compensation circuit pre-calculates and stores the threshold voltage value in a storage capacitor, so that when the device is operated, the threshold voltage effect is already accounted for, eliminating Mura phenomenon without requiring perfect uniformity in the TFT manufacturing process.
Solution Approach 2:
The patent introduces a compensation circuit as an intermediary between the driving transistor and the light emitting device. This intermediary circuit measures the threshold voltage of the driving transistor and uses it to adjust the driving signal, thereby mediating the effect of threshold voltage variations and achieving uniform display without modifying the TFT manufacturing process itself.
2Device complexity
If the threshold voltage of the driving transistor is not compensated, then the pixel circuit structure remains simple, but non-uniformity in display luminance occurs due to threshold voltage variances among different transistors
Solution Approach 1:
The compensation is performed in advance during the initialization phase. The compensation circuit operates before the normal display operation to determine and store the threshold voltage value, so that the actual display operation can proceed with already-compensated signals, minimizing the impact on overall system complexity while achieving luminance uniformity.
Solution Approach 2:
The patent merges the compensation function with the existing pixel circuit components. The compensation circuit shares transistors and capacitors with the driving circuit, combining multiple functions (threshold voltage compensation, data storage, and driving) into a unified structure, thereby reducing the overall device complexity compared to having completely separate compensation and driving circuits.
3Manufacturing precision
If existing pixel circuits are designed with complex structures to remove threshold voltage effects, then display luminance uniformity is improved, but the good manufacturing production rate decreases
Solution Approach 1:
The patent extracts the threshold voltage parameter from the complex circuit operations and handles it separately through a dedicated compensation circuit. By isolating the threshold voltage measurement and compensation function, the main pixel circuit can operate with simpler, faster structures while still achieving luminance uniformity, thus improving manufacturing production rate without sacrificing display quality.
Solution Approach 2:
The threshold voltage compensation is performed as a preliminary step before normal display operation. This pre-compensation approach allows the use of simpler, faster circuits during actual display operation, improving manufacturing throughput while still achieving the luminance uniformity that would otherwise require complex real-time correction circuits.
Data Source
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AI summary
A pixel driving circuit and a driving method thereof, an array substrate and a display apparatus are provided. The pixel driving circuit comprises a data line (Data), a gate line (Gate), a first power supply line (ELVDD), a second power supply line (ELVSS), a reference signal line (ref), a light emitting device (D), a driving transistor (T7), a storage capacitor (C1), a reset unit, a data writing unit, a compensating unit and a light emitting control unit. The pixel driving circuit can compensate and remove non-uniformity in displaying caused by variances in threshold voltage among driving transistors.