Display Pixel Compensation for Threshold Voltage Drift
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Solution Overview
Problem
In flat-panel displays, variations in threshold voltages of driving transistors and operation voltages of luminescence elements lead to inconsistent brightness across pixels, even when receiving the same image signal or driving current, due to manufacturing differences and long-term use.
Innovation Solution
A display system comprising a scan driver, data driver, and pixels with specific control units that manage node levels to compensate for threshold voltage and operation voltage drifts, using a switching unit, driving unit, luminescence unit, storage unit, and controlling unit to generate a driving current that is independent of the threshold voltage and to light the luminescence unit based on a controlled voltage difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If driving transistors with different threshold voltages receive the same image signal, then the driving transistors generate different driving currents, but this causes the luminescence elements to display different brightness
Solution Approach 1:
The patent applies preliminary action by measuring and storing the threshold voltage of each driving transistor before normal operation. During a compensation period before the display period, the system determines the threshold voltage of each driving transistor and stores it in a storage unit. This preliminary measurement allows the system to compensate for threshold voltage variations during normal operation, ensuring consistent brightness across pixels despite manufacturing variations.
2Duration of action of stationary object
If luminescence elements operate for long time, then the operation voltage drifts, but this causes different luminescence elements to display different brightness when receiving the same driving current
Solution Approach 1:
The patent implements feedback by continuously monitoring the operation voltage of luminescence elements and adjusting the driving current accordingly. During the display period, the system measures the operation voltage of each luminescence element and uses this feedback information to compensate for voltage drift. This feedback mechanism ensures that brightness consistency is maintained over long operational periods despite voltage drift in the luminescence elements.
3Reliability
If the system compensates for threshold voltage and operation voltage drifts, then brightness consistency is improved, but the device complexity increases
Solution Approach 1:
The patent applies merging by integrating the compensation functions into the existing pixel structure. The compensation unit, storage unit, and control circuits are merged with the driving transistor and luminescence element within each pixel. This integration allows the system to achieve voltage compensation and brightness consistency without adding significant external complexity, as the compensation mechanisms are embedded within the pixel architecture itself.
Data Source
AI summary
A display system including at least one pixel is disclosed. The pixel includes a switching unit and a controlling unit. The switching unit controls a level of a first node. The controlling unit controls a level of a second node. During a first period, the level of the first node equals to a first reference level and the level of the second node equals to a second reference level. During a second period, the level of the first node equals to a third reference level and the voltage difference between the first and the second nodes equals to a threshold voltage of a driving unit. During a third period, the level of the first node equals to a data signal. During a fourth period, the driving unit lights a luminescence unit according to the voltage difference between the first and the second nodes.