AMOLED Pixel Circuit Compensation for Threshold Voltage Drift
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Solution Overview
Problem
In AMOLED display devices, variations in threshold voltage and other parameters among thin film transistors lead to uneven luminance due to capacitive coupling effects, causing inaccurate compensation and errors in extracting and storing threshold voltage.
Innovation Solution
A compensation method for pixel circuits that includes a data writing circuit, a driving circuit, a sensing circuit, and an energy storage circuit, where the sensing circuit periodically acquires voltage at a second node and adjusts the data voltage output to achieve an ideal charging curve, compensating characteristic parameters by using the adjusted energy storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional pixel circuit with capacitor Cst and control transistors is used for compensation, then threshold voltage variations can be compensated, but capacitive coupling effects cause inaccurate extraction and storage of threshold voltage, leading to compensation errors
Solution Approach 1:
The patent extracts the harmful capacitive coupling effect from the system by separating the sampling switch control from the data writing circuit operation. The sampling switch is controlled independently with a dedicated control signal that ensures it remains off during the data writing phase, thereby eliminating the capacitive coupling effect that was inherent in the conventional integrated circuit structure.
Solution Approach 2:
The patent applies preliminary action by pre-configuring the sampling switch to be off before data writing begins. The control circuit generates the sampling control signal in advance to ensure the sampling switch is in the correct state (off) before the data writing circuit starts operating, preventing the capacitive coupling effect from occurring in the first place.
2Stability of the object's composition
If the control transistor between data writing circuit and driving transistor is turned off during charging, then capacitive coupling is reduced, but the charging curve becomes non-linear and deviates from the ideal straight line
Solution Approach 1:
The patent applies dynamics by making the sampling switch state controllable rather than fixed. The sampling switch can be dynamically adjusted between on and off states based on the operational phase: off during data writing to prevent capacitive coupling, and on during sampling to enable threshold voltage extraction. This dynamic control resolves the contradiction between maintaining charging linearity and ensuring measurement accuracy.
3Measurement precision
If the capacitance of the parasitic capacitor is reduced by process, then the charging curve improves from L3 to L2, but the capacitance cannot become 0, so errors can only be reduced but not eliminated
Solution Approach 1:
The patent converts the harmful capacitive coupling effect into a beneficial controlled state by using the sampling switch to completely disconnect the parasitic capacitor from the circuit during data writing. Instead of merely reducing the capacitance value through difficult process changes, the solution transforms the harmful continuous coupling into a controlled discrete connection that can be completely eliminated when needed, achieving ideal charging linearity without manufacturing complexity.
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 method ensures accurate reflection of driving transistor parameters, achieving a high-linear and accurate charging curve that eliminates the effects of threshold voltage drift, thereby improving luminance uniformity and gray-scale accuracy.
Implementation Method 1
acquiring a voltage of the second node by the sensing circuit
Implementation Method 2
a compensation mechanism that is implemented by a capacitor Cst
Implementation Method 3
adjusting a data voltage outputted by the data writing circuit to the first node based on the acquired voltage of the second node
Implementation Method 4
a light emitting element EL, wherein the first terminal of the driving circuit is a control terminal of the light emitting element EL
Data Source
AI summary
The present disclosure provides a compensation method for pixel circuit, a pixel circuit, and a display device. The pixel circuit includes a data writing circuit, a driving circuit, a sensing circuit, and an energy storage circuit, the compensation method includes: in a charging stage, acquiring a voltage of the second node by the sensing circuit, adjusting a data voltage outputted by the data writing circuit to the first node based on the acquired voltage of the second node, and charging the energy storage circuit by using the adjusted data voltage; and in a compensation stage, compensating characteristic parameters of the driving circuit by the charged energy storage circuit.