Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The existing pixel driving circuits for AMOLED displays face issues with uniform brightness across different pixel points due to shifting threshold voltages of driving transistors, affecting the overall display effect.
Innovation Solution
A pixel driving circuit with a specific configuration including a driving transistor, storage capacitor, and multiple switch transistors controlled by different scan signals, which charges and discharges the capacitor to maintain a voltage difference and applies a jump signal to compensate for threshold voltage variations, ensuring consistent operating current and brightness across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 2T1C pixel driving circuit is used, then the circuit structure is simple, but the threshold voltage variations of driving transistors cause non-uniform brightness across different pixel points
Solution Approach 1:
The pixel driving circuit is segmented into multiple functional modules: a first switching transistor for charging, a second switching transistor for discharging, a third switching transistor for compensation, and a storage capacitor. Each module performs a specific function in the threshold voltage compensation process, allowing the system to address brightness uniformity issues while maintaining manageable circuit complexity
Solution Approach 2:
The circuit performs preliminary charging of the storage capacitor to a first voltage level before the actual display operation. This preliminary action establishes a baseline voltage that enables subsequent compensation for threshold voltage variations, ensuring that brightness uniformity is maintained across all pixel points before the display frame begins
2Illumination intensity
If the storage capacitor is charged to a high voltage level, then the operating current is sufficient for bright display, but the threshold voltage shift effects become more pronounced causing brightness non-uniformity
Solution Approach 1:
The circuit dynamically changes the voltage parameter of the storage capacitor through a two-stage process: first charging to a high voltage level for sufficient operating current, then adjusting to a compensated voltage level that accounts for threshold voltage shifts. This parameter change ensures both adequate brightness and uniformity across different pixel points
Solution Approach 2:
The circuit incorporates a feedback mechanism where the threshold voltage variations are detected through the switching transistor operations, and the storage capacitor voltage is adjusted accordingly. The third switching transistor enables this feedback by allowing the circuit to sense and compensate for threshold voltage shifts, maintaining brightness uniformity
3Manufacturing precision
If multiple switch transistors are added for threshold voltage compensation, then brightness uniformity is improved, but the circuit complexity increases
Solution Approach 1:
The switching transistors in the circuit are designed to perform multiple functions: the first switching transistor serves both as a charging switch and a signal transmission element; the second switching transistor functions as both a discharging switch and a compensation element. This multi-functionality reduces the need for additional dedicated compensation components, balancing brightness uniformity improvement with circuit complexity
Solution Approach 2:
The charging function, discharging function, and threshold voltage compensation function are merged into a coordinated sequence of operations using the same set of switching transistors and storage capacitor. By combining these functions into a unified circuit architecture rather than separate modules, the patent achieves brightness uniformity compensation while limiting the increase in circuit complexity
Data Source
AI summary
There is provide a pixel driving circuit, and the pixel driving circuit comprises a driving transistor (DTFT), organic light emitting diode (OLED) connected with the driving transistor (DTFT), a first to a fourth switch transistors (T1˜T4) and a storage capacitor (Cs). There is provide a driving method for the pixel driving circuit, and it comprises charging the storage capacitor (Cs); discharging the storage capacitor (Cs), so that a voltage difference exists between voltages at two terminals of the storage capacitor (Cs); changing the data voltage (Vdata), so that the voltages at the two terminals of the storage capacitor (Cs) vary as same as variations in the data voltage (Vdata); and driving the organic light emitting diode (OLED) to emit light. The above pixel driving circuit and the driving method can realize a compensation on the threshold voltage for the driving voltage of the driving transistor (DTFT), and in turn an effect on operating current of the organic light emitting diode (OLED) caused by the threshold voltage is eliminated. There is also provided a display apparatus comprising the above pixel driving circuit.