OLED Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
In organic light emitting displays (OLEDs), maintaining consistent current flow through each pixel is challenging due to variations in threshold voltage caused by manufacturing processes and long-term operation of driving transistors, leading to non-uniform image display.
Innovation Solution
A pixel driving circuit is designed with a data line, scanning lines, enabling control line, power supply line, light emitting device, driving transistor, storage capacitor, resetting unit, data writing unit, and light emitting control unit, where the data writing unit writes the threshold voltage and data line voltage into the storage capacitor, and the light emitting control unit ensures the driving transistor connects to the power supply, compensating for threshold voltage variations to maintain consistent current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple pixel driving circuit is used, then device complexity is reduced, but current consistency through OLED pixels deteriorates due to threshold voltage variations
Solution Approach 1:
The patent applies preliminary action by measuring the threshold voltage of the driving transistor during a first period (programming phase) and storing this information in the storage capacitor before the light emitting period. This pre-measurement and storage of threshold voltage information allows the circuit to compensate for threshold voltage variations during normal operation, ensuring current consistency without requiring complex real-time adjustment mechanisms.
Solution Approach 2:
The patent implements feedback by using the stored threshold voltage information from the storage capacitor to adjust the gate voltage of the driving transistor during the light emitting period. The second period operation uses the stored threshold voltage to compensate for any drift or variation, creating a feedback loop that maintains current consistency through OLED pixels despite manufacturing variations and time-dependent changes.
2Device complexity
If threshold voltage variations are not compensated, then device complexity remains low, but image display uniformity deteriorates
Solution Approach 1:
The circuit performs preliminary measurement of the driving transistor's threshold voltage during the first period and stores this information in the storage capacitor. This pre-characterization of the transistor's electrical properties allows for subsequent compensation during the light emitting period, ensuring uniform image display across all pixels despite manufacturing variations in threshold voltage.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the gate voltage of the driving transistor based on the stored threshold voltage information. During the light emitting period, the circuit modifies the gate voltage parameter to compensate for threshold voltage variations, thereby maintaining consistent current flow and uniform image display quality across different pixels.
3Reliability
If real-time threshold voltage adjustment is implemented, then current consistency improves, but device complexity and operation time increase
Solution Approach 1:
The patent applies preliminary action by measuring and storing the threshold voltage information during a dedicated first period before the light emitting period. This pre-computation of threshold voltage data eliminates the need for complex real-time adjustment during normal operation, as the stored information can be directly used for compensation without requiring continuous measurement or complex calculation circuits.
Solution Approach 2:
The patent implements periodic action by dividing the operation into distinct time periods: a first period for measuring and storing threshold voltage information, and a second period for light emission using the stored information. This periodic separation of measurement and operation allows the circuit to maintain simplicity during the light emitting period while achieving current consistency through pre-computed threshold voltage compensation.
Data Source
AI summary
A pixel driving circuit, comprises: a line (Data), a first scanning line (Scan1), a second scanning line (Scan2), an enabling control line (Em), a power supply line (S), a light emitting device (D), a driving transistor (DTFT), a storage capacitor (C), a resetting unit (1), a data writing unit (2) and a light emitting control unit (3), and further discloses a pixel driving method, an array substrate and a display apparatus. The pixel driving circuit of the present disclosure solves the problem of non-uniformity of the threshold voltage caused by the manufacturing process and long-time operation of the pixel point driving transistor by means of compensating, so that the current flowing through each pixel point light emitting device is not affected by the threshold voltage, thereby finally ensuring the uniformity of the image display.