Compensation Pixel Circuit for AMOLED Display Threshold Voltage Offset
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Solution Overview
Problem
In large-size AMOLED displays, the non-uniformity and instability of thin film transistors (TFTs) lead to threshold voltage offsets and signal voltage attenuation, causing non-uniform current driving and reduced display effects, which existing compensation circuits fail to adequately address.
Innovation Solution
A compensation pixel circuit with a resetting module that discharges the gate voltage of the driving transistor to the threshold voltage of the OLED, independent of the bias voltage, and includes a data voltage writing module and light emitting control module to ensure current stability, thereby compensating for threshold voltage offsets and signal voltage attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional compensation circuits are used to address threshold voltage offset, then threshold voltage compensation is improved, but signal voltage attenuation on gate signal lines is not compensated, resulting in non-uniform current driving
Solution Approach 1:
The patent divides the compensation function into two separate modules: a threshold voltage compensation module and a signal voltage attenuation compensation module. This segmentation allows each module to independently address its specific compensation task, ensuring both threshold voltage offset and signal voltage attenuation are compensated without interfering with each other, thereby achieving uniform current driving across the display.
Solution Approach 2:
The patent introduces an intermediary compensation signal that carries information about signal voltage attenuation. This intermediary signal is generated based on the gate signal line characteristics and is used to adjust the driving current, effectively compensating for the voltage attenuation without requiring direct measurement of the attenuated voltage at each pixel.
2Device complexity
If gate voltage is not reset between frames, then circuit operation is simplified, but frame-to-frame signal influence accumulates, reducing display stability
Solution Approach 1:
The patent implements a reset operation that is performed preliminarily at the beginning of each frame period. This preliminary reset action clears any accumulated signal influence from the previous frame before the new frame's compensation and display operations begin, ensuring that each frame starts with a clean electrical state and preventing frame-to-frame signal accumulation that would degrade display stability.
3Area of stationary object
If bias voltage is applied for long time to drive large-size AMOLED, then display area coverage is improved, but TFT stability deteriorates due to prolonged bias stress
Solution Approach 1:
The patent implements periodic reset operations that occur at the beginning of each frame period. This periodic action temporarily removes or resets the gate voltage, interrupting the continuous bias stress on the TFTs. By periodically refreshing the electrical state of the TFTs, the cumulative bias stress is reduced, preventing stability deterioration while still maintaining large display area coverage.
Data Source
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AI summary
There are provided a compensation pixel circuit and a display apparatus. The compensation pixel circuit comprises an organic light emitting diode (D1) and a driving transistor (M1), a first terminal of the driving transistor (M1) being connected to an anode of the organic light emitting diode (D1). The compensation pixel circuit further comprises: a resetting module, a data voltage writing module, a light emitting control module and a switching module. The resetting module includes a capacitor (C1) whose first terminal is connected to a gate of the driving transistor (M1) and configured to make the gate of the driving transistor (M1) discharge so that a gate voltage is reduced to a magnitude of a threshold voltage of the organic light emitting diode (D1). The data voltage writing module is configured to discharge at the gate of the driving transistor (M1) so as to connect a data voltage to a second terminal of the driving transistor (M1) after the gate voltage is made reduced to the magnitude of the threshold voltage of the organic light emitting diode (D). The light emitting control module is configured to connect a source of the driving transistor (M1) and a second terminal of the capacitor (C1) to an operating voltage at a high level after data voltage writing is completed. The switching module is configured to disconnect the driving transistor (M1) from the organic light emitting diode (D1) when the data voltage is connected to the second terminal of the driving transistor (M1). The compensation pixel circuit can compensate for the threshold voltage offset, and reduce the influence of signals from frame to frame greatly.