AMOLED Pixel Circuit Compensation for Threshold Voltage Drift
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Solution Overview
Problem
The luminance uniformity of AMOLED display panels is affected by the drift of the threshold voltage of the driving transistor, and electric leakage in the switch transistor leads to uneven light emission due to changes in the driving voltage of the gate of the driving transistor.
Innovation Solution
A pixel circuit comprising an operation unit, a storage module, a driving module, a compensation module, and a control module, where the compensation module initializes and charges the storage module with a threshold voltage during the data writing and charging phase, and the control module discharges the storage module to the operation unit during the operation phase to compensate for the drift of the threshold voltage, thereby maintaining consistent luminance and addressing voltage changes caused by leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel circuit with a driving transistor and storage capacitor is used, then the circuit structure is simple, but the threshold voltage drift of the driving transistor causes luminance non-uniformity
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: a driving transistor module for controlling OLED operation, a compensation module for threshold voltage compensation, and a storage module for voltage retention. This segmentation allows each module to perform its specific function optimally, with the compensation module specifically addressing the threshold voltage drift issue that causes luminance non-uniformity.
Solution Approach 2:
A compensation transistor is introduced as an intermediary element between the data writing path and the OLED. This compensation transistor works in conjunction with the storage capacitor to compensate for the threshold voltage drift of the driving transistor, thereby maintaining luminance uniformity without significantly increasing overall circuit complexity.
2Ease of operation
If the switch transistor is used to control data writing, then the writing function is achieved, but electric leakage in the switch transistor causes voltage changes and uneven light emission
Solution Approach 1:
The compensation module implements a feedback mechanism where the compensation transistor adjusts its conduction state based on the voltage changes caused by leakage current in the switch transistor. This feedback loop compensates for the voltage drift at the gate of the driving transistor, maintaining consistent OLED brightness despite switch transistor leakage.
Solution Approach 2:
The compensation for switch transistor leakage is performed in advance during the data writing and holding phases. By pre-compensating for the expected voltage drop due to leakage, the circuit ensures that the driving transistor receives the correct gate voltage throughout the OLED emission period, preventing luminance non-uniformity.
Data Source
AI summary
The present invention provides a pixel circuit and a driving method thereof, an array substrate and a display device. The pixel circuit includes: an operation unit, a storage module, a driving module, a compensation module and a control module; in an initialization phase, the compensation module and the driving module are initialized under the control of the first power supply; in a data writing and charging phase, the data signal input terminal charges the storage module via the compensation module and the driving module, such that a threshold voltage corresponding to the driving module is inputted into a voltage difference across two terminals of the storage module; and in an operation phase, the control module is switched on, and the storage module discharges to the operation unit via the driving module to allow the operation unit to emit light.