OLED Driving Transistor Threshold Voltage Compensation Circuit
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Solution Overview
Problem
The threshold voltage of driving thin film transistors (TFTs) in organic light emitting diode (OLED) display devices can shift, leading to variations in current supply to pixels, resulting in uneven luminance despite the same data voltage being applied, as the current depends on the threshold voltage of each pixel.
Innovation Solution
The implementation of a pixel structure that includes a driving TFT, an organic light emitting diode, a first TFT, an initialization control circuit, and capacitors, which allow for real-time sensing and compensation of the threshold voltage within the pixel, ensuring consistent voltage levels across nodes and thus consistent luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional diode-connected threshold voltage compensation structure is used, then the threshold voltage can be sensed during the sensing period, but the gate node and drain node are in a floating state that makes them susceptible to voltage changes, preventing accurate sensing when the threshold voltage shifts to negative values
Solution Approach 1:
The patent introduces a sensing transistor as an intermediary component between the driving transistor's gate and drain nodes. This sensing transistor controls the connection state, allowing the gate and drain to be connected during the sensing period while preventing floating state issues. The intermediary enables accurate threshold voltage sensing even when the threshold voltage shifts to negative values by actively managing the node connection rather than leaving it in a passive floating state.
2Device complexity
If the gate node and drain node are left in a floating state during threshold voltage sensing, then the structure remains simple, but the nodes are easily affected by voltage changes and cannot accurately sense threshold voltage when it shifts to negative values
Solution Approach 1:
The patent applies dynamics by making the connection between gate and drain nodes controllable rather than static. The sensing transistor dynamically adjusts the connection state based on the sensing period requirements. During sensing, the transistor enables connection to establish a defined voltage relationship, while during other periods it can be disconnected. This dynamic control maintains reasonable structural simplicity while achieving accurate threshold voltage sensing across different threshold voltage conditions.
Data Source
AI summary
The organic light emitting diode display device comprising a display panel a plurality of pixels arranged in a matrix form, each of the pixels comprising: a driving TFT including a gate electrode coupled to a first node, a source electrode coupled to a second node, and a drain electrode coupled to a high-potential voltage line; an organic light emitting diode including an anode coupled to the second node and a cathode coupled to a low-potential voltage line; a first TFT supplying a data voltage to the first node in response to a scan signal; a initialization control circuit initializing the first node to a first reference voltage and the second node or the third node to a second reference voltage in response to a initialization signal and an emission signal; and capacitors.