OLED Pixel Circuit Transistor Segmentation for Image Retention
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Solution Overview
Problem
OLED display devices face image retention issues due to current transient response characteristics and insufficient threshold voltage compensation for driving transistors, leading to reduced image quality.
Innovation Solution
A display device with pixel circuits that include a driving transistor, a light-emission control switch transistor, a threshold compensation switch transistor, and a data signal switch transistor, where the transistors of different conductivity types are controlled using specific control signals to provide appropriate threshold compensation and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit with basic threshold compensation is used, then the device complexity is low, but image retention occurs due to insufficient compensation for driving transistor threshold voltage fluctuations
Solution Approach 1:
The pixel circuit is segmented into multiple transistor components with different conductivity types (first conductivity type and second conductivity type). The switch transistor and compensation transistor are separated as distinct elements, each performing specific functions. This segmentation allows for more precise control of threshold voltage compensation while maintaining manageable circuit complexity through functional specialization.
Solution Approach 2:
The invention changes the conductivity type parameter of transistors within the pixel circuit. By using transistors of different conductivity types (N-type and P-type) for different functions (switching vs. compensation), the circuit achieves better threshold voltage compensation performance. This parameter variation enables the circuit to counteract threshold voltage fluctuations more effectively, reducing image retention.
2Reliability
If the pixel circuit uses transistors of the same conductivity type, then the circuit design is simpler, but the threshold voltage compensation effectiveness is reduced leading to image retention
Solution Approach 1:
The pixel circuit employs asymmetric transistor configuration where the switch transistor and compensation transistor have different conductivity types. This asymmetry is intentional and functional: the first transistor of the first conductivity type performs switching, while the second transistor of the second conductivity type performs threshold compensation. This asymmetric design optimizes the compensation effectiveness by leveraging the complementary characteristics of different conductivity type transistors.
3Reliability
If a longer compensation period is used, then the threshold voltage compensation is more effective, but the frame rate and productivity are reduced
Solution Approach 1:
The compensation transistor performs threshold voltage compensation in advance during the non-light-emission period or early in the frame cycle. By conducting the compensation action preliminarily, before the light-emission phase begins, the circuit ensures that threshold voltage fluctuations are corrected beforehand. This preliminary compensation eliminates the need for extended compensation periods during the active display phase, thereby maintaining high frame rates while achieving effective image retention reduction.
Data Source
AI summary
A light-emission control switch transistor and a threshold compensation switch transistor are transistors having different conductivity types. Gate potentials at the light-emission control switch transistor and the threshold compensation switch transistor are controlled using a first control signal. A gate potential at the data signal switch transistor is controlled using a second control signal. A control circuit selects rows sequentially. in a selected one of the rows, the light-emission control switch transistor is maintained off, the threshold compensation switch transistor is maintained on, and the data signal switch transistor is maintained off in a first period. In the selected row, the light-emission control switch transistor is maintained on, the threshold compensation switch transistor is maintained off, and the data signal switch transistor is maintained on in a second period after the first period.