OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Conventional organic light emitting display devices face issues with unequal threshold voltages and mobilities of driving transistors, leading to inconsistent pixel luminance and degradation over time, which affects the display of desired images.
Innovation Solution
The implementation of a pixel circuit with a second capacitor coupled to the gate electrode of a driving transistor and a current sinker to compensate for threshold voltage and mobility variations, as well as organic light emitting diode degradation, by sinking a current and supplying voltages that account for these changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a circuit that compensates for the threshold voltage of a driving transistor is added to each pixel, then the threshold voltage compensation is improved, but the mobility of the driving transistor cannot be compensated and device complexity increases
Solution Approach 1:
The pixel circuit is designed to perform multiple compensation functions simultaneously. The circuit uses the same transistor and capacitor components to achieve both threshold voltage compensation and mobility compensation through a unified compensation mechanism that operates during the same time period, thereby avoiding the need for separate compensation circuits.
Solution Approach 2:
The invention merges the threshold voltage compensation function and mobility compensation function into a single integrated pixel circuit. By combining these functions, the circuit achieves comprehensive compensation for both threshold voltage and mobility variations without requiring separate dedicated circuits for each parameter, thus reducing overall device complexity.
2Manufacturing precision
If the threshold voltages and mobilities of driving transistors are unequal due to process deviation, then manufacturing precision is reduced, but adding compensation circuits increases device complexity
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the compensation capacitor stores voltage information related to threshold voltage and mobility variations. This feedback loop allows the circuit to automatically adjust and compensate for process deviations in transistor parameters, maintaining consistent pixel performance despite manufacturing variations without requiring complex external compensation circuits.
3Illumination intensity
If organic light emitting diodes are degraded over time, then luminance consistency is lost, but without proper compensation mechanisms, device complexity must increase to maintain image quality
Solution Approach 1:
The compensation capacitor is charged in advance during a compensation period before the actual display period. This preliminary action stores the compensation voltage that accounts for threshold voltage and mobility variations, allowing the circuit to maintain accurate current control and luminance consistency throughout the display period without requiring continuous complex adjustments.
Data Source
AI summary
An organic light emitting display device and a method of driving the same. In a method of driving an organic light emitting display device including a second capacitor having a first terminal coupled to a gate electrode of a driving transistor and a first capacitor coupled between the gate electrode of the driving transistor and a first power source, the driving method includes supplying a threshold voltage of an organic light emitting diode to a second terminal of the second capacitor during a period when a first current is sunk via the driving transistor, and supplying a data signal to the second terminal of the second capacitor after a voltage corresponding to a difference between a voltage applied to the gate electrode of the driving transistor and the threshold voltage of the organic light emitting diode is charged in the second capacitor.