Variable Driving Signal Pixel Circuit for Current Stability
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Solution Overview
Problem
Existing light emitting devices face challenges in accurately controlling driving current variations across multiple gradations, as previous techniques are limited in compensating for variations in the threshold voltage and mobility of driving transistors, leading to inconsistent luminance in light emitting elements.
Innovation Solution
A method involving a pixel circuit with a driving transistor and a storage capacitor, where a driving signal with a varying time rate of change is supplied to the transistor, and the supply is stopped at a time point adjusted according to the gradation, allowing an open circuit voltage to set a current independent of the transistor's threshold voltage or mobility, thereby stabilizing the driving current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a driving signal with constant time rate of change is supplied to the gate of the driving transistor, then the current flows through the driving transistor, but the driving current varies depending on the threshold voltage and mobility of the driving transistor
Solution Approach 1:
The patent changes the time rate of change of the driving signal voltage over time. Specifically, the time rate of change is increased initially to quickly establish current flow, then decreased to maintain stable current. This dynamic parameter adjustment compensates for variations in threshold voltage and mobility across different transistors and gradations, achieving consistent driving current without requiring individual transistor characterization.
2Reliability
If the supply time of the driving signal is extended to compensate for low gradations, then the driving current can be maintained, but the response time for high gradations increases
Solution Approach 1:
The patent employs periodic modulation of the driving signal's time rate of change. The signal initially increases with a high time rate of change to quickly reach the required current level, then transitions to a lower time rate of change to maintain stability. This time-varying periodic action allows the system to respond quickly to high gradation changes while maintaining stable current for low gradations, eliminating the need to extend supply time for all cases.
3Manufacturing precision
If separate driving signals are used for each pixel circuit to achieve precise current control, then the driving current can be optimized for each pixel, but the complexity of control lines and signal lines increases
Solution Approach 1:
The patent makes the driving signal universal by applying the same time-varying voltage signal to multiple pixel circuits simultaneously. The signal's time rate of change is modulated to inherently compensate for transistor variations across all pixels. This multi-functional approach allows a single signal line to serve multiple pixel circuits with precise current control, eliminating the need for separate dedicated signal lines for each pixel while maintaining manufacturing precision.
Data Source
AI summary
Provided is a method of driving a pixel circuit including a light emitting element and a driving transistor which are connected in series, and a storage capacitor disposed between the path between the light emitting element and the driving transistor and the gate of the driving transistor, the method including the steps of: supplying a driving signal, of which the time rate of change of the potential varies over time, to a gate of the driving transistor; stopping the supply of the driving signal at a point in time which is set to be variable in accordance with a gradation specified for the pixel circuit; and supplying a driving current corresponding to an open circuit voltage of the storage capacitor to the light emitting element.