Light Emission Drive Circuit for OLED Threshold Voltage Compensation
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Solution Overview
Problem
In light emission drive circuits for organic EL displays, the variation in threshold voltage of thin film transistors over time and production lots leads to unstable light emission at desired luminance gradations, affecting display image quality.
Innovation Solution
A light emission drive circuit with an electric charge accumulating section, a light emission control section, a writing control section, and a voltage control section, which accumulates charges based on gradation sequence signals and controls drive voltage to maintain consistent light emission current, ensuring stable luminance gradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional light emission drive circuit is used, then the circuit structure is simple, but the light emission stability deteriorates due to threshold voltage variation of thin film transistors
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the light emission drive operation. The drive circuit includes a compensation circuit that adjusts the gate voltage of the drive transistor based on measured threshold voltage variations, ensuring stable light emission current from the outset. This preliminary compensation action eliminates the instability caused by threshold voltage variations without requiring complex continuous adjustment mechanisms.
Solution Approach 2:
The patent implements feedback by incorporating a measurement circuit that detects the actual threshold voltage of the drive transistor and feeds this information back to the compensation circuit. The compensation circuit then adjusts the gate voltage accordingly to maintain a constant light emission current. This feedback mechanism ensures long-term stability of light emission despite variations in transistor properties over time and across production batches.
2Reliability
If threshold voltage compensation is implemented, then light emission stability improves, but device complexity increases
Solution Approach 1:
The patent merges the measurement circuit, compensation circuit, and drive transistor control functions into an integrated drive circuit unit. The measurement circuit detects threshold voltage, the compensation circuit processes the measurement data and calculates required voltage adjustments, and the drive transistor executes the controlled current flow. By combining these functions in a unified circuit architecture, the patent achieves stable light emission while minimizing the overall complexity compared to separate discrete compensation components.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the gate voltage parameter of the drive transistor based on measured threshold voltage variations. The compensation circuit modifies the gate voltage parameter in real-time to compensate for transistor property variations, maintaining a constant drain current that controls light emission intensity. This parameter adjustment approach provides stable performance without requiring fundamental changes to the circuit topology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables stable light emission at appropriate luminance gradations over time, improving display image quality by maintaining consistent light emission current values despite variations in transistor properties.
Implementation Method 1
an electric charge accumulating section for accumulating electric charges on the basis of a gradation sequence signal designating a luminance gradation sequence
Data Source
AI summary
A light emission drive circuit includes an electric charge accumulating section for accumulating electric charges on the basis of a gradation sequence signal designating a luminance gradation sequence. A light emission control section flows a light emission drive current having a current value in accordance with an amount of the electric charges accumulated in the electric charge accumulating section. A writing control section controls a supplying state of the electric charges based on the gradation sequence signal to the electric charge accumulating section on the basis of a first control signal. A voltage control section controls a drive voltage for operating the light emission controlling section on the basis of a second control signal.