Drive Current Detection in Organic EL Display Devices
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Solution Overview
Problem
In organic EL display devices, the threshold voltage of drive transistors changes over time, leading to inaccuracies in drive current detection and increased memory requirements due to variations in transistor characteristics, particularly in oxide TFTs like those with indium gallium zinc oxide semiconductor layers.
Innovation Solution
An active matrix-type display device with a display unit comprising scanning lines, data lines, and pixel circuits, where a data line drive circuit provides a voltage between a control terminal and a conduction terminal of the drive transistor to detect drive current, and a display control circuit controls a reference voltage based on stored threshold voltage data to maintain accurate current detection and compensate for transistor variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If threshold voltage compensation is performed using conventional methods, then display quality is improved, but measurement precision of drive current deteriorates due to threshold voltage changes over time
Solution Approach 1:
The patent applies preliminary action by detecting the drive current at multiple time points (initial detection and subsequent detections) and storing the threshold voltage compensation values in advance. This allows the system to proactively adjust for threshold voltage changes before they significantly impact measurement precision, thereby maintaining both display quality and detection accuracy over time.
Solution Approach 2:
The patent implements feedback by continuously monitoring drive current and comparing it against reference values, then adjusting the threshold voltage compensation accordingly. The system uses the detected drive current to update compensation values, creating a closed-loop control that maintains measurement precision while preserving display quality despite threshold voltage drift.
2Manufacturing precision
If per-pixel threshold voltage and gain compensation is performed using stored correction data, then manufacturing precision is improved, but device complexity increases due to additional memory requirements
Solution Approach 1:
The patent applies local quality by implementing compensation specifically for pixels that exhibit threshold voltage or gain variations, rather than uniformly compensating all pixels. By identifying and compensating only the affected pixels using stored correction data, the system achieves improved pixel uniformity while minimizing the memory capacity required to store correction data for only those pixels needing adjustment.
3Ease of operation
If drive current detection is performed externally to the pixel circuit, then ease of operation is improved, but measurement precision deteriorates due to threshold voltage changes affecting detection accuracy
Solution Approach 1:
The patent implements feedback by using the externally detected drive current to update threshold voltage compensation values, which are then applied to subsequent detections. This closed-loop approach maintains measurement precision despite threshold voltage changes, while preserving the ease of operation associated with external detection implementation.
Solution Approach 2:
The patent applies preliminary action by performing initial drive current detection and threshold voltage measurement before normal operation, and storing these values for use during subsequent detections. This preparatory step establishes a baseline that improves the accuracy of external drive current detection while maintaining operational simplicity.
Data Source
AI summary
A data line drive circuit provides a voltage according to a detection voltage and to a reference voltage, between the gate and source of a drive transistor in a pixel circuit, and detects a drive current having passed through the drive transistor and outputted external to the pixel circuit. A threshold voltage correction memory stores, for each pixel circuit, data representing a threshold voltage of the drive transistor. A display control circuit controls the reference voltage based on the data stored in the threshold voltage correction memory. By this, even if the threshold voltage of the drive transistor is changed, the drive current can be detected with a high accuracy. The threshold voltage correction memory may store, for each pixel circuit, data representing a difference between the threshold voltage of the drive transistor and the reference voltage.