Pixel Circuit Saturation Linear Switching Peak Luminance
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Solution Overview
Problem
Existing active matrix organic electroluminescence (organic EL) display devices face limitations in achieving higher peak luminance due to constraints in voltage output range, which restricts the grayscale display range and leads to inefficient utilization of driver voltage output.
Innovation Solution
A pixel circuit configuration that combines a first switching element with a saturation current characteristic and a second switching element with a linear current characteristic, allowing for increased light emitting current through combined current supply lines, enabling higher peak luminance while maintaining appropriate normal grayscale display within a predetermined driver voltage output range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a single TFT element with saturation characteristic is used to control light emitting current, then the grayscale display can be maintained within a predetermined voltage range, but the peak luminance is limited and the driver voltage output range is not effectively utilized
Solution Approach 1:
The single TFT switching element is divided into two separate TFTs: a first TFT (304) with saturation characteristic for normal grayscale display, and a second TFT (305) with linear characteristic for peak luminance enhancement. This segmentation allows each TFT to operate in its optimal characteristic region, enabling the driver to effectively utilize the full voltage output range while achieving higher peak luminance without excessive complexity
Solution Approach 2:
The invention transitions from a single-dimensional control (one TFT) to a two-dimensional control system where the first TFT handles the saturation region for normal grayscales and the second TFT handles the linear region for peak luminance. This dimensional expansion in the control architecture enables independent optimization of normal display and peak luminance performance
2Illumination intensity
If the voltage range for normal grayscale display is narrowed to achieve higher peak luminance, then peak luminance can be increased, but the grayscale display range is restricted and display quality deteriorates
Solution Approach 1:
Different characteristic regions of the TFT I-V curve are assigned to different display purposes: the saturation characteristic region (first TFT) is optimized for normal grayscale display with wide voltage range, while the linear characteristic region (second TFT) is optimized for peak luminance enhancement. This local quality differentiation allows simultaneous optimization of both grayscale range and peak luminance without compromise
Solution Approach 2:
The invention changes the operational parameters by introducing a second TFT with different characteristic (linear vs. saturation) to complement the first TFT. This parameter change enables the system to access different regions of the I-V curve, thereby expanding both the grayscale display range and peak luminance capability beyond what a single TFT can achieve
Data Source
AI summary
A pixel circuit of at least one embodiment of the present invention includes: a display element whose light emitting luminance is controlled by a supplied current; at least one first switching element section whose output current characteristic shows a saturation characteristic in response to an input variable serving as a grayscale signal; and at least one second switching element section whose output current characteristic shows a linear characteristic in response to an input variable serving as a grayscale signal. A first current supply line which outputs a current determined by the first switching element section and a second current supply line which outputs a current determined by the second switching element section are combined, and then succeeded by a current supply line of the display element. This makes it possible to provide a pixel circuit and a display device which can generate higher peak luminance while sufficiently securing a voltage range which causes an appropriate normal grayscale display within a predetermined driver voltage output range.