Light Emitting Device Driving Circuit Luminance Control
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Solution Overview
Problem
The existing light emitting devices, such as those described in Japanese Patent Laid-Open No. 2013-097016, face limitations in luminance range due to the number of bits in the Digital to Analog Converter (DAC), which restricts the range of signal voltages and consequently the luminance that can be achieved.
Innovation Solution
A light emitting device comprising pixels with a driving transistor, a capacitor to hold the threshold voltage, and a driving circuit that controls the connection of signal lines to adjust voltage levels, allowing for a wider range of currents through light-emitting elements by selecting different voltage levels for signal write periods and preparation periods, thereby improving luminance without altering the signal voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the number of bits of digital signals is increased to increase maximum luminance, then the maximum luminance is improved, but the device complexity increases
Solution Approach 1:
The patent applies dynamics by making the voltage level selected by the driving circuit changeable based on the display mode. The driving circuit can dynamically switch between a first voltage level (higher than the maximum signal voltage) and a second voltage level (equal to or lower than the maximum signal voltage), allowing the system to adapt its voltage range according to whether it is in image display mode or aging mode, thereby achieving variable luminance control without changing the DAC bit depth.
Solution Approach 2:
The patent changes the voltage level parameter selected by the driving circuit based on display mode. By selecting different voltage levels (first voltage level for aging mode, second voltage level for image display mode), the system can achieve different luminance ranges using the same DAC, thus expanding the luminance control capability without increasing the number of DAC bits.
2Adaptability or versatility
If the number of bits of digital signals is increased to expand the luminance range, then the luminance range is improved, but the device complexity increases
Solution Approach 1:
The patent makes the driving circuit multi-functional by enabling it to perform both voltage level selection and mode-dependent operation. The driving circuit can select from multiple voltage levels and adapt its behavior based on the display mode (image display or aging), allowing a single circuit to handle multiple luminance requirements without requiring separate DACs or increasing bit depth.
Solution Approach 2:
The system dynamically adjusts the voltage level selected by the driving circuit according to the display mode. In aging mode, it selects the first voltage level to achieve higher maximum luminance and wider luminance range, while in image display mode, it selects the second voltage level for normal operation, thereby achieving adaptable luminance control without increasing DAC complexity.
3Adaptability or versatility
If different voltage levels are selected for different display modes, then the luminance control flexibility is improved, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by having the driving circuit pre-select appropriate voltage levels based on the display mode before actual pixel driving occurs. The system prepares the voltage selection in advance according to whether it is in aging mode or image display mode, ensuring that the correct voltage range is ready for the luminance control operation, which simplifies the real-time control complexity.
Data Source
AI summary
The light emitting device comprises: a plurality of pixels, each having a light-emitting element, a driving transistor configured to drive the light-emitting element, a capacitor configured to hold a threshold voltage of the driving transistor, a signal line, a first switch configured to connect the signal line and a control electrode of the driving transistor, and a second switch configured to connect a first main electrode of the driving transistor and a predetermined node; and a driving circuit configured to drive the signal line. In a preparation period in which the threshold voltage is held in the capacitor, the first switch is controlled to be on and the second switch is controlled to be off, and the driving circuit drives the signal line at a voltage level selected from a plurality of different voltage levels.