Light-Emitting Pixel Circuit With Segmented Transistor Voltage Handling
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Solution Overview
Problem
Existing light emitting apparatuses face issues with luminance variation among light emitting elements due to high withstand voltage transistors, leading to increased chip area and cost, and image quality degradation.
Innovation Solution
The arrangement of a low withstand voltage driving transistor between the light emitting element and a high withstand voltage light emission control transistor, along with a cascode circuit, to suppress luminance variation while minimizing circuit scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high withstand voltage transistor is used as the driving transistor to supply current to the light emitting element, then the transistor can handle the required voltage, but the element size becomes larger, increasing chip area and cost
Solution Approach 1:
The transistor system is segmented into two distinct transistors: a high withstand voltage light emission control transistor (first transistor) and a low withstand voltage driving transistor (second transistor). This segmentation allows each transistor to be optimized for its specific function, with the first transistor handling voltage isolation and the second transistor providing precise current control with smaller size.
Solution Approach 2:
The light emission control transistor acts as an intermediary between the power supply and the driving transistor. It isolates the driving transistor from high voltage fluctuations, allowing the driving transistor to operate at lower voltages with reduced size while still achieving the required current drive capability through controlled voltage transmission.
2Manufacturing precision
If the area of the high withstand voltage transistor is increased to decrease variation of the driving transistor, then the transistor characteristic variation decreases, but the chip area increases
Solution Approach 1:
The system separates the functions of voltage handling and current control into different transistors. The first transistor (light emission control) handles voltage stabilization with high withstand voltage capability, while the second transistor (driving transistor) focuses on precise current control. This functional segmentation allows the driving transistor to achieve low variation without requiring large area, as it operates in a stabilized voltage environment provided by the first transistor.
3Reliability
If a high withstand voltage transistor is arranged between the display panel and driving circuit, then the driving circuit can be formed by low withstand voltage transistors, but the overall circuit scale increases
Solution Approach 1:
The light emission control transistor is merged with the pixel circuit structure, sharing the same physical space and functional integration. This merging approach allows the high withstand voltage functionality to be incorporated into the pixel-level circuit without adding separate external protection circuits, thereby minimizing overall circuit scale while maintaining voltage protection capabilities.
Data Source
AI summary
A light emitting apparatus is provided in which a pixel, that comprises a current path including a light emitting element, a driving transistor configured to supply a current corresponding to a luminance signal to the light emitting element, and a light emission control transistor configured to control light emission or non-light emission of the light emitting element, is arranged. In the current path, the light emission control transistor is arranged between the light emitting element and the driving transistor, and a withstand voltage of the driving transistor is lower than a withstand voltage of the light emission control transistor.