Pixel Circuit With Split Breakdown Voltages for Uniform Luminance
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Solution Overview
Problem
Existing display devices, particularly Head Mounted Displays (HMDs), face challenges in achieving high resolution and efficient pixel performance due to limitations in transistor design and voltage management, leading to issues with luminance uniformity and operational reliability.
Innovation Solution
A pixel design incorporating transistors with varying breakdown voltages and a capacitor configuration, where P-type transistors are used with specific gate connections and timing periods to manage voltage levels effectively, ensuring efficient current supply to light-emitting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transistor design is used in HMD pixels, then device complexity is reduced, but luminance uniformity and operational reliability deteriorate
Solution Approach 1:
The pixel circuit is divided into multiple transistor types with different breakdown voltage characteristics. Specifically, the invention uses a first transistor (drive transistor) with a first breakdown voltage and a second transistor (compensation transistor) with a second breakdown voltage that is lower than the first. This segmentation allows each transistor to be optimized for its specific function, improving overall reliability while managing complexity through specialized design.
Solution Approach 2:
Different regions of the pixel circuit are assigned different transistor characteristics tailored to local requirements. The drive transistor uses higher breakdown voltage to withstand the full drive voltage range, while the compensation transistor uses lower breakdown voltage to effectively compensate for threshold voltage variations. This local optimization of transistor properties enhances luminance uniformity without requiring complete redesign of the entire circuit.
2Reliability
If higher breakdown voltage transistors are used throughout the pixel, then voltage management is simplified, but luminance uniformity deteriorates due to inability to compensate threshold voltage variations
Solution Approach 1:
The invention changes the breakdown voltage parameter of transistors based on their specific function within the pixel circuit. The drive transistor is designed with a first breakdown voltage to handle the main drive signal, while the compensation transistor is designed with a second breakdown voltage (lower than the first) to optimize its compensation function. This parameter differentiation enables effective threshold voltage compensation, improving luminance uniformity across the display.
3Reliability
If more transistors are added to the pixel circuit for voltage management, then voltage range control is improved, but device area increases
Solution Approach 1:
The compensation transistor with lower breakdown voltage serves multiple functions: it compensates for threshold voltage variations in the drive transistor, helps control the voltage range, and assists in maintaining luminance uniformity. By making this single transistor multi-functional, the design achieves improved voltage management without proportionally increasing the pixel area, thus resolving the contradiction between reliability and area.
Data Source
AI summary
A pixel includes: a first transistor, which has a gate electrode connected to a first node and is connected between a second node and a third node; a second transistor, which is connected between the second node and a first power line to which a first driving power source is supplied and has a gate electrode connected to the second node; a third transistor, which is connected between a data line and the first node and has a gate electrode electrically connected to a first scan line; a first capacitor connected between the first node and the third transistor; and a light emitting element connected between the third node and a second power line to which a second driving power source is supplied.