OLED Pixel Circuit Pre-Bootstrap Threshold Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic electroluminescence (EL) display technologies face challenges in achieving high-definition, high-brightness, and high-frame-rate displays due to brightness irregularities and threshold voltage variations in pixel circuits, which hinder the realization of faster driving speeds and improved image quality.
Innovation Solution
The implementation of a pixel circuit configuration that includes a drive transistor, a sampling transistor, a retention capacity, and a signal selector, along with a drive control scanner and write scanner, which performs plural threshold corrections in non-emission periods through pre-bootstrap operations to ensure appropriate gate-source voltage management and prevent threshold correction failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plural threshold corrections are performed in non-emission periods to improve image quality and prevent threshold correction failures, then the driving frequency is limited by the time required for multiple corrections, but higher frame rates and faster driving speeds are demanded
Solution Approach 1:
The patent applies preliminary action by performing pre-bootstrap in a predetermined period immediately before the first threshold correction. This raises the source voltage and gate voltage of the drive transistor in advance, ensuring that the threshold correction can be performed effectively even with shortened correction periods required for high-speed driving. The pre-bootstrap prepares the circuit state beforehand, allowing reliable threshold correction without extending the overall correction time too much.
2Productivity
If the threshold correction period is shortened to enable faster driving, then the gate-source voltage may not be sufficiently reduced during correction, but sufficient correction time is needed to maintain image quality
Solution Approach 1:
The pre-bootstrap operation performs preliminary voltage adjustment before the threshold correction period begins. By raising the source and gate voltages in advance during a predetermined period before the first threshold correction, the circuit is prepared so that when the shortened correction period starts, the gate-source voltage can be sufficiently reduced despite the limited correction time. This enables both fast driving and precise threshold correction.
Solution Approach 2:
The patent changes the voltage parameters dynamically by implementing pre-bootstrap that raises the source voltage and gate voltage before threshold correction. This parameter change allows the threshold correction to be performed effectively even when the correction period is shortened for high-speed driving. The voltage levels are adjusted in advance to compensate for the reduced correction time.
3Reliability
If pre-bootstrap is performed to raise source and gate voltages before threshold correction, then threshold correction reliability improves, but additional control complexity is introduced
Solution Approach 1:
The drive control scanner is designed to perform multiple functions: it controls both the pre-bootstrap operation and the subsequent threshold correction, and also manages the emission period. By making the drive control scanner multi-functional, the patent avoids adding separate dedicated control circuits for pre-bootstrap, thereby reducing overall control circuit complexity while still achieving reliable threshold correction.
Data Source
AI summary
A display apparatus includes: a pixel array in which pixel circuits each having a light emitting device, a drive transistor, a sampling transistor, and a retention capacity; a signal selector that supplies threshold correction reference voltages and a video signal voltages as to signal lines arranged in columns on the pixel array; a drive control scanner that provides power supply pulses to power supply control lines arranged in rows on the pixel array and applies drive voltages to the drive transistors; and a write scanner that provides scan pulses to write control lines arranged in rows on the pixel array to control the sampling transistors and executes input of the threshold correction reference voltages and the video signal voltages to the pixel circuits, and brings the sampling transistors into conduction by the scan pulses at plural times when the signal line voltages are the threshold correction reference voltages in order to execute plural threshold corrections in non-emission periods of one light emission cycles of the pixels circuits.