Light-emitting Device Pixel Circuit for Luminance Uniformity
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Solution Overview
Problem
In active matrix light-emitting devices, variations in threshold voltage and mobility of driving transistors lead to luminance unevenness among pixels, which existing correction methods fail to adequately address, affecting image quality and power consumption.
Innovation Solution
A light-emitting device structure that includes a pixel with a transistor for current control, a switch for gate-drain connection, and a second switch for current extraction, along with a monitor circuit to correct image signals based on drain current information, addressing variations in threshold voltage and mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If only threshold voltage correction is implemented inside pixels, then threshold voltage variations are corrected, but mobility variations and other electrical characteristic variations still cause luminance unevenness
Solution Approach 1:
The correction function is segmented into two parts: in-pixel threshold voltage correction and external mobility correction. The pixel circuit handles threshold voltage compensation locally, while external circuits handle mobility and other electrical characteristic corrections, dividing the correction tasks to achieve comprehensive luminance uniformity
Solution Approach 2:
External correction circuits act as intermediaries between the pixel circuits and the final display output. These intermediary circuits process the image signals to compensate for mobility variations before the signals reach the pixels, enabling correction of electrical characteristics beyond what in-pixel circuits can handle
2Reliability
If external correction circuits are added to correct mobility variations, then luminance uniformity is improved, but device complexity increases
Solution Approach 1:
The external correction circuits are designed to handle multiple electrical characteristic variations (mobility, threshold voltage, and other parameters) through unified correction mechanisms, allowing a single external correction stage to address multiple sources of luminance unevenness simultaneously
Solution Approach 2:
The pixel circuits perform self-correction of threshold voltage variations through built-in compensation circuits, reducing the burden on external correction circuits and allowing the external circuits to focus only on mobility and other electrical characteristic corrections
3Reliability
If correction structures are added to both pixels and external circuits, then comprehensive electrical characteristic correction is achieved, but power consumption increases
Solution Approach 1:
The correction system applies partial correction actions at different stages: in-pixel circuits perform essential threshold voltage correction, while external circuits provide additional mobility correction when needed. This staged approach allows the system to achieve comprehensive correction while consuming power only proportionally to the correction level required
Data Source
AI summary
A light-emitting device in which variation in luminance among pixels is suppressed. The light-emitting device includes a pixel; a first circuit configured to generate a signal containing information on a value of current extracted from the pixel; and a second circuit configured to correct an image signal in accordance with the signal. The pixel includes a light-emitting element; a transistor for controlling supply of the current to the light-emitting element in accordance with the image signal; a first switch configured to control connection between a gate and a drain of the transistor or between the gate of the transistor and a wiring; and a second switch configured to control extraction of the current from the pixel.