Pixel Circuit for OLED Uniform Luminance via Segmented Charging
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Solution Overview
Problem
Conventional organic light emitting displays face challenges in achieving uniform luminance due to non-uniformity of threshold voltages and transistor electron mobility, leading to insufficient time to charge data lines during the scan period.
Innovation Solution
The proposed solution involves a pixel circuit with a capacitor that charges a voltage difference between a first power supply and a data signal, and then controls the current supplied to a second power supply through an organic light emitting diode based on the stored voltage, using a dual signal approach with voltage and current signals during different periods of a horizontal period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If current is supplied as data signal to achieve uniform luminance, then luminance uniformity is improved, but charge time becomes too long exceeding scan time
Solution Approach 1:
The horizontal period is divided into two distinct periods: a first period for voltage signal transmission and capacitor charging, and a second period for current signal transmission. This temporal segmentation allows the data line to be charged during the voltage period without requiring the current to be transmitted simultaneously, thus reducing the charge time requirement below the scan time while maintaining uniform luminance through current signal supply.
Solution Approach 2:
The patent employs periodic action by alternating between voltage signal transmission in the first period and current signal transmission in the second period within each horizontal period. This periodic switching enables the capacitor to be charged during the voltage period and then used during the current period, effectively decoupling the charge time from the scan time requirement.
2Loss of time
If voltage signal is used to charge capacitor, then charge time is reduced within scan time, but luminance uniformity deteriorates due to transistor non-uniformity
Solution Approach 1:
The horizontal period is segmented into two functional periods: the first period dedicated to voltage signal transmission and capacitor charging, and the second period dedicated to current signal transmission for luminance control. This segmentation allows the system to benefit from both voltage-based fast charging and current-based uniform luminance control without compromising either function.
Solution Approach 2:
The capacitor acts as an intermediary energy storage element between the voltage signal and the current signal. During the first period, the capacitor stores energy from the voltage signal; during the second period, this stored energy is released as current through the organic light emitting diode, enabling uniform luminance control independent of transistor non-uniformity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for the stable control of current to the organic light emitting diode, ensuring uniform luminance across the display by effectively charging capacitors during one period and recharging them during another, thereby overcoming the limitations of charging time and non-uniformity.
Implementation Method 1
An organic light emitting display displays an image using an organic light emitting diode that generates light by the recombination of electrons and holes
Implementation Method 2
the scan line and the data line are configured to charge the capacitor in response to the first data signal with a voltage corresponding to a difference between a first power supply and a first data signal and to charge the capacitor with a voltage corresponding to a current signal
Data Source
AI summary
A pixel and an organic light emitting display using the pixel capable of displaying an image of uniform luminance. A pixel circuit is coupled with at least one scan line and at least one data line. The pixel circuit first charges a voltage corresponding to a first data signal across at least one capacitor when the first data signal is supplied from the data lines, and second charges the at least one capacitor when a current as a second data signal is provided. The pixel circuit controls an amount of current supplied to a second power supply from the first power supply through the organic light emitting diode according to the voltage charged in the at least one capacitor. Accordingly, an image of uniform luminescence may be displayed.