Dynamic Drive Transistor Region Switching for OLED Power Reduction
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Solution Overview
Problem
Conventional organic EL display devices face challenges with high power consumption due to unnecessary drain-source voltage, difficulty in achieving high precision display, and short lifetime of organic EL elements, especially in analog gradation drive and time-division digital gradation drive methods.
Innovation Solution
An active-matrix display device with a pixel circuit that includes a drive transistor operating in both saturation and triode regions, using a measurement circuit to determine the operation region and correct the video signal based on measured currents or voltages, thereby optimizing power supply voltage and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drive transistor operates in saturation region to maintain stable current flow through the organic EL element, then the light emission brightness is stable, but the drain-source voltage does not contribute to light emission and only generates heat, resulting in large power consumption
Solution Approach 1:
The invention dynamically switches the drive transistor between saturation region and triode region operation based on the video signal gradation level. For lower gradations, the transistor operates in saturation region to ensure stable current flow and prevent display defects. For higher gradations, it switches to triode region to reduce power consumption by allowing drain-source voltage to contribute to light emission. This dynamic operation mode switching resolves the contradiction between reliability and power consumption.
Solution Approach 2:
The invention changes the operation parameters of the drive transistor by adjusting the data voltage level to control the transistor's operation region. By applying different data voltages corresponding to different gradation levels, the transistor parameter (operation region) is changed to optimize performance - saturation region for stability at low brightness, triode region for efficiency at high brightness.
2Use of energy by moving object
If the drive transistor operates in triode region to reduce power consumption, then power consumption decreases, but the current control precision deteriorates
Solution Approach 1:
The invention dynamically adjusts the operation region based on the required current control precision. For video signal gradations requiring high precision (lower brightness levels), the transistor operates in saturation region where current control is more precise. For gradations where power consumption is more critical (higher brightness levels), it operates in triode region. This dynamic adaptation resolves the precision-power consumption tradeoff.
3Use of energy by moving object
If time-division digital gradation drive is used to control the drive transistor in triode region, then power consumption is reduced, but the operating frequency increases in accordance with the number of gradations, making high precision display difficult
Solution Approach 1:
The invention segments the video signal gradations into two ranges: lower gradations that require saturation region operation for precision, and higher gradations that can use triode region operation for power efficiency. This segmentation allows the system to avoid high-frequency time-division multiplexing while still achieving power consumption reduction, as the triode operation is applied continuously to higher gradations rather than through rapid switching.
Data Source
AI summary
A current measurement circuit measures a current flowing through a drive transistor when a plurality of measurement voltages are written to a pixel circuit in a switching manner, and a current flowing through an organic EL element when another plurality of measurement voltages are written to the pixel circuit in a switching manner. A correction unit obtains a threshold voltage and a gain of the drive transistor and the organic EL element with respect to each pixel circuit based on a measured current, determines in which operation region the drive transistor operates between a saturation region and a triode region with respect to each pixel circuit based on the video signal, and corrects the video signal in accordance with the operation region of the drive transistor. Since the drive transistor operates both in the saturation region and the triode region, it is possible to reduce a power supply voltage and reduce power consumption of a display device.