Pixel Circuit Mode Selection for Display Gradation Control
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Solution Overview
Problem
Existing organic electroluminescent display devices face difficulties in gradation control, particularly when displaying low-level gradations, due to significant changes in drive current with slight changes in data voltage, making precise luminance control challenging.
Innovation Solution
The display device incorporates a pixel circuit with a mode selection circuit that causes short-circuit and open-circuit between the electrodes of a second capacitor, allowing for adjustment of the charge accumulation in a first capacitor to reduce the drive current's sensitivity to data voltage changes, facilitating more precise gradation control by setting the display to low luminance mode for low-level gradations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the data voltage is controlled to a low voltage to display a low-level gradation, then the power consumption is reduced, but the drive current changes significantly with slight voltage changes, making gradation control difficult
Solution Approach 1:
The pixel circuit dynamically switches between two operational modes using a mode selection circuit. In the first mode, the capacitor connected to the gate of the drive transistor is connected to the data line, providing high sensitivity for bright display. In the second mode, the capacitor is disconnected from the data line, providing low sensitivity for dark display with good gradation control. This dynamic reconfiguration allows the circuit to adapt its characteristics based on the required display level.
Solution Approach 2:
The invention changes the electrical parameters of the pixel circuit by switching the connection state of the capacitor. When the mode selection signal changes, the capacitor transitions between being connected to and disconnected from the data line, effectively changing the sensitivity parameter of the drive transistor gate voltage to drive current conversion. This parameter change enables the circuit to operate with different gain characteristics suitable for different luminance ranges.
2Device complexity
If a conventional pixel circuit is used for low-level gradation display, then the circuit structure is simple, but the drive current is highly sensitive to data voltage changes, causing poor gradation control
Solution Approach 1:
The pixel circuit dynamically switches between two operational modes using a mode selection circuit. In the first mode, the capacitor connected to the gate of the drive transistor is connected to the data line, providing high sensitivity for bright display. In the second mode, the capacitor is disconnected from the data line, providing low sensitivity for dark display with good gradation control. This dynamic reconfiguration allows the circuit to adapt its characteristics based on the required display level.
Solution Approach 2:
The mode selection circuit enables the same pixel circuit to serve multiple functions: it can operate in a high-sensitivity mode for bright display and a low-sensitivity mode for dark display with precise gradation control. The capacitor serves dual purposes by being selectively connected or disconnected, allowing the circuit to handle different luminance ranges with appropriate characteristics using a single unified structure.
Data Source
AI summary
A pixel circuit of a display device includes: a light-emitting element; a drive transistor; a write control transistor having one conductive terminal connected to a data line and a control terminal connected to a scanning line; a first capacitor provided between a control terminal of the drive transistor and a conductive terminal of the drive transistor on the light-emitting element side; a second capacitor provided between another conductive terminal of the write control transistor and the control terminal of the drive transistor; and a mode selection circuit provided in parallel to the second capacitor and configured to cause a short-circuit and an open-circuit between electrodes of the second capacitor in accordance with a voltage of a mode selection line. Accordingly, a display device capable of easily performing gradation control is provided.