Pixel Circuit Memory Digital Signal Writing for OLED Displays
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Solution Overview
Problem
Existing organic electro-luminescence (EL) devices in head-mounted displays face challenges in achieving high-resolution, multi-gray-scale, and high-quality images at low power consumption due to variations in voltage-current characteristics and threshold voltage of driving transistors, which are exacerbated by the need for compensating circuits and large capacitive elements.
Innovation Solution
The electro-optical device incorporates a pixel circuit with a memory circuit and transistors that allow digital signal writing, reducing the effect of transistor variations and eliminating the need for compensating circuits, thereby achieving high-resolution and multi-gray-scale displays with reduced power consumption by using a low-voltage power-supply for the memory circuit and a high-voltage power-supply for the light emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a compensating circuit is provided to compensate for variations in voltage-current characteristics and threshold voltage of driving transistor, then display quality is improved, but power consumption increases
Solution Approach 1:
The patent extracts and removes the compensating circuit from the pixel structure, eliminating the source of excessive power consumption. Instead of adding compensation circuitry, the invention uses a simplified pixel structure with a driving transistor, capacitive element, and light emitting element that achieves uniform display quality through analog voltage control without requiring additional compensating components.
Solution Approach 2:
The patent replaces complex, power-consuming compensating circuits with a simpler, more economical pixel structure. The invention uses basic circuit elements (capacitive element for voltage storage, driving transistor for current control) that consume less power while achieving the desired display quality through analog signaling rather than complex digital compensation.
2Adaptability or versatility
If a capacitive element with large capacitance is used to store image signals for multiple-gray-scale display, then multiple-gray-scale display is achieved, but power consumption increases due to charging and discharging
Solution Approach 1:
The patent implements multiple-gray-scale display through periodic scanning signals that refresh the capacitive elements at regular intervals. Instead of requiring large capacitance to maintain analog voltage levels continuously, the system uses periodic rewriting of image signals to sustain gray-scale levels, reducing the capacitance requirement and minimizing charging/discharging power consumption.
Solution Approach 2:
The patent changes the operating parameters of the capacitive elements by optimizing their capacitance values and switching frequencies to achieve multiple gray-scales. By adjusting the scanning frequency and voltage levels rather than increasing capacitance, the system achieves versatile gray-scale display while minimizing power consumption from capacitive charging and discharging.
3Adaptability or versatility
If analog driving is used to control current flowing through organic EL element according to gate potential of driving transistor, then gray-scale display is achieved, but variations in voltage-current characteristics and threshold voltage cause variations in brightness and shifts in gray-scale between pixels
Solution Approach 1:
The patent implements a feedback mechanism where the capacitive element stores the gate potential voltage that directly controls the driving transistor. This stored voltage serves as a reference that compensates for transistor parameter variations, ensuring that the same voltage produces consistent current and brightness across all pixels regardless of manufacturing variations in voltage-current characteristics or threshold voltage.
Solution Approach 2:
The patent uses the capacitive element to maintain equipotential conditions at the gate of the driving transistor. By storing the image signal voltage on the capacitive element, the system ensures that all driving transistors receive the same gate potential voltage, thereby achieving uniform brightness and gray-scale display across the display panel despite variations in transistor characteristics.
Data Source
AI summary
An electro-optical device includes a first scan line, a data line, and a pixel circuit provided at a position corresponding to intersections of the first scan line and the data line. The pixel circuit includes a light emitting element, a memory circuit, a first transistor, and a second transistor. The first transistor is electrically connected in series to the light emitting element, and a gate of the first transistor is electrically connected to the memory circuit. The second transistor is disposed between the data line and an input of a first inverter. The third transistor is disposed between an output terminal of a second inverter and the input of the first inverter. When the second transistor turns from an OFF-state to an ON-state, the third transistor is not in an ON-state.