Pixel Circuit Display Driver for Uniform Light Output
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current-driven displays, such as LEDs and OLEDs, face challenges in maintaining consistent brightness and efficiency due to variations in thin film transistor threshold and mobility, which affect the accuracy and uniformity of light output.
Innovation Solution
A circuit and method that includes a storage node with capacitance, transistors, and a light emitting diode, where a derivative current is generated using stored voltage to drive the diode, ensuring the light output is insensitive to transistor variations, and a sample-and-hold current device is used to produce a scaled replica of the programming current for consistent illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel circuits are used in current-driven displays, then the circuit structure is simple, but the light output accuracy and uniformity deteriorate due to transistor threshold and mobility variations
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a programming circuit for setting the programming current, a storage node for holding the gate voltage, and a derivative current generation circuit. This segmentation allows each block to perform its specific function independently, improving light output uniformity while managing complexity through modular design
Solution Approach 2:
A storage node (capacitor) is introduced as an intermediary between the programming current source and the light emitting diode. This storage node holds the gate voltage that defines the programming current, acting as a mediator that isolates the LED from direct dependence on transistor characteristics, thereby improving light output accuracy
2Ease of manufacture
If thin film transistors with varying threshold and mobility are used, then the device can be manufactured with existing technology, but the brightness consistency deteriorates
Solution Approach 1:
The circuit uses a feedback mechanism where the programming current flows through the thin film transistor and develops a gate voltage that is stored on the storage node. This stored voltage automatically compensates for transistor variations, creating a self-regulating system that maintains brightness consistency despite manufacturing variations in transistor threshold and mobility
Solution Approach 2:
The circuit transforms the problem of transistor parameter variations (threshold voltage and mobility) into a solution by using these variations to automatically set the programming current. The gate voltage developed across the transistor gate, which varies with transistor characteristics, becomes the controlling parameter for the programming current, thereby compensating for the variations rather than being harmed by them
3Reliability
If a derivative current is generated using stored voltage, then the light output becomes insensitive to transistor variations, but the circuit complexity increases
Solution Approach 1:
The storage node performs a preliminary action by storing the gate voltage during a programming phase before the illumination phase. This pre-stored voltage is then used to generate the derivative current that drives the LED, ensuring that the light output is determined by the stored voltage rather than by transistor variations during operation, thereby improving reliability
Solution Approach 2:
The circuit creates a copy of the programming current characteristics through the derivative current. The stored gate voltage is used to generate a derivative current that replicates the desired current characteristics for driving the LED, independent of the original transistor that generated the programming current. This copying mechanism ensures consistent light output despite variations in the programming transistor
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
The solution achieves accurate and uniform light output across pixels, compensating for transistor variations and mobility issues, resulting in improved brightness consistency and power efficiency in current-driven displays.
Implementation Method 1
the storage node includes a first capacitance
Implementation Method 2
a light emitting diode coupled to a second electrode of the second transistor
Implementation Method 3
The light emitting diode may be an organic light emitting diode
Data Source
AI summary
A display includes a plurality of pixels and operates in a selected load period, a separate deselected load period, and a separate illumination period. Light may be generated by the plurality of pixels during the illumination period based on voltages stored in the plurality of pixels during the selected and deselected load periods. Methods of operating a display are also disclosed.