Current Mirror Circuit for Active Matrix Display Panel
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Solution Overview
Problem
As active matrix display panels scale up, parasitic capacitance increases, limiting the speed at which current levels can be varied for each pixel, leading to inaccurate intensity settings and difficulty in matching transistors in distributed current mirror circuits, especially over longer column select conductors.
Innovation Solution
The implementation of additional current mirrors that mirror reference currents and connect in parallel to improve matching accuracy, reduce the influence of parasitic capacitance, and allow for more precise control of current levels across rows, with each current mirror output connected in parallel to enhance accuracy and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the panel is scaled up, then the display area increases, but parasitic capacitance increases which limits the speed of current level variation
Solution Approach 1:
The pixel circuits in a column are divided into multiple groups, with each group having its own current mirror circuit. This segmentation allows independent control of current levels for different groups, enabling faster current variation by avoiding the need to update all pixels simultaneously through a single long column select conductor.
Solution Approach 2:
Current levels for each group are set in advance during a programming phase before the display phase. The current mirror circuits store the programmed current levels, allowing rapid switching between predefined current levels during display without requiring slow sequential updates through the entire column.
2Area of stationary object
If the panel is scaled up, then the display area increases, but matching accuracy of transistors in distributed current mirror circuits decreases
Solution Approach 1:
By dividing the column into multiple groups with separate current mirror circuits, the physical distance between transistors in each current mirror pair is reduced. This segmentation ensures that transistors within each current mirror circuit remain close together, maintaining high matching accuracy despite the overall large panel size.
3Adaptability or versatility
If separate digitally adjustable current sources are used on each column line, then current control flexibility increases, but device complexity increases
Solution Approach 1:
Multiple pixel groups share common current mirror circuits and column select conductors. This merging reduces the total number of independent current sources needed compared to having separate current sources for every pixel, while still maintaining the ability to independently control current levels for each group through selective activation.
Data Source
AI summary
An active matrix display panel comprises a substrate, array of pixel circuits being arranged in a matrix of at least one column and a plurality of rows on the substrate, each pixel circuit comprising a light-emitting element, capable of emitting light of an intensity determined by the value of a current passed through it, and at least one column line, each column line arranged to conduct a reference current, provided by a current driving circuit, when connected to the panel. The pixel circuits in a column are divided into a plurality of groups of at least one pixel circuit. The active matrix display panel comprises at least one current mirror circuit associated with a first group, comprising a first current mirror, arranged to mirror a reference current flowing through a column line to a first current mirror output. Each pixel circuit in the first group comprises at least a first current-memory stage, having an output terminal connected to the light-emitting element, wherein the first current-memory stage is capable of drawing a current determined at least partly by the current mirrored to the first current mirror output through the output terminal. Each current mirror circuit comprises at least one additional current mirror, arranged to mirror a reference current flowing through an associated column line to an additional current mirror output, wherein each additional current mirror output is connected in parallel to the first current mirror output.