Macro-Pixel Display Backplane for High Bit Depth at Small Pixel Pitch
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Solution Overview
Problem
Existing micro-LED display technologies face challenges in achieving high bit depth, low drive current variation, and robust circuit design due to the limited real estate for pixel array driving circuits, especially at small pixel pitches.
Innovation Solution
The macro-pixel architecture is introduced, which groups multiple micro-LEDs and their driving circuits into larger macro-pixels. This architecture allows for the sharing of certain circuits, reduction of transition regions, and inclusion of design-for-test circuits, enabling higher bit depth, reduced drive current variation, and improved manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If micro-LEDs are used with small pixel pitch to achieve high resolution, then display resolution is improved, but available area for driving circuits is reduced
Solution Approach 1:
Multiple micro-LEDs are grouped into a single macro-pixel unit that shares common driving circuits. Specifically, a 2x2 array of micro-LEDs shares a single 6T-SRAM bitcell and associated control logic, reducing the total circuit area required compared to having dedicated circuits for each micro-LED. This merging approach enables high-resolution displays with limited circuit real estate.
2Device complexity
If circuit sharing is implemented in macro-pixels to reduce area, then device complexity is reduced, but drive current variation increases
Solution Approach 1:
The patent implements local quality by introducing dedicated compensation circuits within each macro-pixel that can independently adjust drive current for each micro-LED. The 6T-SRAM bitcell stores compensation data specific to each micro-LED's characteristics, allowing localized current adjustment without affecting other micro-LEDs in the macro-pixel, thus maintaining uniformity despite circuit sharing.
Solution Approach 2:
The patent employs feedback mechanisms where drive current is monitored and adjusted based on actual micro-LED performance. The control logic reads compensation data from the 6T-SRAM bitcell and dynamically adjusts PWM duty cycles to compensate for variations in drive current, ensuring consistent brightness and reducing current variation across shared circuits.
3Manufacturing precision
If transition regions are reduced in macro-pixel architecture to increase pixel density, then manufacturing precision is improved, but circuit design robustness deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-characterizing each micro-LED during manufacturing and storing compensation parameters in the 6T-SRAM bitcell before the display operates. This advance preparation allows the control logic to immediately compensate for manufacturing variations without requiring complex real-time adjustments, maintaining robustness even with minimal transition regions.
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 macro-pixel architecture enables higher bit depth (up to 8 or 9 bits) at small pixel pitches, reduces drive current variation, improves design margins, and enhances test and debug features, leading to improved display quality and robustness.
Implementation Method 1
Light emitting diodes (LEDs) convert electrical energy into optical energy
Implementation Method 2
Light emitting diodes (LEDs) convert electrical energy into optical energy
Data Source
AI summary
A micro-light emitting diode (micro-LED) display backplane includes a plurality of macro-pixels. Each macro-pixel includes: a contiguous two-dimensional (2-D) array of bitcells storing display data bits for driving a set of micro-LEDs of a 2-D array of micro-LEDs; and drive circuits configured to generate, based on the display data bits stored in the contiguous 2-D array of bitcells, pulse-width modulated (PWM) drive signals for driving the set of micro-LEDs of the 2-D array of micro-LEDs. In one example, the plurality of macro-pixels is grouped into a plurality of sub-arrays, where each sub-array of the plurality of sub-arrays includes a set of macro-pixels and a local periphery circuit next to the set of macro-pixels. The local periphery circuit includes, for example, a buffer, a repeater, a clock gating circuit for gating an input clock signal to the sub-array, and/or a sub-array decoder for selecting the sub-array.