Backplane Modulation for LED Color Balance and Gray Scale
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Solution Overview
Problem
Emissive display systems face challenges in achieving efficient multi-color or monochrome LED display operations without objectionable image artifacts, particularly in maintaining color balance and gray scale capability due to varying ideal drive voltages and currents for different semiconductor materials, and the need for rapid pulse-width modulation to avoid color shift and aliasing.
Innovation Solution
A backplane and modulation system utilizing a single crystal silicon process with a minimum number of metal layers, providing suitable operating voltages and currents for each color, and employing a current source or current mirror circuit to independently control each pixel, ensuring rapid duty cycle modulation and maintaining color balance through pulse-width modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different semiconductor materials are used for different LED colors, then color variety is achieved, but drive voltage and current requirements vary making color balance difficult to maintain
Solution Approach 1:
The patent implements separate current sources or current mirrors for each color (red, green, blue LEDs) with independently adjustable parameters. Each color channel has its own drive circuit optimized for that specific semiconductor material's characteristics, allowing local adjustment of drive voltage and current to achieve color balance while maintaining overall system functionality.
2Ease of operation
If voltage modulation is used to control LED intensity, then gray scale control is achieved, but color shift occurs complicating color balance
Solution Approach 1:
The patent replaces voltage modulation with current modulation for LED intensity control. By using current sources or current mirrors to control the drive current to each LED, the system achieves gray scale control without the color shift problems associated with voltage modulation, as current control maintains stable LED forward voltage and thus stable emission wavelength.
3Stability of the object's composition
If pulse width modulation is used to control LED intensity, then color stability is maintained, but rapid modulation is required to avoid flicker and aliasing
Solution Approach 1:
The patent implements pulse width modulation (PWM) at frequencies above the critical flicker frequency (typically >200Hz) to control LED intensity while maintaining color stability. By operating at sufficiently high frequencies, the human eye perceives continuous illumination without flicker, and aliasing artifacts are avoided, while the PWM technique maintains constant average current for color stability.
4Productivity
If separate control circuits are implemented for each pixel to enable independent modulation, then gray scale capability is improved, but device complexity increases
Solution Approach 1:
The patent uses current mirror circuits that can be replicated across multiple pixels with identical or slightly modified structures. Each pixel receives control signals from shared data and clock lines, and the current mirrors automatically generate the appropriate drive currents based on these shared signals, enabling independent pixel control without requiring completely separate control circuits for each pixel.
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 enables efficient operation of multi-color or monochrome LED display systems with improved gray scale capability and color balance, reducing the risk of image artifacts by ensuring each pixel receives a stable and synchronized drive, thus enhancing the overall display quality.
Implementation Method 1
use of a suitable voltage to drive the LED will cause electrons within the LED to combine with electron holes, resulting in the release of energy in the form of photons, a feature referred to as electroluminescence
Data Source
AI summary
A backplane operative to drive an array of emissive pixel elements is disclosed. Each pixel element comprises a pixel circuit drive element and an emissive element, wherein the pixel circuit drive element comprises a memory cell, a current source element, and a modulation element. The present invention improves on an emissive display by providing a backplane and modulation system that enables fabrication of multi-color or monochrome LED display systems that operate efficiently and without objectionable image artifacts. One aspect of the present invention is to realize the backplane in a single crystal silicon process with a minimum number of metal layers while providing each color with a suitable operating voltage and drive current.