MicroLED Backplane PWM Architecture for Uniform Grey Levels
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Solution Overview
Problem
MicroLED displays face challenges in brightness, uniformity, and image quality due to issues such as dynamic false contouring, current mismatch, and parasitic capacitance, especially in bright natural light conditions and high illumination duty cycles.
Innovation Solution
Implementing a sub-pixel digital comparator with a shared pulse width row counter, single pulse width modulation with row-based precise control, and a dynamic current mirror to enhance luminance control and pixel-to-pixel compensation, reducing transistor count and compensating for threshold variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional binary pulse width modulation techniques are used, then transistor count is efficient, but image artefacts occur at high illumination duty cycles
Solution Approach 1:
The patent segments the illumination duty cycle control into multiple bit-planes, where each bit-plane controls a specific portion of the duty cycle. This allows precise control of high illumination duty cycles while maintaining efficient transistor usage, resolving the contradiction between device complexity and image quality.
2Reliability
If single pulse techniques are used, then image artefacts are reduced, but accuracy decreases or transistor count increases
Solution Approach 1:
The patent introduces a temporal dimension by using sequential bit-plane illumination with different duty cycles. Multiple pulses with varying durations are used to achieve precise luminance control, transforming a single-dimension problem into a multi-dimensional solution that maintains both accuracy and image quality.
3Ease of operation
If current sources are used to drive many LEDs, then LED current control is improved, but current mismatch occurs due to FET threshold variation
Solution Approach 1:
The patent implements a feedback mechanism where the actual LED current is measured and used to adjust the control signal. This closed-loop approach compensates for FET threshold variations and ensures uniform current distribution across all LEDs, resolving the contradiction between ease of operation and current uniformity.
4Illumination intensity
If small pulse width modulation and low driving current are used, then low luminance is achieved, but parasitic capacitance cannot be overcome
Solution Approach 1:
The patent applies a preliminary high-current pulse before the main low-current pulse. This preliminary action quickly charges the parasitic capacitance, allowing subsequent low-current pulses to maintain signal integrity and achieve accurate low luminance levels without being overwhelmed by capacitance effects.
Data Source
AI summary
Method, apparatuses, and systems are described to display image data to a sub-pixel within a micro-LED (mLED) display. A sub-pixel image data value is stored at the sub-pixel. The sub-pixel is turned to an ON state. A shared row counter value is provided to the sub-pixel. The shared row counter value and the sub-pixel image data value are compared at the sub-pixel. The sub-pixel is turned to an OFF state if the shared row counter value is equal to or greater than the sub-pixel image data value.