MicroLED Backplane PWM Architecture for Uniform Luminance Control

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Solution Overview

Problem

MicroLED displays face challenges in brightness, image uniformity, and luminance control due to issues like dynamic false contouring, current mismatch, and parasitic capacitance, which affect image fidelity and visibility in bright natural light conditions.

Innovation Solution

Implementing a sub-pixel digital comparator with a shared pulse width row counter, single pulse width modulation, and dynamic current mirror to enhance brightness, accuracy, and uniformity, along with precise luminance control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If traditional binary PWM techniques are used to control LED brightness, then transistor count is efficient, but image artefacts such as dynamic false contouring occur at high illumination duty cycles

Engineering Contradiction:

Improvetransistor countVSAvoidimage fidelity

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The illumination period is divided into multiple sub-periods with different duty cycles. Instead of using a single PWM signal, the system segments the illumination into first and second sub-periods with first and second duty cycles respectively, allowing precise control of luminance while avoiding false contouring artifacts.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically adjusts duty cycles for different sub-periods within each illumination period. The first duty cycle is applied during the first sub-period and the second duty cycle during the second sub-period, enabling adaptive luminance control that maintains image fidelity across varying brightness requirements.

Inventive Principle:

Principle #15Dynamics

2Measurement precision

If current sources are used to drive LEDs, then current control is precise, but current mismatch occurs between LEDs due to FET threshold variation

Engineering Contradiction:

Improvecurrent control accuracyVSAvoidluminance uniformity

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

A calibration process is performed before normal operation to measure and compensate for FET threshold variations. The system pre-determines calibration values for each current source based on actual measurements, storing these values for use during subsequent illumination periods to correct for manufacturing variations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system measures actual current output from each current source and uses this feedback to adjust calibration values. By continuously monitoring and adjusting for threshold variations, the system maintains uniform luminance across all LEDs despite manufacturing tolerances in FET characteristics.

Inventive Principle:

Principle #23Feedback

3Illumination intensity

If small pulse width modulation and low driving current are used for low luminance applications, then desired light output is achieved, but parasitic capacitance inside mLED cannot be overcome

Engineering Contradiction:

Improveluminance levelVSAvoidsignal integrity

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The system uses periodic illumination periods with alternating sub-periods. During the first sub-period, a higher current is applied to charge the parasitic capacitance, and during the second sub-period, the actual low luminance signal is applied. This periodic high-current charging cycle overcomes the parasitic capacitance barrier while maintaining low average luminance output.

Inventive Principle:

Principle #19Periodic action

4Ease of operation

If voltage driving is used for LEDs, then device operation is simple, but small voltage changes result in large current changes due to sharp IV characteristic

Engineering Contradiction:

Improvedriving simplicityVSAvoidcurrent control accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The system replaces direct voltage control with current control using programmable current sources. Instead of adjusting voltage and relying on the LED's IV characteristic, the system directly controls current magnitude, providing linear and precise control over luminance output while maintaining ease of operation through digital programming.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12518677B1Apparatuses, systems, and methods for MicroLED (mLED) backplane architectures

Publication Date: 2026.01.06 FORTH DIMENSION DISPLAYS

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.