μLED PWM Driving Circuit for Low-Luminance Uniformity
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Solution Overview
Problem
Micro light-emitting diode (μLED) displays face inefficiency at low luminance values when driven with constant current, leading to poor internal quantum efficiency and significant variations in optical power across pixels due to operating below peak current density, and existing digital PWM control schemes complicate circuitry for small pixels.
Innovation Solution
A pulse-width-modulation (PWM) control scheme using an analog control signal and a switched current source to maintain current density above a threshold, allowing the μLED to operate near peak efficiency by adjusting the duration of current supply based on desired brightness, rather than constant current, and using an external waveform signal to simplify pixel driver complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If constant current is used to drive μLED, then the circuit control is simple, but the internal quantum efficiency deteriorates at low luminance values and optical power varies significantly across pixels
Solution Approach 1:
The patent applies pulse-width modulation (PWM) to drive the μLED with periodic current pulses instead of constant current. The duty cycle of the PWM signal is adjusted to control the average brightness, while the peak current density during the pulse maintains the μLED operation near peak internal quantum efficiency. This periodic action allows the μLED to operate efficiently across all brightness levels.
2Measurement precision
If PWM control is implemented with digital signaling, then brightness control precision is improved, but circuit complexity increases for small pixels
Solution Approach 1:
The patent transitions from digital PWM control to analog control by changing the nature of the control signal from discrete digital levels to continuous analog voltage or current. This analog control parameter directly modulates the current source, simplifying the circuit architecture while maintaining precise brightness control through continuous adjustment of the control signal amplitude.
Solution Approach 2:
The patent extracts the PWM modulation function from the pixel-level circuitry and implements it externally or at a higher level. This removes the complex timing and switching circuitry from each small pixel, leaving only the essential current source and μLED, thereby significantly reducing device complexity while preserving brightness control precision.
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
This approach enhances operational uniformity across μLED displays by maintaining high internal quantum efficiency and reducing circuit complexity, achieving improved brightness control and energy efficiency while tolerating small variations in performance.
Implementation Method 1
μLEDs are self-emitting elements that generate light in response to a forward bias current that is provided to the diode. The amount of light emitted by the μLED increases as the amount of current supplied to the μLED increases.
Data Source
AI summary
Embodiments relate to a light-emitting-diode (LED) cell that includes a LED and a controller. The controller receives a brightness data signal and generates a driving signal corresponding to the brightness data signal. The controller includes a comparator that receives the brightness data signal and a control waveform signal. The controller is coupled to a switched current source that generates a driving current based on the driving signal.