LED Pixel Array Current Control via Feedback Loop
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Solution Overview
Problem
Micro-LED arrays using pulse width modulation (PWM) control face issues with current variation due to parasitic resistance and crosstalk, leading to inconsistent brightness and operational challenges, particularly in large pixel arrays requiring fine-grained control and high refresh rates.
Innovation Solution
The implementation of a close loop circuit with an operational amplifier (op-amp) decouples current control from PWM switching, using resistors to minimize parasitic resistance effects and reduce crosstalk by providing feedback to regulate LED current, thereby maintaining consistent current magnitude across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PWM control is used for micro-LED arrays, then dimming and color tuning functionality is achieved, but current variation and pixel to pixel crosstalk occur due to parasitic resistance
Solution Approach 1:
The patent divides the control function into two separate circuits: a PWM switching circuit that handles timing/dimming and a separate current control circuit that handles current regulation. This segmentation isolates the current control from PWM switching effects, eliminating crosstalk and current variation caused by parasitic resistance while preserving both dimming and color tuning capabilities
Solution Approach 2:
The patent introduces a current control circuit as an intermediary between the PWM control and the LED array. This intermediary circuit actively regulates current based on feedback, mediating the effects of parasitic resistance and preventing current variation from propagating to the LED pixels, thus maintaining current consistency while enabling PWM-based dimming
2Device complexity
If conventional PWM switching is used, then control simplicity is maintained, but current variation occurs due to parasitic resistance in ground paths
Solution Approach 1:
The patent implements a feedback mechanism where the current control circuit continuously monitors the actual current through the LED and adjusts its output accordingly. This feedback loop compensates for voltage drops caused by parasitic resistance in ground paths, ensuring precise current magnitude consistency across all pixels while maintaining relatively simple control architecture
Solution Approach 2:
The current control circuit serves as an intermediary that sits between the simple PWM control and the LED array. It translates simple PWM timing signals into precisely regulated current waveforms, filtering out the effects of parasitic resistance and delivering consistent current magnitudes to all pixels without complicating the overall control system
3Productivity
If pixels are controlled at high refresh rates, then display quality is improved, but crosstalk between pixels increases during PWM switching
Solution Approach 1:
The patent segments the control functions so that PWM switching occurs in one circuit while current regulation occurs in a separate circuit. This segmentation prevents switching transients from one pixel from coupling into adjacent pixels through shared ground paths, eliminating crosstalk even at high refresh rates while maintaining high productivity
Solution Approach 2:
The current control circuit acts as an intermediary that isolates each pixel's current path from PWM switching effects. By providing individualized current control for each pixel based on feedback, it prevents switching events in one pixel from causing crosstalk in neighboring pixels, enabling high refresh rate operation without harmful interference
Data Source
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AI summary
A light-emitting diode (LED) array includes an array of pixel assemblies and a pulse width modulator. The pulse width modulator generates pulse width modulation (PWM) signals for controlling a duty cycle of each of the pixels. The pixel assemblies each include an LED, a switching circuit, and a close loop circuit. The switching circuit receives a PWM signal and alternately turns on and off the LED based on the PWM signal. The close loop circuit regulates an LED current provided by the switching circuit to the LED based on a feedback signal received from the switching circuit.