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 LED current variation due to parasitic resistance and crosstalk, leading to inconsistent brightness and operational challenges, particularly in large matrix pixel arrays that require fine-grained light intensity and color control.
Innovation Solution
The implementation of a close loop circuit with an operational amplifier (op-amp) and resistors in each pixel, which decouples current control from PWM switching, minimizing the impact of parasitic resistance and crosstalk by regulating LED current based on feedback and reference currents, thereby maintaining consistent current levels across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM control is used for dimming and color tuning, then energy efficiency and brightness control are improved, but LED current variation and pixel to pixel crosstalk increase due to parasitic resistance
Solution Approach 1:
The patent implements a feedback mechanism where the actual LED current is sensed and compared with the reference current, and the difference is used to adjust the PWM duty cycle. This closed-loop feedback system compensates for parasitic resistance variations and ensures consistent LED current across all pixels while maintaining PWM-based energy efficiency.
Solution Approach 2:
The patent introduces an intermediary current sensing circuit and control circuit that mediates between the PWM control signal and the LED current. This intermediary system measures the actual current and adjusts the PWM duty cycle accordingly, isolating the LED from direct PWM switching effects and reducing crosstalk while maintaining energy efficiency.
2Adaptability or versatility
If PWM switching is applied to control pixel intensity, then brightness modulation capability is improved, but crosstalk between adjacent pixels increases due to parasitic capacitance
Solution Approach 1:
The feedback mechanism senses the actual current through each pixel and adjusts the PWM duty cycle to compensate for crosstalk effects. By continuously monitoring and adjusting based on actual current, the system maintains independent brightness control for each pixel while preserving the overall PWM modulation capability.
Solution Approach 2:
The patent dynamically changes the PWM duty cycle parameter based on the sensed current conditions. When crosstalk is detected, the system adjusts the duty cycle parameter to compensate, ensuring that the brightness modulation capability is maintained without introducing harmful crosstalk effects between adjacent pixels.
3Device complexity
If constant input voltage power supply is used with PWM control, then circuit simplicity is maintained, but LED current variation due to parasitic resistance cannot be compensated
Solution Approach 1:
The feedback circuit introduces a sensing mechanism that monitors actual LED current and adjusts PWM duty cycle accordingly. This adds precision to current control without significantly complicating the overall circuit architecture, as the feedback path uses existing components and follows a straightforward control loop.
Solution Approach 2:
The system uses its own operating conditions (actual current) to automatically adjust itself. The feedback mechanism allows the circuit to self-regulate current variations caused by parasitic resistance, achieving current uniformity across pixels without requiring external intervention or complex additional circuitry.
Data Source
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. The close loop circuit in one pixel assembly may receive a reference current from a close loop circuit of another pixel assembly.