LED Driver Synchronization for EMI Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-definition LED display panels face issues with electromagnetic interference (EMI) due to unsynchronized spread spectrum modulation depth controllers, leading to uniformity problems in light intensity caused by phase differences and frequency variations among driver chips.
Innovation Solution
A system control unit generates synchronization start signals to phase locked loop circuits, which include phase frequency detectors, charge pumps, loop filters, voltage controlled oscillators, and sigma delta modulators, to synchronize spread spectrum modulation depth controllers across the LED display panel, ensuring they start synchronously and adjust modulation depth to reduce EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple spread spectrum modulation depth controllers are used to reduce EMI, then EMI radiation is attenuated, but synchronization difficulty increases due to automatic starting influenced by external power ramp rate and IC process skew
Solution Approach 1:
The system performs preliminary actions by first establishing phase-locked loop circuits in each driver chip before enabling spread spectrum modulation. The synchronization signal is prepared in advance and distributed to all driver chips before they start modulation, ensuring all chips are in a synchronized state ready for modulation without causing EMI issues
Solution Approach 2:
The system uses feedback mechanisms through phase-locked loop circuits that continuously monitor and adjust the timing of clock signals. The loop filter and charge pump components provide feedback to maintain synchronization across all driver chips, automatically compensating for variations in power ramp rate and IC process skew
2Object-affected harmful factors
If spread spectrum modulation is implemented to reduce peak EMI value, then electromagnetic interference is reduced, but phase differences between multiple driver chips cause uniformity problems in light intensity
Solution Approach 1:
The system merges the synchronization function into the spread spectrum modulation depth controller by using a centralized synchronization signal that coordinates all driver chips. This combining approach ensures that all chips start modulation at the same reference point, eliminating phase differences while maintaining EMI reduction benefits
Solution Approach 2:
The system creates equipotentiality in timing across all driver chips by distributing synchronization signals that ensure all chips are at the same phase state when modulation begins. The phase-locked loop circuits equalize timing differences, ensuring uniform light intensity output while maintaining spread spectrum EMI reduction
Data Source
AI summary
The apparatus for driving LED display includes a system control unit having a synchronization signal generator configured to generate a synchronization start signal and a plurality of phase locked loop circuits. Each of the phase locked loop circuits includes a divider coupled to the voltage controlled oscillator and configured to change the sequence of dividing ratios over a modulation period, a sigma delta modulator configured to generate a sequence of random numbers to the divider, and a spread spectrum modulation depth controller coupled to the sigma delta modulator and configured to receive the synchronization start signal from the synchronization signal generator. Upon receipt of the synchronization start signal, the spread spectrum modulation depth controller starts a spread spectrum modulation.