PWM Pattern Selection for EMI Spectrum Spreading
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Solution Overview
Problem
Delta-sigma modulator systems combined with pulse width modulators face significant electromagnetic interference (EMI) issues due to radiated energy at switching frequencies and harmonic frequencies, particularly with low-level input signals that generate square wave PWM patterns, exceeding EMI standards.
Innovation Solution
The system spreads the spectrum of harmonic frequencies by selecting multiple PWM patterns for each quantization level, shifting the rising edges of these patterns in time, which reduces energy radiation and EMI. This is achieved through a signal processing system that includes a delta sigma modulator and a pulse width modulator, where multiple PWM patterns are associated with each quantization level, and the PWM output signal generator selects patterns to spread the harmonic frequencies, reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a single PWM pattern is used for each quantization level, then the system operation is simple, but electromagnetic interference is high due to concentrated harmonic energy
Solution Approach 1:
The patent segments the single PWM pattern into multiple alternative patterns (K patterns) for each quantization level. Each pattern has the same pulse width but different temporal positions, allowing the harmonic energy to be distributed across different time slots rather than concentrated in a single pattern, thereby reducing EMI while maintaining functional simplicity
Solution Approach 2:
The system dynamically selects among multiple PWM patterns based on spreading requirements. The PWM pattern selector dynamically chooses different patterns from the K available patterns for different frames, creating temporal variation in the PWM output that spreads the spectral content and reduces concentrated harmonic energy, thus reducing electromagnetic interference
2Object-generated harmful factors
If PWM patterns are shifted in time to spread harmonic frequencies, then EMI is reduced, but the processing complexity increases
Solution Approach 1:
The patent divides the PWM pattern selection into K discrete segments or patterns, each representing a different temporal positioning of the same quantization level. This segmentation allows the system to spread energy by selecting different segments (patterns) without requiring complex continuous adjustment mechanisms
Solution Approach 2:
The system employs periodic switching among multiple PWM patterns with the same pulse width but different temporal positions. By periodically varying the pattern selection across frames, the harmonic frequencies are spread across a broader spectrum, reducing peak energy radiation while maintaining a relatively simple periodic selection mechanism
Data Source
AI summary
The signal processing system includes a pulse width modulator (PWM) that receives a quantizer output signal from a delta sigma modulator. Each quantizer output signal represents one of N quantization levels. For at least one of the quantization levels, the PWM can generate multiple, different PWM patterns. Thus, each quantization level in at least a subset of the N quantization levels is associated with at least two PWM patterns. In at least one embodiment, the subset of quantization levels represents the quantization of low level samples of a quantizer input signal. By associating multiple PWM patterns to at least the subset of the quantization levels, the pulse edges of the PWM patterns in a frame are shifted in time with respect to subsequent PWM patterns, which spreads the spectrum of harmonic frequencies of the PWM output signal. Spreading the spectrum of harmonic frequencies of the PWM output signal can reduce electromagnetic interference (EMI).