Spread Spectrum Switching Circuit Reducing EMI Spurs
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Solution Overview
Problem
Existing spread spectrum techniques for reducing electromagnetic interference (EMI) in switched mode power supplies either fail to adequately address low frequency noise spurs or introduce additional spectral noise in the audio band, leading to increased system costs and size.
Innovation Solution
A method involving a pseudorandom slope selection for modulation curves in spread spectrum switching frequencies, which produces an oscillating signal at varying frequencies within a predetermined range, effectively reducing low frequency noise spurs while maintaining low EMI at fundamental operating frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If board level solutions (shielding, filtering, layout techniques) are used to mitigate EMI, then EMI suppression is improved, but system cost and size increase
Solution Approach 1:
The patent converts the harmful EMI spurs into beneficial spread spectrum signals by intentionally modulating the switching frequency. Instead of trying to suppress EMI through passive components like filters and shields, the system uses active frequency modulation to distribute EMI energy across a wider bandwidth, reducing peak spectral density without adding cost or size
Solution Approach 2:
The patent replaces mechanical/passive EMI mitigation approaches (shielding, filtering, physical layout techniques) with an electronic control approach using spread spectrum frequency modulation. This substitution eliminates the need for additional passive components and complex PCB layout techniques, reducing both system cost and size while maintaining EMI suppression effectiveness
Data Source
AI summary
A method of generating a spread spectrum signal is disclosed. The method includes selecting a first pseudorandom slope for a modulation curve. A current frequency on the modulation curve is selected. An oscillating signal is produced at the current frequency for a respective time. The current frequency is set to a next frequency on the modulation curve. The steps of producing an oscillating frequency and setting the current frequency to a next frequency are repeated until the current frequency is a final frequency on the modulation curve.