Asymmetric Spread Spectrum Clocking for Smoother EMI Profiles
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Solution Overview
Problem
Current methods for reducing electromagnetic interference (EMI) in electronic circuits, particularly with increasing clock speeds, face challenges in effectively suppressing radiated and conducted emissions due to spectral anomalies caused by conventional spread spectrum modulation profiles, which hinder efficient EMI reduction.
Innovation Solution
A clock modulation system that employs a spread spectrum modulation profile generator to modulate the clock frequency using asymmetrical upslew and downslew modulation forms, defined by distinct segments, to generate a clock output with reduced EMI, where the upslew and downslew modulation forms are different and controlled by a phase detector, filter, oscillator, and feedback divider.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional spread spectrum modulation profiles are used to reduce EMI, then EMI suppression is improved, but spectral anomalies (peaks and valleys) are generated that hinder effective EMI reduction
Solution Approach 1:
The patent applies asymmetry by using different upslew and downslew modulation forms in the spread spectrum modulation profile. The upslew modulation form uses one set of modulation parameters while the downslew modulation form uses different parameters, creating an asymmetric profile that eliminates the spectral peaks and valleys caused by symmetric modulation. This asymmetric approach smooths the spectral profile while maintaining EMI suppression effectiveness.
Solution Approach 2:
The patent changes modulation parameters between upslew and downslew phases. Specifically, it uses different modulation depths, frequencies, or waveforms for the upslew and downslew portions of the clock signal cycle. This parameter variation allows the system to achieve smoother spectral characteristics by optimizing each phase independently, resolving the contradiction between EMI suppression and spectral smoothness.
2Productivity
If clock speed is increased to meet performance requirements, then productivity is improved, but EMI radiation increases
Solution Approach 1:
The patent applies periodic action through spread spectrum modulation, which periodically varies the clock frequency around its nominal value. By modulating the clock signal with a pseudorandom sequence or triangular wave, the energy that would concentrate at harmonic frequencies is distributed across a broader frequency range. This periodic frequency variation reduces peak EMI radiation while maintaining the high average clock speed needed for performance.
Solution Approach 2:
The patent makes the clock frequency dynamic by continuously modulating it according to the spread spectrum profile. Instead of a fixed frequency that produces strong harmonic emissions, the frequency dynamically varies within a controlled range. This dynamic approach allows the system to maintain high productivity through elevated average clock speeds while reducing EMI through frequency distribution.
Data Source
AI summary
There is provided a method of modifying a first clock to generate a second clock with reduced electromagnetic interference (EMI). The method comprises receiving the first clock, generating an upslew modulation form during an upslew frequency transition, generating a downslew modulation form during a downslew frequency transition, modulating a frequency of the first clock over a period of time using the upslew modulation form and the downslew modulation form to generate the second clock, and wherein the upslew modulation form and the downslew modulation form are different. The upslew modulation form and the downslew modulation form are defined by upslew modulation values and downslew modulation values, respectively, and the method further comprises receiving the upslew modulation values and the downslew modulation values, and generating fractional upslew modulation values and fractional downslew modulation, respectively, for modulating the frequency of the first clock.