Spread Spectrum Clock Modulation for Flat EMI Distribution
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Solution Overview
Problem
Modern digital electronic circuits face challenges in operating at high clock frequencies while complying with stringent EMI/EMC standards, and existing spread spectrum clock generation methods are ineffective in distributing energy over a wider frequency band, requiring significant silicon area in integrated circuits.
Innovation Solution
A spread spectrum clock generation system using a Digital Frequency Profile Generator with a multilevel error feedback noise shaping structure, providing a near-optimal frequency modulation profile for spectral flatness, and offering flexibility through center-spread and down-spread operating modes without the need for separate profile generators or look-ahead circuits, thus minimizing silicon area and maintaining SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high clock frequency is used to increase operating speed, then productivity is improved, but EMI emissions increase causing harmful effects
Solution Approach 1:
The patent applies periodic frequency modulation to the clock signal, intentionally varying the frequency over time in a periodic manner. This spreads the spectral energy of the clock signal across a wider frequency range, reducing peak EMI emissions while maintaining the high operating frequency needed for productivity.
Solution Approach 2:
The patent changes the frequency parameter of the clock signal dynamically through modulation. By varying the frequency around a nominal value according to a predetermined profile, the signal energy is distributed across multiple frequencies, achieving EMI reduction while maintaining high-speed operation.
2Object-generated harmful factors
If spread spectrum techniques are used to reduce EMI emissions, then harmful effects are reduced, but silicon area increases
Solution Approach 1:
The patent uses a look-ahead circuit that pre-calculates the required frequency compensation values based on the predetermined modulation profile. This allows the frequency adjustment to be prepared in advance, enabling efficient implementation with reduced silicon area by avoiding complex real-time calculation circuits.
Solution Approach 2:
The patent implements a simplified model of the frequency modulation profile using a digital lookup table or pre-stored correction values. Instead of implementing the full complex modulation algorithm, a simplified representation is used that achieves the same EMI reduction effect with minimal silicon area.
3Adaptability or versatility
If separate profile generators are used for center-spread and down-spread modes, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements a single unified frequency profile generator that can operate in both center-spread and down-spread modes by changing control parameters. This multi-functional approach eliminates the need for separate generators for each mode, reducing device complexity while maintaining full adaptability to different operational requirements.
Solution Approach 2:
The patent makes the frequency profile generator dynamically reconfigurable, allowing it to switch between different modulation profiles and modes of operation. This dynamic capability enables a single circuit to perform multiple functions that would otherwise require separate static circuits, reducing overall complexity.
Data Source
AI summary
The present disclosure provides a spread spectrum clock generation system having a digitally controlled phase locked loop (PLL) and a digital frequency profile generator to create a near optimal frequency modulation profile for the purpose of achieving spectral flatness in the output frequency modulated clock. The circuit is combined with a multilevel error feedback noise shaping structure that provides the required noise transfer function for the quantization noise but maintains a unity gain all pass signal transfer function. This arrangement offers minimal degradation of the in-band signal-to-noise ratio (SNR) at the cost of higher out-of-band noise.