Clock Spread Spectrum Circuit for EMI Reduction Without Jitter Disruption
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Solution Overview
Problem
Current methods for reducing electromagnetic interference (EMI) in clock signals, such as shielding and filtering, are costly and inefficient, and clock spread spectrum techniques that introduce periodic jitter can disrupt digital circuit operations.
Innovation Solution
A clock spread spectrum circuit using time-average-frequency direct-period-synthesis (TAF-DPS) technology generates a spread spectrum output signal by varying the frequency control word over time, allowing the clock signal to span a broadband frequency range without introducing additional noise, thus reducing EMI effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional EMI reduction methods such as shielding and filtering are used, then electromagnetic interference is reduced, but cost increases and efficiency decreases
Solution Approach 1:
The patent changes the frequency parameter of the clock signal by introducing spread spectrum modulation. The frequency control word is modified to include a decimal part that varies over time, causing the clock frequency to sweep across a range of values rather than remaining fixed. This parameter change disperses the concentrated EMI energy across a broader frequency spectrum, reducing peak interference levels without requiring additional shielding or filtering components.
2Object-affected harmful factors
If periodic jitter is introduced to reduce EMI through clock spread spectrum, then electromagnetic interference is reduced, but digital circuit operation is disrupted
Solution Approach 1:
The patent implements dynamic frequency adjustment where the frequency control word changes over time according to a controlled modulation pattern. The decimal part of the frequency control word varies continuously, creating a dynamic spread spectrum effect that moves the clock frequency across a range of values. This dynamic approach reduces EMI by distributing energy over time and frequency, while the controlled nature of the modulation ensures that the average frequency remains stable enough for reliable digital circuit operation.
3Object-affected harmful factors
If frequency control word changes discretely with time, then spread spectrum function is achieved, but signal stability may be affected
Solution Approach 1:
The patent employs periodic modulation where the frequency control word changes in a controlled, periodic manner. The decimal part of the frequency control word follows a periodic pattern that sweeps the clock frequency across a designated range and then returns to the starting point. This periodic action achieves the spread spectrum function necessary for EMI reduction while maintaining signal stability through the predictable and repeating nature of the frequency variations, allowing digital circuits to adapt to the regular pattern.
Data Source
AI summary
A clock spread spectrum circuit, an electronic equipment, and a clock spread spectrum method are disclosed. The clock spread spectrum circuit includes a control circuit, a signal generation circuit, and a duty cycle adjustment circuit. The duty cycle adjustment circuit is configured to generate a target voltage having a duty cycle that is equal to a target duty cycle, the control circuit is configured to generate a frequency control word according to a modulation parameter, and the frequency control word changes discretely with time; and the signal generation circuit is configured to receive the target voltage and the frequency control word and generate and output a spread spectrum output signal that is spectrum-spread according to the target voltage and the frequency control word, and the spread spectrum output signal corresponds to the frequency control word and a duty cycle of the spread spectrum output signal is the target duty cycle.