Spread-Spectrum Clock Circuit Using Jitter to Reduce EMI
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Solution Overview
Problem
As digital systems grow, they generate electromagnetic interference due to concentrated current flows, degrading overall system performance, and existing methods to reduce this interference are inadequate.
Innovation Solution
A spread spectrum clock generation device that includes comparators, a latch, and a delaying circuit to generate a clock signal with a wider frequency spectrum by introducing jitter, thereby dispersing power across adjacent frequencies, reducing electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If digital systems use synchronous design with flip-flops updating at clock edges, then system operation is coordinated and controlled, but large current flows at update points generate electromagnetic waves that interfere with communication frequencies
Solution Approach 1:
The patent applies periodic action by introducing artificial jitter to the clock signal, creating periodic variations in the clock edge timing. This causes the current consumption of digital circuits to vary periodically rather than occurring in concentrated bursts, thereby spreading the electromagnetic spectrum and reducing peak power at any single frequency while maintaining coordinated system operation
Solution Approach 2:
The patent changes the timing parameter of the clock signal by adding jitter, which modifies when clock edges occur. This parameter change disperses the instantaneous current demand across a wider time range, transforming the frequency characteristics of generated electromagnetic waves and reducing interference at communication frequencies
2Productivity
If current flows are concentrated at the same point in time, then system updates are synchronized efficiently, but electromagnetic wave power is concentrated at a single frequency causing interference
Solution Approach 1:
By introducing periodic jitter variations to the clock signal, the patent transforms concentrated current flows into periodically varied current flows. This maintains the synchronous updating of digital systems while spreading the electromagnetic energy across multiple frequencies through the periodic timing variations
Solution Approach 2:
The patent converts the harmful concentrated current flows into beneficial dispersed current flows by adding jitter. The artificial timing variations that would normally be considered noise or distortion are instead used to spread spectrum energy, transforming electromagnetic interference into a controlled signal that improves overall system performance
3Object-generated harmful factors
If a spread spectrum clock generator adds artificial jitter to disperse current demand timing, then electromagnetic wave power is dispersed to adjacent frequency regions, but the complexity of the clock generation circuit increases
Solution Approach 1:
The patent implements a nested structure where a jitter generation circuit is embedded within the clock generation circuit, and a delay circuit with multiple delay elements is nested within the jitter generation circuit. This hierarchical nesting allows the complex spread spectrum function to be built from simpler modular components, making the overall complex circuit more manageable and implementable
Data Source
AI summary
A spread spectrum clock generation device that may reduce electromagnetic interference (EMI) includes: a first comparator configured to compare an input signal with a first reference voltage and output a first comparison signal; a second comparator configured to compare the input signal with a second reference voltage and output a second comparison signal; a latch configured to receive the first and second comparison signals as inputs and output an output signal; and a delaying circuit configured to generate the input signal by delaying the output signal to have a different delay time for each time interval.