Spread Spectrum Clock Generation Using Tapped Delay Line
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Solution Overview
Problem
Contemporary digital electronic devices with large clock trees and RF frequency clock sources emit significant electromagnetic radiation, leading to interference and potential security vulnerabilities through predictable frequency patterns, which can be exploited by unauthorized observers for side-channel analysis.
Innovation Solution
The generation of spread spectrum clock signals using delay circuitry that introduces randomness based on a random input value, modulating the clock signal to reduce electromagnetic interference and create a non-deterministic noise profile, making it difficult for attackers to model the device's behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous clock signal at set frequency is used, then synchronous digital electronic devices can operate reliably, but electromagnetic radiation is emitted significantly causing interference and security vulnerabilities
Solution Approach 1:
The patent applies periodic action by using a dithered clock signal that modulates the fundamental clock frequency with a spread spectrum dither signal. This creates a periodic variation in the clock frequency that spreads the electromagnetic energy across a wider frequency band, reducing peak emissions at any single frequency while maintaining synchronous operation through the underlying periodic structure
Solution Approach 2:
The patent changes the frequency parameter of the clock signal by introducing dithering that varies the clock frequency dynamically. The spread spectrum clock signal modifies the instantaneous frequency around the fundamental clock frequency, transforming the electromagnetic radiation profile from concentrated at discrete frequencies to distributed across a broader spectrum, thereby reducing interference
2Measurement precision
If an un-dithered clock source is used, then the frequency spectrum has predictable center frequencies and harmonics, but this predictability allows unauthorized observers to extract confidential information through statistical analysis
Solution Approach 1:
The patent converts the harmful predictability of the clock signal into a beneficial security feature by deliberately introducing controlled randomness through dithering. The spread spectrum technique transforms the predictable frequency spectrum into a randomized spectrum that appears as noise, converting the vulnerability of predictability into a security advantage where the randomness masks confidential operational information
Solution Approach 2:
The patent applies preliminary action by pre-randomizing the clock signal frequency using a dither signal before the clock signal is used for synchronous operation. This preliminary frequency modulation ensures that the clock signal already contains the security-enhancing randomness before it reaches the digital logic, preventing any predictable patterns from emerging during normal operation
Data Source
AI summary
Spread spectrum clocking circuitry may be configured to produce a spread spectrum clock signal that coordinates the actions of functional circuitry. Spread spectrum clocking circuitry may be configured to include delay circuitry configured to generate a random delay signal based on a random input value and generate the spread spectrum clock signal based on the random delay signal. By introducing true randomness into the delay signal, spread spectrum clocking signal may be able to generate a truly random, as opposed to a merely pseudo random, clock signal.