Spread Spectrum Clock Generation with Repetition Number Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spread spectrum clock signal generators require large look-up tables and complex phase movement control units, making them costly and difficult to design, especially when generating multiple constant ppm offset regions, which increases the spectral amplitude of electromagnetic interference (EMI) in high-data-rate applications.
Innovation Solution
A system and method using a repetition number (RN) configured with a phase-locked loop and sigma-delta noise-shaping modulator to generate a spread spectrum clock signal with a constant ppm offset, reducing the need for large look-up tables and simplifying phase movement control by calculating the repetition number for each time slot and modulating the fractional part to create a triangular modulation profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piece-wise linear emulation with multiple constant ppm offset regions is used to generate triangular SSC profile, then the spread spectrum clocking accuracy is improved, but the device complexity increases due to large look-up tables and complex phase movement control units
Solution Approach 1:
The patent replaces the mechanical lookup table approach with a mathematical calculation system. Instead of storing pre-computed phase movement values in large lookup tables, the system uses a phase movement generator that calculates values on-the-fly using formulas involving repetition numbers and fractional parts. This substitution of mechanical storage with mathematical computation significantly reduces hardware complexity while maintaining the same level of ppm offset accuracy.
Solution Approach 2:
The system implements self-service through the phase movement generator that automatically computes the required phase movements using the repetition number and its fractional part. The generator uses the formula involving sin(2πk/N) where k is the repetition number and N is the period, eliminating the need for external control units or pre-stored tables. The system serves itself by generating all necessary control signals through mathematical relationships inherent in the spread spectrum clocking requirements.
2Manufacturing precision
If large look-up tables are used to store phase movement data for multiple ppm offset regions, then the SSC profile generation accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The patent replaces the mechanical lookup table storage system with a computational system that generates phase movement values using mathematical formulas. The phase movement generator computes values using the repetition number and fractional part relationships, eliminating the need for large memory structures. This reduces manufacturing complexity and cost while maintaining the same level of SSC profile generation accuracy through on-the-fly calculations.
3Measurement precision
If complex phase movement control units are implemented to handle multiple constant ppm offset regions, then the triangular SSC profile accuracy is improved, but the ease of operation deteriorates due to difficult programming and calculation
Solution Approach 1:
The patent replaces complex control unit programming with straightforward mathematical calculations. The phase movement generator uses simple formulas based on repetition numbers and fractional parts, eliminating the need for complex control logic programming. This substitution makes the system easier to operate and program while maintaining high triangular SSC profile accuracy through the mathematical relationships inherent in the spread spectrum clocking methodology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the spectral amplitude of electromagnetic interference (EMI) components over a substantial bandwidth, making it easier to program and calculate the SSC modulation profile on-the-fly, thereby improving the efficiency of EMI reduction in high-data-rate applications.
Implementation Method 1
a phase-locked loop circuit to generate a bit clock
Implementation Method 2
a sigma-delta modulator for noise shaping a SSC modulation profile
Data Source
AI summary
A system and method for generating a spread spectrum clock signal with a constant ppm offset as a function of a repetition number. A phase interpolator can be configured in association with of a phase-locked loop circuit in order to provide a phase movement from a bit clock generated by the PLL circuit. A repetition number divider computes the repetition number for each time slot in a piece-wise SSC modulation profile. A noise shaping modulator can be employed for modulating a fractional part associated with the repetition number. A repetition counter and a phase accumulator receives an integer part of the repetition number and counts unit interval clock periods equal to a sum of integer and the sigma-delta modulated fractional parts of the repetition number. The phase accumulator can be incremented and/or decremented based on the sign of the spread spectrum direction.