Spread Spectrum Clock Calibration for Uniform EMI Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spread spectrum clock generators using phase locked loops (PLLs) fail to achieve a perfectly uniform frequency spectrum due to imperfections in real circuit implementations, leading to reduced effectiveness in reducing electromagnetic interference (EMI) as the energy distribution is not evenly spread across the desired frequency range.
Innovation Solution
A spread spectrum clock generator that employs a modulator with a profile memory and an inverse transfer function (ITF) filter to condition a desired triangular waveform, ensuring a uniform frequency change over time, thereby minimizing peaking and achieving a nearly perfect frequency distribution across the band, even in actual circuit implementations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a triangular wave signal is used to vary the clock frequency in a PLL-based spread spectrum generator, then the frequency spectrum is spread over the desired range, but the energy distribution becomes non-uniform due to circuit imperfections, reducing EMI reduction effectiveness
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing compensation values in a lookup table that anticipate the non-linearities of the PLL circuit. The triangular wave is pre-distorted using these compensation values before being applied to the PLL, so that the circuit's imperfections are compensated for in advance, resulting in a uniform frequency spectrum despite real-world circuit variations.
2Object-affected harmful factors
If the frequency of the clock signal is varied using a triangular wave to spread the spectrum, then energy is distributed across a frequency range, but peak EMI levels are not sufficiently reduced due to non-uniform energy distribution
Solution Approach 1:
The patent changes the parameters of the triangular wave signal by applying non-linear transformation through the lookup table. The amplitude and timing parameters of the triangular wave are modified point-by-point based on pre-calculated compensation data, transforming it into a distorted waveform that compensates for PLL non-linearities and achieves uniform energy distribution across the frequency spectrum.
3Adaptability or versatility
If real circuit implementations such as PLLs are used to spread the clock frequency, then the spread spectrum function is achieved, but the frequency spectrum becomes non-uniform, limiting EMI reduction effectiveness
Solution Approach 1:
The patent implements feedback by measuring the actual frequency output of the PLL and using this information to adjust the input triangular wave through the lookup table. The system continuously monitors the PLL's non-linear response and compensates for it in real-time, ensuring uniform spectrum distribution while maintaining the adaptability of the spread spectrum function across different operating conditions.
Data Source
AI summary
In one form, a spread spectrum clock generator includes a clock generator and a modulator. The clock generator modulates a frequency of a reference clock signal using a modulation signal to provide a spread spectrum clock signal. The clock generator has a characteristic transfer function that varies with values of a parameter. The modulator generates the modulation signal according to a desired profile conditioned by an inverse of the characteristic transfer function of the clock generator at a current value of the parameter.