Spread Spectrum Clock Generator With Calibrated Phase Modulation
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Solution Overview
Problem
Conventional EMI prevention methods are inadequate in addressing the significant source of Electronic Magnetic Interference (EMI) from system clocks, including frequency timing generators, crystal oscillators, and phase lock loops, necessitating an efficient and economical solution.
Innovation Solution
A spread spectrum clock generator is designed with a phase lock loop, a delay line, a modulation unit, a scaling unit, and a calibration unit, where the phase of the first input clock is modulated to vary the frequency of the output clock periodically, utilizing a phase/frequency detector, charge pump, low-pass filter, and voltage-controlled oscillator, and a digital or analog delay line to control the phase difference between input clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional EMI prevention measures (EMI filters, ferrite beads, shielding) are used, then some EMI reduction is achieved, but system clocks remain a significant source of EMI and the solution becomes complex and costly
Solution Approach 1:
The patent converts the harmful concentrated clock signal into a beneficial spread spectrum signal by intentionally modulating the clock frequency to vary over time. This frequency modulation spreads the energy across a broader frequency range, transforming the problematic concentrated EMI into a distributed, lower-amplitude signal that complies with regulatory standards while maintaining system functionality
Solution Approach 2:
The patent changes the frequency parameter of the clock signal dynamically over time. By continuously varying the clock frequency within a specified range (e.g., ±50 ppm) using a spread spectrum modulator, the signal's spectral density is reduced at any given frequency point, thereby lowering EMI without requiring additional filtering or shielding components
2Object-affected harmful factors
If conventional EMI prevention measures are implemented, then some EMI reduction is achieved, but compliance time and cost increase
Solution Approach 1:
The patent implements EMI prevention at the source by integrating the spread spectrum modulator directly into the clock generation circuitry. This preliminary action of pre-modulating the clock signal before it propagates through the system eliminates the need for subsequent EMI filtering and shielding, thereby reducing both development time and overall system cost while ensuring regulatory compliance
3Object-affected harmful factors
If spread spectrum clock generation is implemented, then EMI is reduced and compliance is improved, but the clock signal processing becomes more complex
Solution Approach 1:
The patent introduces a spread spectrum modulator as an intermediary component between the clock source and the rest of the system. This modulator serves as a mediator that performs the frequency modulation function, isolating the complexity of spread spectrum generation from the rest of the system while delivering a pre-processed, low-EMI clock signal to downstream components
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 solution effectively reduces EMI by modulating the phase of the input clock, resulting in a periodically varying output clock frequency, enhancing compliance with regulatory standards, reducing time-to-market, and lowering costs while maintaining system performance.
Implementation Method 1
a voltage-controlled oscillator, and outputs an output clock
Implementation Method 2
a low-pass filter coupled to the charge pump and the VCO, wherein the low-pass filter provides a control voltage to the VCO
Implementation Method 3
a phase lock loop generates an output clock according to a first input clock and a second input clock
Data Source
AI summary
Spread spectrum generators and methods are disclosed. In one implementation, a spread spectrum clock generator includes a phase locked loop generating an output clock according to a first clock and a second clock; a delay line coupled between the first clock and the phase locked loop; a modulation unit providing a modulation signal to control the delay line thereby modulating phase of the first clock, such that frequency of the output clock generated by the phase locked loop varies periodically; a scaling unit scaling the modulation signal from the modulation unit according to a scaling ratio, and outputting to the delay line; and a calibration unit generating an output signal for controlling the scaling ratio.