Spread Spectrum Clock Generator for USB EMI Reduction
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Solution Overview
Problem
Current USB technologies face challenges in reducing Electromagnetic Interference (EMI) due to the narrow frequency spectrum of clock signals, which exceeds regulatory limits, especially with the introduction of SuperSpeed data transfer rates like USB 3.0, necessitating a solution to comply with Electromagnetic Compatibility (EMC) regulations.
Innovation Solution
A bridge device with a clock generator that includes a crystal oscillator, inverter, phase locked loop (PLL) circuit, and spread spectrum clock generator (SSCG) is used to generate clock signals with constant and variable frequencies, reshaping electromagnetic emissions and reducing EMI by spreading energy across a wider frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a narrow frequency spectrum clock signal is used for USB data transfer, then data transfer speed can be maintained, but Electromagnetic Interference (EMI) emissions exceed regulatory limits
Solution Approach 1:
The patent applies spread spectrum clock generation to dynamically vary the clock signal frequency around a center frequency, transforming the static narrow-band clock signal into a dynamic wide-band signal. This dynamic frequency modulation spreads the energy spectrum while maintaining the data transfer rate, thereby reducing peak EMI emissions and complying with EMC regulations
Solution Approach 2:
The invention changes the frequency parameter of the clock signal by introducing intentional frequency modulation through spread spectrum techniques. The clock signal frequency is varied within a specified range around the center frequency, which spreads the spectral energy distribution and reduces the peak electromagnetic emissions while preserving the effective data transfer capability
2Object-generated harmful factors
If spread spectrum clock generation is implemented to reduce EMI, then EMI compliance is achieved, but device complexity increases
Solution Approach 1:
The patent integrates the spread spectrum clock generation functionality directly into the USB controller device, merging the clock generation and data transfer functions into a single unified component. This integration approach reduces overall system complexity by eliminating the need for separate external clock generation circuits while achieving EMI compliance
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
The solution effectively decreases EMI emissions, ensuring compliance with EMC regulations by spreading the energy of clock signals, thereby allowing for faster data transfer rates while minimizing electromagnetic interference.
Implementation Method 1
The crystal oscillator has a first terminal and a second terminal
Data Source
AI summary
A clock generator is provided. The clock generator includes a crystal oscillator, an inverter coupled to the crystal oscillator in parallel, a first circuit and a second circuit. The crystal oscillator has a first terminal and a second terminal. The inverter generates a first signal and a second signal at the first and second terminals of the crystal oscillator, respectively. The first circuit coupled to the first terminal of the crystal oscillator generates a first clock signal with a constant frequency according to the first signal. The second circuit coupled to the second terminal of the crystal oscillator generates a second clock signal with a variable frequency according to the second signal.