Clock Spread Spectrum Circuit for EMI Reduction Without Timing Jitter
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Solution Overview
Problem
Current methods for reducing electromagnetic interference (EMI) in clock signals, such as shielding and filtering, are costly and inefficient, and introducing periodic jitter into clock signals to implement clock spread spectrum can make it difficult to determine setup and hold times in digital circuits.
Innovation Solution
A clock spread spectrum circuit that generates a frequency control word based on modulation parameters, using time-average-frequency direct-period-synthesis technology to produce a spread spectrum output signal without introducing additional noise, allowing for effective EMI reduction without affecting normal circuit operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If periodic jitter is introduced into clock signals to implement clock spread spectrum, then electromagnetic interference is reduced, but setup and hold times in digital circuits become difficult to determine
Solution Approach 1:
The patent changes the frequency parameter of the clock signal dynamically by introducing a frequency control word that varies over time. The frequency control word is generated by adding an integer part (based on reference frequency) and a decimal part (based on modulation parameters including spread spectrum depth coefficient, spread spectrum reference value, and modulation rate), causing the clock frequency to spread across a range while maintaining deterministic timing characteristics.
Solution Approach 2:
The patent implements dynamic frequency adjustment by making the frequency control word time-varying through the decimal part generation. The frequency modulation control module generates a frequency modulation clock signal that controls the rate of change of the frequency control word, enabling the clock frequency to dynamically spread while preserving setup and hold time determinism through controlled modulation.
2Object-affected harmful factors
If traditional EMI reduction methods such as shielding and filtering are used, then electromagnetic interference is reduced, but cost increases and circuit system performance is negatively impacted
Solution Approach 1:
The patent replaces physical EMI reduction methods (shielding, filtering, isolation) with a signal processing approach. Instead of using physical barriers or additional hardware components to reduce EMI, the invention uses frequency modulation of the clock signal itself to spread spectral energy, thereby reducing peak electromagnetic radiation without adding physical complexity to the circuit system.
3Object-generated harmful factors
If clock spread spectrum is implemented to disperse energy concentration, then peak electromagnetic radiation is reduced, but additional noise is introduced into the circuit
Solution Approach 1:
The patent carefully controls the modulation parameters (spread spectrum depth coefficient, spread spectrum reference value, modulation mode, and modulation rate) to achieve frequency spreading while minimizing noise generation. The frequency control word structure with integer and decimal parts allows precise control over the frequency deviation, spreading energy across a bandwidth without introducing excessive noise that would degrade signal integrity.
Data Source
AI summary
A clock spread spectrum circuit, an electronic equipment, and a clock spread spectrum method are disclosed. The clock spread spectrum circuit includes a control circuit and a signal generation circuit. The control circuit is configured to generate a frequency control word according to a modulation parameter, and the frequency control word changes discretely with time; and the signal generation circuit is configured to receive the frequency control word and generate and output a spread spectrum output signal that is spectrum-spread according to the frequency control word, and the spread spectrum output signal corresponds to the frequency control word.