Clock Spread Spectrum Circuit Using TAF-DPS for Low-EMI Timing
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Solution Overview
Problem
Current methods for reducing electromagnetic interference (EMI) in circuit systems, such as shielding and filtering, are costly and inefficient, and clock spread spectrum techniques that introduce periodic jitter to clock signals can make it difficult to determine setup and hold times in digital circuits.
Innovation Solution
A clock spread spectrum circuit using time-average-frequency direct-period-synthesis (TAF-DPS) technology generates a spread spectrum output signal by varying the frequency control word over time, allowing for broadband frequency spectrum without introducing additional noise, thus reducing EMI without affecting circuit performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional EMI reduction methods (shielding, filtering, isolation) are used, then electromagnetic interference is reduced, but cost increases and circuit performance is negatively impacted
Solution Approach 1:
The patent changes the frequency parameter of the clock signal by introducing periodic jitter through spread spectrum modulation. The clock signal frequency is modulated according to a predetermined modulation signal, transforming the single-frequency clock into a multi-frequency signal that disperses electromagnetic energy across a wider bandwidth, thereby reducing peak EMI emissions without adding physical shielding or filtering components
Solution Approach 2:
The patent employs periodic modulation signals (such as triangular, sinusoidal, or random sequences) to continuously vary the clock frequency over time. This periodic action creates a spread spectrum effect where the clock energy is distributed across multiple frequency components, reducing concentrated electromagnetic radiation at any single frequency while maintaining the essential timing function of the clock signal
2Object-affected harmful factors
If clock spread spectrum with periodic jitter is used to reduce EMI, then electromagnetic radiation peak value is reduced, but setup and hold time determination becomes difficult
Solution Approach 1:
The patent applies partial jitter by limiting the frequency deviation to a predetermined range that is sufficient for EMI reduction but controlled enough to maintain timing precision. The modulation depth and frequency are carefully selected to achieve EMI mitigation while ensuring that the cumulative timing error remains within acceptable bounds for reliable setup and hold time establishment in digital circuits
Solution Approach 2:
The system incorporates timing monitoring mechanisms that observe the actual setup and hold time margins in the circuit. Based on this feedback, the spread spectrum modulation parameters can be adjusted to optimize the balance between EMI reduction and timing precision, ensuring that the jitter introduced does not compromise critical timing relationships in the digital logic
3Object-affected harmful factors
If frequency control word changes continuously to achieve broadband spectrum, then EMI is reduced, but additional noise is introduced
Solution Approach 1:
The patent converts the potential harm of frequency variations into a beneficial spread spectrum effect. By intentionally introducing controlled frequency modulations, the system transforms what could be perceived as noise or instability into a systematic distribution of energy across multiple frequencies. This deliberate frequency variation reduces peak emissions and improves EMI compliance while the modulation follows predetermined patterns that maintain signal integrity and avoid introducing harmful random noise
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 (10) includes a control circuit (11) and a signal generation circuit (12). The control circuit (11) 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 (12) 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.