Delay-Controlled Spread Spectrum Clock With Constant Modulation
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Solution Overview
Problem
Conventional semiconductor integrated circuits face challenges in reducing Electromagnetic Interference (EMI) due to manufacturing variations, supply voltage, and temperature changes, which affect the modulation of clock signals, leading to inconsistent EMI reduction and potential circuit malfunctions.
Innovation Solution
A spread spectrum clock generation circuit using a delay control type oscillator with a maximum modulation value determination circuit and a modulation signal generation circuit, which maintains a constant degree of modulation by adjusting the oscillation period based on a control signal, ensuring a stable frequency-modulated clock signal despite manufacturing variations or environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spread spectrum modulation is performed by changing M and N values using conventional VCO and filter circuits, then clock frequency modulation is achieved, but manufacturing variations and environmental changes cause inconsistent modulation degree and potential circuit malfunction
Solution Approach 1:
The patent changes the control parameter from analog voltage (prone to variations) to digital delay control values. The delay control type oscillator uses digital delay elements whose delay amounts are controlled by digital signals, making the oscillation period less sensitive to manufacturing variations and environmental changes. This ensures consistent modulation degree across different devices and conditions.
Solution Approach 2:
The patent replaces the conventional analog VCO and filter circuit system with a digital delay control type oscillator system. Instead of using analog components (VCO, filter) that are sensitive to manufacturing variations, the invention uses digital delay elements and digital control signals, which provide more stable and predictable performance.
2Object-affected harmful factors
If EMI countermeasure components such as EMI filter or decoupling capacitor are mounted on printed circuit board, then EMI regulation value can be controlled, but occupied area and cost increase
Solution Approach 1:
The patent extracts the EMI reduction function from external components (EMI filters, decoupling capacitors) and implements it directly within the clock generation circuit itself. The spread spectrum clock generation circuit inherently reduces EMI through frequency modulation, eliminating the need for separate EMI countermeasure components on the printed circuit board.
Solution Approach 2:
The clock generation circuit performs its own EMI reduction function through spread spectrum modulation. The circuit generates a frequency-modulated clock signal that inherently reduces peak spectral density and EMI radiation, making the system self-sufficient without requiring external EMI filtering components.
3Object-generated harmful factors
If spread spectrum modulation is performed by changing M and N values, then clock frequency is modulated to reduce peak spectrum, but manufacturing variations prevent desired degree of modulation
Solution Approach 1:
The patent changes the control mechanism from analog voltage control to digital delay control. The delay control type oscillator responds to digital control signals that directly adjust the delay amount through switching delay elements, providing more precise and consistent control over the oscillation period. This ensures the desired modulation degree is achieved reliably despite manufacturing variations.
Solution Approach 2:
The patent incorporates a feedback mechanism where the actual oscillation period is measured and used to adjust the control signal. The delay control type oscillator monitors its own performance and makes real-time adjustments to maintain the desired modulation degree, compensating for manufacturing variations and environmental changes.
Data Source
AI summary
A delay-type phase adjusting circuit including a first variable delay circuit for receiving a reference clock signal and adding a delay to the reference clock signal, for output a phase comparator for receiving an output of the first variable delay circuit and the reference clock signal and detecting a phase difference therebetween a control circuit for generating a control signal for variably controlling a delay value of the first variable delay circuit based on a result of phase comparison by said phase comparator a second variable delay circuit for receiving an input signal and adding a delay to the input signal, for output a computation circuit for receiving a predetermined value and the control signal and variably controlling a delay value of the second variable delay circuit.