Digital Spread-Spectrum Clock Synthesis for EMI and PVT Stability
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Solution Overview
Problem
Existing spread-spectrum clock generation techniques, particularly those based on phase-locked loops, face challenges in programming modulation parameters, achieving precise frequency control, and reducing electromagnetic interference (EMI) due to variations in process, supply voltage, and temperature (PVT), as well as difficulties in automated testing and distortion of clock signals.
Innovation Solution
A digital clock synthesis method employing a clock generating circuit, multiplexing circuit, clock synthesizing circuit, and state machine circuit to dynamically control clock signal selection, allowing for the generation of a spread-spectrum clock with adjustable frequency and reduced EMI, using a state machine to programmatically control the transitions and frequency of the synthesized clock signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If PLL-based spread-spectrum clock generation is used, then EMI reduction is achieved, but modulation parameters cannot be easily programmed and the system suffers from PVT variations
Solution Approach 1:
The patent replaces the analog PLL-based spread-spectrum clock generation with a digital delay-locked loop (DLL) based system. The digital system uses a bank of delay elements and multiplexers to generate spread-spectrum clock signals, eliminating the analog components that are sensitive to PVT variations and difficult to reprogram. The digital architecture allows modulation parameters to be easily changed through digital control signals.
Solution Approach 2:
The patent implements a dynamic system where the delay values of the delay elements can be dynamically adjusted through digital control. The state machine or control logic can modify the delay settings in real-time, allowing the spread-spectrum modulation parameters to be changed without hardware reconfiguration, thus improving ease of operation while maintaining EMI reduction benefits.
2Adaptability or versatility
If analog VCO-based spread-spectrum generation is used, then frequency modulation is achieved, but the system is subject to PVT variation and supply voltage changes
Solution Approach 1:
The patent substitutes the analog VCO with a digital delay-locked loop that uses a ring oscillator followed by a digital delay bank. The spread-spectrum frequency modulation is achieved by digitally controlling the delay values rather than varying an analog VCO frequency, which eliminates sensitivity to PVT variations and supply voltage changes while maintaining frequency modulation capability.
Solution Approach 2:
The patent changes the operating parameters from analog voltage-controlled frequency adjustment to digital delay-controlled frequency adjustment. By using digital delay elements with fixed, precise delay values that are selected and combined through multiplexers, the system achieves frequency modulation without the reliability issues of analog VCOs subject to PVT variations.
3Measurement precision
If PLL bandwidth is reduced to avoid distortion, then modulation signal fidelity improves, but VCO noise suppression and settling time requirements cannot be met
Solution Approach 1:
The patent replaces the PLL architecture with a DLL architecture that generates spread-spectrum clock signals. This digital approach eliminates the need for a narrow PLL bandwidth compromise, as the delay-based frequency modulation inherently provides clean spectral spreading without the noise suppression and settling time issues that plague analog VCO-based systems.
4Extent of automation
If digital clock synthesis with multiplexing is used, then automated testing is simplified, but the circuit complexity increases
Solution Approach 1:
The patent segments the clock generation function into separate modular components: a bank of delay elements, multiple multiplexers for selecting and combining delay outputs, and a digital control unit. This segmentation makes the system more complex in structure but enables automated testing through digital control and simplifies parameter programming through modular architecture.
Data Source
AI summary
A state machine circuit may be used to control a multiplexing circuit that selects and provides respective ones of multiple input clock signals to a clock-synthesizing circuit that generates a synthesized clock signal in response to such input clock signals. The state machine circuit may, for example, be configured so that the synthesized clock signal is a spread-spectrum clock signal and/or a clock signal having a nominal frequency that is greater than a nominal frequency of each of the input clock signals.