Spread Spectrum Clock Modulation for Low-Spur EMI Reduction

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Solution Overview

Problem

Spread spectrum clock generators using delta-sigma modulators produce spurious components due to quantization noise, which hinder effective Electromagnetic Interference (EMI) reduction and power consumption optimization.

Innovation Solution

Incorporating a delta-sigma modulator that outputs multibits, specifically 1.5-bit digital values, to improve quantization noise suppression and reduce spurious components by using a quantizer that quantizes to ternary values, and employing a divider that switches between multiplication numbers N−1, N, and N+1 to control the output clock signal, thereby enhancing EMI reduction capabilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a delta-sigma modulator is used to generate spread spectrum clock signal, then EMI reduction is achieved, but spurious components are produced due to quantization noise

Engineering Contradiction:

ImproveEMIVSAvoidspurious components

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent changes the quantization bit depth parameter from conventional 1-bit to 1.5-bit in the delta-sigma modulator. This parameter change reduces quantization noise by increasing the number of quantization levels, thereby suppressing spurious components while maintaining the spread spectrum EMI reduction capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite modulation approach combining delta-sigma modulation with spread spectrum technique. The delta-sigma modulator processes the spread spectrum signal, and the combination of these two methods creates a composite system that achieves both EMI reduction and spurious component suppression through the 1.5-bit quantization

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If filter band is reduced to lower power consumption, then power efficiency improves, but spurious components increase

Engineering Contradiction:

Improvepower consumptionVSAvoidspurious components

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary noise suppression by using 1.5-bit delta-sigma modulation before the signal reaches the filter stage. This preliminary action reduces quantization noise at the source, allowing the filter band to be reduced for lower power consumption without compromising spurious component levels

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9660657B2Spread spectrum clock generator

Publication Date: 2017.05.23 RENESAS ELECTRONICS CORP

AI summary

A spread spectrum clock generator includes: a phase comparing unit that receives a reference clock signal and a feedback clock signal, and generates a control voltage corresponding to a phase difference between the reference clock signal and the feedback clock signal; a voltage-controlled oscillator that oscillates at an oscillating frequency corresponding to the control voltage, and generates an output clock signal; a delta-sigma modulator that receives a waveform signal for controlling spreading of a spectrum of the output clock signal, and outputs bits larger than 1 bit based on the waveform signal; a control circuit that controls a multiplication number according to an output signal of the delta-signal modulator; and a divider that generates the feedback clock signal by dividing the output clock signal according to the multiplication number controlled by the control circuit, and supplies the feedback clock signal to the phase comparing unit.