SSCG Clock Generator Using Tangent Modulation to Suppress Spectrum Peaks

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Solution Overview

Problem

In spread spectrum clock generators (SSCGs), the output clock frequency of the voltage-controlled oscillator (VCO) does not quickly follow changes, leading to peaks at the lower and upper limits of the frequency modulation range, which increases electromagnetic radiation energy.

Innovation Solution

A clock generator that uses a modulation waveform generation unit to produce a tangent waveform or a waveform combining a tangent and triangular waveform, increasing the frequency change rate before and after the frequency modulation range limits, thereby suppressing spectrum peaks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If a conventional modulation waveform (e.g., triangular or Hershey-kiss) is used in the SSCG, then the circuit can be implemented, but spectrum peaks appear at the lower and upper limits of the frequency modulation range due to slow frequency following, increasing electromagnetic radiation energy

Engineering Contradiction:

Improveelectromagnetic radiation energyVSAvoidfrequency following speed

Core Design Contradiction:

Object-generated harmful factorsVSSpeed

Solution Approach 1:

The patent changes the waveform parameter from conventional triangular or Hershey-kiss waveforms to a tangent-based modulation waveform. This parameter change in the waveform shape creates a frequency modulation pattern that accelerates the frequency following speed at the modulation range limits, thereby suppressing spectrum peaks and reducing electromagnetic radiation energy without requiring additional circuit complexity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies a tangent waveform which introduces curvature characteristics to the modulation pattern. The tangent function's inherent curvature properties create a smoother, more gradual frequency transition at the modulation limits compared to linear triangular waveforms, improving the frequency following speed and eliminating the sharp peaks that cause electromagnetic radiation

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Object-generated harmful factors

If the frequency modulation range is increased to spread spectrum energy, then electromagnetic radiation is reduced at the center frequency, but spectrum peaks appear at the modulation limits due to slow frequency response

Engineering Contradiction:

Improvespectrum peak valueVSAvoidfrequency response accuracy

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

By changing the modulation waveform parameter to a tangent-based function, the patent achieves both wide frequency modulation range and accurate frequency response. The tangent waveform's mathematical properties ensure that even at extended modulation limits, the frequency follows the modulation signal accurately without creating peaks, thus maintaining reliability while spreading spectrum energy effectively

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8669796B2Clock generator, semiconductor device, and clock generating method

Publication Date: 2014.03.11 RENESAS ELECTRONICS CORP

AI summary

There is provided a clock generator for generating a modulation waveform which is high in the effect of suppressing a spectrum and making a circuit scale smaller than a modulation system using the Hershey-kiss waveform. More specifically, a modulation waveform generation unit generates a tangent waveform or a tangent+triangular waveform as an SSCG modulation waveform and provides an oscillator with a signal in which the SSCG modulation waveform is combined with the output of a low pass filter of a PLL loop.