DDS Frequency Reference Using Nyquist-Zone Aliasing

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Solution Overview

Problem

Conventional frequency reference signal generating systems for telecommunication systems often require expensive and complex circuitry, leading to high costs and increased phase noise due to the use of frequency multipliers and mixers.

Innovation Solution

The system employs a 10 MHz crystal oscillator coupled with a direct digital synthesizer and a bandpass filter to select an aliased output signal from a Nyquist zone other than the first Nyquist zone, eliminating the need for mixing processes and utilizing inexpensive components to generate a stable frequency reference signal with reduced phase noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional frequency multipliers and mixers are used to generate frequency reference signals, then the frequency reference can be generated, but the system cost increases and phase noise increases

Engineering Contradiction:

Improvefrequency reference signal stabilityVSAvoidcircuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the frequency multiplier and mixer components from the conventional frequency reference signal generation system. By using a direct digital synthesizer (DDS) with a bandpass filter to select an aliased output signal from a higher Nyquist zone, the system achieves frequency multiplication functionality without the need for traditional frequency multipliers and mixers, thereby reducing device complexity and phase noise while maintaining frequency reference stability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/electronic frequency multiplication process (using frequency multipliers and mixers) with a digital signal processing approach. The DDS generates digital signals that are converted to analog waveforms, and a bandpass filter selects the desired frequency from higher Nyquist zones through aliasing, substituting the conventional mechanical frequency multiplication mechanism with a digital-based system that reduces phase noise and complexity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If frequency multipliers and mixers are used in the frequency reference signal generating system, then the desired frequency can be synthesized, but the system cost increases

Engineering Contradiction:

Improvefrequency synthesis capabilityVSAvoidsystem cost

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent employs inexpensive components such as a standard 10 MHz crystal oscillator, off-the-shelf DDS integrated circuits, and simple bandpass filters to replace expensive frequency multipliers and mixers. The digital signal processing approach using readily available DDS chips and basic filtering components achieves the same frequency synthesis functionality at a lower cost, making the system more economical while maintaining adaptability for generating frequency reference signals at various frequencies

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Measurement precision

If conventional mixing processes are used to generate frequency reference signals, then frequency synthesis is achieved, but close-in phase noise increases

Engineering Contradiction:

Improvefrequency reference accuracyVSAvoidphase noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the aliasing phenomenon, which is typically considered a harmful distortion in digital signal processing, into a beneficial mechanism for frequency multiplication. By intentionally selecting and filtering aliased output signals from higher Nyquist zones produced by the DDS, the system achieves frequency synthesis without the phase noise degradation associated with conventional mixing processes. The aliasing effect becomes a useful tool rather than a nuisance, eliminating the need for mixing operations that generate close-in phase noise

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach reduces system costs and phase noise, providing a more accurate frequency reference signal by eliminating mixing processes and utilizing low-cost components for filtering, resulting in lower close-in phase noise compared to conventional methods.

Implementation Method 1

selecting an aliased output signal from the digital to analog converter at a Nyquist zone other than the first Nyquist zone

Methodology Applied

Scientific EffectAliasing:

Data Source

PatentUS8310315B2Frequency reference signal generating system and method for frequency synthesizers

Publication Date: 2012.11.13 COMTECH SATELLITE NETWORK TECH INC

AI summary

A system for generating a frequency reference signal comprising an oscillator, a direct digital synthesizer coupled to the oscillator and configured to receive a signal output from the oscillator, a digital to analog converter coupled to the direct digital synthesizer and configured to receive a sampled signal from the direct digital synthesizer and to convert the sampled signal to an analog waveform, and a bandpass filter coupled to the digital to analog converter and configured to select an aliased output signal from the digital to analog converter at a Nyquist zone other than a first Nyquist zone and to output the frequency reference signal.