DDS Filter Network for High-Frequency Spur Suppression

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Solution Overview

Problem

Signal processing systems face challenges in achieving high spurious free dynamic range (SFDR) performance, particularly at high frequencies, due to degraded spurious emission performance in direct digital synthesizers (DDS), which limits their use in devices like RF receivers.

Innovation Solution

A system comprising a direct digital synthesizer (DDS) with an anti-aliasing filter and an output filter network, including broadband non-reflective switches and band-pass filters, is configured to receive an input clock frequency, providing a wideband and narrowband SFDR of -40 dBc or better by using a frequency plan with clean frequencies that are sub-multiples of the DDS reference frequency, and applying a clean frequency control word to select these frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a direct digital synthesizer (DDS) is used for signal generation, then frequency tuning flexibility and speed are improved, but spurious emission performance deteriorates at high frequencies

Engineering Contradiction:

Improvefrequency tuning flexibilityVSAvoidspurious emission

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The output spectrum is segmented into multiple sub-bands using band-pass filters, with each filter targeting a specific frequency range. This segmentation allows spurious emissions in different bands to be independently managed and suppressed, resolving the contradiction between frequency flexibility and spurious emission control.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the operating parameters of the DDS by using a frequency plan where output frequencies are selected as sub-multiples of the reference frequency. This parameter change optimizes the spurious emission characteristics while maintaining frequency tuning flexibility.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If output filtering is applied to reduce spurious emissions, then spurious free dynamic range is improved, but device complexity increases

Engineering Contradiction:

Improvespurious free dynamic rangeVSAvoidfilter network complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The filtering function is segmented into multiple band-pass filters, each responsible for a specific frequency sub-band. This segmentation reduces the complexity of any single filter while achieving comprehensive spurious emission suppression across the entire output spectrum.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Broadband non-reflective switches are introduced as intermediary components to selectively connect different band-pass filters to the output. These switches act as mediators that enable dynamic filter selection without requiring complex filter designs, thus improving SFDR while managing device complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If broadband non-reflective switches are used in the filter network, then frequency selection flexibility is improved, but insertion loss increases

Engineering Contradiction:

Improvefrequency selection flexibilityVSAvoidinsertion loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The operating parameters of the broadband switches are optimized by selecting specific switch technologies and configuring them to operate in their optimal performance ranges. This parameter optimization reduces insertion loss while maintaining the frequency selection flexibility provided by the switchable filter network.

Inventive Principle:

Principle #35Parameter changes

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 configuration significantly improves spurious emission performance, allowing for reduced unwanted spurs and enhanced SFDR, enabling the use of DDS technology in high-frequency applications like RF receivers with improved sensitivity and reduced interference.

Implementation Method 1

an anti-aliasing filter (AAF) operatively coupled with the DDS

Methodology Applied

Scientific EffectFiltering: Filter (electronic)

Implementation Method 2

the plurality of filters includes at least one band-pass filter

Methodology Applied

Scientific EffectFrequency selective filtering: Filter (electronic)

Implementation Method 3

a direct digital synthesizer (DDS) configured to receive an input clock frequency

Methodology Applied

Scientific EffectDirect digital synthesis:

Data Source

PatentUS9002916B1Techniques for enhancing spurious free dynamic range performance

Publication Date: 2015.04.07 BAE SYSTEMS INFORMATION ANDELECTRONIC SYSTEMS INTEGRATION INC

AI summary

Techniques and architecture are disclosed for improving spurious performance in a signal generator/system. The disclosed techniques/architecture can be used, for example, to enhance/improve the wideband and/or narrowband spurious free dynamic range (SFDR) between a given carrier signal and spurious signals. In some example instances, wideband and/or narrowband SFDR may be improved to about −40 dBc or better. In some other example instances, wideband and/or narrowband SFDR may be improved to about −70 dBc or better. The disclosed techniques/architecture can be implemented in a wide variety of signal generators/systems, such as a direct digital synthesizer (DDS)-based system, and over a wide range of input clock frequencies (e.g., in the range of about 10 MHz to 40 GHz, or higher).