NCO IP Core: User Guide

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ID 683406
Date 11/06/2017
Public
Document Table of Contents
Document Table of Contents x
1. About the NCO IP Core 2. NCO IP Core Getting Started 3. NCO IP Core Functional Description A. NCO IP Core User Guide Document Archives 4. Document Revision History
1. About the NCO IP Core x
1.1. Intel® DSP IP Core Features 1.2. NCO IP Core Features 1.3. DSP IP Core Device Family Support 1.4. NCO IP Core MegaCore Verification 1.5. NCO IP Core Release Information 1.6. NCO IP Core Performance and Resource Utilization
2. NCO IP Core Getting Started x
2.1. Installing and Licensing Intel® FPGA IP Cores 2.2. IP Catalog and Parameter Editor 2.3. Generating IP Cores ( Intel® Quartus® Prime Pro Edition) 2.4. Simulating Intel® FPGA IP Cores
2.1. Installing and Licensing Intel® FPGA IP Cores x
2.1.1. Intel® FPGA IP Evaluation Mode 2.1.2. NCO IP Core Intel® FPGA IP Evaluation Mode Timeout Behavior
2.3. Generating IP Cores ( Intel® Quartus® Prime Pro Edition) x
2.3.1. IP Core Generation Output ( Intel® Quartus® Prime Pro Edition)
3. NCO IP Core Functional Description x
3.1. NCO IP Core Architectures 3.2. Multichannel NCOs 3.3. Frequency Hopping 3.4. Phase Dithering 3.5. Frequency Modulation 3.6. Phase Modulation 3.7. NCO IP Core Parameters 3.8. NCO IP Core Interfaces and Signals
3.1. NCO IP Core Architectures x
3.1.1. Large ROM Architecture 3.1.2. Small ROM Architecture 3.1.3. CORDIC Architecture 3.1.4. Multiplier-Based Architecture
3.7. NCO IP Core Parameters x
3.7.1. Architecture Parameters 3.7.2. Frequency Parameters 3.7.3. Optional Ports Parameters
3.8. NCO IP Core Interfaces and Signals x
3.8.1. Avalon-ST Interfaces in DSP IP Cores 3.8.2. NCO IP Core Signals 3.8.3. NCO IP Core Timing Diagrams
1. About the NCO IP Core
2. NCO IP Core Getting Started
3. NCO IP Core Functional Description
A. NCO IP Core User Guide Document Archives
4. Document Revision History

3.4. Phase Dithering

All digital sinusoidal synthesizers suffer from the effects of finite precision, which manifests itself as spurs in the spectral representation of the output sinusoid. Because of angular precision limitations, the derived phase of the oscillator tends to be periodic in time and contributes to the presence of spurious frequencies. You can reduce the noise at these frequencies by introducing a random signal of suitable variance into the derived phase, thereby reducing the likelihood of identical values over time. Adding noise into the data path raises the overall noise level within the oscillator, but tends to reduce the noise localization and can provide significant improvement in SFDR.

The extent to which you can reduce spur levels is dependent on many factors. The likelihood of repetition of derived phase values and resulting spurs, for a given angular precision, is closely linked to the ratio of the clock frequency to the desired output frequency. An integral ratio clearly results in high-level spurious frequencies, while an irrational relationship is less likely to result in highly correlated noise at harmonic frequencies.

The Altera NCO IP core allows you to finely tune the variance of the dither sequence for your chosen algorithm, specified precision, and clock frequency to output frequency ratio, and dynamically view the effects on the output spectrum graphically.

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