Embedded DSP Spectrum Analyzer

May 0104

April 25, 2001

Teradyne Corp

Julie DickersonBill Black

Prihamdhani Amran EERyan Butler CprEAaron Delaney EENicky Hilton CprE

Team Number:

Date:

Client:

Advisors:

Team Members:

Presentation Outline

Introduction

Problem Statement

Design Objectives

End Product Description

Assumptions & Limitations

Risks and Concerns

Technical Approach

Project Success

Future Work

Human and Financial Budgets

Lessons Learned

Summary

Introduction

Teradyne – very high end test equipment

Several Teradyne sponsored groupsGroup 1 – PC spectrum analyzerGroup 2 – Embedded DSP spectrum analyzerGroup 3 – Single board DSP spectrum analyzerGroup 4 – Replicating analyzers on single board

Purpose of projects – Replace ‘serial’ method of testing with faster ‘parallel’ approach

Key ConceptsDynamic range

Ratio of signal levels expressed in dB

DSP - Digital signal processing

Fourier Transform – Translates signal from time domain to frequency domain

Notch filter - Rejects signals within a narrow band of frequencies and passes all other signals

Anti-aliasing filterA low-pass filter to prevent aliasing

What is Aliasing?

Aliasing is the generation of a false (alias) frequency along with the correct one when doing frequency sampling.

Dynamic Range

CD player: 96 dB

Tester must have dynamic range that is a factor of 10 better

Ratio V(tester) to V(cd player) = 10

20 * log(10) = 20 dB

Our tester – another factor of 10!!!

96 dB + 20 dB + 20 dB = 136 dB

Fourier Transform

More than one signal present

Signal broken into frequency components

Time domain Frequency domain

Problem Statement

Evaluate analog input signal between DC and 1MHz (bandwidth)

Process signal on external hardware

Display signal properties on PC

Design ObjectivesDynamic range

Total dynamic range -135dBDigitizer -96 dBFilters approx. -40/50 dB

Signal propertiesMeasure five harmonicsMeasure THD, SNR, Noise floorMeasure amplitude of fundamental & harmonic frequenciesMeasure input frequencies from DC to 1MHz

Intended users and usesFuture Teradyne senior design teams

End Product Description

External hardware

System componentsSignal generator

Filter board

A/D converter

Digital signal processor

Host computer

PC softwareGUI interface

DSP program

Assumptions

Hardware selectionFinding A/D and DSP would be easy

Hardware integrationInterfacing A/D and DSP would be difficult

Software packageDevelopment tools for DSP available

Filter designHigh quality parts for filters available

Financial BudgetTeradyne will cover all costs

Limitations

Technical knowledgeAnalog filter design

Limited experience with DSP

Hardware selectionReading data sheets

Available digitizer/DSP boards

SoftwareNo experience writing in Lab View

Project Risks and Concerns

Hardware selectionDelay part orders

Delay system integration

Delay software development

Integrating hardwareFrying expensive equipment

Technical Approach

Required specificationsExternal hardware approachTwin-T notch filtersAnalog Devices products

Design choices

HardwareCustom/commercial board design

Anti-aliasing filters

SoftwareLabView/C/C++/Java

E.A.G.L.E software

OrCAD p-spice

Technical Approach

Step 1 – Filtering

frequency by 40-50 dB

Filter board4 filters laid out on custom board

Anti-aliasingMakes sure no signals over1 MHz enter the system

Notch filtersKnocks down fundamental

Notch Filter

Before notch filter After notch filter

Noise floorNoise floor

Step 2 – A/D Conversion

Analog Devices 976A 16 bit

Signal from filter is digitized

Data passed to DSP

A/D channel determines which filter will be used.

Step 3 – Signal Processing

Analog Devices DSP 40 MHz

Store digitized signal in DSP memory

Perform Fast Fourier Transform

Calculate signal properties of interest

Step 4 – Calibration

Reduces total system error

Determines notch frequency of each filter

Calibration stepsGenerate white noise

Perform FFT

Find notch

Generate signal at notch frequency

Notch Filter Calibration

White noise FFT of noise

Step 5 – Display Data

DSP data sent to PC

Lists all signal properties of interest

Evaluation of Project Success

Completed tasksFilter designFilter board designFilter board fabricationGUI code writtenDSP code written

 

Tasks not completedHardware integrationDSP and host PC communication code

Future WorkHardware

Redesign to meet frequency specificationSingle board solution

FilteringMore filters addedPrefabricated filter banks

SoftwareRewrite DSP code for single board solutionOptimize algorithms for real time processing Add functionality to software

Financial Budget

$0

$1,000

$2,000

$3,000

$4,000

$5,000

$6,000

$7,000

$8,000

$9,000

Actual $85 $248 $895 $0 $2,445 $3,673

Estimated $750 $200 $800 $2,000 $5,000 $8,750

Filter Poster Software A/D DSP Total

Human Budget

0 Hours

100 Hours

200 Hours

300 Hours

400 Hours

500 Hours

600 Hours

700 Hours

800 Hours

900 Hours

Actual 81 Hours 89 Hours 188 Hours 106 Hours 464 Hours

Estimated 160 Hours 197 Hours 237 Hours 270 Hours 864 Hours

Amran Butler Delaney Hilton Total

Lessons Learned

Keep ahead of deadlines

Make backup plansOrdering/Receiving partsSoftware problems

More documentationKeep better lab notesDocumentation for next team

Closing Summary

Learned a lot about DSP and analog filter design

Team skills improvedUseful information passed to next group

AcknowledgementsTeradyneJulie Dickerson & Bill BlackBrian Nowak & Neeraj Nayak

Questions