EE 198 B

Senior Design Project

Spectrum AnalyzerSpectrum Analyzer

Designed by

Archanna Srinivasan Shweta Upadhyaya Nelson Chen Wing Chan Xingli Zhu

Details

Advisor: Professor Freeman Date of Presentation: May 14th 2004 San Jose State University

Special Thanks to:

Professor Freeman Professor Strasilla Ms. Irma Alarcon NI Representatives

Purpose of the Project

To implement a Spectrum Analyzer in LabVIEW Software that is cost efficient.

Definition of an Analyzer

Analyzes the spectral content (amplitude and frequency) of the input signal.

Analyzes the various harmonics present in the signal.

Application Used to measure signal characteristics

such as carrier level, sidebands, harmonics, and phase noise.

Used to measure the spectral purity of multiplex signals and the percentage of modulation of AM signals.

Can analyze distortion and spurious signals, and can determine the non-linearity in a system.

Specifications:

Input Frequency: 0-500 KHz Dc Voltage Maximum: +/- 5 V

amplitude Number of Bits = 8 bits Resolution: 0.04 V FS: Sampling Frequency = 20 MHz Number of Harmonics used = 3

FunctionGenerator

Power Supply

Circuit Board

OscilloscopeCOMPUTERPentium 4

256 MB RAM

NI PCI 5102 Digitizer

BLOCK DIAGRAM OF THE SYSTEM

Block Diagram of Software

Low Pass Filter

DistortionMeasurement

Input

FFT (Spectral)

ToneMeasurement

Amplitude& Level

Measurement

Write LabVIEW

Analysis of the BlocksAnalysis of the Blocks

Block Diagram of the Input

NI Scope Initialize

NI Scope Auto Setup

NI Scope Multi Read

NI Scope Close Error Handler

Index Array Un bundle by Name

Build Waveform

Convert to Dynamic Data

Input to the Express VI’s

Input A cluster of waveforms are

accessed. The waveforms are separated out

into indices in an array. A single waveform is extracted and

expanded to three signals wide. The single resulting waveform is

converted to dynamic data for use by the Express VI’s.

Low pass Filter

Why Butterworth? It has a smooth response at all

frequencies and it is maximally flat.

Why order 3? High order is chosen to give more

accuracy.

Fast Fourier Transform (FFT)

Main calculation block for the output.

Displays the frequency response - Vrms (dB) versus frequency.

Also displays the phase in degrees or radians.

Harmonic Distortion Measurement Block Integral multiples of the

fundamental frequency (f): 2f, 3f, 4f...and so on are called harmonics.

The higher the number and amplitude of the harmonics, the more distorted is the system.

Helps to measure the non-linearity of a system.

Distortion Parameters

THD: is the sum of the powers of all harmonic frequencies above the fundamental frequency to the power of the fundamental frequency.

Specific Harmonic: returns the value of the harmonic that is specified, in this case it is three.

Tone Measurements

Finds the single tone with the highest amplitude.

Searches a specified frequency range to find the single tone with the highest amplitude.

All outputs (Amplitude, Frequency and Phase) have numeric displays.

Amplitude/Level Measurements

Performs voltage measurements and analysis on the input signal.

Returns the DC voltage, AC Positive Peak and Negative Peak, Peak to Peak voltage, RMS (root mean square) of the input signal.

Above parameters have numeric display at the front panel.

Write LabVIEW Writes data to a LabVIEW data

measurement file. It receives input from Spectrum

Measurement Block’s FFT. The File Name and Comments Input are

entered through Dialog Box by the user. The outputs are File Name, Saving Data. This file can be accessed using Microsoft

Excel.

How is ours Better?

The input from the NI-Scope Digitizer was made compatible with the LabVIEW Express VI’s for the first time ever.

Cost Analysis

How is our project cost-effective?

Cost Comparison HP/Agilent 860E Spectrum Analyzer (input

frequency: 30hz – 2.9Ghz) sold at $27,530

Our cost DAQ Card + Probes = $1500 Computer = $900 Software = Free…Student Version Total = $2400

Examples

Low Pass Filter

First Order Low Pass Filter

Low Pass Filter Gain from the Spectrum Analyzer (up to 100 KHz)

Gain vs. Freq (Analyzer)

-16

-14

-12

-10

-8

-6

-4

-2

0

2

0 20000 40000 60000 80000 100000 120000

Freq (Hz)

Ga

in (

rms

dB

)

Series1

Common Emitter Amplifier

Gain vs. Freq

0

2

4

6

8

10

12

14

16

18

20

0 200000 400000 600000 800000 1000000 1200000

Freq (Hz)

Ga

in (

dB

)

Scope

Analyzer

Common Emitter Gain vs. Freq (Scope & Analyzer)

Demo

High Pass Filter

Testing Spectrum Analyzer

First order high pass filter using LM741 Op-Amp.

Compare results taken from the Spectrum Analyzer with results from the Oscilloscope.

Resulting graphs are plotted in Excel.

High Pass Filter Circuit

High pass filter Excel graph:up to 50 kHz

-30

-25

-20

-15

-10

-5

0

0 10000 20000 30000 40000 50000

Frequency(Hz)

Gai

n(dB

)

Illustration of Non-Idealities in an Op-amp

From 100 kHz to 4MHz

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 1000000 2000000 3000000 4000000 5000000

Frequency(Hz)

Gain

(dB

)

Results Found The graphs from the Oscilloscope and the

Spectrum Analyzer follows the same shape. They follow the same characteristics of a first

order high pass active filter using LM741 Op Amp.

Data from the scope are taken using the scope itself, while data from the Spectrum Analyzer are taken from the FFT graph.

As the frequency of a High Pass increases, the performance of the filter degrades as shown in the graph.

QUESTIONS???