Transcript PC Based Spectrum Analyzer

PC Based Spectrum Analyzer
Team May00-04
Advisors: Dr. Dickerson & Dr. Black
Client: Lee Moore, ISU BSEE 1982
TERADYNE, North Reading, MA
Team Members
Chris Van Oosbree, CprE
Emmetsburg, Iowa
Fazal Baloch, EE
Balochistan, Pakistan
Yew-Kwong Soo, EE
Kuantan, Malaysia
Wee-Liat Tay, EE
Taiping, Malaysia
Walter Wedan, EE
Duluth, Minnesota
Background
•What is a spectrum analyzer?
•Time domain vs. Frequency domain
•Fourier Transform
•Applications
•TERADYNE J750
Spectrum Analyzers
•Display a time domain signal in the frequency domain
•Make noise measurements of a signal.
•How “pure” is the signal?
Spectrum analyzers
Oscilliscopes
display
diplay
signals
in time
the
signals
in the
frequency domain
domain
Time Domain vs. Frequency Domain
Fourier
Transform
Time Domain vs. Frequency Domain
Harmonic Distortion
Fundamental
Signal with
Harmonic Distortion
2nd Harmonic
Harmonic Distortion
Fundamental
Signal with
Harmonic Distortion
2nd Harmonic
Teradyne’s INTEGRA J750
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Automatic VLSI test
platform
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Up to 1024 I/O pins
•
Typically used on
semiconductor
fabrication lines
VLSI (Very Large Scale Integration) is the art
of putting 100,000+ transistors onto a single
integrated circuit
Technical Approach
J750
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Input
Digitizer Card
Module/Filters
Analyzer PC
Control PC
Capture sinusoidal signals
Display spectrum (Fourier transform) of signal
Measure total harmonic distortion
Controlled by another PC
Technical Approach
HP 33120A
Input
Module/Filters
Digitizer Card
Analyzer PC
• Capture sinusoidal signals
• Display spectrum (Fourier transform) of signal
• Measure total harmonic distortion
Technical Approach
• Software based approach
– LabWindows/CVI used for coding
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High speed digitizer card
Filters to “condition” the source signal
Filter calibration
Design of input module
Requirements
• Measure THD of a sinusoidal source at 3
frequencies
– 10 kHz
– 100 kHz
– 10 MHz
• THD measurements up to the 3rd harmonic
• Noise floor is –135 dB below the the fundamental
• 2 update rates
• Free run mode
• Slow / lowest noise
Software Overview
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Have digitizer card capture signal
Compute Fourier Transform of the signal
Display signal spectrum
Compute and display THD
Display options
– Harmonic Spectrum
– Spectrogram
Screen Shot
Configuration Options
• Sampling Rate
• Windowing
• Number of samples used in Fourier analysis
– More samples = Better accuracy
– Less samples = Faster computation
• Averaging
– To reduce effects of noise
– Slower computation
Analyzer PC
• Dell Precision 410
• Dual 600 MHz Pentium III
Processors
• 1 Gigabyte RAM
Digitizer Card
• Sampling rate vs. Voltage Resolution
• Faster sampling rate means lower resolution
• Transtech ICS-650
• Available off the shelf
• 12 bit resolution
• Greater number of bits increases “horizontal”
resolution
• 65 MHz sampling rate
• 3rd harmonic of a 10 MHz signal is 30 MHz. Must
sample at at least 60 MHz (Nyquist)
Signal Filtering
Notch
•Limited resolution of the digitizer card
•Attenuating the fundamental makes the
harmonics more “visible”
•The harmonics are attenuated slightly.
•Must be compensated for in software
Spectrum Reconstruction
• The software filter is a discrete
representation of the analog filter’s
frequency response.
• The software filter is calibrated to
match the analog filter’s response
during FILTER CALIBRATION.
Filter Calibration Procedure
User interface allows the user to specify:
• Filter Notch Frequency
10kHz, 100kHz, 10MHz
• Calibration Type
Harmonic, Full Sweep
• Sample Window Length
Number of discrete frequency elements for the sample window,
resultant DFT, and software filter
1024 – 16384
Filter Calibration Procedure
• With the filter in-line generate a sine wave of
known amplitude.
• Find amplitude of filtered sine wave
• Divide this amplitude by the amplitude of the
unfiltered sine wave
• Convert to decibels
– 20 log10(filtered / unfiltered)
• Increase sine wave frequency and repeat.
Spectrum Reconstruction
•Compensating for the filter in software
ensures that analysis results are correct
Filter Design
• Twin-T network design is used for building
filters attenuating signals at 10kHz and
100kHz
• Twin-T has simple basic design that gives
good attenuations
• A 5th order Chebyshev Band Stop Filter will
be tested for attenuation of signals at
10MHz
Problems
• The sensitivity of the Twin-T filter
• Twin-T filter unsuitable for attenuating high
frequencies such as 10MHz
• Getting the components for the filter
Schematic
TWIN-T filter
Schematic (cont.)
Filter Response
Attenuation at 10kHz
Filter Response (cont.)
Attenuation at 10MHz
Input Module
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Vishay Siliconix DG534A
4x1 Multiplexer
Wide Bandwidth 500MHz
Controlled via Parallel Port
Input Module Block Diagram
10kHz Filtered
Input
100kHz Filtered
Input
10MHz Filtered
Input
Vishay
DG534A
Unfiltered Input
Parallel Port Control
Selected
Output
Personnel Effort Budget
Personnel
Original Estimated Effort
Revised Estimated Effort
Fazal
100 hours
75 hours
Soo
100 hours
70 hours
Tay
100 hours
70 hours
Chris
100 hours
125 hours
Walter
100 hours
75 hours
Total Estimated Effort
500 hours
415 hours
Financial Budget
Item
Original Estimated
Cost
Revised Estimated
Cost
Computer
$ 6,000.00
$ 6,500.00
Digitizer Card
$ 4,000.00
$ 5,500.00
Software
$ 1000.00
$ 0.00
$ 100.00
$ 122.00
Programming Books
$ 0.00
$ 70.00
GPIB Card
$ 0.00
$ 800.00
$ 11,000.00
$ 12,992.00
Project Poster
Total Estimated Cost
Funds provided by TERADYNE
Problems Encountered
• Filter and input module parts were never
ordered because of long lead time
• Original specification was for VisualBasic,
chose LabWindows instead
Future Work
• Control via external PC
• Faster signals (up to 100 MHz)
• Build filters and input module
Lessons Learned
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Order parts early
Meet often with advisor
Team mailing list
Reduce scope of project if necessary
Milestone Summary
• Successfully wrote code to control digitizer
card
• Analyzer software is finished and being
documented
• Filter calibration software is finished
Questions ???