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Transcript
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 • Automatic VLSI test platform • 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 • • • • 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 • • • • 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 • • • • • 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 • • • • 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 • • • • 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 ???