PC Based Spectrum Analyzer

1. PC Based Spectrum Analyzer Team May00-04 Advisors: Dr. Dickerson & Dr. Black Client: Lee Moore, ISU BSEE 1982 TERADYNE, North Reading, MA

2. 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

3. Background • What is a spectrum analyzer? • Time domain vs. Frequency domain • Fourier Transform • Applications • TERADYNE J750

4. Spectrum Analyzers • Display a time domain signal in the frequency domain • Make noise measurements of a signal. • How “pure” is the signal? Spectrum analyzers diplay signals in the frequency domain Oscilliscopes display signals in the time domain

5. Time Domain vs. Frequency Domain Fourier Transform

6. Time Domain vs. Frequency Domain

7. Fundamental Signal with Harmonic Distortion 2nd Harmonic Harmonic Distortion

8. Harmonic Distortion Fundamental Signal with Harmonic Distortion 2nd Harmonic

9. Teradyne’s INTEGRA J750 VLSI (Very Large Scale Integration) is the art of putting 100,000+ transistors onto a single integrated circuit • Automatic VLSI test platform • Up to 1024 I/O pins • Typically used on semiconductor fabrication lines

10. Technical Approach J750 Input Module/Filters Digitizer Card Analyzer PC Control PC • Capture sinusoidal signals • Display spectrum (Fourier transform) of signal • Measure total harmonic distortion • Controlled by another PC

11. Technical Approach HP 33120A Input Module/Filters • Capture sinusoidal signals • Display spectrum (Fourier transform) of signal • Measure total harmonic distortion Digitizer Card Analyzer PC

12. TechnicalApproach • Software based approach • LabWindows/CVI used for coding • High speed digitizer card • Filters to “condition” the source signal • Filter calibration • Design of input module

13. 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

14. 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

15. Screen Shot

16. 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

17. Analyzer PC • Dell Precision 410 • Dual 600 MHz Pentium III Processors • 1 Gigabyte RAM

18. 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)

19. Notch Signal Filtering • 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

20. 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.

21. 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

22. 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.

23. Spectrum Reconstruction • Compensating for the filter in software ensures that analysis results are correct

24. 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

25. 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

26. Schematic TWIN-T filter

27. Schematic (cont.)

28. Filter Response Attenuationat 10kHz

29. Filter Response (cont.) Attenuation at 10MHz

30. Input Module • Vishay Siliconix DG534A • 4x1 Multiplexer • Wide Bandwidth 500MHz • Controlled via Parallel Port

31. Input Module Block Diagram 10kHz Filtered Input Vishay DG534A 100kHz Filtered Input Selected Output 10MHz Filtered Input Unfiltered Input Parallel Port Control

32. Personnel Effort Budget

33. Financial Budget Funds provided by TERADYNE

34. Problems Encountered • Filter and input module parts were never ordered because of long lead time • Original specification was for VisualBasic, chose LabWindows instead

35. Future Work • Control via external PC • Faster signals (up to 100 MHz) • Build filters and input module

36. Lessons Learned • Order parts early • Meet often with advisor • Team mailing list • Reduce scope of project if necessary

37. Milestone Summary • Successfully wrote code to control digitizer card • Analyzer software is finished and being documented • Filter calibration software is finished

38. Questions ???