ZTEC Instruments. Oscilloscope Measurement Fundamentals: Avoiding Common Pitfalls Creston Kuenzi, Applications Engineer

Transcription

1 ZTEC Instruments Oscilloscope Measurement Fundamentals: Avoiding Common Pitfalls Creston Kuenzi, Applications Engineer

2 Purpose Learn About Oscilloscope Measurement Capabilities in Order to Avoid Inaccurate or Misunderstood Results 2

3 Agenda Introduction to Modular Oscilloscopes Vertical-Axis Measurements Horizontal-Axis Measurements Frequency-Domain Measurements Conclusions 3

4 Introduction to Modular Oscilloscopes

5 Benchtop Scope Pros & Cons Benchtop Oscilloscope Powerful Hardware Functionality Intuitive Front Panel Slow Throughput to PC Difficult Integration Large Footprint 5

6 PC-Based Digitizer Pros & Cons Flexible Software Integration High-Speed Throughput to PC Small Footprint Lacks Built-In Hardware Functionality Non-intuitive Soft Front Panel High-Speed Digitizer 6

7 Modular Oscilloscopes Modular Oscilloscope Flexible Software Integration High-Speed Throughput to PC Small Footprint Powerful Hardware Functionality Intuitive Soft Front Panel for Interactive Measurements Modular Oscilloscopes Combine the Power of a Benchtop Oscilloscope and the Flexibility of a High-Speed Digitzer 7

8 Oscilloscope Capabilities ZTEC Modular Oscilloscope Advanced Triggering Multiple Acquisition Modes Oscilloscope Memory Multiple Options Flexible Signal Conditioning On-board Signal Processing Oscilloscope Interface Input Signal A/D Converter Data Memory Data Bus 8

9 Today s Demo System ZT530PXI (16-bit, 400 MS/sec Arb) ZT410PXI (16-bit, 400 MS/sec Oscilloscope) 9

10 Oscilloscope Measurements

11 Oscilloscope On-Board Measurement Variations All True Oscilloscopes Have On-Board Measurements These Measurements May Differ from Vendor to Vendor in Quantity, Name, and by the Algorithms Used Today s Discussion Will Show ZTEC Scope On-Board Measurements Some of These Same Measurements are Found on Other Oscilloscopes. 11

12 Categories of Onboard Measurements Vertical-Axis Measurements Horizontal-Axis Measurements Frequency-Domain Measurements 12

13 Vertical-Axis Measurements

14 Vertical-Axis Measurements Analyze the vertical component of the applied signal Most often describe a signal in terms of a voltage level Can also correspond to current, power, or any other physical phenomena converted to voltage via a probe or transducer 14

15 Common Vertical Measurements Amplitude Peak To Peak Overshoot Undershoot Maximum Minimum Average RMS Etc 15

16 Common Vertical Measurements 16

17 Vertical-Axis Measurement Demo 17

18 AC RMS, DC RMS, & Average Average Mean Value of Waveform DC RMS Direct Current (DC) Root Mean Square (RMS) DC RMS = ( V 2 ) / Number of points Average Power of Signal AC RMS Alternating Current (AC) Root Mean Square (RMS) AC RMS = ( (V-Vavg) 2 ) / Number of points Average Power of Signal Excluding DC Offset 18

19 AC RMS, DC RMS, & Average 19

20 AC RMS, DC RMS, & Average Partial Cycles Can Return Inaccurate Measurements 20

21 Avoiding Partial Cycle Problem Acquire Longer Waveforms to Reduce Affect Use Cycle RMS and Cycle Average Measurements Use Gated Waveform Measurements 21

22 AC RMS, DC RMS, & Average Demo 22

23 Histogram Processing vs Waveform Processing Histogram Processing Generates a Histogram of the Voltage Values and Looks for a Single Characteristic Very Fast Measurements but Less Accurate Examples: Amplitude and PTPeak Measurements Waveform Processing Uses an Algorithm on Every Waveform Sample More Accurate but Slower than Histogram Processing Examples: Average, DC RMS, and AC RMS Measurements 23

24 Histogram Processing vs Waveform Processing Histogram of Voltage Values in an 8-bit Oscilloscope 24

25 DC Power Supply Example Transient Signal Generated from DC Power Supply 25

26 Horizontal-Axis Measurements

27 Horizontal-Axis Measurements Analyze the horizontal time axis of the applied signal Usually describe the signal in terms of time May also return a value expressed as a ratio, radians, or in Hertz 27

28 Common Horizontal Measurements Waveform Measurements Period Frequency Edge Measurements Crossing Time Rise Time Fall Time 28

29 Common Horizontal Measurements 29

30 Common Horizontal Edge Measurements 30

31 Demo of Horizontal Measurements 31

32 Noise Issue on Vertical Axis Causes Edge Problems Vertical Noise Can Affect Horizontal Measurements 32

33 Demo of Vertical Noise Causing Horizontal Measurement Error 33

34 Telecommunications T1 Example T1 Signal Mask of Horizontal Measurements 34

35 Frequency-Domain Measurements

36 Frequency-Domain Measurements Translate a time-domain waveform with a fast Fourier transform (FFT), and then measure the noise and distortion characteristics in the frequency domain. Provide magnitude and phase characteristics versus frequency. Reveal signal characteristics that cannot be seen within the time-domain. 36

37 Fast Fourier Transform (FFT) 37

38 FFT Windows Used to increase spectral resolution in the frequency-domain. The Rectangular Window provides the best frequency and worst magnitude resolution. It is almost the same as no window. The Blackman-Harris Window provides the best magnitude and worst frequency resolution. The Hamming Window provides better frequency and worse magnitude resolution than the Rectangular Window. It provides slightly better frequency resolution than the Hanning Window. The Hanning Window provides better frequency and worse magnitude resolution than the Blackman Window. It provides slightly better magnitude frequency than the Hamming Window 38

39 Demo of FFTs and Windows 39

40 Common Frequency-Domain Measurements Signal-to-Noise Ratio (SNR) is the ratio of the RMS amplitude of the fundamental frequency to the RMS amplitude of all nonharmonic noise sources. Total Harmonic Distortion (THD) is the ratio of the RMS amplitude of the sum of the first nine harmonics to the RMS amplitude of the fundamental. Spurious-Free Dynamic Range (SFDR) is the ratio of the RMS amplitude of the fundamental to the RMS amplitude of the largest spurious signal. Signal-to-Noise and Distortion (SINAD) is the ratio of the RMS amplitude of the fundamental to the RMS amplitude of the sum of all noise and distortion sources. Effective Number of Bits (ENOB) is another way of expressing SINAD. It provides a measure of the input signal dynamic range as if the signal were converted using an ideal ADC. 40

41 Demo of Frequency-Domain Measurements 41

42 High-Speed ADC Test Example FFT of ADC Two-Tone Distortion Test 42

43 Summary Modular Oscilloscopes Have Powerful Onboard Measurements The Three Categories on Measurements are Vertical- Axis, Horizontal-Axis, and Frequency Domain Understanding These Measurements Will Help You Improve Your Tests and Avoid Problems 43

44 Questions?

45 Thank you! ZTEC Instruments The Leader in Modular Oscilloscopes Tiburon St. NE Albuquerque, NM Phone: (505)