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Oscilloscopes and Accessories 62 Years World Class Leader

p. X. Oscilloscopes and Accessories 62 Years World Class Leader. Voltage. Time. Oscilloscopes Show How Signals Change. Draws a graph of an electrical signal Vertical (Y) axis is voltage Horizontal (X) axis is time. The Role of Oscilloscopes.

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Oscilloscopes and Accessories 62 Years World Class Leader

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  1. p X Oscilloscopes and Accessories 62 Years World Class Leader Politecnico di Milano

  2. Voltage Time Oscilloscopes Show How Signals Change • Draws a graph of an electrical signal • Vertical (Y) axis is voltage • Horizontal (X) axis is time Politecnico di Milano

  3. The Role of Oscilloscopes Oscilloscopes have played an important role in all major developments in electronics. • The first computers • Microprocessors and personal computers • The space program • Telecommunications • Entertainment • Radar and avionics • Medical instrumentation Tektronix founders, Jack Murdock and Howard Vollum, with an oscilloscope from the 1950s. Politecnico di Milano

  4. Today’s Oscilloscopes • Small and portable • Color displays • Digital memory • Fast • Connect with PCs Oscilloscopes are still the main tool to debug and troubleshoot electronic circuits. Politecnico di Milano

  5. Understanding Waveforms • The generic term for a pattern that repeats over time is a wave. • Waveform shapes reveal a great deal about a signal. Politecnico di Milano

  6. How Can They Give UsIncorrect Information? By: • Not showing waveshape information that really exists - when detail of interest occurs during holdoff, between samples, or is too fast for the writing speed of the oscilloscope to display • Showing waveshape information that does not exist - such as aliasing, aberrations or distortion Politecnico di Milano

  7. Choosing the Right Oscilloscope Key parameters to evaluate: • Bandwidth • Rise Time • Sample Rate • Record Length Politecnico di Milano

  8. What Is Oscilloscope Bandwidth? Bandwidth = Sine Wave -3 dB Point of a System - 3 dB 4.2 div at bandwidth 0 dB 6 div at 50 kHz Bandwidth x Risetime = 0.35* 100 MHz Bandwidth = 3.5 nsec Risetime * This constant is based on a one pole model. For higher bandwidth instruments, this constant can range as high as 0.45. Politecnico di Milano

  9. 0.35* BW = trise Bandwidth vs. Amplitude Accuracy 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 100 }3% 97.5 95 92.5 90 87.5 85 82.5 80 77.5 75 72.5 70.7 (- 3 dB) • At the 3dB bandwidth frequency, the vertical amplitude error will be approximately 30%. • Vertical amplitude error specification is typically 3% maximum for the oscilloscope. Politecnico di Milano

  10. Fundamental (1st Harmonic) 3rd Harmonic 5th Harmonic Fourier Square Wave (1st – 5th) Use Caution with Complex Signals • Complex signals contain many spectral components that cumulatively form a signal over time. • Spectral components are sine waves at varying frequencies and varying amplitudes which are added together to collectively form one signal. Politecnico di Milano

  11. > Bandwidth 5th Harmonic Avoiding Bandwidth Measurement Errors • Follow the 5 Times Rule for Bandwidth • For less than +/- 2% measurement error Politecnico di Milano

  12. Rise Time = Signal Rise Time 5 2 2 Measured Rise Time Oscilloscope Rise Time Signal Rise Time = + Key Performance Considerations: Rise Time • Insufficient rise time will affect your signal • Many logic families have faster rise times than clock rates suggest • Required Rise Time Actual Measured Politecnico di Milano

  13. > > 2.5 X fHighest 10 X fHighest Sample Rate Sample Rate For sin(x)/x interpolation For linear interpolation Key Performance Considerations: Sample Rate • Determines how frequently an oscilloscope takes a sample • Faster sample rate, greater resolution and waveform detail • Required Sample Rate 5X oversampling is recommended to avoid aliasing and to capture signal details. Politecnico di Milano

  14. Key Performance Considerations: Record Length • Determines how much “time” and detail can be captured in a single acquisition • Longer record length, longer time window with high resolution Record Length Time = Sample Rate Politecnico di Milano

  15. Voltage Current Transducers Logic Temperature Optical Passive Passive Passive Active Active Active Z0 High Z AC DC HighVoltage Differential Differential Basic Probe Types Politecnico di Milano

  16. V CC • Gain = - RC • RE C R C C f0 = 1 2 RCCC V IN R C P P • Gain = - (RC||RP) • RE R E 1 f0 = 2 (RC||RP)(CC+CP) Probes Affect the Measurement SystemAs Well As the DUT • Without probe & Oscilloscope • With probe & Oscilloscope DUT PROBE & OSCILLOSCOPE NOTE: VCC is an AC Ground Politecnico di Milano

  17. CABLE Rin =  Cin = 0 BANDWIDTH =  The Ideal Voltage Probe • Infinite Bandwidth • Zero Input Capacitance • Infinite Input Resistance • Infinite Dynamic Range • Attenuation of 1 • Zero Delay • Zero Phase Shift • Mechanically well suited to application The ideal probe would have no effect on the signal being measured, zero loading. Politecnico di Milano

  18. 1X Probe Model (Length of Cable) 6 feet DUT SCOPE Probe Tip Rsource PROBE CABLE 8 - 10 pF/ft * 1.5 ns/ft 20 pF 1 M Vsource LGround Lead PROBE Advantages: • 1X (No Attenuation) • Inexpensive Disadvantages: • Very High Reflections • Very High Input C • Very Low Bandwidth * Typical 50  cable has about30 pF/ft of capacitance Politecnico di Milano

  19. DUT SCOPE 6 feet Probe Tip Rsource 9 M 1 M 500  PROBE CABLE 8 - 10 pF/ft 1.5 ns/ft Vsource 20 pF LGround Lead 7 - 50 pF PROBE Typical High Z 10X Passive Probe Model Advantages: • High Input R • Wide Dynamic Range • Inexpensive • Mechanically Rugged • Low Input C vs 1X Probe Disadvantages: • Input C Too High • Not Compatible with 50  Systems • Must be Compensated Politecnico di Milano

  20. UNDER COMPENSATED OVER COMPENSATED COMPENSATED 1 ms/div 1 ms/div 1 ms/div 1 µs/div 1 µs/div 1 µs/div 50 kHz 50 kHz 50 kHz Compensation Effects Politecnico di Milano

  21. ~ tr 2.2 (Rsource * Cin) ~ Rise Time Increase Due To Capacitance Loading ~ 220 nsecFor 1X Probe Probe Tip ~ Cin= 100pF Rsource 1 k 10 M tRise Time 3 ns ~ 22 nsecFor 10X Probe CIn ~ Cin= 10pF Vsource LGround Lead 100% 100% 90% 90% 10% 10% 0% 0% • Rise Time Waveform forthe 1X Passive Probe • Rise Time Waveform for the 10X Passive Probe Probe Tip Capacitance and Source Impedance Effects Politecnico di Milano

  22. Probe Tip Rsource 50  tRise Time 1 ns 10 M CIn Lsource LGround Lead Vsource 10 pF 0.5 - 1 H (combined typical) For a 10X Passive Probe with Cin = 10 pF and a 6” Diameter Ground Cable Loop • Ring Frequency Using a 10 pF Input Capacitance 10X High Z Passive Probe and 6” Ground Lead. ~ ~ RingAmplitude 50% Error Typical RingFrequency From6” DiameterGround Loop 1 2  50 - 70 MHz OR tr = 7 - 5 ns = = LC Circuit Under Test Inductance Effects Politecnico di Milano

  23. 6 feet DUT SCOPE 450  0.5 pF Rsource PROBE CABLE 50  50  Vsource Probe Tip LGround Lead PROBE 50  Divider Probe (Z0) Model (10X) Advantages: • Low Input C • Wide Bandwidth • Compatible with 50  Systems and 1 M with Termination Resistor • No Compensation Necessary Disadvantages: • Low Input R • Must be Terminated into 50  Politecnico di Milano

  24. 6 feet SCOPE DUT Probe Tip Rsource CABLE50  BUFFERAMP Vsource PROBE 50  LGround Lead Active Probe Model Advantages: • Low Input Capacitance • Wide Bandwidth • High Input R • Compatible with 50 Systems and 1 M with Termination Resistor • No Compensation Necessary Disadvantages: • Higher Cost • Limited Dynamic Range • Mechanically Less Rugged • Requires Power Politecnico di Milano

  25. Scope Ch 1 Amplifier Scope Ch 2 Amplifier Algebraic Difference Probing Analog “CH1 + Inv Ch2” PROBES SCOPE Typical CMRR - 100 : 1 @ DC 20 : 1 @ 1 MHz • Advantages: • Already Have StandardPassive Probes • Wide Dynamic Range • Mechanically Rugged • Probes Test Points That Are Large Distances Apart • Disadvantages: • Very Low CMRR • Uses Two Scope Channels • Few Matching Adjustments in the Probe or the Amplifier • Must be LF Compensated Politecnico di Milano

  26. Scope Ch 1 Amplifier Active Differential Probes PROBE HEAD SCOPE + _ VOUT Typical CMRR 10,000 : 1 @ DC 2000 : 1 @ 20 MHz • Advantages: • Lower Input Capacitance • Higher CMRR vs Frequency Than Passive Differential Pair • Uses One Scope Channel • Disadvantages: • Higher Cost • Limited Dynamic Range • Requires Power Politecnico di Milano

  27. Passive Current Probe Model DUT SCOPE PROBE Vsource Rsource CABLE 50 ohm 18 inches 1 M /50  50 L reflected 50 R reflected Electromagnetic Shield • Advantages: • Wide AC Bandwidth • Inexpensive • Provides Electrical Isolation • Lower DUT Loading(Rreflected typically 1 to 2  Lreflected typically 5 H) • Disadvantages: • AC Measurements Only • Fixed Core Requires Opening Conductor For Attachment • DC Currents Can Saturate Core Limiting Performance Politecnico di Milano

  28. High Frequency Amplifier Low Frequency Amplifier Active Current Probe Model SCOPE PROBE L reflected 1 M /50  50  50  R reflected Hall Bias • Advantages: • DC & AC Current Measurements • Compatible With 50 and 1 M Single-ended Systems • Lower DUT Loading(Rreflected typically <<1  Lreflected typically <5 H) • Direct Connection Types • Disadvantages: • Higher Cost • Mechanically Less Rugged and Larger Size • Requires Power • Non Direct Connection Require Additional Amplifier Politecnico di Milano

  29. Oscilloscope Technology Overview Politecnico di Milano

  30. Scope Technology ART 1950 MarketDrivers • Military • Vacuum tube technology • Emerging solid state technology • Broadcast video Customer Challenges • Device characterization • Signal edges and waveshapes Evolution of Oscilloscopes Politecnico di Milano

  31. The General Radio Oscilloscope (1931),with sweep circuit (right). DelayLine Vert Amp Amp Display Trigger Horiz Sweep Analog Oscilloscope Definition Webster, 1906: “An instrument in which variations in a fluctuating electrical quantity appears temporarily as a visible waveform on the fluorescent screen of a cathode-ray tube.” 1998:An instrument used for visually observing and measuring electronic signals. Politecnico di Milano

  32. Basic Oscilloscope Block Diagram VerticalSystem Display System ~ Signal Trigger System Horizontal System Politecnico di Milano

  33. Oscilloscope Vertical System ART Only ~ Signal Amp Pre Amp Attenuator Delay Line ART CRT or DSO A/D Converter and Display Coupling Position Volts/div Mode Trigger System Horizontal Time Base System Politecnico di Milano

  34. Micro Channel Plate (MCP) • Provides the Ability to See Single-Shot “Fast” Signals on an Analog Real Time Scope • The “Writing Speed” is 100 to 1000 Times Faster Than That of a Normal Analog Scope Politecnico di Milano

  35. Analog Oscilloscope Benefits • Direct visual impression of actual signal behavior • Intensity grading (frequency of occurrence information) • No quantizing error or aliasing • Very fast waveform capture rate • Single level user interface Politecnico di Milano

  36. Analog Oscilloscope Shortcomings • Purely visual information • Blink and miss • Limited bandwidth performance • Edge triggering • No pre-trigger information • Optimized for single channel operation • Limited writing speed for low repetition rate signals Politecnico di Milano

  37. Scope Technology ART DSO 1980 1950 MarketDrivers • Military • Vacuum tube technology • Emerging solid state technology • Broadcast video • Computers • LSI • Digital data • Mixed signal environments • Faster microprocessor clock rates • System integration • Quality assurance Customer Challenges • Device characterization • Signal edges and waveshapes • Signal data • High-frequency effects • Documentation Evolution of Oscilloscopes Politecnico di Milano

  38. Digital Storage Oscilloscope Definition • Digital Storage OscilloscopeAn instrument that digitizes electrical signals and post processes the data to construct a displayed waveform. DeMUX Acqui-sition Memory DisplayMemory Amp uP Display SerialProcessing DSO A/D Politecnico di Milano

  39. A-D-C Analog -To- Digital Conversion Politecnico di Milano

  40. Record Lengthis thenumber of samplesacquiredin a single acquisition Sample Rate is measured as Samples per Second (S/s, kS/s, MS/s, GS/s) Real-Time Digital Performance DefinesSample Rate and Record Length Analog Digital Sample Rate Record Length A/D Memory Analog Signal Analog Signal Electron Beam • Beam is bright only when enough electrons can strike the phosphor (Writing Speed) Politecnico di Milano

  41. Sampling TAKING SAMPLES OF AN INPUT SIGNALAT SPECIFIC POINTS IN TIME • Samples Equally Spaced in Time • Sample Rate Measured in Sample/Second(S/s, kS/s, MS/s, GS/s) Samples Sample Interval Hold Time Needed for Digitizing Politecnico di Milano

  42. Memory Storage Digitizing Sampling Signal 1 1 0 0 1 0 1 1 1 1 1 1 1 0 1 1 1 0 0 1 . . . . . 1 0 0 1 0 1 1 1 0 0 1 0 1 1 0 0 1 1 1 0 (Convert to Number) (Sequence Store) (Sample, Hold) Scope Screen Screen Displays a Selected Portion of Memory What Happens To The Samples? Politecnico di Milano

  43. Resolution Versus Accuracy • Resolution is the ability to visually distinguish a signal and its smallest individual parts. • Accuracy is the deviation from perfect or near perfect standards. • Resolution and accuracy go hand in hand. Politecnico di Milano

  44. Types of Digital Resolution • Vertical 1/# Levels % of Full Scale 6-Bits  1/64 1.56% 8-Bits  1/256  0.39% 10-Bits  1/1024  0.097% 12-Bits  1/4096  0.024% (8-Bits Is Most Popular) • Horizontal = Time/Sample = 1/Sample Rate Politecnico di Milano

  45. What Is Effective Bits of Resolution? Simply Stated ... • An RMS Measure of How Well an A/D System Can Digitize the Shape of an Ideal Sinewave Input • Is Related to Harmonic Distortion Politecnico di Milano

  46. To Specify Effective Bits Remember to Qualify ... • Sample Rate • Ratio of Sample Rate to Frequency • Record Length • Percent of Full Scale (Amplitude) • Acquisition Mode (Record/ET, Sample/P-P/Average, Etc.) Politecnico di Milano

  47. What About Horizontal Resolution? Two criteria are affected when improving resolution (decreasing time) between samples for a giventime window. You need ... • More Sample Rate (or Speed) • More Record Length (or Memory) Politecnico di Milano

  48. For Example Assume: • Maximum Sample Rate = 100 MS/s • Time Base Set at 1 sec/div Sample Rate Time Base Setting # of Div’s # of Samples X X = 1 sec/div 100 MS/s X X 10 Div’s = 1-Billion Samples But ... No Scope Can Display 1-Billion Samples WHY? Politecnico di Milano

  49. Time Between Two Displayed Sample Points 10 sec = = 0.01 sec 1000 Displayed Horizontal Resolution For: • 1000 Horizontal Display Points • 1 sec/div Time Base THERE ARE MEMORY LENGTH ANDSPEED LIMITS Politecnico di Milano

  50. Basic Types of Digital Storage Oscilloscope (DSO) Capabilities • Real Time Digitizing (RTD) • samples single-shot events in real time. • Equivalent Time Digitizing (ETD) • uses repetitive sampling to reconstruct the shape of a high frequency repeating waveform over many triggered acquisition cycles. Politecnico di Milano

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