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Oscilloscope Capabilities and Demonstration April 2004 Trace Hitt Account Manager Tektronix, Inc. 1 Oscilloscopes – Why Do We Need Them? To Verify: Measure and Control Known Operation Calibrate Characterize Analyze To Troubleshoot: Find Unknown Operation Search for a Problem or Defect Test for Limits Observe New Phenomena Through Research 2 How Can They Give Us Incorrect 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 3 Evaluate Your Needs The key to any good oscilloscope system is its ability to accurately reproduce your waveform. 4 Agenda Bandwidth and Rise Time Acquisition and Display Modes Sampling and Digitizing Aliasing, Sample Rate and Interpolation Waveform Capture Rate Triggering Modes DPO 5 Select the Right Bandwidth 0 dB 6 div at 50 kHz - 3 dB 4.2 div at 100 MHz Bandwidth is sine wave frequency where amplitude is down 30% or 3dB. Bandwidth x Risetime = 0.35* i.e. 100 MHz Bandwidth will have 3.5 nsec Rise Time When system bandwidth increases, system rise time decreases. * This constant is based on a one pole model. For higher bandwidth instruments, this constant can range as high as 0.45. 6 Rise Time of Step Waveform 100% 90% 10% 0% Rise Time of Waveform, tr 7 Bandwidth and Amplitude Accuracy 0.1 0.2 0.3 0.4 0.5 } 3% Sine Wave Amplitude Sine Wave Frequency 0.6 0.7 0.8 0.9 1.0 100% 97.5 95 92.5 90 87.5 85 82.5 80 77.5 75 72.5 70.7 (- 3 dB) 0.35* BW = At the 3dB bandwidth frequency, the vertical amplitude error tris will be approximately 30%. e Vertical amplitude error specification is typically 3% maximum for the oscilloscope. When you depend on the specified maximum vertical amplitude error, divide the specified bandwidth by 3 to 5 as a rule of thumb, unless otherwise stated. 8 Measurement System Bandwidth Requirements = 0.35* trise Measurement Bandwidth for 3% Rolloff Error Measurement Bandwidth For 1.5% Rolloff Error Device Under Test Typical Signal Rise Times Analog Video, ElectroMechanical 5 - 20 ns 17.5 - 70 MHz 58 – 233 MHz 87.5 - 350 MHz TTL, Digital TV 2 ns 175 MHz 580 MHz 875 MHz CMOS 500 ps 700 MHz 2.33 GHz 3.5 GHz HDTV, LV CMOS 200 ps 1.75 GHz 5.8 GHz 8.75 GHz trise (displayed) = 9 Calculated Signal Bandwidth (trise (scope + probe) )2 + (trise (source) )2 Choose the Right Voltage Probe For the Application 10 Type Bandwidth Rise Time Input C Input R 1X Passive Probe 15 MHz 23 ns 100 pF 1M 10X Passive Probe 100 MHz 500 MHz 3.5 ns 700 ps 13 pF 8 pF 10 M Z0 Passive Probe 3 GHz 9 GHz 120 ps 40 ps 1 pF 0.15 pF 500 Active Probe 500 MHz 6 GHz 700 ps 80 ps 2 pF 0.4 pF 1M20 k Vertical Position Moves the Volts/Div Reference Point On Screen Is Expressed In Divisions Ref at +4 Divs Ref at -4 Divs Possible Display Screens 11 Vertical Offset Changes the Volts/Div Reference From 0 to Some Other Voltage Is Expressed In Volts +5 Volts 100 mV/Div 12 What About Horizontal Time Resolution? Two criteria are affected when improving resolution (decreasing time) between samples for a given time window. You need ... More Sample Rate (Speed) for less time between acquisition samples. More record length (Memory), or total number of acquisition points. 13 DSO Acquisition Modes Can Help Isolate Signal Details Sample When time per division is increased for a given displayed record length, displayed sample rate is decreased. Peak Detect Detects peaks between displayed samples. Envelope Accumulates peaks over multiple acquisitions. High Resolution Box car averages between displayed samples. Average Averages (normal or weighted) over multiple acquisitions. 14 Digital Peak Detect Can Discover Glitches Between Displayed Samples Glitch Displayed Samples Screen Trace Glitch falls between sample points and would be missed in sample mode. Max Min Glitch Screen Max Trace Max Min Displayed Samples Max Min More samples taken for peak detect. 15 Max Min Min Additional samples taken, min/max displayed, glitch captured in peak detect mode. Envelope Mode Can Accumulate Noise Average Mode Can Filter Out Noise First Trace Envelope Mode Shows Maximum Noise Second Trace Average Mode Reduces Noise 16 Hi-Res Mode Is a Low Pass Filter That Improves Resolution for Each Acquisition As time/division is increased, better vertical amplitude resolution and noise removal can occur for a single triggered acquisition, at lower bandwidth. Used for High Resolution Acquisition Mode. Actual Signal Averaged Display Points Time Between Actual Samples 17 Digitized Samples to be Averaged For the Next Display Point Digital Storage Oscilloscope Display Modes Can Help to Better See the Waveform Dots Replaces old acquired and displayed dots with new ones. Vectors Joins the acquisition dots in time with straight lines. Persistence or Accumulate Holds acquired and displayed dots for a defined amount of time. Infinite persistence holds acquired and displayed dots until erased. 18 Dot Mode Displays Can Be Hard To Interpret 19 Vector Mode, or Linear Interpolation Can Help To See The Real Signal 20 Sampling and Digitizing What Happens To The Samples? Record Length Is Equal To The Total Number of Acquisition Points Signal Sampling Digitizing 10111001 (Sample, Hold) 1 0 1 10111001 1 1 0 0 1 (Convert to Number) Acquisition Time Window = 21 Memory Storage Record Length Sample Rate 1 1 1 1 0 1 0 1 0 0 1 . . . . . 1 0 1 1 0 (Sequence Store) Scope Screen Real Time Digitizing (RTD) Acquires a Complete Waveform With One Trigger Samples Single-shot Events in Real Time With Samples Equally Spaced in Time With Selectable Pre/Post Trigger Pre-trigger Post-trigger Trigger 22 Equivalent Time Digitizing (ETD) Acquires a Waveform Over Many Triggers Uses repetitive sampling to reconstruct the shape of a high frequency repeating waveform over many triggered acquisition cycles Allows bandwidth to increase to the DSO’s analog bandwidth 23 Random Equivalent Time Digitizing Digitized samples are accumulated randomly before and after each trigger point. Time must be measured from the trigger point to the next sample in order to correctly place the digitized samples in the display memory. T1 S1 24 S2 S3 Random Equivalent Time Digitizing Digitized samples are accumulated randomly before and after each trigger point. Time must be measured from the trigger point to the next sample in order to correctly place the digitized samples in the display memory. T1 S1 25 S2 T2 S3 S4 S5 S6 Random Equivalent Time Digitizing Digitized samples are accumulated randomly before and after each trigger point. Time must be measured from the trigger point to the next sample in order to correctly place the digitized samples in the display memory. T1 S1 26 S2 T2 S3 S4 S5 T3 S6 S7 S8 S9 Random Equivalent Time Digitizing Digitized samples are accumulated randomly before and after each trigger point. Time must be measured from the trigger point to the next sample in order to correctly place the digitized samples in the display memory. T1 S1 S2 T2 S3 S4 S5 T3 S6 S7 S8 S9 TN Multiple samples per trigger provide faster update rate. Pre/post trigger capability is preserved. 27 S(T1) S(TN) Sequential Equivalent Time Digitizing Digitized samples are accumulated in time sequence after each trigger point with one sample per trigger. T1 S1 28 Sequential Equivalent Time Digitizing Digitized samples are accumulated in time sequence after each trigger point with one sample per trigger. T1 S1 29 T2 S2 Sequential Equivalent Time Digitizing Digitized samples are accumulated in time sequence after each trigger point with one sample per trigger. T1 S1 30 T2 S2 T3 S3 Sequential Equivalent Time Digitizing Digitized samples are accumulated in time sequence after each trigger point with one sample per trigger. T1 S1 T2 T3 S2 S3 TN No Pre-trigger S1 31 SN What Happens When Too Few Samples Are Acquired? Aliasing or False Waveform Reproduction 32 Single Event Bandwidth Must Have Enough Sample Points to Reconstruct Waveform Is Determined By the DSO’s Analog Bandwidth, Maximum Sample Rate, and Method of Waveform Reconstruction Amplitude 33 Time Actual Aliasing Will Display False Waveform Reproduction Caused by Under Sampling the Signal Cannot be Corrected With Digital Signal Processing Because the Maximum Sinewave Frequency In the Waveform Is More Than Half of the Digitized Sample Rate Reproduces the Waveform Shape at a Lower Frequency Nyquist Theory Violated 34 Slow Sample Rate Can Miss Important Signal Details Slower sample rate means more time between samples. Slow Sample Rate Misses High Speed Details 35 Fast Sample Rate and/or Peak Detect Mode Captures High Speed Details Perceptual Aliasing Can Exist When Nyquist Theory Is Satisfied The Eye Cannot Interpret or Connect Dots in the Proper Sequence Improved by “Connecting the Dots” 36 Perceptual Aliasing Can Be Reduced With Interpolation The Eye Cannot Interpret or Connect Dots in the Proper Sequence Sine Interpolation Improved by “Connecting the Dots” Linear Interpolation 37 More Waveform Capture Rate Displays More Details of Complex Signals Analog Real-Time Digital Storage DPO More Waveform Capture Rate Will Capture More Waveform Anomalies On a Repeating Signal 38 Waveform Capture Rate For Different Oscilloscopes Waveform Capture Rate (Waveforms/Second) 1000000 Analog Real Time 2467B with Micro Channel Plate Up To 500,000 Waveforms/Sec TDS7000 with DPX™ Enhanced DPO Acquisition >400,000 Waveforms/Sec 100000 10000 1000 TDS1000/TDS2000 >180 Waveforms/Sec TDS3000B with DPO Acquisition >3500 Waveforms/Sec 100 Typical DSO <100 Waveforms/Sec 10 1 0.1 5 ms/div 500 ps/div Sweep Speed (Log Scale) 39 Typical DSO Acquisition Misses Infrequent Waveform Information 40 Fast Waveform Capture Rate Captures Infrequent Waveform Anomalies 41 Triggering System Controls Allow for Isolating the Signal of Interest Signal ~ Vertical System Display System Internal Triggers External Trigger Source Trigger System Horizontal System (Channel, Line) Coupling (AC/DC, HF/LF Rej) Level (P-P Auto, Norm) Slope Mode (Auto, TV, Single Sweep, Glitch, Width, Runt, Slew Rate, Setup/Hold, Logic) Holdoff 42 Advanced Triggering Allows for Acquiring Specific Signal Details Pulse (Width, Glitch, Runt, Slew Rate, Setup/Hold) Logic (And, Or, Nand, Nor) Timing (Four Channels) State (Three Channels + One Clock) TV/Video Field Selection Line Counting 43 Pulse Width Triggering Accept only (or reject only) those triggers defined by pulse widths that are between two defined time limits, with +/- polarity selected. (+) T1 Time T2 (-) “Accept Only” is the same as “Within Limits” or “Equal To +/- 5%” “Reject Only” is the same as “Outside Limits” or “Not Equal To +/- 5%” 44 Pulse Glitch Triggering Accept only (or reject only) those triggers defined by pulse widths that are below a defined time limit, with +/-/either polarity selected. (+) Time (Either) (-) “Accept Only” is the same as “Less Than” the defined time “Reject Only”is the same as “More Than” the defined time 45 Pulse Runt Triggering Accept only those triggers defined by pulses that enter and exit between two defined amplitude thresholds, with +/-/either polarity selected. (+) Time (Either) (-) 46 Slew Rate Triggering Trigger if the time interval from the low-to-high and/or high-to-low thresholds is slower (larger) than, or faster (smaller) than a specified time, with +/-/either polarity selected. High Threshold + Polarity Low-to-High Time Interval - Polarity High-to-Low Time Interval Time Low Threshold Trigger If Slower Than Trigger If Faster Than 47 Trigger If Slower Than Trigger If Faster Than Setup/Hold Triggering Trigger if a + or - data edge (transition) occurs within the defined setup and hold time window of the positive (or negative, if selected) clock edge. Clock Source (Any Channel) Time Trigger Reference X Clock Level Hold Time Violation Data Source (Any Channel) Data Level Setup Time Violation Setup Time 48 X Trigger Reference Hold Time A Breakthrough Solution The Digital Phosphor Oscilloscope Digital Phosphor Oscilloscope An instrument that digitizes electrical signals and displays, stores, and analyzes three dimensions of signal information in real time. Digital Phosphor DPO Amp A/D Acquisition Rasterizer DPX Waveform Imaging Processor Display Memory Display uP 49 Parallel Processing DPO Is Not A Persistence Mode Analog DSO Persistence DPO DPOs provide intensity grading, in real-time, as part of the acquisition system Limited only by acquisition (trigger) rate Provides intensity graded display information on dynamic signals Captures dynamic signal variations, in real-time, enabling the user to see actual signal behavior Allows vector waveforms Rapidly builds a statistical representation of actual signal behavior 50 DPO Helps to Solve Today’s Measurement Challenges Dynamic-Complex Signals Example: Composite Video Need: Accurate representation of dynamic-complex signal Challenges: Make measurement on: Multiple modulation types Multiple periods Highly dynamic signals Detailed signal information over long time intervals Distribution of occurrence information 51 DPO Helps to Solve Today’s Measurement Challenges Infrequent Event Capture Example: Metastable event in high speed logic Need: Detection and analysis of rare signal events Challenges: Find and analyze infrequent faulty digital signals that have: Low frequency of occurrence Potentially non-repetitive characteristics Vastly different durations from the primary signal Highly dynamic characteristics Unknown characteristics 52 DPO Helps to Solve Today’s Measurement Challenges Edge Jitter Evaluation Example: High speed optical communications links Need: Understanding of signal edge timing characteristics Challengers: Analyze optical communications signals that have: Highly dynamic characteristics Distribution of occurrence information Critical timing issues Behaviors that require rapid statistical characterization 53 DPO Helps to Solve Today’s Measurement Challenges Long-Time Interval Capture Example: Hard disk drive read channel Need: Detecting subtle patterns of signal behavior over long time intervals Challenges: Find and characterize disk drive signal faults and variations that have: Rapid signal variations within long time window Multiple time windows Distribution of occurrence information 54 DPO Helps to Solve Today’s Measurement Challenges Complex Modulation Example: Digital Cellular (Constellation Diagram) Need: Detect phase and offset of I and Q signals Challenges: Analyze and characterize digital cellular inphase (I) and quadrature (Q) signal details that have: Highly dynamic characteristics Qualitative and quantitative information Distribution of occurrence information Dual axis bandwidth characteristics 55 Evaluate Your Needs Choose the Right Oscilloscope 56 Advantages of Digital Storage Allows Up to 7 GHz Bandwidth Acquisitions for Single-shot Events Finds Glitches with Peak Detect/Envelope Finds Anomalies with DPX™ Enhanced DPO Acquisition Acquires Waveforms Before the Trigger Allows High Resolution Single-shot Averaging Makes Accurate Timing Measurements Provides Highest Bandwidth with Equivalent Time Digitizing Enables Digital Signal Processing Allows a Color Display 57 Advantages of Digital Phosphor Oscilloscope (DPO) Simulates the Characteristics of an Analog Real Time Oscilloscope’s Fast Waveform Capture Rate and Intensity Graded Display Provides Intensity and/or Color Graded Display Showing Distribution of Amplitude Over Time, All In Real Time Integrates An Image Over Many Real Time Traces of the Signal 58 Advanced Triggering Can Provide: Pulse Characteristic Selection Width, Glitch, Runt, Slew Rate, Setup/Hold Logic Condition Qualification Filtering HF/LF/Noise Reject TV/Video Triggering 59 Remember Probing and Vertical Amplifier Issues Such as: Loading Effects Differential Measurements Current Sensing High Voltage Breakdown Transducer Characteristics Vertical Range and Linearity Vertical Sensitivity SMT Connection 60 For Ease of Use and Productivity Consider: Human Interface Issues Auto Set Limit Testing Cursors/Readout Store/Recall Settings/Waveforms Floppy Disk Storage Color Displays Programmability Printer/Plotter/Computer Interfaces Accessories 61 Thank You For Your Attendance 62