數位示波器原理準確量測與除錯技巧 浩網科技股份有限公司應用工程暨高速數位測試中心 - 處長賴德謙 (Ted Lai ) 1 2014 INFINET TECHNOLOGY
Agenda 異常波型範例, Ghostly Waveform Examples 示波器當為抓鬼特攻隊的重要特性 : 頻寬 & 採樣率 記憶體儲存深度 波形更新率 示波器實際量測操作技巧 進階的參數觸發設定條件 針對不常出現的事件執行觸發 擷取與分析 利用分段記體體擷取更多波形 2 2014 INFINET TECHNOLOGY
Infrequent Non-monotonic Edge Waveform Ghost Example #1: Non-monotonic Edge 3
Infrequent Metastable State Waveform Ghost Example #2: Metastable State 4
Very Infrequent Glitch Waveform Ghost Example #3: Glitch (1 in 1,000,000) 5
Infrequent Runt Pulse Waveform Ghost Example #4: Runt Pulse 6
Infrequent Setup Time Violation Waveform Ghost Example #5: Setup Time Violation 7
Oscilloscope Ability to Capture Anomalies Myth #1 Higher sample rates improve a scope s probability of capturing waveform ghosts. Real-time bandwidth (and its associated minimum required sample rate) is a prerequisite for capturing fast & narrow events. Higher sample rates do NOT improve the probability of capturing random & infrequent events. Myth #2 Deeper acquisition memory improve a scope s probability of capturing waveform ghosts. Deep acquisition memory can actually hide waveform ghosts and decrease a scope s probability of capturing random & infrequent events. 8
Attenuation Oscilloscope Bandwidth Definition Scope swept response measurement 0dB -3dB Maximally-flat Response Gaussian Response BW Frequency 9
Selecting the Right Bandwidth What does a 100-MHz clock signal really look like? Response using a 100-MHz BW scope Response using a 500-MHz BW scope Required BW for analog applications: 3X highest sine wave frequency. Required BW for digital applications: 5X highest digital clock rate. More accurate BW determination based on signal edge speeds. 10
Required Bandwidth Based on Edge Speed Step #1: Determine fastest rise/fall times of device-under-test. Step #2: Determine highest signal frequency content (f max ). f max = 0.5/RT (10% - 90%) f max = 0.4/RT (20% - 80%) Step #3: Determine degree of required measurement accuracy. Required Accuracy Gaussian Response Maximally-flat Response 20% BW = 1.0 x f max BW = 1.0 x f max 10% BW = 1.3 x f max BW = 1.2 x f max 3% BW = 1.9 x f max BW = 1.4 x f max Step #4: Calculate required bandwidth. Source: Dr. Howard W. Johnson, High-speed Digital Design A Handbook of Black Magic 11
Required Bandwidth Example Determine the minimum bandwidth of an oscilloscope (assume Gaussian frequency response) to measure signals that have rise times as fast as 500 ps (10-90%): f max = (0.5/0.5 ns) = 1 GHz 20% Accuracy: Scope Bandwidth = 1.0 x 1 GHz = 1.0 GHz 3% Accuracy: Scope Bandwidth = 1.9 x 1 GHz = 1.9 GHz Keysight s Recommendation: Select a scope that has sufficient bandwidth to accurately capture the highest frequency content of your signals. 12
Sample Rate How much sample rate is required? Professor Smart has total trust in Dr. Nyquist and says: 2X over the scope s bandwidth. Professor Wise doesn t trust Dr. Nyquist and says: 10X to 20X over the scope s bandwidth. The truth lies somewhere in between! 13
Nyquist s Sampling Theorem Nyquist s sampling theorem states that for a limited bandwidth (bandlimited) signal with maximum frequency f max, the equally spaced sampling frequency f s must be greater than twice of the maximum frequency f max, i.e., f s > 2 f max in order to have the signal be uniquely reconstructed without aliasing. Dr. Harry Nyquist, 1889-1976, articulated his sampling theorem in 1928 The frequency 2 f max is called the Nyquist sampling frequency (f S ). Half of this value, f max, is sometimes called the Nyquist frequency (f N ). 14
Attenuation Ideal Brick-wall Response w/ BW @ Nyquist (f N ) 0dB -3dB Frequency f N f S 15
Attenuation Gaussian Response w/ BW @ f s /4 (f N /2) SR = BW x 4 0dB -3dB Aliased Frequency Components f S /4 Frequency f N f S 16
Attenuation Maximally-Flat Response w/ BW @ f s /2.5 (f N /1.25) SR = BW x 2.5 0dB -3dB Aliased Frequency Components f S /2.5 Frequency f N f S 17
1-GHz Bandwidth Oscilloscope Input test signal: 1 ns wide pulse with 500 ps rise time SR = BW x 5 SR = BW x 2.5 5 GSa/s 2.5 GSa/s RT = 580 ps ± 60 ps RTσ = 24 ps RT = 550 ps ± 30 ps RTσ = 8.7 ps PW = 985 ps ± 30 ps PWσ = 9.5 ps PW = 964 ps ± 50 ps PWσ = 20 ps 18
2-GHz Bandwidth Oscilloscope Input test signal: 1 ns wide pulse with 500 ps rise time SR = BW x 5 SR = BW x 10 10 GSa/s 20 GSa/s RT = 515 ps ± 30 ps RTσ = 6.4 ps PW = 996 ps ± 14 ps PWσ = 3.2 ps Diminishing Returns RT = 514 ps ± 22 ps RTσ = 5.3 ps PW = 996 ps ± 11 ps PWσ = 2.7 ps Higher bandwidth = Improved measurement accuracy Higher sample rate = Slightly improved measurement resolution Higher sample rate = Degraded measurement resolution on some scopes due to sampling noise Higher bandwidth & sample rate = Higher price Higher bandwidth & sample rate = Decreased probability if pulse is random & infrequent (a ghost) 19
Oscilloscope Memory Depth Acquisition Time = Memory Depth / Sample Rate 4M samples/5gsa/s = 800 µs But where s the ghost? Deeper Memory: Will improve probability of capturing a ghost on a single-shot acquisition Will hide possible ghost acquisitions Will reduce waveform update rates significantly 20
Searching through Deep Memory for Ghosts It is a Catch 22 situation! 2 Glitches Found 4M samples/5gsa/s = 800 µs Zoom Display Search Criteria But where s the ghost? Many scopes have automatic parametric Search & Navigation capability. Searching requires that you know something about the waveform characteristics of the ghosts in order to set up search criteria. But how do you know what to search for if it hasn t yet been revealed? Visually searching or playing through deep memory records is time-consuming. 21
Oscilloscope dead-time hides waveform ghosts Display Window Dead-time Display Window Acquisition #1 Acquisition #2 All oscilloscopes have dead-time or blind time. Dead-time is often orders of magnitude longer than acquisition time. Infrequent anomalies will usually occur during the scope s dead-time. 22
Faster Waveform Update Rates Reveal Ghostly Waveforms Display Window Dead-time Display Window Acquisition #1 Acquisition #2 All oscilloscopes have dead-time or blind time. Dead-time is often orders of magnitude longer than acquisition time. Decreasing dead-time increases waveform update rates and thus improves probability of capturing and displaying infrequent anomalies (ghosts). 23
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Digital Oscilloscope Structure Front End Attenuator & Pre-Amp. Probe Attenuat or Pre- Amp. Ultraspeed A/D Converter Ultraspeed Acquisition Memory CPU Display Memory 25 2014 INFINET TECHNOLOGY
Capturing an Infrequent Non-monotonic Edge 1,000 waveforms per second 300,000 waveforms per second Invisible Ghost Ghost Revealed Capturing random and infrequent events is based on statistical probabilities. 26
Isolate Waveform Ghosts with Advanced Violation Triggering See the ghost trigger on the ghost bust the ghost! Min & Max Rise Times Rise/Fall Time Trigger Help Screen 27
Rise Time Trigger: Isolates a Non-monotonic Edge Ghost Trigger on just rising edges that are slower than 165 ns But there is actually an easier way to isolate these ghosts. 請觀賞影片 : Keysight 4000X Rise Time Debug 28
Infrequent Non-monotonic Edge Zone Trigger Example #1: Edge Trigger Only Edge + Zone Trigger If you can see it, InfiniiScan Zone Trigger can catch it! 29
Infrequent Metastable State Zone Trigger Example #2: Edge + Zone Trigger Edge Trigger Only If you can see it, InfiniiScan Zone Trigger can catch it! 30
Very Infrequent Glitch Zone Trigger Example #3: Edge Trigger Only Edge + Zone Trigger If you can see it, InfiniiScan Zone Trigger can catch it! 31
Narrow Runt Pulse Zone Trigger Example #4: Edge + Dual Zone Trigger Edge Trigger Only If you can see it, InfiniiScan Zone Trigger can catch it! 32
Wide Runt Pulse Zone Trigger Example #5: Edge + Dual Zone Trigger Edge Trigger Only If you can see it, InfiniiScan Zone Trigger can catch it! 33
Setup Time Violation Zone Trigger Example #6: Edge + Zone Trigger Edge Trigger Only 請觀賞影片 : Keysight 4000X Zone Trigger 34
Memory Depth Re-Visited: Traditional Deep Memory Acquisition Acquisition Time = Memory Depth/Sample Rate 800 µs 400 µs MSO4000X Example: Max Sample Rate = 5 GSa/s Max Memory = 4 MegaBytes Max Acquisition Time = 800 µs Max Pulses = 2 35
Segmented Memory Acquisition Selectively captures more waveform data with precise time-stamps for each segment 400 ms... #1 #2 #3 #4 #5 #6 #7 #8 #1000 1 2 3 4.... 1000 Segment #1000 @ t = 400 ms Equivalent Memory = Time-span x Sample Rate 2 Giga Samples = 400 ms x 5 GSa/s 36
Setting up a Segmented Memory Acquisition Step #1: Rising Edge Trigger Step #2: Pulse-width Trigger In normal acquisition mode, fast waveform update rate reveals random and infrequent metastable state (ghost) while triggering on any rising edge. In normal acquisition mode, pulse-width triggering isolates the ghosts, but only captures one ghost per acquisition. 37
Step:3: Capture 1000 Consecutive Ghosts 1000 consecutive & random glitches captured over a 298 second time-span Equivalent Memory = 298 sec x 5 GSa/s = 1.5 TB 請觀賞影片 : Keysight 4000X Segmented Memory Segmented memory optimizes acquisition memory 1000 consecutive ghosts captured based on advanced trigger Normal waveforms between each ghost not captured Precise time-stamp shows time of each ghost relative to the 1st ghost 38
Waveform Intensity Modulation Waveform intensity indicates relative frequency-of-occurrence Bright = Frequent Dim = Infrequent Keysight s MegaZoom IV technology provides 64 levels of intensity 39
Summary Real-time bandwidth is a prerequisite. Sampling faster does NOT improve the scope s probability of capturing waveform ghosts. Deep memory acquisitions will hide waveform ghosts. Faster waveform update rates are the key improving a scope s probability of capturing waveform ghosts. Zone trigger makes ghost isolation quick & easy. Segmented memory can be used to capture and analyze more ghosts. If you can see it, InfiniiScan Zone trigger can catch it! 40
Additional Technical Resources Application Notes & How to Videos Publication # Evaluating Oscilloscope Bandwidths for your Applications Oscilloscope Sample Rates vs. Sampling Fidelity Oscilloscopes Waveform Update Rate Determines Probability of Capturing Elusive Events Synchronizing on Infrequent Anomalies and Complex Signals using InfiniiScan Zone Trigger Oscilloscope Display Quality Impacts Ability to View Subtle Signal Details Segmented Memory Acquisition for InfiniiVision Series Oscilloscopes Introducing the 4000 X-Series Oscilloscope (1:29) InfiniiScan Zone Trigger using the 4000 X-Series Oscilloscope (4:31) Debugging Infrequent Events using the 4000 X-Series Oscilloscope (4:24) Debugging a Slow Rise Time using the 4000 X-Series Oscilloscope (4:05) Segmented Memory using the 4000 X-Series Oscilloscope (4:40) 5989-5733EN 5989-5732EN 5989-7885EN 5991-1107EN 5989-2003EN 5989-7833EN YouTube Video YouTube Video YouTube Video YouTube Video YouTube Video Literature - http://cp.literature.keysight.com/litweb/pdf/xxxx-xxxxen.pdf (Insert pub # in place of xxxx-xxxx ) www.youtube.com/user/keysightoscilloscopes 41
Keysight s InfiniiVision X-Series Scopes Engineered for Best Signal Visibilty Series Bandwidth Sample Rate Mem (Max) Seg Mem Update Rate MSO Option Serial Options WaveGen Option Zone Trig 2000X 70 to 200 MHz 2 GSa/s 100k Option 50k/sec 8-ch No 1 Ch No 3000X 100 MHz to 1 GHz 4 GSa/s, 5 GSa/s 4M Option 1M/sec 16-Ch Yes 1 Ch w/awg No 4000X 200 MHz to 1.5 GHz 5 GSa/s 4M Std 1M/sec 16-Ch Yes 2 Ch w/awg Std
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