Measuring Multi-Gb/s Signals… ‘What type of Oscilloscope should I use?’
Presented by: Pascal GRISON Digital Design Application Engineer Signal Integrity Seminar 2007
A sampling oscilloscope or a real-time oscilloscope?
86100C “Equivalenttime” sampling oscilloscope Let’s call it ETS Signal Integrity Seminar 2007
80000B “Real-time” oscilloscope Let’s call it RTS
Oscilloscope Block Diagram
Real Time Oscilloscope
Sampling Oscilloscope Signal Integrity Seminar 2007
Oscilloscope Bandwidth
• Sufficient bandwidth is essential for an accurate waveform display • Just 3 Years ago Real-time Scopes reached >12GHz BW But • Sampling scopes achieved 20 GHz bandwidths over 15 years ago! • Almost 90 GHz was achieved several years ago on Equivalent Time Scopes. Signal Integrity Seminar 2007
Bandwidth and sample rate Real-time oscilloscopes sample at a rate faster than the signal being observed – Sample rates up to 40 GSa/s – Bandwidths > 12 GHz
Equivalent-time (“sampling”) oscilloscopes sample at a rate slower than the signal being observed – Sample rates 80 GHz
Signal Integrity Seminar 2007
Sampling scope bandwidth is independent of the sample rate Sampler input
S Sampler control pulse
Sampler pulse: Low bandwidth Signal Integrity Seminar 2007
Measurement bandwidth is affected by how narrow the sampler control pulse is (can be just a few picoseconds) Since only one sample is taken, the A-D process can be very high resolution (up to 15 bits) with very low noise
High bandwidth
Eye diagram construction with a sampling oscilloscope PRBS Trigger Point
Re-Arm Time
Clock Trigger Reconstructed Waveform One Bit
Signal Integrity Seminar 2007
Sampling Point
ETS Eye diagrams: Samples acquired with highly synchronous precision but at random locations in the data PRBS Trigger Point
Re-Arm Time
Clock Trigger Reconstructed Waveform One Bit
Signal Integrity Seminar 2007
Sampling Point
Eye diagrams can be generated for random as well as repeating data signals PRBS Trigger Point
Re-Arm Time
Sampling Point
Clock Trigger Reconstructed Waveform One Bit
MYTH!: “Sampling scopes can only display repetitive signals” Signal Integrity Seminar 2007
Eye Diagram using Golden PLL Extraction Use a PLL to derive the signal to trigger the scope/jitter analyzer • Jitter within the PLL loop BW is common to the transmitter signal and the instrument trigger is not observed in the measured result
Actual TX signal Derived Clock
Observed waveform Signal Integrity Seminar 2007
Loop Bandwidth: Impact on Mask Margin
Clock recovery removes low frequency jitter = greater mask margin
Signal Integrity Seminar 2007
Clock Recovery Module now becomes Flexible Optical and Electrical Inputs Unbanded Continuous Tuning: 150Mb/s to 13.5Gb/s PLL adjustable from 15KHz to 10MHz Phase Noise Measurement capabilities: Clock Frequency 25MHz to 6.75GHz Data rate 50Mb/s to 13.5Gb/s Measurement BW: 300Hz to 20MHz
Signal Integrity Seminar 2007
High Speed Serial signal in Lossy Transmission Line might requires Equalization in Receiver Signal at end of transmission line has collapsed! But real Hardware Receiver integrate Linear Feedforward Equalization Let’s simulate Receiver LFE! Once Equalized, the Eye observed is now representative of the Eye as seen by receiver!
We can now proceed to Eye Opening and Jitter Measurements Signal Integrity Seminar 2007
What About Single valued Waveforms?
Signal Integrity Seminar 2007
Equivalent Time Sampling Technique Extremely wide bandwidths at a low sample rate 244-1=15 -1=15 bits bits
2244-1=15 bits
PRBS Trigger Point
Sampling Point Sequential Delay
Pattern Trigger Reconstructed Waveform
A sample is taken, the data pattern repeats and the next sample is taken at a slight delay compared to the previous sample
Signal Integrity Seminar 2007
ETS Trigger rate is defined by Pattern Lenght 24-1=15 bits
24-1=15 bits
PRBS Trigger Point
Sampling Point Sequential Delay
Pattern Trigger Reconstructed Waveform
In practice, samples are very close together (can be less than 100 fs apart). Through multiple passes of the signal, the waveform can be precisely reconstructed
Signal Integrity Seminar 2007
Pattern Lock: Internally Generated Pattern Trigger
Generate pattern trigger in DCA
on pattern repeat
Don t need a source with a pattern trigger Any rate the DCA supports Select bit to trigger on Pattern lengths up to 223 bits (8 Megabits) Any pattern (e.g. doesn t require PRBS)
Requires information cases
Can auto-detect in most
Pattern length Just the length - don t need specific pattern
Data rate Ratio of data rate to trigger clock rate
The key enabler for Eyeline and Jitter Mode
Signal Integrity Seminar 2007
Eyeline
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Steps the pattern trigger through the bits each bit in the pattern Enables averaging of eye diagrams Examine specific signal trajectories
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• Can catch individual mask violations and isolate the bit sequence that caused them
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Timing Jitter & Amplitude Interferences Analysis
Signal Integrity Seminar 2007
Let’s Switch to Realtime Scope
Signal Integrity Seminar 2007
RTS Trigger: Capturing Waveforms & Glitches
Vast capability in the ‘trigger’ space! • Any Individual channel or from auxiliary source • Positive going, Negative going Edges or ANY edge • Any Logic between the channels • Conditional ON or OFF state—pulse duration • Glitch Triggering • Specific analog event or software processing (Infiniscan)
Signal Integrity Seminar 2007
Real Time (Single Shot) Sampling Technique Used with either Repetitive or Single-Shot Signals All Samples Are Taken From a Single Trigger Trigger can be achieved on signal itself Samples from Previous Triggers are Erased Sample Rate May Limit Scope’s Overall Bandwidth Best Resolution Depends Directly on Sample Rate Low Sampling Jitter is critical to Achieve good signal reconstruction
Each Trigger Identical Signal Integrity Seminar 2007
Page 9
RTS: Post processing and data analysis Tools Search data for events-> glitch Mathematical functions- FFT, filters Processing-- clock recovery Eye diagrams 8b/10b Decoding Jitter
Signal Integrity Seminar 2007
Serial Data Analysis with Clock Recovery Measurement setup wizard Clock recovery 1st or 2nd order PLL, explicit, explicit +PLL Real-time eye display Masks for PCI Express, SATA, SAS, FC, GbE, XAUI,USB2… Eye mask unfolding 8b/10b decode with symbol search and trigger
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RTS: Creating an Eye Diagram Recovered clock
Data pattern
1, 4, 7,& 10 Overlaid
Signal Integrity Seminar 2007
2, 5, 8,& 11 Overlaid
3, 6, 9,& 12 Overlaid
All Sections Overlaid
Concept of industry standards for jitter There are two sides to the problem • How much jitter should the transmit side produce • How much jitter can the receive side tolerate • A well designed standard specifies each side properly to guarantee system level performance (bit-error-ratio)
Signal Integrity Seminar 2007
Where Does Jitter Come From?
Transmitter
Receiver
•Lossy interconnect (ISI) •Impedance mismatches (ISI) •Crosstalk (PJ)
•Thermal Noise (RJ) •DutyCycle Distortion (DCD) •Power Supply Noise (RJ, PJ) •On chip coupling (PJ, ISI)
Signal Integrity Seminar 2007
•Termination Errors (ISI)
How Do Real Time Scopes Measure Jitter? NRZ Serial Data Recovered Clock Jitter Trend Jitter Spectrum
Units in Time Units in Time
Jitter Histogram
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Jitter Analysis: Multiple Views Real Time scopes Provide many views to aid understanding: Sampled Waveform
Jitter Histogram
Jitter Analysis Acquire Waveform Threshold crossings Clock Recovery Evaluate Jitter values in time/freq
Jitter Trend Jitter Spectrum
Jitter Separation Evaluate data dependent jitter Analyze RJ/PJ Histogram Combine for Total Jitter estimate Signal Integrity Seminar 2007
Jitter Spectrum
Jitter Histograms
RJ/PJ Histogram
DDJ
Jitter analysis with an equivalent time sampling oscilloscope Advanced triggering system locks onto the pattern Data dependent jitter: Walk scope through pattern to determine location of each edge versus ideal Uncorrelated jitter: Look at any single edge and determine how it varies in position versus time. FFT of population yields RJ and PJ PJ absolute amplitudes and frequencies also derived to rates ~data rate/4 RJ and DJ combined to precisely estimate TJ
Extremely fast and accurate: For details, see Product note 86100C-1 Signal Integrity Seminar 2007
The Precision Jitter Transmitter* 2.5 Gb/s Single ended, ± 0.25 V levels PRBS7 pattern Calibration of applied jitter signals is traceable to reference standards * Described in Precision Jitter Transmitter, Jim Stimple, Ransom Stephens, DesignCon 2005 Available at www.Agilent.com
Signal Integrity Seminar 2007
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JitterFest 3 Results Feb. 2005
Fast TJ Estimate (ps)
300
TRUE JF3 DCAJ JF3 EZJIT Plus
225
150
75
0 0
50
Signal Integrity Seminar 2007
10 0Actual TJ (p s )150
200
2 50
ETS: TDR & S Parameters Measurements
Signal Integrity Seminar 2007
ETS Signal path quality Measurement Time Domain Reflectometer
Launch a fast step into the DUT What reflected back?
– Returned voltage measured with wide bandwidth scope, indicates how much impedance changed
• What transmitted through? – Transmitted voltage measured with a wide bandwidth scope indicates the ’speed’ of the path
200 mV
(as fast as 10 ps) Signal Integrity Seminar 2007
ETS TDR Measures can be transformed into a Vector Network Analyzer S-Parameters
Time domain TDR/TDT Signal Integrity Seminar 2007
Transformed TDR to Sparameters
How do you decide which type of oscilloscope to use?
Widest Bandwidth!
Signal Integrity Seminar 2007
Picking the Right Tool Sometimes the choice is easy, sometimes hard
Carving a decorative detail on a board Cutting a hole in sheetrock Cutting some molding Cutting a 2x4 Cutting a pipe
Signal Integrity Seminar 2007
Choosing the right type oscilloscope Key question: What tasks are you trying to perform? 1) How much measurement BW is required and/or how precise does the waveform result need to be?
Signal Integrity Seminar 2007
How fast can signals be before the scope bandwidth is a problem? 2.5 Gb/s waveform 20/80 risetimes 84 ps risetime
Real-time oscilloscope Signal Integrity Seminar 2007
83 ps risetime
Sampling oscilloscope
How fast can signals be before the scope bandwidth is a problem? 5 Gb/s waveform 40 ps risetime
Real-time oscilloscope Signal Integrity Seminar 2007
33 ps risetime
Sampling oscilloscope
How fast can signals be before the scope bandwidth is a problem? 10 Gb/s waveform 33 ps risetime
Real-time oscilloscope Signal Integrity Seminar 2007
18 ps risetime
Sampling oscilloscope
Choosing the right type oscilloscope 2) Observing small signals? Example: (18 mVpp, 5 Gb/s)
Real-time oscilloscope Signal Integrity Seminar 2007
Sampling oscilloscope
3) Troubleshooting and Probing important? Could be this…
SMA
IC
Or this…
PCB IC
IC
Backplane Connector
But, more likely, something like this…
Signal Integrity Seminar 2007
IC
IC IC
Signal Access
Solder-On
IC
SMA Remember:
Socket
Browser
IC IC
1. The BW of measurement is determined by the lowest BW component. 2. Ensure the probes show what is there---NOT what could be! Signal Integrity Seminar 2007
4) Compliance Testing? Test Selection Screen
1. Select Your Test 2. Set Your Configuration 3. Connect Your Device as shown in the picture 4. Run the Test! Test Results/Summary Screen Connection Screen
Summary and margin info
Agilent ’s Largest Agilent Offers Offers Industry Industry’s Largest Set Set of of Application Application Packages Packages Signal Integrity Seminar 2007
Compliance test High-speed optical transmitters are generally tested with a “reference receivers”: A wide bandwidth photodetector combined with a 4th order Bessel-Thomson low pass filter
Reference receiver frequency response must be precisely controlled
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Analysis of Wireless Digital Modulation
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Comparing the two systems strengths Equivalent-time oscilloscope
Real-time oscilloscope
• Bandwidth to > 80 GHz
• Sample rates to 40 GSa/s
• Data rates to > 50 Gb/s
• Flexibles Differential Probing 12GHz
• Time Domain Reflectometer
• High resolution single shot capture
• Lowest Noise & Jitter
• Data rates up to 8Gbs
• High precision “long term” view
• Flexible Software Clock Recovery
• Precision optical receivers
• Rich and Flexible Triggering
•Access to Real-time Scope 12GHz Differential Probing Solutions
• Low Noise with Noise/BW Reduction
• Price
•Wireless UWB MB-OFDM Analysis
Signal Integrity Seminar 2007
Considerations in Selecting a Real time Oscilloscope Your Goal: Superior Signal Integrity and Probing for your Application Bandwidth
Upgradeable BW from 2-13GHz
Noise and Distortion Performance Probing Requirements and Probing Fidelity Memory Price Triggering Applications DSO81204B with industry leading noise floor at only 400uV Signal Integrity Seminar 2007
Considerations in Selecting a Sampling Oscilloscope A wide bandwidth sampling oscilloscope is a modular instrument. Flexible configurations to match your test needs: Channel BW (20, 50, 70 or 80 GHz) TDR Optical receivers Flexible Hardware clock recovery Push Button Jitter Analysis 12GHz Differential Probing options Product Note 86100-6 Signal Integrity Seminar 2007
5989-3854EN
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Complete Coverage with Both Sampling and Realtime Oscilloscopes Realtime
Sampling
Easiest in-circuit measurements
Most accurate waveform Lowest noise & jitter Impedance characterization
Compliance Testing
Rich triggering features
Eye Diagram
Contiguous data set
Flexible configurations
Signal Integrity Seminar 2007
Jitter
Software clock recovery
References Product Note 86100C-1 Product Note 86100-5 Probing High-speed Signals with the Agilent 86100 Series Product Note 86100-6.pdf Jitter Analysis The dual-Dirac Model 5989-3206EN.pdf Application Note 1556: Picking the Optimal Oscilloscope for Serial
Data Signal Integrity Validation and Debug
DSO 80000B 2 to 13 GHz Real-time Oscilloscopes 86100C DCA-J Jitter Application info Signal Integrity Seminar 2007
www.agilent.com/find/dso80000b www.agilent.com/find/dca www.agilent.com/find/jitter_info
