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Transcript
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
1M20 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