1 oscilloscope capabilities and demonstration april 2004 trace hitt account manager tektronix, inc

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Oscilloscope Capabilitiesand Demonstration

April 2004Trace Hitt

Account Manager Tektronix, Inc.

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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

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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

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Evaluate Your Needs

The key to any good oscilloscope system is its ability to accurately

reproduce your waveform.

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Agenda

Bandwidth and Rise Time

Acquisition and Display Modes

Sampling and Digitizing

Aliasing, Sample Rate and Interpolation

Waveform Capture Rate

Triggering Modes

DPO

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Select the Right Bandwidth

Bandwidth is sine wave frequencywhere amplitude is down 30% or 3dB.

Bandwidth x Risetime = 0.35*i.e. 100 MHz Bandwidth will have 3.5 nsec Rise TimeWhen system bandwidth increases, system rise time

decreases.

0 dB6 div at 50 kHz

- 3 dB4.2 div at 100 MHz

* This constant is based on a one pole model. For higherbandwidth instruments, this constant can range as high as 0.45.

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Rise Time of Step Waveform

Rise Time of Waveform, tr

100%90%

10%

0%

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Bandwidth and Amplitude Accuracy

At the 3dB bandwidth frequency, the vertical amplitude errorwill be approximately 30%.

Vertical amplitude error specification is typically 3% maximumfor 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.

70.7 (- 3 dB)

0.1 0.2 0.3 0.4 0.5 0.6 0.8 0.9 1.00.7100%97.595

92.59087.585

82.58077.5

7572.5

} 3%

trise

0.35*BW =Sine Wave Frequency

Sine WaveAmplitude

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Measurement SystemBandwidth Requirements

(trise (scope + probe) )2 + (trise (source) )2

5 - 20 ns 17.5 - 70 MHz

2 ns 175 MHz

500 ps 700 MHz

200 ps 1.75 GHz

58 – 233MHz 87.5 - 350 MHz

580 MHz 875 MHz

2.33 GHz 3.5 GHz

5.8 GHz 8.75 GHz

Analog Video, Electro-

MechanicalTTL,

Digital TV

CMOS

HDTV, LV CMOS

DeviceUnderTest

TypicalSignal

Rise Times

MeasurementBandwidthfor 3%RolloffError

MeasurementBandwidthFor 1.5%

RolloffError

CalculatedSignal

Bandwidth

= 0.35*trise

trise (displayed) =

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Choose the Right Voltage ProbeFor the Application

15 MHz 23 ns 100 pF 1 M

100 MHz -500 MHz

3.5 ns -700 ps

13 pF -8 pF 10 M

3 GHz -9 GHz

120 ps -40 ps

1 pF -0.15 pF 500

500 MHz -6 GHz

700 ps -80 ps

2 pF -0.4 pF

1 M -20 k

1X PassiveProbe

10X PassiveProbe

Z0 PassiveProbe

Active Probe

Type Bandwidth Input C Input RRise Time

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Vertical Position

Moves the Volts/Div Reference Point On Screen Is Expressed In Divisions

Ref at+4 Divs Ref at

-4 DivsPossible

Display Screens

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Vertical Offset

Changes the Volts/Div Reference From 0 to Some Other Voltage

Is Expressed In Volts

+5 Volts100 mV/Div

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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.

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DSO Acquisition ModesCan 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.

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Digital Peak Detect Can DiscoverGlitches Between Displayed Samples

Glitch

Screen Trace

Displayed Samples

Glitch falls between sample points and would be missed in sample mode.

Min

Max

Max

MinMin

More samples taken for peak detect.

Max

Min

GlitchScreen Trace

Max

Displayed Samples

Additional samples taken, min/max displayed,glitch captured in peak detect mode.

MinMax

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Envelope Mode Can Accumulate NoiseAverage Mode Can Filter Out Noise

First Trace Envelope Mode Shows Maximum

Noise

Second Trace Average Mode Reduces Noise

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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.

Time BetweenActual Samples

Digitized Samples to be Averaged For the Next Display Point

AveragedDisplayPoints

ActualSignal

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Digital Storage Oscilloscope Display ModesCan 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.

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Dot Mode DisplaysCan Be Hard To Interpret

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Vector Mode, or Linear Interpolation Can Help To See The Real Signal

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Sampling and DigitizingWhat Happens To The Samples?

1 0 1 1 1 0 0 1

10111001

11110101

00110110

. . . . .

Signal Sampling DigitizingMemoryStorage

(Sample,Hold)

(Convert to Number)

(SequenceStore)

Record LengthSample Rate

1 0 1 1 1 0 0 1

ScopeScreen

Record Length Is Equal ToThe Total Number of Acquisition Points

Acquisition Time Window =

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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

Post-triggerPre-trigger

Trigger

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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

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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 S3

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T1 T2

S1 S2 S3 S4 S5 S6

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T1 T2 T3

S1 S2 S3 S4 S5 S6 S7 S8 S9

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Multiple samples per trigger provide faster update rate.

Pre/post trigger capability is preserved.



T1 T2 T3

TN

S1 S2 S3 S4 S5 S6 S7 S8 S9

S(T1) S(TN)

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Sequential Equivalent Time Digitizing

Digitized samples are accumulated in time sequence after each trigger point with one sample per trigger.

T1

S1

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T1

S1

T2

S2

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T1

S1

T2

S2

T3

S3

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No Pre-trigger


T1

S1

T2

S2

T3

S3

S1 SN

TN

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What Happens When Too Few Samples Are Acquired?

Aliasingor

False WaveformReproduction

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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 Time

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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

Actual AliasingWill Display False Waveform Reproduction

Nyquist Theory Violated

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Slow Sample RateCan Miss Important Signal Details

Slow Sample RateMisses High Speed Details

Fast Sample Rateand/or Peak Detect Mode

Captures High Speed Details

Slower sample rate means more time between samples.

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Perceptual AliasingCan Exist When Nyquist Theory Is Satisfied

The Eye Cannot Interpret or Connect Dots in the Proper Sequence

Improved by “Connecting the Dots”

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Perceptual AliasingCan Be Reduced With Interpolation

The Eye Cannot Interpret or Connect Dots in the Proper Sequence

Improved by “Connecting the Dots”

Sine Interpolation

Linear Interpolation

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Analog Real-Time

DPO

Digital Storage

More Waveform Capture RateDisplays More Details of Complex Signals

More Waveform Capture Rate Will Capture More Waveform Anomalies

On a Repeating Signal

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Waveform Capture Rate For Different Oscilloscopes

Waveform Capture Rate(Waveforms/Second)

Sweep Speed (Log Scale)5 ms/div 500 ps/div0.1

1

10

100

1000

10000

100000

1000000

Typical DSO<100 Waveforms/Sec

TDS7000 with DPX™Enhanced DPO Acquisition>400,000 Waveforms/Sec

Analog Real Time2467B with

Micro Channel PlateUp To 500,000 Waveforms/Sec

TDS3000B with DPOAcquisition >3500 Waveforms/Sec

TDS1000/TDS2000>180 Waveforms/Sec

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Typical DSO Acquisition Misses Infrequent Waveform Information

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Fast Waveform Capture RateCaptures Infrequent Waveform Anomalies

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Triggering System ControlsAllow for Isolating the Signal of Interest

Source(Channel, Line)

Coupling(AC/DC, HF/LF Rej)

HorizontalSystem

TriggerSystem

VerticalSystem

InternalTriggers

ExternalTrigger

Level (P-P Auto, Norm)SlopeMode (Auto, TV, Single Sweep, Glitch,Width, Runt, Slew Rate, Setup/Hold, Logic)Holdoff

DisplaySystem

Signal

~

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Advanced Triggering Allows forAcquiring 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

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Pulse Width Triggering

Accept only (or reject only) those triggers defined by pulse widths that are between two defined time limits,

with +/- polarity selected.

Time

T1(+)

(-)

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%”

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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

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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)

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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.

Trigger If Faster Than

Trigger IfSlower Than

Trigger If Faster Than

Trigger IfSlower Than

HighThreshold

LowThreshold

+ PolarityLow-to-HighTime Interval

- PolarityHigh-to-LowTime Interval

Time

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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) Clock

Level

X

X

Setup Time Hold Time

DataLevel

TriggerReference

TriggerReference

Hold Time Violation

Setup Time Violation

Data Source(Any Channel)

Time

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A Breakthrough SolutionThe Digital Phosphor Oscilloscope

Digital Phosphor OscilloscopeAn instrument that digitizes electrical signals and displays, stores, and analyzes three dimensions of signal information in real time.

DPO Amp A/D Display

uP

DPXWaveform ImagingProcessor

ParallelProcessing

Acqui-sition

Rasterizer

DigitalPhosphor

DisplayMemory

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DPO Is Not A Persistence Mode

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

Analog DSO Persistence DPO

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DPO Helps to SolveToday’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

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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

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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

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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

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Complex Modulation Example: Digital Cellular (Constellation Diagram) Need: Detect phase and offset of I and Q signals Challenges: Analyze and characterize digital cellular in-

phase (I) and quadrature (Q) signal details that have: Highly dynamic characteristics Qualitative and quantitative

information Distribution of occurrence

information Dual axis bandwidth

characteristics

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Choosethe

Right Oscilloscope

Evaluate Your Needs

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Advantages ofDigital 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

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Advantages ofDigital 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

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Advanced TriggeringCan Provide:

Pulse Characteristic Selection Width, Glitch, Runt, Slew Rate, Setup/Hold

Logic Condition Qualification Filtering

HF/LF/Noise Reject

TV/Video Triggering

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Remember Probing andVertical Amplifier Issues

Such as: Loading Effects Differential Measurements Current Sensing High Voltage Breakdown Transducer Characteristics Vertical Range and Linearity Vertical Sensitivity SMT Connection

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For Ease of Use and ProductivityConsider:

Human Interface Issues Auto Set Limit Testing Cursors/Readout Store/Recall Settings/Waveforms Floppy Disk Storage Color Displays Programmability Printer/Plotter/Computer Interfaces Accessories

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Thank YouFor Your Attendance

1 oscilloscope capabilities and demonstration april 2004 trace hitt account manager tektronix, inc

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