Tektronix XYZs User manual

XYZs of Oscilloscopes
oscilloscopes

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Table of Contents
Introduction ....................................................................3
Signal Integrity
The Significance of Signal Integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Why is Signal Integrity a Problem? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Viewing the Analog Origins of Digital Signals . . . . . . . . . . . . . . . . . . . . . . . . . . .5
The Oscilloscope
Understanding Waveforms and Waveform Measurements . . . . . . . . . . . . . . . . . .6
Types of Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Sine Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Square and Rectangular Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Sawtooth and Triangle Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Step and Pulse Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Periodic and Non-periodic Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Synchronous and Asynchronous Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Complex Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Waveform Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Frequency and Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Waveform Measurements with Digital Oscilloscopes . . . . . . . . . . . . . . . . . .10
The Types of Oscilloscopes
Analog Oscilloscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Digital Oscilloscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Digital Storage Oscilloscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Digital Phosphor Oscilloscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Digital Sampling Oscilloscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
The Systems and Controls of an Oscilloscope
Vertical System and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Position and Volts per Division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Input Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Bandwidth Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Alternate and Chop Display Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Horizontal System and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Acquisition Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Acquisition Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Starting and Stopping the Acquisition System . . . . . . . . . . . . . . . . . . . . . . .23
Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Sampling Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Sampling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Real-time Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Real-time Sampling with Interpolation . . . . . . . . . . . . . . . . . . . . . . . . .25
Equivalent-time Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Random Equivalent-time Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Sequential Equivalent-time Sampling . . . . . . . . . . . . . . . . . . . . . . . . . .26
Position and Seconds per Division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Time Base Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
XY Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Z Axis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
XYZ Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Trigger System and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Trigger Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Trigger Level and Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Trigger Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Trigger Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Trigger Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Trigger Holdoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Display System and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Other Oscilloscope Controls
Math and Measurement Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
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The Complete Measurement System
Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Passive Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Active and Differential Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Probe Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
Performance Terms and Considerations
Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Rise Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Sample Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Waveform Capture Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Record Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Triggering Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Effective Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Frequency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Vertical Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Sweep Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Gain Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Horizontal Accuracy (Time Base) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Vertical Resolution (Analog-to-digital Converter) . . . . . . . . . . . . . . . . . . . . . . . .41
Connectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Expandability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Ease-of-use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Operating the Oscilloscope
Setting Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
Ground the Oscilloscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
Ground Yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
Setting the Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Using Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Connecting the Ground Clip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Compensating the Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
Oscilloscope Measurement Techniques
Voltage Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Time and Frequency Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Pulse Width and Rise Time Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Phase Shift Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
Other Measurement Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
Written Exercises
Part I
Vocabulary Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Application Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52
Part II
Vocabulary Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
Application Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
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Introduction
Nature moves in the form of a sine wave, be it an ocean wave, earth-
quake, sonic boom, explosion, sound through air, or the natural frequency
of a body in motion. Energy, vibrating particles and other invisible forces
pervade our physical universe. Even light – part particle, part wave – has
a fundamental frequency, which can be observed as color.
Sensors can convert these forces into electrical signals that you can
observe and study with an oscilloscope. Oscilloscopes enable scientists,
engineers, technicians, educators and others to “see” events that change
over time.
Oscilloscopes are indispensable tools for anyone designing, manufacturing
or repairing electronic equipment. In today’s fast-paced world, engineers
need the best tools available to solve their measurement challenges
quickly and accurately. As the eyes of the engineer, oscilloscopes are
the key to meeting today’s demanding measurement challenges.
The usefulness of an oscilloscope is not limited to the world of electronics.
With the proper transducer, an oscilloscope can measure all kinds of
phenomena. A transducer is a device that creates an electrical signal in
response to physical stimuli, such as sound, mechanical stress, pressure,
light, or heat. A microphone is a transducer that converts sound into an
electrical signal. Figure 1 shows an example of scientific data that can be
gathered by an oscilloscope.
Oscilloscopes are used by everyone from physicists to television repair
technicians. An automotive engineer uses an oscilloscope to measure
engine vibrations. A medical researcher uses an oscilloscope to measure
brain waves. The possibilities are endless.
The concepts presented in this primer will provide you with a good starting
point in understanding oscilloscope basics and operation.
The glossary in the back of this primer will give you definitions of
unfamiliar terms. The vocabulary and multiple-choice written exercises
on oscilloscope theory and controls make this primer a useful classroom
aid. No mathematical or electronics knowledge is necessary.
After reading this primer, you will be able to:
Describe how oscilloscopes work
Describe the differences between analog, digital storage, digital phosphor,
and digital sampling oscilloscopes
Describe electrical waveform types
Understand basic oscilloscope controls
Take simple measurements
The manual provided with your oscilloscope will give you more specific
information about how to use the oscilloscope in your work. Some
oscilloscope manufacturers also provide a multitude of application
notes to help you optimize the oscilloscope for your application-
specific measurements.
Should you need additional assistance, or have any comments or
questions about the material in this primer, simply contact your
Tektronix representative, or visit www.tektronix.com.
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Photo Cell
Light Source
Figure 1. An example of scientific data gathered by an oscilloscope.

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Signal Integrity
The Significance of Signal Integrity
The key to any good oscilloscope system is its ability to accurately recon-
struct a waveform – referred to as signal integrity. An oscilloscope is
analogous to a camera that captures signal images that we can then
observe and interpret. Two key issues lie at the heart of signal integrity.
When you take a picture, is it an accurate picture of what actually happened?
Is the picture clear or fuzzy?
How many of those accurate pictures can you take per second?
Taken together, the different systems and performance capabilities of an
oscilloscope contribute to its ability to deliver the highest signal integrity
possible. Probes also affect the signal integrity of a measurement system.
Signal integrity impacts many electronic design disciplines. But until a
few years ago, it wasn’t much of a problem for digital designers. They
could rely on their logic designs to act like the Boolean circuits they were.
Noisy, indeterminate signals were something that occurred in high-speed
designs – something for RF designers to worry about. Digital systems
switched slowly and signals stabilized predictably.
Processor clock rates have since multiplied by orders of magnitude.
Computer applications such as 3D graphics, video and server I/O
demand vast bandwidth. Much of today’s telecommunications equipment
is digitally based, and similarly requires massive bandwidth. So too
does digital high-definition TV. The current crop of microprocessor
devices handles data at rates up to 2, 3 and even 5 GS/s (gigasamples per
second), while some memory devices use 400-MHz clocks as well as data
signals with 200-ps rise times.
Importantly, speed increases have trickled down to the common IC
devices used in automobiles, VCRs, and machine controllers, to name
just a few applications. A processor running at a 20-MHz clock rate
may well have signals with rise times similar to those of an 800-MHz
processor. Designers have crossed a performance threshold that means,
in effect, almost every design is a high-speed design.
Without some precautionary measures, high-speed problems can
creep into otherwise conventional digital designs. If a circuit is
experiencing intermittent failures, or if it encounters errors at voltage
and temperature extremes, chances are there are some hidden signal
integrity problems. These can affect time-to-market, product reliability,
EMI compliance, and more.
Why is Signal Integrity a Problem?
Let’s look at some of the specific causes of signal degradation in today’s
digital designs. Why are these problems so much more prevalent today
than in years past?
The answer is speed. In the “slow old days,” maintaining acceptable
digital signal integrity meant paying attention to details like clock
distribution, signal path design, noise margins, loading effects,
transmission line effects, bus termination, decoupling and power
distribution. All of these rules still apply, but…
Bus cycle times are up to a thousand times faster than they were
20 years ago! Transactions that once took microseconds are now
measured in nanoseconds. To achieve this improvement, edge speeds
too have accelerated: they are up to 100 times faster than those of
two decades ago.
This is all well and good; however, certain physical realities have kept
circuit board technology from keeping up the pace. The propagation time
of inter-chip buses has remained almost unchanged over the decades.
Geometries have shrunk, certainly, but there is still a need to provide
circuit board real estate for IC devices, connectors, passive components,
and of course, the bus traces themselves. This real estate adds up to
distance, and distance means time – the enemy of speed.
It’s important to remember that the edge speed – rise time – of a digital
signal can carry much higher frequency components than its repetition
rate might imply. For this reason, some designers deliberately seek IC
devices with relatively “slow” rise times.
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The lumped circuit model has always been the basis of most calculations
used to predict signal behavior in a circuit. But when edge speeds are
more than four to six times faster than the signal path delay, the simple
lumped model no longer applies.
Circuit board traces just six inches long become transmission lines
when driven with signals exhibiting edge rates below four to six
nanoseconds, irrespective of the cycle rate. In effect, new signal paths
are created. These intangible connections aren’t on the schematics, but
nevertheless provide a means for signals to influence one another in
unpredictable ways.
At the same time, the intended signal paths don’t work the way they
are supposed to. Ground planes and power planes, like the signal
traces described above, become inductive and act like transmission
lines; power supply decoupling is far less effective. EMI goes up as
faster edge speeds produce shorter wavelengths relative to the bus
length. Crosstalk increases.
In addition, fast edge speeds require generally higher currents to produce
them. Higher currents tend to cause ground bounce, especially on wide
buses in which many signals switch at once. Moreover, higher current
increases the amount of radiated magnetic energy and with it, crosstalk.
Viewing the Analog Origins of Digital Signals
What do all these characteristics have in common? They are classic
analog phenomena. To solve signal integrity problems, digital designers
need to step into the analog domain. And to take that step, they need
tools that can show them how digital and analog signals interact.
Digital errors often have their roots in analog signal integrity problems.
To track down the cause of the digital fault, it’s often necessary to turn
to an oscilloscope, which can display waveform details, edges and noise;
can detect and display transients; and can help you precisely measure
timing relationships such as setup and hold times.
Understanding each of the systems within your oscilloscope and how to
apply them will contribute to the effective application of the oscilloscope
to tackle your specific measurement challenge.
The Oscilloscope
What is an oscilloscope and how does it work? This section answers
these fundamental questions.
The oscilloscope is basically a graph-displaying device – it draws a
graph of an electrical signal. In most applications, the graph shows how
signals change over time: the vertical (Y) axis represents voltage and the
horizontal (X) axis represents time. The intensity or brightness of the
display is sometimes called the Z axis. (See Figure 2.)
This simple graph can tell you many things about a signal, such as:
The time and voltage values of a signal
The frequency of an oscillating signal
The “moving parts” of a circuit represented by the signal
The frequency with which a particular portion of the signal is occurring relative to
other portions
Whether or not a malfunctioning component is distorting the signal
How much of a signal is direct current (DC) or alternating current (AC)
How much of the signal is noise and whether the noise is changing with time
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Z (intensity)
Y (voltage)
X (time)
Y (voltage)
X (time)
Z (intensity)
Figure 2. X,Y, and Z components of a displayed waveform.

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Understanding Waveforms and
Waveform Measurements
The generic term for a pattern that repeats over time is a wave – sound
waves, brain waves, ocean waves, and voltage waves are all repetitive
patterns. An oscilloscope measures voltage waves. One cycle of a wave
is the portion of the wave that repeats. A waveform is a graphic
representation of a wave. A voltage waveform shows time on the
horizontal axis and voltage on the vertical axis.
Waveform shapes reveal a great deal about a signal. Any time you see
a change in the height of the waveform, you know the voltage has
changed. Any time there is a flat horizontal line, you know that there
is no change for that length of time. Straight, diagonal lines mean a
linear change – rise or fall of voltage at a steady rate. Sharp angles on
a waveform indicate sudden change. Figure 3 shows common waveforms
and Figure 4 displays sources of common waveforms.
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Sine Wave Damped Sine Wave
Square Wave Rectangular Wave
Sawtooth Wave Triangle Wave
Step Pulse
Complex
Figure 3. Common waveforms.
Figure 4. Sources of common waveforms.

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Types of Waves
You can classify most waves into these types:
Sine waves
Square and rectangular waves
Triangle and saw-tooth waves
Step and pulse shapes
Periodic and non-periodic signals
Synchronous and asynchronous signals
Complex waves
Sine Waves
The sine wave is the fundamental wave shape for several reasons. It has
harmonious mathematical properties – it is the same sine shape you may
have studied in high school trigonometry class. The voltage in your wall
outlet varies as a sine wave. Test signals produced by the oscillator circuit
of a signal generator are often sine waves. Most AC power sources pro-
duce sine waves. (AC signifies alternating current, although the voltage
alternates too. DC stands for direct current, which means a steady current
and voltage, such as a battery produces.)
The damped sine wave is a special case you may see in a circuit that
oscillates, but winds down over time. Figure 5 shows examples of sine and
damped sine waves.
Square and Rectangular Waves
The square wave is another common wave shape. Basically, a square
wave is a voltage that turns on and off (or goes high and low) at regular
intervals. It is a standard wave for testing amplifiers – good amplifiers
increase the amplitude of a square wave with minimum distortion.
Television, radio and computer circuitry often use square waves for
timing signals.
The rectangular wave is like the square wave except that the high and
low time intervals are not of equal length. It is particularly important when
analyzing digital circuitry. Figure 6 shows examples of square and
rectangular waves.
Sawtooth and Triangle Waves
Sawtooth and triangle waves result from circuits designed to control
voltages linearly, such as the horizontal sweep of an analog oscilloscope or
the raster scan of a television. The transitions between voltage levels of
these waves change at a constant rate. These transitions are called
ramps. Figure 7 shows examples of saw-tooth and triangle waves.
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Sawtooth Wave Triangle Wave
Figure 7. Sawtooth and triangle waves.
Sine Wave Damped Sine Wave
Figure 5. Sine and damped sine waves.
Square Wave Rectangular Wave
Figure 6. Square and rectangular waves.

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Step and Pulse Shapes
Signals such as steps and pulses that occur rarely, or non-periodically,
are called single-shot or transient signals.A step indicates a sudden
change in voltage, similar to the voltage change you would see if you
turned on a power switch.
A pulse indicates sudden changes in voltage, similar to the voltage
changes you would see if you turned a power switch on and then off
again. A pulse might represent one bit of information traveling through
a computer circuit or it might be a glitch, or defect, in a circuit. A
collection of pulses traveling together creates a pulse train. Digital
components in a computer communicate with each other using pulses.
Pulses are also common in x-ray and communications equipment.
Figure 8 shows examples of step and pulse shapes and a pulse train.
Periodic and Non-periodic Signals
Repetitive signals are referred to as periodic signals, while signals that
constantly change are known as non-periodic signals. A still picture is
analogous to a periodic signal, while a moving picture can be equated to
a non-periodic signal.
Synchronous and Asynchronous Signals
When a timing relationship exists between two signals, those signals are
referred to as synchronous. Clock, data and address signals inside a
computer are an example of synchronous signals.
Asynchronous is a term used to describe those signals between which no
timing relationship exists. Because no time correlation exists between the
act of touching a key on a computer keyboard and the clock inside the
computer, these are considered asynchronous.
Complex Waves
Some waveforms combine the characteristics of sines, squares, steps,
and pulses to produce waveshapes that challenge many oscilloscopes.
The signal information may be embedded in the form of amplitude, phase,
and/or frequency variations. For example, although the signal in Figure 9
is an ordinary composite video signal, it is composed of many cycles of
higher-frequency waveforms embedded in a lower-frequency envelope.
In this example, it is usually most important to understand the relative
levels and timing relationships of the steps. To view this signal, you need
an oscilloscope that captures the low-frequency envelope and blends in
the higher-frequency waves in an intensity-graded fashion so that you can
see their overall combination as an image that can be visually interpreted.
Analog and digital phosphor oscilloscopes are most suited to viewing
complex waves, such as video signals, illustrated in Figure 9. Their
displays provide the necessary frequency-of-occurrence information, or
intensity grading, that is essential to understanding what the waveform
is really doing.
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Complex
Figure 9. An NTSC composite video signal is an example of a complex wave.
Step Pulse Pulse Train
Figure 8. Step, pulse and pulse train shapes.

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Waveform Measurements
Many terms are used to describe the types of measurements that you
make with your oscilloscope. This section describes some of the most
common measurements and terms.
Frequency and Period
If a signal repeats, it has a frequency.The frequency is measured in
Hertz (Hz) and equals the number of times the signal repeats itself in
one second, referred to as cycles per second. A repetitive signal also
has a period – this is the amount of time it takes the signal to complete
one cycle. Period and frequency are reciprocals of each other, so that
1/period equals the frequency and 1/frequency equals the period. For
example, the sine wave in Figure 10 has a frequency of 3 Hz and a period
of 1/3 second.
Voltage
Voltage is the amount of electric potential – or signal strength – between
two points in a circuit. Usually, one of these points is ground, or zero
volts, but not always. You may want to measure the voltage from the
maximum peak to the minimum peak of a waveform, referred to as the
peak-to-peak voltage.
Amplitude
Amplitude refers to the amount of voltage between two points in a circuit.
Amplitude commonly refers to the maximum voltage of a signal measured
from ground, or zero volts. The waveform shown in Figure 11 has an
amplitude of 1 V and a peak-to-peak voltage of 2 V.
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0°90°180°270°360
+1 V
–1 V
0
2 V
°
Figure 11. Amplitude and degrees of a sine wave.
period
1 second
3 Cycles per
Second = 3 Hz
Frequency
123
Figure 10. Frequency and period of a sine wave.

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Phase
Phase is best explained by looking at a sine wave. The voltage level of
sine waves is based on circular motion. Given that a circle has 360°, one
cycle of a sine wave has 360°, as shown in Figure 11. Using degrees, you
can refer to the phase angle of a sine wave when you want to describe
how much of the period has elapsed.
Phase shift describes the difference in timing between two otherwise sim-
ilar signals. The waveform in Figure 12 labeled “current” is said to be 90°
out of phase with the waveform labeled “voltage,” since the waves reach
similar points in their cycles exactly 1/4 of a cycle apart (360°/4 = 90°).
Phase shifts are common in electronics.
Waveform Measurements with Digital Oscilloscopes
Modern digital oscilloscopes have functions that make waveform
measurements easier. They have front-panel buttons and/or screen-based
menus from which you can select fully automated measurements. These
include amplitude, period, rise/fall time, and many more. Many digital
instruments also provide mean and RMS calculations, duty cycle, and
other math operations. Automated measurements appear as on-screen
alphanumeric readouts. Typically these readings are more accurate
than is possible to obtain with direct graticule interpretation.
Fully automated waveform measurements available on some
digital phosphor oscilloscopes include:
Period Duty cycle + High
Frequency Duty cycle – Low
Width + Delay Minimum
Width – Phase Maximum
Rise time Burst width Overshoot +
Fall time Peak-to-peak Overshoot –
Amplitude Mean RMS
Extinction ratio Cycle mean Cycle RMS
Mean optical power Cycle area
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0
Phase = 90°
Voltage
Current
Figure 12. Phase shift.

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The Types of Oscilloscopes
Electronic equipment can be classified into two categories: analog and
digital. Analog equipment works with continuously variable voltages,
while digital equipment works with discrete binary numbers that represent
voltage samples. A conventional phonograph is an analog device, while
a compact disc player is a digital device.
Oscilloscopes can be classified similarly – as analog and digital types.
For many applications, either an analog or digital oscilloscope will do.
However, each type has unique characteristics that may make it more or
less suitable for specific applications. Digital oscilloscopes can be further
classified into digital storage oscilloscopes (DSOs), digital phosphor oscil-
loscopes (DPOs) and sampling oscilloscopes.
Analog Oscilloscopes
Fundamentally, an analog oscilloscope works by applying the measured
signal voltage directly to the vertical axis of an electron beam that moves
from left to right across the oscilloscope screen – usually a cathode-ray
tube (CRT). The back side of the screen is treated with luminous
phosphor that glows wherever the electron beam hits it. The signal
voltage deflects the beam up and down proportionally as it moves
horizontally across the display, tracing the waveform on the screen.The
more frequently the beam hits a particular screen location, the more
brightly it glows.
The CRT limits the range of frequencies that can be displayed by an
analog oscilloscope. At very low frequencies, the signal appears as a
bright, slow-moving dot that is difficult to distinguish as a waveform.
At high frequencies, the CRT’s writing speed defines the limit.When the
signal frequency exceeds the CRT’s writing speed, the display becomes
too dim to see. The fastest analog oscilloscopes can display frequencies
up to about 1 GHz.
When you connect an oscilloscope probe to a circuit, the voltage signal
travels through the probe to the vertical system of the oscilloscope.
Figure 13 illustrates how an analog oscilloscope displays a measured
signal. Depending on how you set the vertical scale (volts/div control),
an attenuator reduces the signal voltage and an amplifier increases the
signal voltage.
Next, the signal travels directly to the vertical deflection plates of the CRT.
Voltage applied to these deflection plates causes a glowing dot to move
across the screen. The glowing dot is created by an electron beam that
hits the luminous phosphor inside the CRT.A positive voltage causes the
dot to move up while a negative voltage causes the dot to move down.
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Attenuator
Sweep
Generator Horizontal
Amplifier
Display
System
CRT
Horizontal System
Probe
Trigger
System
Vertical System
Vertical
Amplifier
Ramp Time Base
Figure 13. The architecture of an analog oscilloscope.

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The signal also travels to the trigger system to start, or trigger, a
horizontal sweep. Horizontal sweep refers to the action of the
horizontal system that causes the glowing dot to move across the screen.
Triggering the horizontal system causes the horizontal time base to move
the glowing dot across the screen from left to right within a specific time
interval. Many sweeps in rapid sequence cause the movement of the
glowing dot to blend into a solid line. At higher speeds, the dot may
sweep across the screen up to 500,000 times per second.
Together, the horizontal sweeping action and the vertical deflection
action trace a graph of the signal on the screen. The trigger is necessary
to stabilize a repeating signal – it ensures that the sweep begins at the
same point of a repeating signal, resulting in a clear picture as shown in
Figure 14.
In addition, analog oscilloscopes have focus and intensity controls that
can be adjusted to create a sharp, legible display.
People often prefer analog oscilloscopes when it is important to display
rapidly varying signals in “real time” – or, as they occur. The analog
oscilloscope’s chemical phosphor-based display has a characteristic
known as intensity grading that makes the trace brighter wherever the
signal features occur most often. This intensity grading makes it easy to
distinguish signal details just by looking at the trace’s intensity levels.
Digital Oscilloscopes
In contrast to an analog oscilloscope, a digital oscilloscope uses an
analog-to-digital converter (ADC) to convert the measured voltage into
digital information. It acquires the waveform as a series of samples, and
stores these samples until it accumulates enough samples to describe a
waveform. The digital oscilloscope then re-assembles the waveform for
display on the screen. (see Figure 15)
Digital oscilloscopes can be classified into digital storage oscilloscopes
(DSOs), digital phosphor oscilloscopes (DPOs), and sampling oscilloscopes.
The digital approach means that the oscilloscope can display any
frequency within its range with stability, brightness, and clarity. For
repetitive signals, the bandwidth of the digital oscilloscope is a
function of the analog bandwidth of the front-end components of
the oscilloscope, commonly referred to as the –3dB point. For
single-shot and transient events, such as pulses and steps, the
bandwidth can be limited by the oscilloscope’s sample rate. Please
refer to the Sample Rate section under Performance Terms and
Considerations for a more detailed discussion.
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Untriggered Display Triggered Display
Figure 14. The trigger stabilizes a repetitive waveform, creating a
clear picture of the signal.
ADC
1010
0001
0010
0101
Analog Oscilloscopes
Trace Signals Digital Oscilloscopes Samples
Signals and Construct Displays
Figure 15. Analog oscilloscopes trace signals, while digital oscilloscopes
sample signals and construct displays.

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Digital Storage Oscilloscopes
A conventional digital oscilloscope is known as a digital storage
oscilloscope (DSO). Its display typically relies on a raster-type screen
rather than luminous phosphor.
Digital storage oscilloscopes (DSOs) allow you to capture and view
events that may happen only once – known as transients. Because the
waveform information exists in digital form as a series of stored binary
values, it can be analyzed, archived, printed, and otherwise processed,
within the oscilloscope itself or by an external computer. The waveform
need not be continuous; it can be displayed even when the signal
disappears. Unlike analog oscilloscopes, digital storage oscilloscopes
provide permanent signal storage and extensive waveform processing.
However, DSOs typically have no real-time intensity grading; therefore,
they cannot express varying levels of intensity in the live signal.
Some of the subsystems that comprise DSOs are similar to those in
analog oscilloscopes. However, DSOs contain additional data-processing
subsystems that are used to collect and display data for the entire
waveform. A DSO employs a serial-processing architecture to capture
and display a signal on its screen, as shown in Figure 16. A description of
this serial-processing architecture follows.
Serial-processing Architecture
Like an analog oscilloscope, a DSO’s first (input) stage is a vertical
amplifier. Vertical controls allow you to adjust the amplitude and position
range at this stage.
Next, the analog-to-digital converter (ADC) in the horizontal system
samples the signal at discrete points in time and converts the signal’s
voltage at these points into digital values called sample points. This
process is referred to as digitizing a signal. The horizontal system’s
sample clock determines how often the ADC takes a sample. This
rate is referred to as the sample rate and is expressed in samples
per second (S/s).
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Amp A/D DeMUX DisplayuP Display
Memory
Acquisition
Memory
Figure 16. The serial-processing architecture of a digital storage oscilloscope (DSO).

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The sample points from the ADC are stored in acquisition memory as
waveform points. Several sample points may comprise one waveform
point. Together, the waveform points comprise one waveform record.
The number of waveform points used to create a waveform record is
called the record length.The trigger system determines the start and
stop points of the record.
The DSO’s signal path includes a microprocessor through which the
measured signal passes on its way to the display. This microprocessor
processes the signal, coordinates display activities, manages the front
panel controls, and more. The signal then passes through the display
memory and is displayed on the oscilloscope screen.
Depending on the capabilities of your oscilloscope, additional processing
of the sample points may take place, which enhances the display.
Pre-trigger may also be available, enabling you to see events before
the trigger point. Most of today’s digital oscilloscopes also provide a
selection of automatic parametric measurements, simplifying the
measurement process.
A DSO provides high performance in a single-shot, multi-channel
instrument (see Figure 17). DSOs are ideal for low-repetition-rate or
single-shot, high-speed, multi-channel design applications. In the real
world of digital design, an engineer usually examines four or more
signals simultaneously, making the DSO a critical companion.
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Figure 17. The TDS694C delivers high-speed, single-shot acquisition across
multiple channels, increasing the likelihood of capturing elusive glitches and
transient events.

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Digital Phosphor Oscilloscopes
The digital phosphor oscilloscope (DPO) offers a new approach to
oscilloscope architecture. This architecture enables a DPO to deliver
unique acquisition and display capabilities to accurately reconstruct
a signal.
While a DSO uses a serial-processing architecture to capture, display
and analyze signals, a DPO employs a parallel-processing architecture
to perform these functions, as shown in Figure 18. The DPO architecture
dedicates unique ASIC hardware to acquire waveform images, delivering
high waveform capture rates that result in a higher level of signal visualization.
This performance increases the probability of witnessing transient events
that occur in digital systems, such as runt pulses, glitches and transition
errors. A description of this parallel-processing architecture follows.
Parallel-processing Architecture
A DPO’s first (input) stage is similar to that of an analog oscilloscope – a
vertical amplifier – and its second stage is similar to that of a DSO – an
ADC. But, the DPO differs significantly from its predecessors following the
analog-to-digital conversion.
For any oscilloscope – analog, DSO or DPO – there is always a holdoff
time during which the instrument processes the most recently acquired
data, resets the system, and waits for the next trigger event. During
this time, the oscilloscope is blind to all signal activity. The probability
of seeing an infrequent or low-repetition event decreases as the holdoff
time increases.
It should be noted that it is impossible to determine the probability of
capture by simply looking at the display update rate. If you rely solely
on the update rate, it is easy to make the mistake of believing that the
oscilloscope is capturing all pertinent information about the waveform
when, in fact, it is not.
The digital storage oscilloscope processes captured waveforms serially.
The speed of its microprocessor is a bottleneck in this process because it
limits the waveform capture rate.
The DPO rasterizes the digitized waveform data into a digital phosphor
database. Every 1/30th of a second – about as fast as the human eye
can perceive it – a snapshot of the signal image that is stored in the
database is pipelined directly to the display system. This direct rasterization
of waveform data, and direct copy to display memory from the database,
removes the data-processing bottleneck inherent in other architectures.
The result is an enhanced “live-time” and lively display update. Signal
details, intermittent events, and dynamic characteristics of the signal are
captured in real-time. The DPO’s microprocessor works in parallel with
this integrated acquisition system for display management, measurement
automation and instrument control, so that it does not affect the
oscilloscope’s acquisition speed.
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• Snapshots of the Digital Phosphor contents are periodically
sent directly to the display without stopping the acquisition.
• Waveform math, measurements, and front panel
control are executed by the microprocessor parallel
to the integrated acquisition/display system.
Amp A/D Display
uP
Digital
Phosphor
Figure 18. The parallel-processing architecture of a digital phospor oscilloscope (DPO).

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A DPO faithfully emulates the best display attributes of an analog
oscilloscope, displaying the signal in three dimensions: time, amplitude
and the distribution of amplitude over time, all in real time.
Unlike an analog oscilloscope’s reliance on chemical phosphor, a DPO uses
a purely electronic digital phosphor that’s actually a continuously updated
database. This database has a separate “cell” of information for every
single pixel in the oscilloscope’s display. Each time a waveform is
captured – in other words, every time the oscilloscope triggers – it
is mapped into the digital phosphor database’s cells. Each cell that
represents a screen location and is touched by the waveform is
reinforced with intensity information, while other cells are not. Thus,
intensity information builds up in cells where the waveform passes
most often.
When the digital phosphor database is fed to the oscilloscope’s display,
the display reveals intensified waveform areas, in proportion to the signal’s
frequency of occurrence at each point – much like the intensity grading
characteristics of an analog oscilloscope. The DPO also allows the display
of the varying frequency-of-occurence information on the display as
contrasting colors, unlike an analog oscilloscope. With a DPO, it is easy
to see the difference between a waveform that occurs on almost every
trigger and one that occurs, say, every 100th trigger.
Digital phosphor oscilloscopes (DPOs) break down the barrier between
analog and digital oscilloscope technologies. They are equally suitable for
viewing high and low frequencies, repetitive waveforms, transients, and
signal variations in real time. Only a DPO provides the Z (intensity) axis in
real time that is missing from conventional DSOs.
A DPO is ideal for those who need the best general-purpose design and
troubleshooting tool for a wide range of applications (see Figure 19).
A DPO is exemplary for communication mask testing, digital debug of
intermittent signals, repetitive digital design and timing applications.
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Figure 19. Some DPOs can acquire millions of waveforms in just seconds,
significantly increasing the probability of capturing intermittent and elusive
events and revealing dynamic signal behavior.

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Digital Sampling Oscilloscopes
When measuring high-frequency signals, the oscilloscope may not be
able to collect enough samples in one sweep. A digital sampling
oscilloscope is an ideal tool for accurately capturing signals whose
frequency components are much higher than the oscilloscope’s sample
rate (see Figure 21). This oscilloscope is capable of measuring signals
of up to an order of magnitude faster than any other oscilloscope. It can
achieve bandwidth and high-speed timing ten times higher than other
oscilloscopes for repetitive signals. Sequential equivalent-time
sampling oscilloscopes are available with bandwidths to 50 GHz.
In contrast to the digital storage and digital phosphor oscilloscope
architectures, the architecture of the digital sampling oscilloscope
reverses the position of the attenuator/amplifier and the sampling
bridge, as shown in Figure 20. The input signal is sampled before any
attenuation or amplification is performed. A low bandwidth amplifier
can then be utilized after the sampling bridge because the signal has
already been converted to a lower frequency by the sampling gate,
resulting in a much higher bandwidth instrument.
The tradeoff for this high bandwidth, however, is that the sampling
oscilloscope’s dynamic range is limited. Since there is no attenuator/
amplifier in front of the sampling gate, there is no facility to scale the
input. The sampling bridge must be able to handle the full dynamic
range of the input at all times. Therefore, the dynamic range of most
sampling oscilloscopes is limited to about 1 V peak-to-peak. Digital
storage and digital phosphor oscilloscopes, on the other hand, can
handle 50 to 100 volts.
In addition, protection diodes cannot be placed in front of the sampling
bridge as this would limit the bandwidth. This reduces the safe input
voltage for a sampling oscilloscope to about 3 V, as compared to 500 V
available on other oscilloscopes.
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Figure 21. Time domain reflectometry (TDR) display from a TDS8000
digital sampling oscilloscope and 80E04 20-GHz sampling module.
Sampling
Bridge
Amplifier
50 Ω
Input
(3 V Max)
Figure 20. The architecture of a digital sampling oscilloscope.

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The Systems and Controls
of an Oscilloscope
A basic oscilloscope consists of four different systems – the vertical
system, horizontal system, trigger system, and display system.
Understanding each of these systems will enable you to effectively
apply the oscilloscope to tackle your specific measurement challenges.
Recall that each system contributes to the oscilloscope’s ability to
accurately reconstruct a signal.
This section briefly describes the basic systems and controls found on
analog and digital oscilloscopes. Some controls differ between analog and
digital oscilloscopes; your oscilloscope probably has additional controls not
discussed here.
The front panel of an oscilloscope is divided into three main sections
labeled vertical,horizontal, and trigger. Your oscilloscope may have
other sections, depending on the model and type – analog or digital – as
shown in Figure 22. See if you can locate these front-panel sections in
Figure 22, and on your oscilloscope, as you read through this section.
When using an oscilloscope, you need to adjust three basic settings
to accommodate an incoming signal:
The attenuation or amplification of the signal. Use the volts/div control to adjust
the amplitude of the signal to the desired measurement range.
The time base. Use the sec/div control to set the amount of time per division
represented horizontally across the screen.
The triggering of the oscilloscope. Use the trigger level to stabilize a repeating
signal, or to trigger on a single event.
Vertical System and Controls
Vertical controls can be used to position and scale the waveform vertically.
Vertical controls can also be used to set the input coupling and other
signal conditioning, described later in this section. Common vertical
controls include:
Termination
1M Ohm
50 Ohm
Coupling
DC
AC
GND
Bandwidth Limit
20 MHz
250 MHz
Full
Position
Offset
Invert – On/Off
Scale
1-2-5
Variable
Zoom
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Figure 22. Front-panel control section of an oscilloscope.