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This application note provides an overview of oscilloscope fundamentals. You will

learn what an oscilloscope is and how it operates. We will discuss oscilloscope

applications and give you an overview of basic measurements and performance

characteristics. We will also take a look at the different types of probes and

discuss their advantages and disadvantages.

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . 1

Electronic Signals . . . . . . . . . . . . . . . . 2

Wave properties . . . . . . . . . . . . . . . . . . . 2

Waveforms . . . . . . . . . . . . . . . . . . . . . . . 3

Analog versus digital signals . . . . . . . . . 4

What is an Oscilloscope and

Why Do You Need One? . . . . . . . . . . . 5

Signal integrity . . . . . . . . . . . . . . . . . . . . 5

What an oscilloscope looks like . . . . . . 6

An oscilloscope’s purpose . . . . . . . . . . . 7

Types of oscilloscopes . . . . . . . . . . . . . . 8

Where oscilloscopes are used . . . . . . . 10

Basic Oscilloscope Controls and

Measurements . . . . . . . . . . . . . . . . . . 11

Basic front-panel controls . . . . . . . . . . 11

Softkeys . . . . . . . . . . . . . . . . . . . . . . . . . 14

Basic measurements . . . . . . . . . . . . . . 15

Basic mathematical functions . . . . . . . 16

Important Oscilloscope

Performance Characteristics . . . . . . 17

Bandwidth . . . . . . . . . . . . . . . . . . . . . . . 17

Channels . . . . . . . . . . . . . . . . . . . . . . . . 17

Sample rate . . . . . . . . . . . . . . . . . . . . . . 18

Memory depth . . . . . . . . . . . . . . . . . . . . 19

Update rate . . . . . . . . . . . . . . . . . . . . . . 20

Oscilloscope connectivity . . . . . . . . . . 20

Oscilloscope Probes . . . . . . . . . . . . . 21

Loading . . . . . . . . . . . . . . . . . . . . . . . . . 21

Passive probes . . . . . . . . . . . . . . . . . . . 21

Active probes . . . . . . . . . . . . . . . . . . . . 21

Current probes . . . . . . . . . . . . . . . . . . . 22

Probe accessories . . . . . . . . . . . . . . . . 22

Conclusion . . . . . . . . . . . . . . . . . . . . . 23

Sales and Service . . . . . . . . . . . . . . . 24

Agilent Technologies

Oscilloscope Fundamentals

Application Note 1606

Introduction

Electronic technology permeates

our lives. Millions of people

use electronic devices such as

cell phones, televisions, and

computers on a daily basis.

As electronic technology

has advanced, the speeds at

which these devices operate

have accelerated. Today, most

devices use high-speed digital

technologies.

Engineers need the ability

to accurately design and test

the components in their high-

speed digital devices. The

instrumentation engineers use to

design and test their components

must be particularly well-suited

to deal with high speeds and

high frequencies. An oscilloscope

is an example of just such an

instrument.

Oscilloscopes are powerful tools

that are useful for designing

and testing electronic devices.

They are vital in determining

which components of a system

are behaving correctly and

which are malfunctioning. They

can also help you determine

whether or not a newly designed

component behaves the way you

intended. Oscilloscopes are far

more powerful than multimeters

because they allow you to see

what the electronic signals

actually look like.

Oscilloscopes are used in a

wide range of fields, from the

automotive industry to university

research laboratories to the

aerospace-defense industry.

Companies rely on oscilloscopes

to help them uncover defects and

produce fully functional products.

Oscilloscopes are essential

to meeting the needs of their

customers with new and better

electronic products.

Summary of content (24 pages)

PAGE 1
Agilent Technologies Oscilloscope Fundamentals Application Note 1606 This application note provides an overview of oscilloscope fundamentals. You will learn what an oscilloscope is and how it operates. We will discuss oscilloscope applications and give you an overview of basic measurements and performance characteristics. We will also take a look at the different types of probes and discuss their advantages and disadvantages. Introduction Table of Contents Introduction . . . . . . . . . . . . . . . . . .
PAGE 2
Electronic Signals Wave properties The main purpose of an oscilloscope is to display electronic signals. By viewing signals displayed on an oscilloscope, you can determine whether a component of an electronic system is behaving properly. So, to understand how an oscilloscope operates, it is important to understand basic signal theory. Wave properties Electronic signals are waves or pulses.
PAGE 3
Electronic Signals (continued) Waveforms Waveforms A waveform is the shape or representation of a wave. Waveforms can provide you with a great deal of information about your signal. For example, it can tell you if the voltage changes suddenly, varies linearly, or remains constant. There are many standard waveforms, but this section will cover the ones you will encounter most frequently.
PAGE 4
Electronic Signals (continued) Waveforms Triangular/sawtooth waves In a triangular wave, the voltage varies linearly with time. The edges are called ramps because the waveform is either ramping up or ramping down to certain voltages. A sawtooth wave looks similar in that either the front or back edge has a linear voltage response with time. However, the opposite edge has an almost immediate drop. Pulses A pulse is a sudden single disturbance in an otherwise constant voltage.
PAGE 5
What Is an Oscilloscope and Why Do You Need One? Signal integrity Signal integrity The main purpose of an oscilloscope is to give an accurate visual representation of electrical signals. For this reason, signal integrity is very important. Signal integrity refers to the oscilloscope’s ability to reconstruct the waveform so that it is an accurate representation of the original signal.
PAGE 6
What Is an Oscilloscope and Why Do You Need One? (continued) What an oscilloscope looks like What an oscilloscope looks like In general, modern digitizing oscilloscopes look similar to the one seen in Figure 8. However, there are a wide variety of oscilloscope types, and yours may look very different. Despite this, there are some basic features that most oscilloscopes have.
PAGE 7
What Is an Oscilloscope and Why Do You Need One? (continued) An oscilloscope’s purpose An oscilloscope’s purpose An oscilloscope is a measurement and testing instrument used to display a certain variable as a function of another. For example, it can plot on its display a graph of voltage (y-axis) versus time (x-axis). Figure 10 shows an example of such a plot. This is useful if you want to test a certain electronic component to see if it is behaving properly.
PAGE 8
What Is an Oscilloscope and Why Do You Need One? (continued) Types of oscilloscopes Types of oscilloscopes Analog oscilloscopes The first oscilloscopes were analog oscilloscopes, which use cathode-ray tubes to display a waveform. An electron beam is scanned across a series of many horizontal lines while being gated on and off. Photoluminescent phosphor on the screen illuminates when an electron hits it, and as successive bits of phosphor light up, you can see a representation of the signal.
PAGE 9
What Is an Oscilloscope and Why Do You Need One? (continued) Types of oscilloscopes Mixed signal oscilloscopes (MSOs) In a DSO, the input signal is analog and the digital-to-analog converter digitizes it. However, as digital electronic technology expanded, it became increasingly necessary to monitor analog and digital signals simultaneously. As a result, oscilloscope vendors began producing mixed-signal oscilloscopes that can trigger on and display both analog and 4 analog channels digital signals.
PAGE 10
What Is an Oscilloscope and Why Do You Need One? (continued) Types of oscilloscopes Economy oscilloscopes Economy oscilloscopes are reasonably priced, but they do not have as much performance capability as high-performance oscilloscopes. These oscilloscopes are typically found in university laboratories. The main advantage of these oscilloscopes is their low price. For a relatively modest amount of money, you get a very useful oscilloscope.
PAGE 11
Basic Oscilloscope Controls and Measurements Basic front-panel controls Basic front-panel controls Typically, you operate an oscilloscope using the knobs and buttons on the front panel. In addition to controls found of the front panel, many highend oscilloscopes now come equipped with operating systems, and as a result, they behave like computers. You can hook up a mouse and keyboard to the oscilloscope and use the mouse to adjust the controls through drop down menus and buttons on the display as well.
PAGE 12
Basic Oscilloscope Controls and Measurements (continued) Basic front-panel controls Trigger controls As we mentioned earlier, triggering on your signal helps to provide a stable, usable display and allows you to see the part of the waveform you are interested in. The trigger controls let you pick your vertical trigger level (for example, the voltage at which you want your oscilloscope to trigger) and choose between various triggering capabilities.
PAGE 13
Basic Oscilloscope Controls and Measurements (continued) Basic front-panel controls Pulse-width triggering – Pulse width triggering is similar to glitch triggering when you are looking for specific pulse widths. However, it is more general in that you can trigger on pulses of any specified width and you can choose the polarity (negative or positive) of the pulses you want to trigger on. You can also set the horizontal position of the trigger. This allows you to see what occurred pre-trigger or post-trigger.
PAGE 14
Basic Oscilloscope Controls and Measurements (continued) Softkeys Softkeys Softkeys are found on oscilloscopes that do not have Windows-based operating systems (refer to Figure 8 for a picture of softkeys). These softkeys allow you to navigate the menu system on the oscilloscope’s display. Figure 21 shows what a popup menu looks like when a softkey is pressed. The specific menu shown in the figure is for selecting the trigger mode.
PAGE 15
Basic Oscilloscope Controls and Measurements (continued) Basic measurements Basic measurements Digital oscilloscopes allow you to perform a wide range of measurements on your waveform. The complexity and range of measurements available depends on the feature set of your oscilloscope. Figure 22 shows the blank display of an Agilent 8000 Series oscilloscope. Notice the measurement buttons/icons lined up on the far-left side of the screen.
PAGE 16
Basic Oscilloscope Controls and Measurements (continued) Basic mathematical functions Basic mathematical functions In addition to the measurements discussed above, there are many mathematical operations you can perform on your waveforms. Examples include: Fourier transform This math function allows you to see the frequencies that compose your signal. Absolute value This math function shows the absolute value (in terms of voltage) of your waveform.
PAGE 17
Important Oscilloscope Performance Properties Bandwidth and channels Many oscilloscope properties dramatically affect the instrument’s performance and, in turn, your ability to accurately test devices. This section covers the most fundamental of these properties. It also will familiarize you with oscilloscope terminology and describe how to make an informed decision about which oscilloscope will best suit your needs.
PAGE 18
Important Oscilloscope Performance Properties (continued) Sample rate Sample rate The sample rate of an oscilloscope is the number of samples the oscilloscope can acquire per second. It is recommended that your oscilloscope have a sample rate that is at a least 2.5 times greater than its bandwidth. However, ideally the sample rate should be 3 times the bandwidth or greater. You need to be careful when you evaluate an oscilloscope’s sample rate banner specifications.
PAGE 19
Important Oscilloscope Performance Properties (continued) Memory depth Memory depth As we mentioned earlier, a digital oscilloscope uses an A/D (analog-to-digital) converter to digitize the input waveform. The digitized data is then stored in the oscilloscope’s high-speed memory. Memory depth refers to exactly how many records and, therefore, what length of time can be stored. Memory depth plays an important role in the sampling rate of an oscilloscope.
PAGE 20
Important Oscilloscope Performance Properties (continued) Update rate and oscilloscope connectivity Update rate Update rate refers to the rate at which an oscilloscope can acquire and update the display of a waveform. While it may appear to the human eye that the scope is displaying a “live” waveform, it is because the updates are occurring so fast that the human eye cannot detect the changes. In actuality, there is some deadtime in between acquisitions of the waveform (Figure 28).
PAGE 21
Oscilloscope Probes The oscilloscope is just one piece of the system that determines how accurately you are able to display and analyze your signals. Probes, which are used to connect the oscilloscope to your device under test (DUT), are crucial in terms of signal integrity. If you have a 1-GHz oscilloscope but only have a probe that supports a bandwidth of 500 MHz, you are not fully utilizing the bandwidth of your oscilloscope. This section discusses the types of probes and when you should use each one.
PAGE 22
Oscilloscope Probes (continued) Current probes Probe accessories Current probes are used to measure the current flowing through a circuit. They tend to be big and have limited bandwidth (100 MHz). Probes also come with a variety of probe tips. There are many different types of probes tips, everything from bulky tips that can wrap around cables to tips the size of several hairs. These tips make it easier for you to access various parts of a circuit or a device under test. Figure 31.
PAGE 23
Conclusion Oscilloscopes are a powerful tool in the technological world we currently live in. They are used in a wide range of fields and offer many advantages over other measurement and testing devices. After reading this app note, you should have a good feel for oscilloscope fundamentals. Take this knowledge and continue to read more advanced topics so you can make the most of your time with an oscilloscope.
PAGE 24
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