Tektronix Lab Experiment User Manual
Introduction to Oscilloscopes
Lab Experiment
A collection of lab exercises to introduce you to the basic
controls of a digital oscilloscope in order to make common
electronic measurements.
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Introduction to Oscilloscopes Lab Experiment
Table of Contents
LABORATORY EXPERIMENT INTRODUCTION........................................................................................ 3
OBJECTIVES ...............................................................................................................................................3
EQUIPMENT LIST.........................................................................................................................................3
OVERVIEW OF AN OSCILLOSCOPE.........................................................................................................4
INTRODUCTION............................................................................................................................................ 4
PERFORMANCE TERMS AND CONSIDERATIONS .............................................................................................5
INITIAL SETUP AND SCREEN EXPLANATION......................................................................................... 6
CREATING A STABLE DISPLAY.....................................................................................................................6
SCREEN EXPLANATION ............................................................................................................................... 7
INSTRUMENT CONTROLS .........................................................................................................................8
VERTICAL CONTROLS...............................................................................................................................9
INTRODUCTION............................................................................................................................................ 9
VERTICAL POSITION/SCALE CONTROLS ....................................................................................................... 9
HORIZONTAL CONTROLS ....................................................................................................................... 10
INTRODUCTION.......................................................................................................................................... 10
HORIZONTAL POSITION/SCALE CONTROLS................................................................................................. 10
SETTING THE RECORD LENGTH ................................................................................................................. 10
TRIGGER CONTROLS...............................................................................................................................11
INTRODUCTION.......................................................................................................................................... 11
TRIGGER LEVEL CONTROL ........................................................................................................................11
TRIGGER MENU ........................................................................................................................................ 12
OSCILLOSCOPE MEASUREMENTS........................................................................................................13
INTRODUCTION.......................................................................................................................................... 13
MANUAL MEASUREMENTS .........................................................................................................................14
CURSOR MEASUREMENTS ......................................................................................................................... 14
AUTOMATED MEASUREMENTS...................................................................................................................15
FINAL EXERCISE ......................................................................................................................................16
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Introduction to Oscilloscopes Lab Experiment
Laboratory Experiment Introduction
Objectives
1. Understand the block diagram and basic controls of a digital oscilloscope.
2. Setup an oscilloscope for a stable display of the applied signal.
3. Make common electronic measurements with a digital oscilloscope.
Equipment List
1. One Tektronix MSO2000 or DPO2000 Series digital oscilloscope.
2. One Tektronix P2221 1X/10X passive probe.
3. One Host/Device USB cable.
4. One Tektronix 878-0456-xx demonstration board.
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Introduction to Oscilloscopes Lab Experiment
Overview of an Oscilloscope
Introduction
An oscilloscope is an electronic test instrument that displays electrical signals graphically, usually as a
voltage (vertical or Y axis) versus time (horizontal or X axis) as shown in figure 1. The intensity or
brightness of a waveform is sometimes considered the Z axis. There are some applications where other
vertical axes such as current may be used, and other horizontal axes such as frequency or another
voltage may be used.
Oscilloscopes are also used to measure electrical signals in response to physical stimuli, such as
sound, mechanical stress, pressure, light, or heat. For example, a television technician can use an
oscilloscope to measure signals from a television circuit board while a medical researcher can use an
oscilloscope to measure brain waves.
Oscilloscopes are commonly used for
measurement applications such as:
• observing the wave shape of a signal
• measuring the amplitude of a signal
• measuring the frequency of a signal
• measuring the time between two events
• observing whether the signal is direct
current (DC) or alternating current (AC)
• observing noise on a signal
An oscilloscope contains various controls that assist in the analysis of waveforms displayed on a
graphical grid called a graticule. The graticule, as shown in figure 1, is divided into divisions along both
the horizontal and vertical axes. These divisions make it easier to determine key parameters about the
waveform. In the case of the MSO/DPO2000 Series oscilloscope, there are 10 divisions horizontally
and 8 divisions vertically.
A digital oscilloscope acquires a waveform by conditioning the input signal in the analog vertical
amplifier, sampling the analog input signal, converting the samples to a digital representation with an
analog-to-digital converter (ADC or A/D), storing the sampled digital data in its memory, and then
reconstructing the waveform for viewing on the display.
Figure 1: Typical Oscilloscope Display
Figure 2: Typical Digital Oscilloscope Block Diagram
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Introduction to Oscilloscopes Lab Experiment
Performance Terms and Considerations
There are many ways to specify digital oscilloscope performance, but the most important are bandwidth,
rise time, sample rate, and record length.
Bandwidth
Bandwidth is the first specification to consider. Bandwidth is the frequency range of the oscilloscope,
usually measured in Megahertz (MHz). It is the frequency at which the amplitude of the displayed sine
wave is attenuated to 70.7% of the original signal amplitude.
When measuring high-frequency or fast rise-time signals, oscilloscope bandwidth is especially critical.
Without adequate bandwidth, an oscilloscope will not be able to display and measure high-frequency
changes. It is generally recommended that the oscilloscope’s bandwidth be at least 5 times the highest
frequency that needs to be measured. This “5-times rule” allows for the display of the 5
signal and assures that measurement errors due to bandwidth are minimized.
th
5≥
Example: If the signal of interest is 100 MHz, the oscilloscope would need a bandwidth of 500 MHz.
signalofharmonicbandwidthpeoscillosco
Rise Time
The edge speed (rise time) of a digital signal can carry more high-frequency content than its repetition
rate might imply. An oscilloscope and probe must have a sufficiently fast rise time to capture the higher
frequency components, and therefore show signal transitions accurately. Rise time is the time taken by
a step or a pulse to rise from 10% to 90% of its amplitude level. There is another “5-times rule” that
recommends that the oscilloscope’s rise time be at least 5 times faster than the rise time of the signal
that needs to be measured.
timerisesignal
timerisepeoscillosco ≤
5
Example: If the signal of interest has a rise time of 5
μ
faster than 1
sec.
μ
sec, then the oscilloscope rise time should be
th
harmonic of the
Sample Rate
Digital oscilloscopes sample the input signals at a frequency called the sample rate, measured in
samples / second (S/sec). To properly reconstruct the signals, Nyquist sampling requires that the
sample rate be at least twice the highest frequency being measured. That’s the theoretical minimum. In
practice, sampling at least 5 times as fast is generally desirable.
fratesample ∗≥ 5
Highest
Example: The correct sample rate for a 450 MHz signal would be ≥ 2.25 GS/sec.
Record Length
Digital oscilloscopes capture a specific number of samples or data points, known as the record length,
for each acquired waveform. The record length, measured in points or samples, divided by the sample
rate (in Samples/second) specifies the total time (in seconds) that is acquired.
timeacquired =
lengthrecord
ratesample
Example: With a record length of 1 Mpoints and a sample rate of 250 MS/sec, the oscilloscope will
capture a signal 4 msec in length.
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Introduction to Oscilloscopes Lab Experiment
Exercise
What minimum oscilloscope performance is required to properly capture 2 msec of a 1 V
sine wave?
• Bandwidth:
• Sample Rate:
• Record Length:
, 250 MHz
pk-pk
Initial Setup and Screen Explanation
Creating a Stable Display
1. The following steps will describe how to automatically create a stable oscilloscope display using a
1 kHz, 5 V
a. Power up the MSO/DPO2000 Series oscilloscope by pressing the power button on the lower
left corner of the instrument.
b. Press the front panel Default Setup button to set the oscilloscope to a known starting point.
c. Connect a P2221 1X/10X passive probe to the channel 1 input. To connect a BNC connector,
push and turn the probe connector until it slides on the connector. Then, turn the locking ring
clockwise to lock the connector in place.
d. Use the probe slide switch to set the probe attenuation to 10X.
e. Attach the probe’s alligator style ground lead to the ground connector on the lower right
corner of the oscilloscope.
f. Attach the probe tip to the PROBE COMP connector just below the ground lead connector. The
PROBE COMP connector provides a 1 kHz square wave that this lab will use to demonstrate
the operation of an oscilloscope.
g. Press the front panel Autoset button to
cause the oscilloscope to automatically
set the vertical, horizontal and trigger
settings for a stable display of the
PROBE COMP 1 kHz square wave.
square wave.
pk-pk
Key Points to Remember
1. To return the oscilloscope to a known state, press the Default Setup button.
2. The Autoset button adjusts the vertical, horizontal and trigger settings such that four or five cycles
of the waveform are displayed with the trigger near the middle of the screen
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